Final Report

RTI Project No. 0215472

FSIS Contract No. 

AG-3A94-D-16-0130

January 23, 2022

Food Safety Consumer Research Project:

Meal Preparation Experiment on Grilling

Prepared For

USDA, FSIS, OPACE,

Food Safety Education Staff

1400 Independence Ave., S.W.

Washington, DC 20250-3700

Prepared By

Ellen Shumaker

Sheryl C. Cates

Jenna Brophy

RTI International

3040 E. Cornwallis Road

Research Triangle Park, NC

27709-2194

Benjamin Chapman Emily Kingston

Lisa A. Shelley Esa Puntch

Rebecca M. Goulter Brian Chesanek

Lydia Goodson Jaclyn Merrill

Catherine Sander Lee-Ann Jaykus

Jason Frye

North Carolina State University

Raleigh, NC 27695

_________________________________

RTI International is a trade name of Research Triangle Institute. RTI and the RTI logo are U.S. registered trademarks of Research 

Triangle Institute.

iii

Contents

Section Page

Executive Summary ES-1

1. Introduction 1-1

1.1 Background and Project Overview ..............................................................1-1

1.2 Objectives of Grilling Meal Preparation Experiment.......................................1-2

1.3 Organization of Report..............................................................................1-4

2. Study Methods 2-1

2.1 Meal Preparation Experiment Methodology ..................................................2-1

2.1.1 Research Design ............................................................................2-1

2.1.2 Study Procedures ...........................................................................2-2

2.1.3 Pilot Testing ..................................................................................2-5

2.2 Recruitment Procedures ............................................................................2-5

2.3 Coding of Observation Data and Analysis ....................................................2-7

2.4 Microbiological Data and Analysis ...............................................................2-7

2.5 Post-observation Interviews and Analysis....................................................2-8

3. Results 3-1

3.1 Sample Characteristics .............................................................................3-1

3.2 Thermometer Use ....................................................................................3-5

3.3 Handwashing Compliance........................................................................3-11

3.4 Cleaning and Sanitizing...........................................................................3-18

3.5 Produce Washing ...................................................................................3-24

3.6 Cross-Contamination and Microbiological Analysis ......................................3-25

3.7 Participants’ Response to Intervention (Treatment Groups Only)..................3-27

4. Conclusion 4-1

4.1 Impact of Intervention (Control vs. T1 and Control vs. T2) ............................4-1

4.2 Impact of Celebrity Chef Endorsement (T1 vs. T2) .......................................4-2

References R-1
iv

Appendixes

A Recipes...................................................................................................A-1

B Observation Script ...................................................................................B-1

C List of Equipment Provided in Each Test Kitchen ..........................................C-1

D Microbiological Methods ........................................................................... D-1

E Post-observation Interview Guide...............................................................E-1

F Screening Questionnaire ...........................................................................F-1

G Observation Rubric for Coding Participant Actions in the Kitchen ................... G-1
v

Figures

Number Page

2-1. Study Procedures for Meal Preparation Experiment on Grilling Bratwurst and 

Hamburgers .................................................................................................2-3

3-1. Bratwurst with Heat Maps Showing Thermometer Placement by Group ................3-9

3-2. Hamburger with Heat Maps Showing Thermometer Placement by Group ............3-10
vi

Tables

Number Page

1–1. Research Questions, Data Sources, and Location of Results in Report ..................1-3

2-1. Summary of Information Collected in the Post-observation Interviews .................2-8

3-1. Sample Characteristics...................................................................................3-2

3-2. Comparison of the Study Sample with Recruitment Targets ................................3-3

3-3. Self-reported Participant Experience with Purchasing and Preparing Bratwurst 

and Hamburgers ...........................................................................................3-4

3-4. Observed Preparation of Bratwurst and Hamburgers..........................................3-5

3-5. Self-Reported Thermometer Use .....................................................................3-7

3-6. Comparison of Thermometer Use for Annual Meal Preparation Experiments 

(Control Group Participants) .........................................................................3-11

3-7. Observed Handwashing Compliance before Meal Preparation ............................3-12

3-8. Observed Handwashing Compliance during Meal Preparation ............................3-14

3-9. Self-reported Handwashing Behaviors............................................................3-15

3-10. Comparison of Handwashing Compliance for Annual Meal Preparation 

Experiments (Control Group Participants).......................................................3-17

3-11. Observed Cleaning and Sanitizing during Chub Preparation ..............................3-19

3-12. Self-reported Behaviors for Cleaning and Sanitizing When Preparing Bratwurst 

and Hamburgers at Home ............................................................................3-20

3-13. Observed Repackaging of Unused Ground Beef ...............................................3-22

3-14. Self-reported Behaviors for Preparing, Handling, and Storage When Preparing 

Bratwurst and Hamburgers at Home..............................................................3-23

3-15. Observed Salad Preparation: Produce Washing ...............................................3-24

3-16. Prevalence of Surrogate Contamination and Level of Contamination for 

Locations in the Kitchen ...............................................................................3-26

3-17. Treatment Group Participants’ Response to Intervention ..................................3-27

3-18. T2 Group Participants’ Response to Food Safety Instructions and Celebrity 

Chefs ..................................................................................................3-30
ES-1

Executive Summary

The Food Safety and Inspection Service (FSIS) of the U.S. Department of Agriculture 

(USDA) contracted with RTI International and its subcontractor North Carolina State 

University (NCSU) to conduct meal preparation experiments to evaluate consumer food 

handling behaviors in a test kitchen. The research team is conducting five separate 

iterations of meal preparation experiments to address a specific consumer behavior and to 

determine the effectiveness of a behavior change intervention. The meal preparation 

experiments are part of a larger 5-year annual study that also includes focus groups (two 

iterations) and web surveys (two iterations). This report describes the results of the fourth 

iteration of the meal preparation experiment.

RTI and NCSU conducted the study in a test kitchen facility located in Raleigh, North 

Carolina (Wake County), with three identical test kitchens. For this study, we explored the 

impact of including food safety instructions in recipes on participants’ food safety practices. 

Participants were randomized to one of three conditions: the control group, recipes without 

food safety instructions; Treatment 1 (T1), recipes with food safety instructions; or 

Treatment 2 (T2), recipes with food safety instructions and a celebrity endorsement. A total 

of 200 people participated in the study (66 control, 66 T1, 68 T2). Food safety information 

was formatted using the Partnership for Food Safety Education’s Safe Recipe Style Guide1

and included instructions on washing hands at the beginning of cooking and after touching 

uncooked ground beef, using a food thermometer to check for doneness, cleaning and 

sanitizing surfaces and utensils after touching uncooked ground beef, and washing the apple 

and carrot by rubbing under cold water. For the outcomes of interest, we conducted 

statistical testing for the difference between the control vs. T1, control vs. T2, and 

T1 vs. T2. 

In each test kitchen, eight cameras recorded participants’ actions at various locations 

throughout the kitchen and recorded the meal preparation from beginning to end. 

Participants in the control and treatment groups were observed while grilling bratwurst and 

hamburgers (inoculated with harmless traceable nonpathogenic E. coli strain DH5-Alpha) 

and preparing a ready-to-eat (RTE) salad (bagged lettuce, carrots, and apples) to determine 

whether they used a food thermometer, adhered to recommended handwashing practices, 

safely prepared the RTE salad, and safely handled and stored uncooked ground beef from a 

chub. Following meal preparation and participants’ cleaning and/or sanitizing of the kitchen, 

the study team collected microbiological samples from surfaces and lettuce from the 

prepared RTE salad and analyzed the samples for prevalence and level of DH5-Alpha. 

Participants participated in a post-observation interview to collect information on their usual 

food preparation practices. 

1 https://www.saferecipeguide.org/
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ES-2

ES.1 Key Findings

The key findings from the study are summarized below.

Food Thermometer Use

▪ Thermometer use was significantly higher in the two treatment groups (95% for T1

and 96% for T2) when compared with the control group (55%) for determining 

doneness of bratwurst.

▪ Thermometer use was significantly higher in the two treatment groups (95% for T1 

and 99% for T2) when compared with the control group (58%) for determining 

doneness of hamburgers.

▪ Among participants in all groups, most participants who used a thermometer 

checked the doneness of the two hamburgers and all five bratwurst.

▪ Among participants using a thermometer, most participants failed to insert the 

thermometer in the proper location when checking the doneness of the hamburgers 

and bratwurst.

▪ Comparing thermometer use among control group participants for Years 1 through 4 

of the study, thermometer use varied by the type of product cooked. Thermometer 

use was significantly higher for hamburgers (58%) compared with turkey burgers 

(34%).

Handwashing

▪ Handwashing attempts before meal preparation were significantly higher in the two 

treatment groups (62% for T1 and 65% for T2) when compared with the control 

group (44%).

▪ There was not a statistically significant difference in the rate of handwashing 

attempts between the three groups for events requiring handwashing during meal 

preparation. 

▪ As in Years 1 through 3, few handwashing attempts included all steps necessary to 

be considered an adequate handwashing event as defined by the Centers for Disease 

Control and Prevention’s recommended steps, and the most documented reason for 

not successfully washing hands was failing to rub hands with soap for at least 

20 seconds.

▪ For handwashing before meal preparation, the rate of attempting handwashing 

(44%) was significantly lower compared with rates observed for study Year 2 (74%) 

and Year 3 (71%) among control group participants.

2 We speculate that the lower 

rate for Year 4 may be because participants used the hand sanitizer station upon

arrival, which was not present in prior years, as a COVID-19 precaution. Other 

reasons are possible, such as differences in the characteristics of the study sample

and social distancing measures during the participant introduction to the test 

kitchen, which led them to touch meal preparation surfaces (e.g., drawers/cabinets),

thus commencing meal preparation before washing their hands. Additional analysis is 

needed to understand why the rates are different. 

2 For Year 1, data were not available by when handwashing took place (i.e., before the start of or 

during meal preparation).
Executive Summary

ES-3

Handling, Preparation, and Storage of Chub/Ground Beef

▪ Most participants placed the chub on a cutting board or plate to prepare the 

hamburgers or dumped the ground beef into a bowl without letting the ground beef 

or chub packaging touch a surface. Some participants (15 to 20% depending on 

study group) prepared the ground beef directly on the counter, which is not 

recommended.

▪ Immediately after handling the chub, 31% of control group participants, 53% of T1 

participants, and 46% of T2 participants attempted cleaning/sanitizing the surface 

used to prepare the uncooked ground beef from the chub; the difference between

the control group and T1 was statistically significant, but not between the control 

group and T2.

▪ Most participants stored the uncooked ground beef from the chub in the refrigerator 

(instead of placing in freezer). Few participants labeled the package.

Cross-contamination and Microbiological Analysis

▪ Across all participants, the surface most often contaminated was the sink basin (28% 

of participants). The rate of contamination for the spice containers was 12%. Rates 

of contamination were relatively low for the cupboard handle (8%) and the counter 

area where the chub was opened (3%). 

▪ Among participants handwashing the plate or cutting board used to prepare the 

hamburgers from the chub, 32% of participants did not thoroughly wash the 

plate/cutting board (i.e., it was contaminated with the surrogate). 

▪ Across all participants, the prevalence for contamination on the salad lettuce was 

17%.

▪ For the sink basin, the prevalence rate for contamination was higher for the control 

group (32%) compared with T1 (17%). Prevalence rates for the other surfaces and 

the salad lettuce were not significantly different between the control group and the 

two treatment groups.

Washing Produce

▪ Rates of properly washing the carrot for the RTE salad were higher in the treatment 

groups (84% for T1 and 75% for T2) than the control group (71%); however, the 

differences were not statistically significant.

▪ Rates of properly washing the apple for the RTE salad were higher in the treatment 

groups (83% for T1 and 79% for T2) than the control group (72%); however, the 

differences were not statistically significant.

▪ For both the carrot and apple, about 40% of control group participants did not 

attempt washing, whereas nearly all T1 and T2 participants attempted washing, 

although some failed to rub it with their hands, so the attempt was unsuccessful. 

▪ Most participants in all three groups did not wash the bagged lettuce as 

recommended.
Food Safety Consumer Research Project:

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ES-4

ES.2 Implications for OPACE Outreach Efforts

The key implications for OPACE outreach efforts based on the study results are summarized 

below:

▪ Inclusion of food safety instructions positively affected some food safety 

practices. The study results suggest that the food safety instructions included in the 

recipes positively affected using the thermometer, attempting handwashing before 

meal preparation, and attempting cleaning/sanitizing immediately after handling the 

chub but did not affect attempting handwashing during meal preparation and 

properly washing the carrot and apple. Lower rates of cross-contamination were also 

found for certain kitchen surfaces. In the post-observation interviews with treatment 

group participants, many participants reported using recipes when cooking at home,

and most reported that they noticed the food safety instructions in the recipes

provided for the meal preparation experiment. 

▪ The addition of a celebrity chef endorsement for food safety instructions in 

recipes did not influence food safety practices. Recognition of the celebrity chef 

(Kenji Lopez-Alt) featured in T2 was low (15%), which likely led to the lack of 

statistically significant differences between T1 and T2 for the behaviors of interest. 

Although most T2 participants said they trust celebrity chefs in general, only about a 

third agreed they would follow food safety instructions because a celebrity chef 

endorsed them. These findings suggest that the addition of a celebrity chef 

endorsement for food safety instructions in recipes may not influence consumers’

food safety behaviors and that inclusion of food safety instructions alone may be 

sufficient to motivate behavior change.

▪ Providing consumers with information on food safety practices at the point 

of use (i.e., during meal preparation) may help facilitate behavior change.

Prompting consumers with food safety instructions at the time of meal preparation 

and as part of the recipe positions a consumer to adhere to food safety instructions 

as part of the process, even if it is not something they normally do. The Partnership 

for Food Safety Education’s Food Safety Style Guide could also be used as a 

reference point for media organizations when developing news segments about food 

safety and include examples on how to handle food safely to help prevent foodborne 

illness.
1-1

1. Introduction

This report describes the study methods and presents the results from a meal preparation 

study related to grilling bratwurst and hamburgers on an indoor grill and handling and 

storage of uncooked ground beef from a chub conducted as part of the Food Safety

Consumer Research Project (FSCRP). The study, conducted in test kitchens, used an 

experimental design to measure consumers’ adherence to recommended food safety 

practices between participants who received an educational intervention and those who did 

not. The grilling study is the fourth of five iterations of a meal preparation experiment in 

which consumers are observed while preparing meat and poultry products regulated by the 

U.S. Department of Agriculture’s (USDA’s) Food Safety and Inspection Service (FSIS). This 

report details the study design, data collection procedures, and data analysis approach and 

presents the results of the Year 4 meal preparation experiment. Additionally, the report 

compares key behavioral outcomes for Years 1 through 4 of the study. 

1.1 Background and Project Overview

USDA FSIS’ Office of Public Affairs and Consumer Education (OPACE) ensures that all 

segments of the farm-to-table chain receive valuable food safety information. The consumer 

education programs developed by OPACE’s Food Safety Education Staff inform the public on 

how to safely handle, prepare, and store meat, poultry, and egg products to minimize the 

incidence of foodborne illness.

OPACE strives to continuously increase consumer awareness of recommended food safety 

practices with the intent to improve food handling behaviors at home. OPACE shares its 

messages through consumer education campaigns, social media, the Meat and Poultry 

Hotline and Ask USDA (an online database of frequently asked food safety questions), the 

FSIS web site, FoodSafety.gov, publications, and events. These messages are focused on 

the four core food safety behaviors: clean, separate, cook, and chill. Additionally, OPACE’s 

public education and outreach initiatives reach vulnerable and underserved populations.

By testing new consumer messaging and tailoring existing messaging, FSIS can help ensure 

that it is effectively communicating with the public and promoting behavior change with a 

goal of improving consumer food safety practices. FSIS contracted with RTI International to 

conduct consumer research over a 5-year period, fiscal year 2017 through fiscal year 2022. 

RTI is teaming with researchers at North Carolina State University (NCSU) to conduct the 

project. This behavioral research will include observation studies of food preparation in test 

kitchens using an experimental design (five iterations), focus group studies (two iterations), 

and web surveys (two iterations). Each iteration of each data collection activity will address 

different research questions and use a different sample of consumers. This research will 

provide insight into the effect FSIS consumer outreach activities have on consumers’ food 
Food Safety Consumer Research Project:

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1-2

safety behaviors. FSIS will use the results of this research to enhance messaging and 

accompanying materials to improve food safety behaviors of consumers.

1.2 Objectives of Grilling Meal Preparation Experiment

Previous research suggests that self-reported data collected through surveys on consumers’

food safety practices may be unreliable because consumers tend to overreport their 

behavior (e.g., simply rinsing their hands instead of washing with soap and water for 20 

seconds as recommended) (Redmond & Griffith, 2003). Because of this limitation,

observation is often a preferred approach for collecting information on consumers’ food 

safety practices.

Studies that have used direct observation of consumer food handling have reported that 

many consumers commit errors during preparation and self-report actions that are different

from the ones they took (Anderson et al., 2004; DeDonder et al., 2009; Jay, Comar, & 

Govenlock, 1999; Kendall et al., 2004; Redmond, Griffith, Slader, & Humphrey, 2004). The 

results of the meal preparation experiments will help FSIS assess adherence to the four 

recommended food safety behaviors of clean, separate, cook, and chill; determine whether 

food safety messaging focused on those behaviors affects consumers’ safe food handling 

behaviors; and determine whether consumers introduce cross-contamination during food 

preparation for certain raw meat and poultry products.

Each iteration of the meal preparation experiment addresses a specific consumer behavior.

The fourth iteration examined thermometer use, handwashing practices, and handling and 

storage of uncooked ground beef from a chub. For this study, we explored the impact of 

including food safety instructions in recipes on participants’ food safety practices. 

Participants were randomized to one of three conditions: the control group, recipes without 

food safety instructions; Treatment 1 (T1), recipes with food safety instructions; or 

Treatment 2 (T2), recipes with food safety instructions and a celebrity endorsement. 

Participants were asked to grill bratwurst and hamburgers and prepare a ready-to-eat (RTE)

salad (bagged lettuce, carrots, and apples). The study also assessed pathogen transfer 

during meal preparation and included the collection of microbiological samples from lettuce 

(from the prepared RTE salad) and kitchen surfaces. We observed participants throughout 

meal preparation to determine whether they used a food thermometer, adhered to 

recommended handwashing practices, safely prepared the RTE salad, and safely handled 

and stored uncooked ground beef from a chub. Post-observation interviews collected 

information on participants’ reasons for following or not following recommended food safety 

practices during the meal preparation and their response to the intervention (treatment 

groups). Additionally, to provide information to the Food and Drug Administration (FDA), 50 

additional participants prepared guacamole to examine preparation of an RTE product using 

avocado and cilantro; these data were not included as part of the experimental study and 

will be described in a separate memorandum.
Section 1 — Introduction

1-3

Table 1-1 lists the study’s research questions, data sources, and the corresponding section 

of this report with the results of the analysis conducted to address each research question.

Table 1–1. Research Questions, Data Sources, and Location of Results in Report

Research Questions Data Source Location in Report

Is the rate of thermometer use on the bratwurst

and hamburgers higher for T1 compared with the 

control group? Is the rate higher for T2 compared 

with the control group? Is the rate for T2 higher 

compared with T1?

Observations Section 3.2; Table 3-4 

Is the mean number of items (bratwurst or 

hamburgers) checked for doneness higher for T1 

compared with the control group? Is the mean 

number higher for T2 compared with the control 

group? Is the mean number higher for T2 

compared with T1?

Observations Section 3.2; Table 3-4 

What methods are used to determine doneness of 

bratwurst and hamburgers in lieu of a food 

thermometer for the control and treatment 

groups?

Observations, postobservation 

interviews

Section 3.2; Table 3-4

Is the rate of handwashing attempts higher for T1 

compared with the control group? Is the rate 

higher for T2 compared with the control group? Is 

the rate for T2 higher compared with T1?

Observations Section 3.3; Tables 3-7, 

3-8

Is the rate of cleaning/sanitizing attempts higher 

for T1 compared with the control group? Is the 

rate higher for T2 compared with the control 

group? Is the rate for T2 higher compared with 

T1?

Observations Section 3.4; Table 3-11

How do participants handle and store uncooked 

ground beef from a chub to be prepared later? 

Observations, postobservation 

interviews

Section 3.4; Tables 3-12, 

3-13, 3-14

Is the rate of successfully washing apples and 

carrots higher for T1 compared with the control 

group? Is the rate higher for T2 compared with 

the control group? Is the rate for T2 higher 

compared with T1? Do participants wash 

commercially bagged lettuce and do the rates 

vary by group?

Observations Section 3.5; Table 3-15

Is the prevalence of contamination lower for T1 

compared with the control group? Is the 

prevalence lower for T2 compared with the 

control group? Is the prevalence for T2 lower 

compared with T1?

Microbiological 

sampling data

Section 3.6; Table 3-16

(continued)
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Table 1–1. Research Questions, Data Sources, and Location of Results in Report

(continued)

Research Questions Data Source Location in Report

Did participants recall the food safety 

instructions? If so, did participants self-report 

that the instructions influenced food preparation? 

(T1 and T2)

Post-observation 

interviews

Section 3.7; Table 3-17

Did participants self-report that food safety 

messaging from a celebrity chef influenced food 

preparation? (T2 only)

Post-observation 

interviews

Section 3.7; Table 3-18

What differences are there between key 

behavioral outcomes for Years 1–4 of the study?

Observation Section 3.2, Table 3-6; 

Section 3.3, Table 3-10

1.3 Organization of Report

This report is organized as follows:

▪ Section 2 describes the research design, data collection procedures, and analysis 

approach.

▪ Section 3 presents and discusses the results of the study for thermometer use, 

handwashing compliance, and other behaviors, as well as participants’ responses to 

the intervention.

▪ Section 4 concludes the report by summarizing the key findings and discussing the 

implications of the study results for OPACE’s consumer food safety education and 

outreach efforts.

The final report includes the following appendixes:

▪ Appendix A: Recipes 

▪ Appendix B: Observation Script 

▪ Appendix C: List of Equipment Provided in Each Test Kitchen

▪ Appendix D: Microbiological Methods 

▪ Appendix E: Post-observation Interview Guide

▪ Appendix F: Screening Questionnaire

▪ Appendix G: Observation Rubric for Coding Participant Actions in the Kitchen
2-1

2. Study Methods

This section describes the methodology for the meal preparation experiment, the 

recruitment procedures, and the approach for coding and analyzing the observations and 

post-interview data. The Office of Management and Budget (OMB control number 

0583-0169, expiration date 8/31/2023) and NCSU’s Institutional Review Board (IRB) 

approved the study protocol and materials.

2.1 Meal Preparation Experiment Methodology

2.1.1 Research Design

The fourth iteration of the meal preparation experiment focused on the food safety behavior 

of “cook,” specifically whether participants used a food thermometer when grilling bratwurst

and hamburgers. The study also examined whether participants followed recommended 

practices for repackaging remaining uncooked ground beef from a chub, proper 

handwashing, and safe preparation of an RTE salad. Study participants were adult 

individuals who self-reported cooking ground beef burgers on an outdoor grill within the 

past 6 months.

The intervention was incorporated into recipes provided to participants. The study had two 

intervention groups: (1) T1, recipe included food safety instructions and (2) T2, recipe 

included the same food safety instructions and an endorsement by a celebrity chef, J. Kenji 

López-Alt, such as “Kenji’s Spicy Burgers and Brats” (see Appendix A for a copy of each 

version of the recipes). Food safety 

information was formatted using the 

Partnership for Food Safety Education’s 

(PFSE’s) Safe Recipe Style Guide3(see 

sidebar). The control group’s recipes did 

not include food safety instructions or 

reference to a celebrity chef. Eligible 

participants were randomly assigned to 

the control group (no exposure) or one of 

the two treatment (intervention) groups.

The purpose of the experimental 

intervention was to evaluate whether including food safety instructions in recipes leads to 

greater adherence to recommended safe food handling practices compared with the control 

group (T1 vs. control), whether including food safety instructions in recipes and a celebrity 

chef endorsement leads to greater adherence to recommended safe food handling practices

compared with the control group (T2 vs. control), and whether including food safety 

3 https://www.saferecipeguide.org/

Food Safety Instructions Included in Recipes for 

the Two Treatment Groups

▪ Wash hands with soap and water [included at the 

beginning of each recipe].

▪ Wash hands with soap and water after handling 

uncooked ground beef.

▪ Clean and then sanitize the counter and utensils 

after touching uncooked ground beef.

▪ Gently rub apples/carrots under cold running 

water.

▪ Grill burgers and brats until internal temperature 

reaches 160°F on food thermometer. 
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2-2

instructions in recipes and a celebrity endorsement leads to greater adherence to 

recommended safe food handling practices than food safety information alone (T2 vs. T1).

Maughan et al. (2016) conducted a similar experiment using a recipe modified with safe 

food handling instructions to promote safe food handling behaviors for participants when 

preparing a baked chicken breast and a ground turkey patty and observed for handwashing 

and thermometer use behaviors. Adherence to safe handling behaviors between participants 

exposed to food safety instructions in the recipe and those not exposed to food safety 

instructions ranged from 24 to 66%.

The COVID-19 pandemic and subsequent requirements for social distancing and other 

precautions to ensure the safety of participants and research staff limited the number of 

participant appointments that could be scheduled each day and the number of 

microbiological samples that could be processed each day to a total of 200 participants. We 

used a balanced design with 66 participants randomly assigned to each study condition. 

2.1.2 Study Procedures

Figure 2-1 summarizes the study procedures. We conducted the study in a test kitchen 

facility located in Raleigh, North Carolina (Wake County) with three identical test kitchens. 

Each test kitchen has a sink, refrigerator, and stove/oven and was stocked with the same 

meal preparation equipment (dishes, knives, utensils, cutting boards, thermometer). In 

each test kitchen, eight cameras recorded participants’ actions at various locations 

throughout the kitchen and recorded the meal preparation from beginning to end. We 

implemented procedures to mitigate risks of COVID-19 to participants and research staff.4

We used convenience sampling to recruit participants using a variety of approaches. 

Section 2.2 describes the participant screening criteria and recruitment procedures. 

Participants received a $75 gift card and gift (food thermometer, mentioned after the 

completion of the research) for taking part in the study, which could take up to 90 minutes. 

Participant recruitment began November 10, 2020. We conducted observations beginning on 

December 2, 2020, and ending May 14, 2021.

4 To mitigate risks of COVID-19 to participants and research staff, the following safety precautions 

were implemented: access to the kitchens was limited; participants were scheduled at times that did 

not overlap; waiting room furniture was spaced 6 feet apart; floor markers were placed in the test 

kitchens to ensure 6 feet of distance between researcher and observer during introduction to the 

kitchen equipment; all researchers and participants wore face masks during the entire observation; 

researchers wore gloves when swabbing surfaces in the kitchen; kitchen equipment and surfaces were 

sanitized before each observation (three rounds of sanitizing); high-touch surfaces in the observation 

room were wiped down with disinfecting wipes after each observation; and researchers adhered to 

strict personal hygiene guidelines, including washing hands following Centers for Disease Control and 

Prevention (CDC) guidelines and use of hand sanitizer while in the observation room. In addition, hand 

sanitizer stations were located at the entrances to the building and test kitchen; participants were not 

required to use them.
Section 2 — Study Methods

2-3

We randomly assigned participants to the control or one of the treatment groups when the 

appointment was scheduled with the goal of 66 participants in each group. The study team

scheduled appointments at the test kitchen location based on kitchen availability with 

observations scheduled during the week, on weekends, and at different times of day (e.g., 

morning, afternoon, and evening). Once participants arrived at the test kitchen, a study 

team member greeted them and instructed them to read and sign an informed consent 

form. 

Figure 2-1. Study Procedures for Meal Preparation Experiment on Grilling 

Bratwurst and Hamburgers

Using a script to ensure consistency in delivery (see Appendix B), the study team member

described what participants could expect during the study. Initially, we told participants the 

purpose of the study was recipe testing. Consistent with the approach used in other 

observation studies, we informed participants of the real purpose of the study following the 

post-observation interview and why it was important from a scientific perspective to inform 
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them after the study was completed

5

(Chapman, Eversley, Fillion, MacLaurin, & Powell, 

2010; DeDonder et al., 2009).

A study team member instructed participants to grill the package of bratwurst and two 

hamburgers on the grill provided. Participants were provided with a laminated recipe card

(see Appendix A) for preparing the bratwurst and hamburgers, as well as a side salad, and 

told the location of the ingredients. A study team member pointed out that cabinets 

contained utensils, dishes, pans, and cleaning supplies and were labeled accordingly. 

Appendix C provides a list of equipment provided in each test kitchen and a picture of one of 

the test kitchens. Participants were instructed to prepare the bratwurst and hamburgers

first. Using this approach, it would reduce the time required in the kitchen and provide the 

opportunity for cross-contamination. Participants were also instructed to prepare only half of 

the ground beef and to repackage the remaining ground beef from the chub as they would 

at home, and the locations of common materials for repackaging were shown

(plastic/freezer bags, plastic containers, plastic wrap, aluminum foil). Participants were 

asked to clean up as they would at home once they were done cooking.

In the second year of the annual FSCRP study, the NCSU microbiology team provided the 

FSIS’ Office of Public Health Science (OPHS) with scientific justification for using a 

nonpathogenic Escherichia coli strain, tagged with green fluorescent protein (E. coli DH5-

Alpha), as a surrogate for pathogenic Salmonella in whole chicken pieces and OPHS 

approved the use of this surrogate. For this study, we inoculated ground beef packaged in 

chub-like bags and used the same nonpathogenic E. coli strain, as approved by OPHS, as a 

surrogate for pathogenic E. coli, such as O157, found in ground beef.

The use of nonpathogenic E. coli strains as surrogates for pathogenic E. coli in beef is well 

documented in the literature (Cabrera-Diaz et al., 2016; Ingham et al., 2016; Keeling et al., 

2009; Vasan et al., 2016) and reviewed in Hu and Gurtler (2017). In these studies, no 

significant differences were observed between pathogenic E. coli and fluorescent protein–

marked nonpathogenic E. coli for growth parameters, acid resistance, thermal resistance, 

cell surface hydrophobicity, attachment to beef carcass surfaces (Cabrera-Diaz et al., 2016)

and for freezing, refrigeration, fermentation, and thermal inactivation (Keeling et al., 2009). 

It can be reasonably assumed from the literature that the use of nonpathogenic fluorescent 

protein-marked E. coli surrogate (E. coli DH5-Alpha) will provide representative information 

as to how a pathogenic E. coli strain would behave during meal preparation involving 

ground beef packaged in chubs. The inoculated chubs were packaged in a 1-pound package.

We cleaned and sanitized all accessible kitchen surfaces (e.g., counters, drawer pulls, stove 

top) and appliances after each participant to ensure that any potentially remaining E. coli

DH5-Alpha contamination was removed before the next participant entered the kitchen.

5 After being informed of the study’s purpose, participants could opt out of the study and have their 

data excluded from the analysis. No participants chose to opt out of the study.
Section 2 — Study Methods

2-5

Additional cleaning protocols were put into place to reduce the risk of COVID-19 

transmission to participants and research staff: Before the first observation of the day, all 

counter and stove surfaces, refrigerator handles and shelves, trash can lids, sinks, and sink 

faucets were sanitized using bleach/disinfecting wipes. After each observation, research

staff conducted this cleaning and disinfecting procedure for three rounds of cleaning and 

sanitizing. The entry (main) door handle and the door handles of all test kitchens and the 

observation room were wiped down three times after each observation. Meal preparation 

items (e.g., knives, utensils, plates) were cleaned and sanitized in the dishwasher. Items 

that could not be placed in the dishwasher were cleaned and disinfected using either a 

disinfectant spray or wiped three times with a disinfecting wipe after each observation.

To confirm effective decontamination of the kitchen between participants, one cleaning 

validation surface swab was taken before a participant began preparing the meal. A total of 

six surface samples and one lettuce sample were taken for each observation, resulting in 

seven total samples per meal preparation event. An NCSU lab team member processed the 

swabs to determine the presence and concentration of the E. coli DH5-Alpha. Appendix D

provides a complete description of the selection of the surrogate and the microbiology 

methodology.

Supplementing the observations, we conducted semistructured post-observation interviews 

to provide insight into participants’ views, opinions, and experiences during the meal 

preparation experiment. Interviews lasted approximately 20 minutes (see Appendix E for 

the post-observation interview guide). The total time for the observation and interview was 

approximately 90 minutes.

2.1.3 Pilot Testing

Before initiating the full-scale data collection, we conducted a pilot study to test the study 

materials, procedures, and the time allotted for data collection. We conducted the pilot with

two subjects recruited through mutual acquaintances of NCSU staff working on the project.

Based on the pilot observations, we updated the procedures by instructing participants to 

cook the bratwurst and hamburgers first, adding additional information to the T2 recipes 

about the celebrity chef, and providing additional clarification about other items in the 

recipes. The post-observation interview guide was simplified and clarified, and questions 

were added to ask whether COVID-19 has influenced participant handwashing practices. The 

pilot study also helped finalize the sampling locations throughout the kitchen. Following the 

pilot study, NCSU submitted their COVID-19 safety protocols to the IRB, which was required 

to ensure research staff and participant safety.

2.2 Recruitment Procedures

The study team used convenience sampling with quotas to obtain a mix of participants with 

regard to race, ethnicity, age, education level, and presence of children in the household.
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We recruited participants using social media outlets (e.g., Facebook, Twitter) and online 

advertising platforms (e.g., Craigslist).

Participants had to meet specific inclusion and exclusion criteria. The inclusion criteria were 

as follows:

▪ are 18 to 64 years old (excluded individuals 65 years or older because of increased 

COVID-19 risk)

▪ speak English6

▪ have cooked ground beef hamburgers on an outdoor grill within the past 6 months

The exclusion criteria were as follows:

▪ have cooked or worked professionally in a food preparation setting in the past 5 

years

▪ have received any type of food safety training, such as ServSafe, in the past 5 years

▪ participated in a study about cooking within the past 3 years

Recruitment materials directed prospective participants to call or email the study team to be 

screened for eligibility or to a web link that hosted the screening questionnaire (see 

Appendix F). For participants screened by phone, we invited eligible participants to 

participate in the study and scheduled an appointment during the screening call. For 

participants who completed the web-based screener, we contacted eligible participants by 

phone, invited them to participate in the study, and scheduled an appointment. 

Appointments were scheduled during work hours, evenings, and weekends to allow for a 

broad participant pool. After an appointment was scheduled, we sent one confirmation email

and two text messages leading up to the scheduled appointment. These reminders included 

a reminder about the mandatory use of face coverings. The consent form included an 

addendum describing the additional cleaning/sanitizing procedures taking place, as well as 

requirements for face coverings and social distancing. Each participant was required to state 

they had not interacted with someone who had been diagnosed with or exhibited symptoms 

of COVID-19, that they were not experiencing any symptoms of COVID-19, that they 

agreed to follow all safety procedures, and that they allowed their information to be 

recorded for potential contact-tracing purposes.

A total of 200 people participated in the experimental study: 66 in the control group, 66 in 

T1, and 68 in T2. Section 3 provides information on the demographic characteristics of 

participants. The overall eligibility rate (percentage of cases that completed the web-based 

or phone screening and met the eligibility criteria) was 42%. Among the 200 study 

participants, we recruited 73% using social media (Facebook and Twitter), 13% using 

6 The recruiting materials were available in Spanish to reach English-speaking Hispanics, but the study 

was conducted only in English.
Section 2 — Study Methods

2-7

Craigslist, and 14% using other recruiting efforts such as word of mouth. The no show rate

not including cancellations was 17.5%.

2.3 Coding of Observation Data and Analysis

We used notational analysis to assess recorded actions and their frequencies during meal 

preparation. Notational analysis is a generic tool used to collect observed events and place 

them in an ordered sequence (Hughes & Franks, 1997); it has been used to track food 

safety behaviors because it enables the recording of specific details about events in the 

order in which they occur by associating a time stamp with actions (Clayton & Griffith, 

2004). Notational analysis has been used in both nonparticipant and participant consumer 

food safety behavior observation studies, as well as participant foodservice observation 

(Chapman et al., 2010; Clayton & Griffith, 2004; Green et al., 2006; Redmond et al., 2004).

We developed coding rubrics (see Appendix G) to characterize the following behaviors:

▪ thermometer usage and other methods to determine doneness of bratwurst and 

hamburgers

▪ handwashing compliance according to CDC guidelines

▪ indirect cross-contamination (failure to properly clean and sanitize surfaces)

▪ storing of uncooked ground beef from a chub

▪ method used to wash the apple and carrot

A trained coder viewed each video and followed the rubric to indicate level of adherence to 

recommended behaviors while observing the participants. Coders were trained by reviewing 

the coding rubric and using practice food safety handling scenarios to compare inter- and 

intracoding reliability. Incorrect and inconsistent coding situations were discussed with 

coders to ensure that proper and consistent training occurred. 

For each behavior of interest (identified by the use of bold text in the result tables shown in 

Section 3), we calculated proportions for the control group and each of the two treatment

groups and conducted statistical testing using a chi-squared test for the differences between 

groups (control vs. T1, control vs. T2, and T1 vs. T2). We used a p value of ≤.05 to indicate 

statistical significance.

2.4 Microbiological Data and Analysis

As previously noted, a nonpathogenic strain of E. coli DH5-Alpha that fluoresces under UV 

light was used as the surrogate. We determined the concentration of DH5-Alpha on swab 

samples by enumerating the bacteria on selective media and visualizing colonies under UV 

light. To confirm effective decontamination of the kitchen between participants, one cleaning 

validation surface swab was taken before a participant began preparing the meal. We 

collected five additional surface samples and one lettuce sample from the prepared RTE 
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salad. Appendix D provides additional information on the microbiological analysis

procedures.

For each surface and lettuce sample, we calculated prevalence and level of contamination 

by study group. For prevalence, we conducted statistical testing using a chi-squared test for 

the differences between groups (control vs. T1, control vs. T2, and T1 vs. T2). We used a p

value of ≤.05 to indicate statistical significance.

2.5 Post-observation Interviews and Analysis

The post-observation interviews collected information on participants’ behaviors while 

preparing the bratwurst, hamburgers, and RTE salad in the test kitchen and their usual 

behavior at home and other information. For the treatment groups, the interviewer probed 

for recall of the food safety instructions in the recipe and for T2 recall of the celebrity chef 

information (aided recall). If participants recalled the food safety information, they were 

asked if the information influenced their actions in the kitchen during the study and whether 

they believed the information would influence how they cook at home in the future. For T2, 

participants were also asked whether the celebrity chef’s inclusion of food safety instructions 

influenced their behavior in the kitchen. Table 2-1 summarizes the information collected in 

the post-observation interviews (Appendix E provides the interview guide).

Table 2-1. Summary of Information Collected in the Post-observation Interviews

Self-reported Participant Behavior in the 

Test Kitchen and at Home

Response to Food Safety Instructions in 

Recipes

▪ Washing hands after handling bratwurst and 

ground beef during meal preparation

▪ Recalled food safety instructions in the 

recipes (unaided and aided recall)

▪ Preparation of bratwurst and hamburgers and 

food thermometer use

▪ Whether food safety instructions influenced 

actions during meal preparation (e.g., used 

thermometer, reinforced normal practices)

▪ Concerns about cross-contamination when 

handling raw meat products

▪ Whether food safety instructions will 

influence actions when cooking at home

▪ Experience with repackaging remaining 

ground beef in chubs

▪ Familiarity with celebrity chef who endorsed

recipes for T2

▪ Cleaning/sanitizing practices ▪ Whether having the food safety instructions 

coming from a celebrity chef influenced how 

they prepared the meal

▪ Whether COVID-19 has played a role in how 

often or when wash hands

▪ Whether the celebrity chef who endorsed the 

T2 recipes or other celebrity chefs are trusted 

sources of food safety information

We audio-recorded the interviews and transcribed and coded the interview transcripts. Most 

of the questions were open ended, so to analyze the data, we coded the responses. We 
Section 2 — Study Methods

2-9

used QSR International NVivo, Version 12 software to organize and code the data. We 

assigned a unique case number to each participant to link the screener data and postobservation data. We outputted the coded data to Excel and tabulated the responses by the 

three study groups.

3-1

3. Results

This section describes the characteristics of the study sample and presents the results of the 

meal preparation experiment for grilling bratwurst and hamburgers, handwashing 

compliance, cleaning and sanitizing, storing uncooked ground beef from a chub, and 

washing produce. We also present the results of the microbiological analysis that assessed 

cross-contamination during meal preparation. 

3.1 Sample Characteristics

Of the 200 participants in the study sample, 75% were White and 90% were non-Hispanic. 

Participants represented a variety of ages with 28% in the 18 to 34 years old age category, 

49% in the 35 to 54 years old age category, and 23% in the 55 years or older age category. 

About a third (34%) of participants had a 4-year college degree or more education, and 

37% had at least one child living in the household (≤17 years). About 30% of participants 

had at least one individual in the household at risk for foodborne illness (i.e., adult aged 60 

years or older; pregnant woman; child aged 5 years or younger; or individual diagnosed 

with diabetes, kidney disease, or another condition that weakens the immune system) (see 

Table 3-1). Table 3-2 compares the demographic characteristics of the study sample to the 

recruiting targets that were set for the study. The study generally met the recruiting 

targets. 

The screening questionnaire collected information on participants’ experience with 

purchasing and preparing bratwurst and hamburgers (Table 3-3). Many participants (87%) 

have experience buying fresh bratwurst and 74% had grilled bratwurst outdoor in the past 6 

months. Seventy percent of participants reported purchasing chubs at least once in the past 

3 months, with 42% reported purchasing chubs 1 to 3 times. The most common cited 

reasons for purchasing chubs were price (71%), convenience (42%), and size option (39%). 

Eighty-one percent of participants reported purposefully purchased meat or poultry in large 

quantities to repackage for cooking at a later date.
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Table 3-1. Sample Characteristics

Characteristic

All 

Participants

(n = 200)

Control: 

Standard 

Recipes

(n = 66)

T1: Food 

Safety 

Recipes

(n = 66)

T2: Food 

Safety 

Recipes+

Celebrity 

Endorsement 

(CE)

(n = 68)

Gender

Female 34% (67) 36% (24) 38% (25) 27% (18)

Male 65% (130) 61% (40) 62% (41) 72% (49)

Other/prefer not to answer 2% (3) 3% (2) 0% (0) 1% (1)

Race

Caucasian or White 75% (151) 71% (47) 76% (50) 79% (54)

Black or African American 16% (32) 14% (9) 17% (11) 18% (12)

Other racea 9% (17) 15% (10) 8% (5) 3% (2)

Ethnicity

Not Hispanic or Latino 90% (181) 89% (59) 92% (61) 90% (61)

Hispanic or Latino 10% (19) 11% (7) 8% (5) 10% (7)

Age

18–34 28% (55) 24% (16) 29% (19) 29% (20)

35–54 49% (99) 46% (30) 56% (37) 47% (32)

55–64b 23% (46) 30% (20) 15% (10) 24% (16)

Education

Less than high school, high 

school diploma/GED, or technical 

or vocational school

26% (52) 21% (14) 21% (14) 18% (12)

Some college 40% (80) 41% (27) 39% (26) 42% (29)

Bachelor’s degree 19% (38) 20% (13) 20% (13) 25% (17)

Graduate or professional degree 15% (30) 18% (12) 20% (13) 15% (10)

Have child 17 or younger living in 

household

37% (74) 33% (22) 39% (26) 38% (26)

Have at-risk individual living in 

householdc

30% (60) 20% (13) 29% (19) 41% (28)

a Other race includes American Indian or Alaska Native, Asian, Native Hawaiian or Other Pacific 

Islander, and two or more races.

b People 65 years or older were excluded from the study because of increased COVID-19 risk.

c At-risk populations are people who are 60 years of age or older, children 5 years of age or younger, 

pregnant women, people diagnosed with diabetes or kidney disease, and people diagnosed with a 

condition that weakens the immune system.

Note: Responses may not sum to 100% because of rounding.

Source: 2020–2021 meal preparation experiment—screening questionnaire. 
Section 3 — Results

3-3

Table 3-2. Comparison of the Study Sample with Recruitment Targets

Characteristic

Study Sample 

(n = 200)

Recruitment 

Target (%)

Race

White 75% (151) 75%

Non-Whitea 25% (49) 25%

Ethnicity

Not Hispanic or Latino 90% (181) 90%

Hispanic or Latino 10% (19) 10%

Age

18–34 28% (55) 25%

35–54 49% (99) 49%

55–64b 23% (46) 26%

Education

Less than high school, high school diploma/GED, or technical 

or vocational school

26% (52) 26%

Some college 40% (80) 40% 

Bachelor’s degree 19% (38) 19% 

Graduate or professional degree 15% (30) 15% 

Household status

Children (0–17) 37% (74) 35%

No children 63% (126) 65%

a Non-White includes Black or African American, American Indian or Alaska Native, Asian, Native 

Hawaiian and Other Pacific Islander, other races, or two or more races.

b People 65 years or older were excluded from the study because of increased COVID-19 risk.

Note: Responses may not sum to 100% because of rounding.

Source: 2020–2021 meal preparation experiment—screening questionnaire. 
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Table 3-3. Self-reported Participant Experience with Purchasing and Preparing 

Bratwurst and Hamburgers

Characteristic

All 

Participants

%

Control: 

Standard 

Recipes

%

T1: Food 

Safety Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Bratwurst

Participant has cooked raw/fresh 

bratwurst/sausages purchased at a 

meat counter 

87% (174) 82% (54) 89% (59) 90% (61)

Participant has grilled product 

outdoors in the past 6 months

74% (148) 71% (47) 77% (51) 74% (50)

Hamburgers

Frequency that participant 

purchased ground beef in a chuba

within the past 3 months

Never 30% (59) 30% (20) 29% (19) 29% (20)

1 to 3 times 42% (83) 44% (29) 42% (28) 38% (26)

4 to 6 times 17% (34) 14% (9) 14% (9) 24% (16)

7 to 12 times 8% (15) 5% (3) 14% (9) 4% (3)

More than 12 times 5% (9) 8% (5) 2% (1) 4% (3)

Reasons for purchasing chubsb

Price 71% (100) 80% (37) 66% (31) 67% (32)

Convenience 42% (59) 35% (16) 43% (20) 48% (23)

Size option 39% (55) 41% (19) 36% (17) 40% (19)

Shelf life 17% (24) 20% (9) 11% (5) 21% (10)

Brand preference 11% (16) 13% (6) 11% (5) 10% (5)

Other 11% (16) 4% (2) 17% (8) 13% (6)

Participant has purposefully

purchased meat or poultry in large 

quantities to repackage for cooking 

at later date 

81% (161) 77% (51) 86% (57) 78% (53)

Number of participants 200 66 66 68

a Because participants may not be familiar with the word “chub,” we asked the question as follows: 

“During the past 3 months, about how often did you purchase ground beef that is not sold in 

Styrofoam trays? This type of packaging is sometimes referred to as a chub. Chubs are a tube-like 

package that looks like a sausage with the ends sealed by metal crimps or clips.”

b Only participants (n = 141) who reported purchasing chubs in the past 3 months answered this 

question. Participants could provide multiple responses, so the total may sum to more than 100%.

Note: Responses may not sum to 100% because of rounding. Participants who did not purchase the 

product were excluded from the calculations for prepare product and frequency of preparing the 

product.

Source: 2020–2021 meal preparation experiment—screening questionnaire. 
Section 3 — Results

3-5

3.2 Thermometer Use

The recipes for the two treatment groups instructed participants to “[g]rill burgers and brats 

until internal temperature reaches 160°F on food thermometer.” Table 3-4 summarizes 

thermometer use for checking doneness of the bratwurst and hamburgers. There was a 

statistically significant difference between the percentage of control group participants who 

used a food thermometer to check the doneness of at least one bratwurst (55%) compared 

with T1 participants—recipe with food safety instructions (95%). Likewise, there was a 

statistically significant difference between the percentage of control group participants who 

used a food thermometer to check the doneness of at least one bratwurst (55%) compared 

with T2 participants—recipe with food safety instructions + celebrity endorsement (96%). 

The difference between the two treatment groups was not statistically significant. Among 

the five bratwurst cooked, the mean number of bratwurst checked for doneness averaged 

four for each group. The recommendation is to check the temperature of each item being 

cooked because of possible variations in temperatures.

Table 3-4. Observed Preparation of Bratwurst and Hamburgers

(continued)

Behavior

Control: 

Standard 

Recipes

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Bratwurst n = 66 n = 66 n = 68

Participant used thermometer to check 

donenessa

55% (36)1,2 95% (63)1 96% (65)2

SE = 0.06 SE = 0.03 SE = 0.03

Among participants who used thermometer, 

number of bratwurst checked

n = 36 n = 63 n = 65

All bratwurst (five) 72% (26) 75% (47) 65% (42)

Two to four 17% (6) 24% (15) 23% (15)

One 11% (4) 2% (1) 12% (8)

Mean number checkedb 4.22 4.46 4.05

SE = 0.23 SE = 0.12 SE = 0.18

Method used to determine doneness n = 66 n = 66 n = 68

Only used thermometer 23% (15) 67% (44) 54% (37)

Only used touch (e.g., firmness) 21% (14) 2% (1) 0% (0)

Only used time 9% (6) 2% (1) 3% (2)

Only used visual cue (i.e., cut open to look 

inside)

6% (4) 2% (1) 0% (0)

Observed using more than one method, 

including thermometer

32% (21) 29% (9) 41% (28)

Observed using more than one method, not 

including thermometer

9% (6) 0% (0) 1% (1)
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Table 3-4. Observed Preparation of Bratwurst and Hamburgers (continued)

a We calculated p value significance testing using a chi-squared test for the difference between groups 

(control vs. T1, control vs. T2, and T1 vs. T2). Pairs of superscripted numbers indicate proportions

that are significantly different at p ≤.05.

b We calculated p value significance testing using repeated measures of analysis of variance (i.e., 

ANOVA) (control vs. T1, control vs. T2, and T1 vs. T2). Pairs of superscripted numbers indicate

means that are significantly different at p ≤ .05.

Notes: Responses may not sum to 100% because of rounding. SE = standard error

Source: 2020–2021 meal preparation experiment—coding of food preparation.

Some participants, especially those in the control group, attempted to determine doneness

of the bratwurst using indicators other than a thermometer. For the control group, 21% of 

participants relied solely on firmness (e.g., touch), 9% relied solely on time, and 6% relied 

solely on a visual cue (e.g., color). About one-third of participants (32%) used a

thermometer and another indicator to determine doneness. 

There was a statistically significant difference between the control group and each of the 

two treatment groups for the percentage of participants using a food thermometer to check 

the doneness of hamburgers; 58% of control group participants used a food thermometer 

Behavior

Control: 

Standard 

Recipes

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Hamburgers n = 66 n = 66 n = 68

Participant used thermometer to check 

donenessa

58% (38)1,2 95% (63)1 99% (67)2

SE = 0.06 SE = 0.03 SE = 0.01

Among participants who used thermometer, 

number of hamburgers checked

n = 38 n = 63 n = 67

One 8% (3) 0% (0) 6% (4)

Two 92% (35) 100% (63) 94% (63)

Mean number checkedb 1.9 2.0 1.9

SE = 0.04 SE = 0.00 SE = 0.03

Method used to determine doneness n = 66 n = 66 n = 68

Only used thermometer 12% (8) 30% (20) 34% (23)

Only used touch (e.g., firmness) 21% (14) 3% (2) 0% (0)

Only used visual cue (i.e., cut open to look 

inside)

3% (2) 0% (0) 0% (0)

Only used time 0% (0) 0% (0) 0% (0)

Observed using more than one method, 

including thermometer

45% (30) 65% (43) 65% (44)

Observed using more than one method, not

including thermometer

18% (12) 2% (1) 1% (1)
Section 3 — Results

3-7

on at least one hamburger, while 95% of T1 and 99% of T2 used a food thermometer. The 

difference between the two treatment groups was not statistically significant. Nearly all 

participants in each of the three groups checked the doneness of both hamburgers.

Similarly to bratwurst, participants used other methods to determine doneness for the 

hamburgers. Twenty-one percent of control group participants relied solely on firmness 

(e.g., touch) and 3% relied solely on a visual cue (e.g., color); 45% of control group 

participants used more than one method not including a thermometer to determine 

doneness (see Table 3-4). Participants in the treatment groups rarely used other indicators 

to test for doneness.

According to the post-observation interviews (Table 3-5), 88% of all participants reported 

owning a food thermometer. About one-half of treatment group (T1 and T2) participants 

who reported owning a thermometer and using it in the test kitchen said they usually use 

one when grilling at home, whereas thermometer use in the test kitchen ranged from 95 to 

99% for the two treatment groups, depending on the product.

Table 3-5. Self-Reported Thermometer Use

Question

All 

Participants

%

Control: 

Standard 

Recipes

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Self-reported food thermometer 

ownership 

88% (176) 92% (61) 89% (59) 82% (56)

If own thermometer (n = 176), selfreported use of thermometer in test 

kitchen for bratwurst and/or 

hamburgers

88% (155) 70% (43) 97% (57) 98% (55)

If reported using thermometer 

(n = 155), do you usually use one to 

determine doneness when grilling at 

home?

Yes 55% (85) 65% (28) 53% (30) 49% (27)

No 27% (42) 21% (9) 28% (16) 31% (17)

Depends on the food 18% (28) 14% (6) 19% (11) 20% (11)

Number of participants (unless 

otherwise noted)

200 66 66 68

Source: 2020–2021 meal preparation experiment—post-observation interview.

We attempted to code the final endpoint temperature by viewing the videos but were unable 

to ascertain the temperature for most participants (81%). Participants frequently stood in 

front of the camera or turned the thermometer away from them (and the camera) to read 

it, so few temperatures were visible. Because of the small number of participants, these 
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data are not shown. For the Year 5 study, we plan to purchase data-logging thermometers 

that will allow us to collect reliable data on final endpoint temperatures.

Figure 3-1 is a diagram of a bratwurst with a heat map indicating thermometer placement 

for the control and treatment group participants. The red-colored dots indicate points of 

thermometer insertion from the top, while green-colored dots indicate insertion from the

ends of the bratwurst. Overall, participants inserted the thermometer into the top of the 

bratwurst most frequently (red dots), whereas the correct placement is into one of the ends 

of the bratwurst (green dots).

Figure 3-2 is a diagram of a hamburger with a heat map indicating thermometer placement 

for the control and treatment group participants. The red-colored dots indicate points of 

thermometer insertion from the top, while green-colored dots indicate insertion from the 

side. The majority of participants for all three groups inserted the thermometer into the top 

of the patty, whereas the correct placement is into the side of the patty (green dots).
Section 3 — Results

3-9

Figure 3-1. Bratwurst with Heat Maps Showing Thermometer Placement by Group

Note: Participants placed the bratwurst both vertically and horizontally on the grill. For bratwurst 

placed vertically, the tip pointing toward the top of the grill is labeled “North,” and for bratwurst 

placed horizontally, the tip facing away from the stovetop is labeled “North.” Red dots indicate 

thermometer insertion into the top of the bratwurst. Green indicates thermometer insertion into the 

end of the bratwurst. Heat maps reflect the first bratwurst that was checked for doneness. n = 36 

(control), 63 (T1), 65 (T2)

Source: 2020–2021 meal preparation experiment—coding of food preparation.
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Figure 3-2. Hamburger with Heat Maps Showing Thermometer Placement by 

Group

Note: “North” is the part of the grill that is farthest from the participant. Red dots indicate 

thermometer insertion into the top of the patty. Green indicates thermometer insertion into the side 

of the patty. Heat maps reflect the first hamburger that was checked for doneness. n = 38 (control), 

63 (T1), 67 (T2)

Source: 2020–2021 meal preparation experiment—coding of food preparation.
Section 3 — Results

3-11

Table 3-6 compares the results for Years 1 through 4 for thermometer use for control group 

participants (i.e., not exposed to an intervention). In Year 1, participants prepared turkey 

burgers with a garnish and a chef salad (Cates et al., 2018), in Year 2, participants who 

self-identified as poultry washers prepared chicken thighs and a mixed green salad, and in 

Year 3, participants prepared breaded not-ready-to-eat (NRTE) chicken cordon bleu from 

frozen (Cates et al., 2020). Thermometer use varied depending on the product cooked; the 

rate was highest for the NRTE chicken product and lowest for turkey burgers. The rate of 

thermometer use was significantly higher for hamburgers (58%) compared with turkey 

burgers (34%). Among thermometer users, checking the temperature of multiple items 

ranged from 76% for chicken thighs to 92% for hamburgers. 

Table 3-6. Comparison of Thermometer Use for Annual Meal Preparation

Experiments (Control Group Participants) 

Year 1

Turkey 

Burgers

(n = 185)

Year 2

Chicken 

Thighs

(n = 154)

Year 3

Frozen, 

Breaded 

NRTE 

Chicken 

(n = 196)

Year 4

Bratwurst

(n = 66)

Year 4

Hamburgers

(n = 66)

% used thermometer on 

at least one item

34% 44% 77% 55% 58%

% checked temperature 

of multiple items (among 

thermometer users)

79% 76% 85% 89% 92%

Note: NRTE = not ready to eat

Sources: 2017, 2018, 2019, and 2020-2021 meal preparation experiments—coding of food 

preparations.

3.3 Handwashing Compliance

The recipes for the two treatment groups instructed participants to “[w]ash hands with soap 

and water” both before beginning to prepare food and after handling raw ground beef.

Inadequate handwashing has been identified as a contributing factor to foodborne illness, 

especially when preparing raw meat and poultry. Hands can become vectors that move 

pathogens around sites for foodborne pathogens found in raw meat and poultry and that 

contribute to home-acquired foodborne illnesses. The frequency and level of contamination 

of hands have not been well studied. 

The total handwashing events required per observation were determined during the coding 

for each observation. A handwashing event was required for each of the following instances:

▪ before onset of food preparation

▪ anytime between touching the packaging for the bratwurst or hamburgers and then 

touching a different item
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▪ after touching another person or self

▪ after touching a cell phone

▪ after multitasking (chores)

▪ after touching contaminated (post-meal) trash or a trash can

The total number of attempts per observation was the number of times a participant 

washed their hands. Each handwashing event was coded as successful or unsuccessful

based on CDC’s criteria: wet hands with water; rub hands with soap for at least 20 seconds; 

rinse hands with water; and dry hands using a clean, one-use towel. For example, 

participant 001T was required to wash her hands nine times but attempted only two times. 

Of these two times, neither was coded as successful because she did not rub her hands with 

soap for a total of 20 seconds. Our analysis only considered compliance with CDC’s 

handwashing criteria; we did not consider risk reduction from participants following some 

but not all required steps of a successful handwashing event. It is estimated that proper 

handwashing results in approximately 1 log reduction (Montville, Chen, & Schaffner, 2002).

Drying hands using a clean, one-use towel is an important step in handwashing because it 

can physically remove microbes and contaminants from hands, resulting in up to 1 

additional log reduction (Huang, Ma, & Stack, 2012).

Table 3-7 summarizes handwashing compliance before meal preparation. The percentage of 

handwashing attempts was significantly higher among the two treatment groups (62% for 

T1 and 65% for T2) compared with the control group (44%). Among handwashing attempts, 

few contained all steps of a correct handwashing event according to CDC’s criteria and were 

considered successful attempts: 3% for the control group, 5% for T1, and none for T2. The 

most common reason for unsuccessful handwashing was not rubbing hands with soap for at 

least 20 seconds (71% for the control group, 74% for T1, and 77% for T2), followed by not 

wetting hands with water (71% for the control group, 44% for T1, and 66% for T2). 

Table 3-7. Observed Handwashing Compliance before Meal Preparation

Control: 

Standard 

Recipes 

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Did not attempt 56% (37) 38% (25) 35% (24)

Attemptsa, b 44% (29)1, 2 62% (41)1 65% (44)2

Successful attemptsc 3% (1) 5% (2) 0% (0)

Unsuccessful attempts 97% (28) 95% (39) 100% (44)

(continued)
Section 3 — Results

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Table 3-7. Observed Handwashing Compliance before Meal Preparation

(continued)

Control: 

Standard 

Recipes 

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Reasons for unsuccessful attemptd

Did not first wet hands with water 71% (20) 44% (17) 66% (29)

Did not use soap 0% (0) 0% (0) 2% (1)

Did not rub hands with soap for at least 20 

seconds

71% (20) 74% (29) 77% (34)

Did not rinse hands with water 18% (5) 5% (2) 2% (1)

Did not dry hands 0% (0) 0% (0) 2% (1)

Dried hands with surface other than clean, 

one-use towel (e.g., wiped hands on clothing 

or used previously used towel)

0% (0) 0% (0) 2% (1)

Number of participants 66 66 68

a We calculated p value significance testing using a chi-squared test for the difference between groups

(control vs. T1, control vs. T2, and T1 vs. T2). Pairs of superscripted numbers indicate proportions

that are significantly different at p ≤.05.

b “Attempt” was defined as any time that a participant appeared to wash their hands; the attempt 

could be successful or unsuccessful.

c A successful attempt was defined as a participant meeting all CDC criteria for handwashing: wet 

hands with water; rub hands with soap for at least 20 seconds; rinse hands with water; and dry 

hands using a clean, one-use towel.

d There may be multiple reasons for unsuccessful attempts, so the total may sum to more than 100%.

Source: 2020–2021 meal preparation experiment-observed behavior.

Table 3-8 summarizes handwashing compliance during meal preparation. For each group, 

we observed between 496 (T2) and 570 (C) cases in which a handwashing event was 

required to prevent cross-contamination during meal preparation. Required handwashing 

events varied by person based on each participant’s handling behaviors; as a result, some 

participants had a greater number of required handwashing events than others (e.g., 

touched the packaging of the ground beef chub more often). 
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Table 3-8. Observed Handwashing Compliance during Meal Preparation

Control: 

Standard 

Recipes

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Handwashing event required 570 496 498

Did not attempt 75% (430) 71% (353) 70% (349)

Attemptsa, b 25% (140) 29% (143) 30% (149)

Successful attemptsc 3% (4) 6% (9) 7% (11)

Unsuccessful attempts 97% (136) 94% (134) 93% (138)

Reasons for unsuccessful attemptd

Did not wet hands with water 46% (63) 35% (46) 36% (49)

Did not use soap 15% (20) 14% (18) 13% (18)

Did not rub hands with soap for at least 20 

seconds

85% (116) 80% (106) 88% (122)

Did not rinse hands with water 39% (53) 23% (31) 13% (18)

Did not dry hands 19% (26) 23% (31) 20% (27)

Dried hands with surface other than clean, oneuse towel (e.g., wiped hands on clothing or 

used previously used towel)

24% (32) 27% (35) 32% (44)

Number of participants 66 66 68

a We calculated p value significance testing using a chi-squared test for the difference between groups 

(control vs. T1, control vs. T2, and T1 vs. T2). Pairs of superscripted numbers indicate proportions

that are significantly different at p ≤.05.

b “Attempt” was defined as any time that a participant appeared to wash their hands; the attempt 

could be successful or unsuccessful.

c A successful attempt was defined as a participant meeting all CDC criteria for handwashing: wet 

hands with water; rub hands with soap for at least 20 seconds; rinse hands with water; and dry 

hands using a clean, one-use towel.

d There may be multiple reasons for unsuccessful attempts, so the total may sum to more than 100%.

Source: 2020–2021 meal preparation experiment—observed behavior.

The percentage of handwashing attempts was 25% for the control group, 29% for T1, and 

30% for T2. Among handwashing attempts, few contained all steps of a correct 

handwashing event according to CDC’s criteria and were considered successful attempts: 

3% for the control group, 6% for T1, and 7% for T2. There were no statistically significant 

differences in handwashing rates between the three groups. The most common reason for 

unsuccessful handwashing was not rubbing hands with soap for at least 20 seconds (85% in 

the control group, 80% in T1, and 88% in T2), followed by not wetting hands with water as 

a first step (46% in the control group, 35% in T1, and 36% in T2).

Participants were asked about their handwashing behavior during the post-observation 

interview (see Table 3-9). Nearly all participants (96%) said that washing hands before 
Section 3 — Results

3-15

cooking was something they typically do at home, whereas the observed rate for attempting

handwashing was much lower (ranging from 44 to 65% depending on the group). When 

cooking at home and touching food, nearly half of participants (48%) said they wash their 

hands after handling raw meat or poultry, 27% said it varies with the type of food, and 13% 

said they do so between handling each item. The observed rate for attempting handwashing 

for required events ranged from 25 to 30% depending on the group.

For Year 4, we asked about the role that the COVID-19 pandemic and associated 

handwashing guidance from CDC may have played in changing participants’ handwashing 

behaviors. Forty percent of participants said government recommendations influence their 

decision to wash their hands to some extent. These participants described the 

recommendations as “common sense” or viewed these recommendations as public health 

measures. Some participants noted that their food service background also influenced their 

handwashing. About 78% of participants said that COVID-19 played a role in increasing the 

frequency of handwashing; however, participants said this increase in handwashing is not 

specific to meal preparation times but also included returning home from work or shopping.

Table 3-9. Self-reported Handwashing Behaviors 

Question

All 

Participants

%

Control: 

Standard 

Recipes

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Did you wash your hands before 

cooking today (in the test kitchen)?

Yes 96% (193) 92% (61) 98% (65) 99% (67)

No 4% (7) 8% (5) 2% (1) 1% (1)

If washed hands (n = 193), is this 

something you usually do when 

cooking at home?

Yes 95% (184) 96% (59) 97% (63) 93% (62)

No 1% (2) 2% (1) 0% (0) 1% (1)

Sometimes 4% (7) 2% (1) 3% (2) 6% (4)

When cooking at home and you 

touch food, when do you wash your 

hands?a

After handling raw meat or 

poultry

48% (96) 45% (30) 48% (32) 50% (34)

Varies by type of food 27% (54) 21% (14) 32% (21) 28% (19)

Between handling each item 13% (25) 14% (9) 12% (8) 12% (8)

Answer unclear 8% (16) 11% (7) 6% (4) 7% (5)

Before cooking 4% (7) 8% (5) 2% (1) 1% (1)

At the end of meal preparation 1% (2) 2% (1) 0% (0) 1% (1)

(continued)
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Table 3-9. Self-reported Handwashing Behaviors (continued)

Question

All 

Participants

%

Control: 

Standard 

Recipes

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Do government recommendations 

influence your decision to wash your 

hands?

No 60% (119) 62% (41) 56% (37) 60% (41)

Some 40% (81) 38% (25) 44% (29) 40% (27)

Has COVID-19 played a role in how 

often or when you wash your hands?

Yes 78% (156) 68% (45) 86% (57) 79% (54)

No 22% (44) 32% (21) 14% (9) 21% (14)

Number of participants (unless 

otherwise noted)

200 66 66 68

a Participants could provide multiple responses, so the total may sum to more than 100%.

Note: Responses may not sum to 100% because of rounding.

Source: 2020–2021 meal preparation experiment—post-observation interview.

Table 3-10 compares the results for Years 1 through 4 for handwashing compliance among 

control group participants, which varied by study year. The handwashing rate for before 

meal preparation, which should not be influenced by the type of food prepared, was 

significantly lower for Year 4 (44%) compared with Year 2 (74%) and Year 3 (71%). We 

speculate that the lower handwashing rate for Year 4 may be due to participants using hand 

sanitizer upon arrival as a COVID-19 precaution. Two hand sanitizer stations, which were 

not provided in previous years of the study, were available to participants before they

entered the kitchen. Social distancing measures may also have influenced handwashing 

rates. In previous years of the study, researchers were able to walk the participant around 

the kitchen during the introduction and clearly show the participant the location of utensils 

and dishes in drawers and cabinets. Because of mandatory social distancing, the 

introduction and orientation were limited. The lower handwashing rates might reflect 

participants opening cabinets and drawers to become familiar with the kitchen when starting 

meal preparation (these participants would have been coded as not washing their hands 

before starting meal preparation even if they then washed their hands before touching any 

food). Because we did not ask participants during the post-observation interviews why they 

did not wash their hands before meal preparation, we do not know the reason with 

certainty. We will ask follow-up questions about reasons for not washing hands before meal 

preparation and record the first surface touched at the start of meal preparation in the 

forthcoming Year 5 study. Other reasons for differences in handwashing rates by study year 

are also possible, such as differences in the characteristics of the study sample. The study 

sample for Year 4 was limited to people who cook on an outdoor grill and had a larger 
Section 3 — Results

3-17

percentage of males relative to Years 2 and 3. Additional analysis is needed to understand 

why the rate of handwashing before meal preparation varied by study year.

For handwashing during meal preparation, the rates for attempting handwashing were 26% 

for Year 2, 3% for Year 3, and 25% for Year 4. The results suggest that handwashing rates 

varied by product; the rates for chicken thighs and bratwurst/hamburgers were similar 

(about 25%), whereas the rate for frozen, breaded NRTE chicken was much lower (3%). 

Consistent with prior years, most Year 4 participants attempting handwashing before and 

during meal preparation did so unsuccessfully, and the most common reason for failure was

not rubbing hands with soap for 20 seconds.

Table 3-10. Comparison of Handwashing Compliance for Annual Meal Preparation 

Experiments (Control Group Participants) 

Year 1

Turkey Burgers

Year 2

Chicken Thighs

Year 3

Frozen, 

Breaded NRTE

Chicken

Year 4

Bratwurst and 

Hamburgers

Handwashing event 

required before the start 

of or during meal 

preparationa

1,195 — — —

% did not attempt 69% — — —

% attempt 31% — — —

% successful attempt 

(out of all attempts)

3% — — —

Handwashing before the 

start of meal preparation

— 154 196 66

% did not attempt — 26% 29% 56%

% attemptb — 74%1 71%2 44%1,2

% successful attempt 

(out of all attempts)

— 1% 4% 3%

Handwashing event 

required during meal 

preparation

— 1,145 499 570

% did not attempt — 74% 97% 75%

% attempt — 26% 3% 25%

% successful attempt 

(out of all attempts)

— 1% 0% 3%

a For Year 1, data were not available by when handwashing took place (i.e., before the start of or 

during meal preparation), so the combined data are presented.

b We calculated p value significance testing using a chi-squared test for the difference between years. 

Pairs of superscripted numbers indicate proportions that are significantly different at p ≤ .05.

Sources: 2017, 2018, 2019, and 2020–2021 meal preparation experiment—coding of food 

preparations.
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3.4 Cleaning and Sanitizing 

The recipes for the two treatment groups instructed participants to “[c]lean and then 

sanitize the counter and utensils after touching uncooked ground beef.” Cleaning and then 

sanitizing kitchen surfaces and equipment can help prevent cross-contamination. Cleaning is 

defined by CDC as washing a surface with soap and warm water to remove dirt and debris. 

Sanitizing reduces the number of bacteria present on a surface by using a specific sanitizing 

compound such as a solution of chlorine bleach, quaternary ammonia, or an alcohol-based 

solution to spray the surface with a specified contact time and either letting it dry or wiping 

it dry with a clean, one-use towel so that bacterial loads, including pathogens, can be 

reduced.

Tables 3-11 provides information on the surface where the chub was placed during 

preparation, the number of attempts, successful attempts (cleaning and then sanitizing), 

and unsuccessful attempts (e.g., cleaning only or sanitizing only) by study group specific to 

the surface where the chub was placed during preparation. Results are shown for two 

events: immediately following handling of the chub and the end of the observation. Most 

participants placed the chub on a cutting board or plate to prepare the hamburgers or 

dumped the ground beef into a bowl without letting the ground beef or chub packaging 

touch a surface. Some participants (15 to 20% depending on the study group) prepared the 

chub directly on the counter, which is not recommended.

Immediately after handling the chub, 31% of control group participants, 53% of T1 

participants, and 46% of T2 participants attempted cleaning and sanitizing; the higher rate 

of attempts for T1 compared with the control group was statistically significant. The rate of 

successful attempts (cleaned and then sanitized) ranged from 42 to 53%. Most of the 

unsuccessful events were due to a failure to sanitize.

At the end of meal preparation, 63% of control group participants, 36% of T1 participants, 

and 43% of T2 participants attempted cleaning and sanitizing; the lower rate of attempts 

for T1 compared with the control group was statistically significant (among participants who 

had not previously cleaned/sanitized the surface). The rate of successful attempts (cleaned 

and then sanitized) ranged from 67 to 75%. Most of the unsuccessful events were due to a 

failure to sanitize.
Section 3 — Results

3-19

Table 3-11. Observed Cleaning and Sanitizing during Chub Preparation 

Control: 

Standard 

Recipes

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Surface where chub was placed

Cutting board 65% (43) 68% (45) 76% (52)

Counter 20% (13) 17% (11) 15% (10)

Othera 12% (8) 14% (9) 9% (6)

Plate 3% (2) 1% (1) 0% (0)

Event—Immediately following handling chub

Attemptb, c 31% (20)1 53% (31)1 46% (30)

Successful attemptsd (cleaned and then 

sanitized)

50% (10) 42% (13) 53% (16)

Unsuccessful attempts 50% (10) 58% (18) 47% (14)

Water onlye 0% (0) 11% (2) 7% (1)

Clean onlyf 90% (9) 72% (13) 71% (10)

Sanitize onlyg 10% (1) 17% (3) 21% (3)

Did not attempt 69% (44) 47% (27) 54% (35)

Not applicableh (excluded from analysis) 3% (2) 12% (8) 4% (3)

Event—End of observation

Attemptb, c 63% (27)1 36% (21)1 43% (28)

Successful attemptd (cleaned and then 

sanitized)

74% (20) 67% (14) 75% (21)

Unsuccessful attempts 26% (7) 33% (7) 25% (7)

Water onlye 14% (1) 0% (0) 29% (2)

Clean onlyf 71% (5) 100% (7) 71% (5)

Sanitize onlyg 14% (1) 0% (0) 0% (0)

Did not attempt 37% (16) 64% (37) 57% (37)

Not applicableh or cleaned and/or sanitized 

immediately after handling chub (excluded from 

analysis)

35% (23) 12% (8) 4% (3)

Number of participants 66 66 68

a “Other” refers to instances where the participant opened the package midair with scissors and then 

dumped the meat into a bowl and immediately threw the packaging away.

b We calculated p value significance testing using a chi-squared test for the difference between groups 

(control vs. T1, control vs. T2, and T1 vs. T2). Pairs of superscripted numbers indicate proportions

that are significantly different at p ≤.05.

c “Attempt” was defined as any time that a participant appeared to clean the surface; the attempt 

could be successful or unsuccessful. 

d “Successful” refers to cleaning the surface, followed by sanitizing.
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Table 3-11. Observed Cleaning and Sanitizing during Chub Preparation 

(continued)

e “Water only” refers to if the participant only used water to rinse the surface and did not use soap, 

detergent, or any of the provided sanitizers.

f “Clean only” refers to the use of only soap or detergent to clean.

g “Sanitize only” refers to the use of one of the provided sanitizers (containing chlorine bleach, 

quaternary ammonia, or alcohol-based) to spray the surface and wiped it dry with a clean, one-use 

towel. 

h Some participants opened the packaging on tin foil, plastic wrap, or paper towels laid on the counter 

and then discarded these items, so these are considered N/A cleaning attempts and were excluded 

from the analysis.

Source: 2020–2021 meal preparation experiment—observed behavior

Participants were asked about their cleaning and sanitizing practices in the post-observation 

interview (see Table 3-12). Ninety-six percent of participants believed that raw bratwurst

could spread germs to other food in the kitchen. When asked what else might spread germs 

for the meal prepared in the test kitchen, 35% mentioned produce, 32% mentioned utensils 

or other surfaces, and 12% mentioned hamburger.7 Overall, 68% of participants said that 

they use chlorine bleach or sanitizer when cleaning up after preparing bratwurst at home, 

while 18% clean with soap, and 8% wash their hands. 

Table 3-12. Self-reported Behaviors for Cleaning and Sanitizing When Preparing 

Bratwurst and Hamburgers at Home

Question

All 

Participants

%

Control: 

Standard 

Recipes

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Can raw bratwurst spread germs to 

other food in your kitchen?

Yes 96% (192) 97% (64) 94% (62) 97% (66)

No 3% (5) 2% (1) 5% (3) 1% (1)

Answer unclear 2% (3) 2% (1) 2% (1) 1% (1)

For the meal you prepared today, what 

else might spread germs?a

Produce 35% (69) 35% (23) 36% (24) 32% (22)

Utensils or other surfaces 32% (63) 33% (22) 32% (21) 29% (20)

Hamburger 12% (24) 14% (9) 9% (6) 13% (9)

Hands 3% (5) 3% (2) 5% (3) 0% (0)

Things in the air 1% (1) 2% (1) 0% (0) 0% (0)

Grill 1% (1) 2% (1) 0% (0) 0% (0)

(continued)

7 We did not ask a follow-up question on whether participants believed that raw hamburger could 

spread germs.
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3-21

Table 3-12. Self-reported Behaviors for Cleaning and Sanitizing When Preparing 

Bratwurst and Hamburgers at Home (continued)

Question

All 

Participants

%

Control: 

Standard 

Recipes

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Pets 1% (1) 0% (0) 2% (1) 0% (0)

Nothing else 2% (3) 3% (2) 2% (1) 0% (0)

Other 14% (27) 5% (3) 12% (8) 24% (16)

Answer unclear 3% (6) 5% (3) 3% (2) 1% (1)

When preparing bratwurst at home, how 

do you clean up after you are finished?

Use chlorine bleach or another 

sanitizer

68% (136) 71% (47) 70% (46) 63% (43)

Clean with soap/wipe down surfaces 18% (35) 20% (13) 20% (13) 13% (9)

Wash hands 8% (16) 8% (5) 8% (5) 9% (6)

Use only water 1% (1) 0% (0) 0% (0) 1% (1)

Throw away packaging 1% (1) 0% (0) 0% (0) 1% (1)

Answer unclear 6% (11) 2% (1) 3% (2) 12% (8)

If you purchased a large quantity of 

ground beef with the plan to use part of 

it for a meal and to store the rest, when 

would you store ground beef not used 

for the meal? 

Just before meal preparation 45% (90) 45% (30) 39% (26) 50% (34)

During meal preparation 23% (46) 26% (17) 27% (18) 16% (11)

When coming home from store 20% (40) 21% (14) 18% (12) 21% (14)

End of meal preparation 9% (18) 5% (3) 12% (8) 10% (7)

Did not specify when 2% (4) 2% (1) 3% (2) 1% (1)

Not asked 1% (2) 2% (1) 0% (0) 1% (1)

Number of participants 200 66 66 68

a Participants could provide multiple responses, so the total may sum to more than 100%.

Note: Responses may not sum to 100% because of rounding.

Source: 2020–2021 meal preparation experiment—post-observation interview.

When purchasing large quantities of group beef, 45% of participants would store the meat 

they do not plan to cook just before meal preparation, 23% would store it during meal 

preparation, and 20% would store it after coming home from the store. Few (9%) would 

wait until the end of meal preparation. 

Participants were observed when repackaging the unused ground beef from the chub (see 

Table 3-13). Most participants (91 to 95%) placed the remaining ground beef in the 
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refrigerator instead of the freezer. One participant left the ground beef on the counter. Few 

participants (11 to 16%) labeled the package. Among participants who labeled the package, 

all wrote the date on the label, and most (71 to 80%) provided a description.

Table 3-13. Observed Repackaging of Unused Ground Beef 

Question

Control: 

Standard 

Recipes

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Location of stored beef

Refrigerator 95% (61) 92% (56) 91% (60)

Freezer 5% (3) 8% (5) 8% (5)

Left on counter -- -- 1% (1)

Labeled the package

Yes 16% (10) 11% (7) 12% (8)

No 84% (54) 89% (54) 88% (58)

If yes, information provided on label

Date 100% (10) 100% (7) 100% (8)

Description 80% (8) 71% (5) 75% (6)

Number of participants 64 61 66

Note: Data were not available for nine participants because pictures failed to upload.

Source: 2020–2021 meal preparation experiment—pictures taken after completion of meal 

preparation.

Participants were also asked about how they would typically prepare, handle, and store 

bratwurst and hamburgers when cooking at home (Table 3-14). As previously noted, we 

instructed participants to prepare the bratwurst and hamburgers before the salad. Overall, 

66% of participants said they would prepare bratwurst and hamburgers before preparing 

the salad when cooking at home whereas preparing the salad first would help to reduce the 

risk of cross-contamination. Participants said they would place the raw meat on a plate 

(31%), bowl (28%), or cutting board (11%) before putting it on the grill. Most participants 

said they would put any ground beef that they did not cook in a plastic/freezer bag (75%). 

About two-thirds of participants (64%) said they would label the package, whereas few 

participants did so in the test kitchen (11 to 16%).
Section 3 — Results

3-23

Table 3-14. Self-reported Behaviors for Preparing, Handling, and Storage When 

Preparing Bratwurst and Hamburgers at Home

Question

All 

Participants

%

Control: 

Standard 

Recipes

%

T1: Food 

Safety 

Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Which food would you typically 

prepare first at home?

Bratwurst/hamburgers 66% (131) 71% (47) 53% (35) 72% (49)

Salad 34% (67) 27% (18) 47% (31) 26% (18)

Depends on the situation 1% (2) 2% (1) 0% (0) 1% (1)

What would you place the raw meat on 

before putting on the grill?

Plate 31% (61) 29% (19) 32% (21) 31% (21)

Bowl 28% (56) 30% (20) 24% (16) 29% (20)

Cutting board 11% (21) 9% (6) 11% (7) 12% (8)

Wax/parchment paper 6% (11) 5% (3) 6% (4) 6% (4)

Baking sheet/tray 6% (12) 6% (4) 8% (5) 4% (3)

Did not explain step by step 4% (7) 9% (6) 2% (1) 0% (0)

Other 16% (32) 12% (8) 18% (12) 18% (12)

What would you put the unused 

ground beef in?

Plastic/freezer bag 75% (150) 76% (50) 73% (48) 76% (52)

Wrap plastic over the chub package 13% (26) 11% (7) 14% (9) 15% (10)

Plastic container 6% (12) 6% (4) 9% (6) 3% (2)

Aluminum foil 1% (1) 2% (1) 0% (0) 0% (0)

Other 5% (10) 5% (3) 5% (3) 6% (4)

Answer unclear 1% (1) 2% (1) 0% (0) 0% (0)

Would you label the ground beef?

Yes 64% (127) 71% (47) 58% (38) 62% (42)

No 36% (71) 27% (18) 42% (28) 37% (25)

Answer unclear 1% (2) 2% (1) 0% (0) 1% (1)

Number of participants 200 66 66 68

Note: Responses may not sum to 100% because of rounding.

Source: 2020–2021 meal preparation experiment—post-observation interview.
Food Safety Consumer Research Project:

Meal Preparation Experiment on Grilling

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3.5 Produce Washing

Table 3-15 summarizes participants’ behaviors for produce washing (one carrot and one 

apple) when preparing the RTE salad. The FDA recommends that consumers wash produce 

such as carrots and apples by rubbing them under cold running water; this instruction was 

included in the recipes for T1 and T2. Rates of properly washing the carrot for the RTE salad 

were slightly higher in the treatment groups (84% for T1 and 75% for T2) than the control 

group (71%); however, the differences were not statistically significant. Similarly, rates of 

properly washing the apple for the RTE salad were slightly higher in the treatment groups 

(83% for T1 and 79% for T2) than the control group (74%); however, the differences were 

not statistically significant. For both the carrot and apple, about 40% of control group 

participants did not attempt washing, whereas nearly all T1 and T2 participants attempted 

washing, although some failed to rub the product with their hands so the attempt was 

unsuccessful. 

The FDA recommends that consumers not wash or rinse commercially bagged lettuce to 

avoid cross-contamination. Compared with the control group (80%), the percentage of 

participants not washing the bagged lettuce was higher among the two treatment groups 

(89% for T1 and 87% for T2); however, the differences were not statistically significant. 

Table 3-15. Observed Salad Preparation: Produce Washing 

Control: 

Standard 

Recipes

%

T1: Food 

Safety Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Carrots

Attempts 62% (41) 95% (63) 94% (64)

Successful attempt—rubbed with hands 

under running watera

71% (29) 84% (53) 75% (48)

Unsuccessful attemptb 29% (12) 16% (10) 25% (16)

Did not attempt 38% (25) 5% (3) 6% (4)

Apples

Attemptsc 59% (39) 97% (64) 100% (68)

Successful attempt– rubbed with 

hands under running watera

74% (29) 83% (53) 79% (54)

Unsuccessful attemptb 26% (10) 17% (11) 19% (13)

Did not attempt 41% (27) 3% (2) 0% (0)

(continued)
Section 3 — Results

3-25

Table 3-15. Observed Salad Preparation: Produce Washing (continued)

Control: 

Standard 

Recipes

%

T1: Food 

Safety Recipes

%

T2: Food 

Safety 

Recipes+CE

%

Bagged lettuce

Washed or rinsed 20% (13) 11% (7) 13% (9)

Did not washa 80% (53) 89% (59) 87% (59)

Number of participants (unless otherwise 

noted)

66 66 68

a We calculated p value significance testing using a chi-squared test for the difference between groups 

(control vs. T1, control vs. T2, and T1 vs. T2). Pairs of superscripted numbers indicate proportions

that are significantly different at p ≤.05.

b Unsuccessful attempts including rinsing with water without rubbing and soaking in water.

c One T2 participant scrubbed the apple with their hands and also soaked it. This participant was 

excluded, so successful and unsuccessful attempts sum to 67 rather than 68.

Source: 2020–2021 meal preparation experiment—observed behavior

3.6 Cross-Contamination and Microbiological Analysis

To assess the extent of cross-contamination during meal preparation, we examined the 

spread of E. coli DH5-Alpha from the ground beef packaged in chubs to various surfaces in 

the kitchen and the prepared RTE salad. Lack of or failed handwashing attempts and failure 

to properly clean and sanitize surfaces that come into contact with raw meat can spread 

pathogens to high-touch surfaces through contact of contaminated hands to surfaces and 

foods. 

We used the microbiological data to identify both the direct and indirect cross-contamination 

events that occurred during the meal preparation experiment. Direct cross-contamination is 

defined as when raw meat or raw meat packaging (in this case ground beef) comes into 

direct contact with an RTE food or a food handling surface or utensil and the area is not 

cleaned and sanitized after contact. Indirect cross-contamination is when utensils, surfaces, 

or hands make contact with a contaminant and then are not cleaned or sanitized adequately 

before the next use; any time between touching raw meat or packaging and then touching a 

nonmeat item; touching a mobile device; or touching trash. We analyzed the data for the 

counter area where the chub was opened, the sink basin, spice containers, cupboard 

handles, the plate or cutting board if it was handwashed, and the lettuce from the prepared 

RTE salad. Table 3-16 shows the prevalence and level of contamination for these sites, as 

well as the prevalence and level of contamination on the salad lettuce. 

Across all participants, the surface most often contaminated was the sink basin (28% of 

participants). The rate of contamination for the spice containers was 12%. Rates of 

contamination were relatively low for the cupboard handle (8%) and the counter area where 
Meal Preparation Experiment on GrillingFood Safety Consumer Research Project: 

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Table 3-16. Prevalence of Surrogate Contamination and Level of Contamination for Locations in the Kitchen

Location

All 

Participants

Control: 

Standard 

Recipes

T1: Food 

Safety 

Recipes

T2: Food 

Safety 

Recipes+CE

Salad lettuce Prevalence contaminated % (n)

a 17.09% 

(198)

13.64% 

(66)

20.31% 

(64)

17.65% 

(68)

Level of contamination ± SD, log CFU/25 g (n) 1.69 ± 0.81 

(34)

1.51 ± 0.52 

(9)

1.73 ± 0.97 

(13)

1.78 ± 0.83 

(12)

Counter area where 

chub was opened

Prevalence contaminated % (n)

a 2.51% 

(199)

4.55% 

(66)

0.00%

(65)

2.94% 

(68)

Level of contamination ± SD, log CFU/100 cm2

(n)

2.30 ± 0.65 

(5)

1.87 ± 0.33 

(3)

0.00 ± 0.00 

(0)

2.94 ± 0.37 

(2)

Sink basin Prevalence contaminated % (n)

a 28.28% 

(198)

32.31%1

(65)

16.92%1,2

(65)

35.29%2

(68)

Level of contamination ± SD, log CFU/100 cm2

(n) 

1.88 ± 0.85 

(56)

1.63 ± 0.72 

(21)

2.10 ± 1.12 

(11)

1.99 ± 0.79 

(24)

Spice containers Prevalence contaminated % (n)

a 12.06% 

(199)

16.67% 

(66)

10.77% 

(65)

8.82% 

(68)

Level of contamination ± SD, log CFU/100 cm2

(n)

1.78 ± 0.83 

(24)

1.62 ± 0.90 

(11)

1.59 ± 0.44 

(7)

2.30 ± 0.96 

(6)

Cupboard handle Prevalence contaminated % (n)

a 8.04% 

(199)

12.12% 

(66)

4.62% 

(65)

7.35% 

(68)

Level of contamination ± SD, log CFU/100 cm2

(n)

1.52 ± 0.66 

(16)

1.61 ± 0.79 

(8)

1.57 ± 0.52 

(3)

1.34 ± 0.60 

(5)

Plate or cutting 

board if hand 

washed

Prevalence contaminated % (n)

a 32.08% 

(53)

45.45%

(11)

36.84%

(19)

21.74%

(23)

Level of contamination ± SD, log CFU/100 cm2

(n)

b

2.33 ± 1.08b

(16)

c

2.36 ± 1.09b

(4)

c

2.08 ± 1.07 

(7)

2.66 ± 1.23 

(5)

Number of samples 199 66 65 68

a We calculated p value significance testing using a chi-squared test for the difference between groups (control vs. T1, control vs. T2, and T1 

vs. T2). Pairs of superscripted numbers indicate proportions that are significantly different at p ≤ .05.

b Mean and SD do not include one control group sample determined to be an outlier because it was too high to count (>6.5 log CFU/100 cm2).

c Total count of positive samples includes one sample found to have >6.5 log CFU/100 cm2 (determined to be an outlier). 

Notes: A positive result was any colony that fluoresced under ultraviolet light when grown on selective media. One observation was not 

included due to detecting surrogate in the cleaning validation sample. (n) = number of samples used in the analysis; SD = standard deviation

Source: 2020–2021 meal preparation experiment—microbiological samples.
Section 3 — Results

3-27

the chub was opened (3%). Among participants handwashing the plate or cutting board 

used to prepare the hamburgers from the chub, 32% of participants did not thoroughly 

wash the plate/cutting board (i.e., it was contaminated with the surrogate). Across all 

participants, the prevalence for contamination of the salad lettuce was 17%.

We examined whether differences in the prevalence rates for contamination were 

statistically significant (control vs T1, control vs T2, and T1 vs T2). For the sink basin, the 

prevalence rate was higher for the control group (32%) compared with T1 (17%); the 

prevalence rates for T1 (17%) and T2 (35%) were also significantly different. No other 

differences were observed.

3.7 Participants’ Response to Intervention (Treatment Groups 

Only)

During the post-observation interviews, we collected information about the treatment group 

participants’ responses to the food safety instructions included in the recipes (see 

Table 3-17). As previously noted, the questions asked were generally open ended, and the 

responses were coded into the categories shown in the table. Many participants in the two 

treatment groups reported typically cooking from a recipe (70% for T1 and 63% for T2). 

Most participants reported that they noticed the food safety instructions in the recipes (92% 

for T1 and 90% for T2). About 52% of T1 and 36% of T2 participants had previously noticed 

food safety instructions. The sources most commonly cited were recipes and food 

packaging. 

Table 3-17. Treatment Group Participants’ Response to Intervention

Question

T1: 

Food Safety 

Recipes

%

T2: 

Food Safety 

Recipes+CE 

%

Do you usually cook from a recipe?

Yes 70% (46) 63% (43)

No 30% (20) 37% (25)

Did you notice food safety instructions in the recipes today?

Yes 92% (61) 90% (61)

No 8% (5) 10% (7)

(continued)
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Table 3-17. Treatment Group Participants’ Response to Intervention (continued)

Question

T1: 

Food Safety 

Recipes

%

T2: 

Food Safety 

Recipes+CE 

%

Have you ever noticed instructions like these before?

Yes 52% (32) 36% (22)

No 48% (29) 64% (39)

If yes, where? (n = 32 for T1 and n = 22 for T2)

Recipes 38% (12) 45% (10)

Food packaging 25% (8) 27% (6)

Cooking shows/cooking magazines 6% (2) 0% (0)

Other 3% (1) 5% (1)

Did not specify 28% (9) 23% (5)

If recalled food safety instructions, did the instructions influence how 

you prepared the meal today? (n = 61 for T1 and n = 61 for T2)

Yes, influenced actions 74% (45) 75% (46)

Followed the recipe closely 27% (12) 7% (3)

Used thermometer 22% (10) 24% (11)

Reinforced usual practices 11% (5) 33% (15)

Provided general awareness 7% (3) 7% (3)

Washed hands and cleaned up 7% (3) 13% (6)

Washed produce 4% (2) 2% (1)

Concerned about what meat touched 0% (0) 2% (1)

Reason not stated or unclear 22% (10) 13% (6)

No, did not influence actions 26% (16) 25% (15)

Reinforced usual practices 75% (12) 80% (12)

Reason not stated or unclear 25% (4) 20% (3)

If recalled, do you think the information will influence your food 

preparation in the future? (n = 61 for T1 and n = 61 for T2)

Yes, will influence 64% (39) 66% (40)

Will use new food safety measures 44% (17) 35% (14)

Will reinforce usual practices 31% (12) 38% (15)

Will seek out new recipes 13% (5) 15% (6)

Answer unclear 13% (5) 13% (5)

No, will not influence 36% (22) 31% (19)

Will reinforce usual practices 23% (5) 26% (5)

Other 59% (13) 63% (12)

Answer unclear 0% (0) 3% (2)

(continued)
Section 3 — Results

3-29

Table 3-17. Treatment Group Participants’ Response to Intervention (continued)

Question

T1: 

Food Safety 

Recipes

%

T2: 

Food Safety 

Recipes+CE 

%

Are there additional food safety instructions you would add to the 

recipes?

Yes 38% (23) 33% (20)

Information about cross-contamination 35% (8) 35% (7)

Information about proper storage 17% (4) 15% (3)

Information about washing produce 17% (4) 20% (4)

Wash hands, clean up more often 9% (2) 10% (2)

Other (e.g., time/temperature relationship, water 

temperature)

13% (3) 20% (4)

General tips (not related to food safety) 9% (2) 0% (0)

No 57% (35) 67% (41)

Answer unclear/question not asked 5% (3) 0% (0)

Note: Responses may not sum to 100% because of rounding.

Source: 2020–2021 meal preparation experiment—post-observation interview.

Among the participants who recalled the food safety instructions, about three-fourths of 

participants said the information influenced their actions during meal preparation (74% for

T1 and 75% for T2). When asked how the inclusion of the food safety instructions 

influenced their behavior, these participants most often mentioned that they followed the 

recipe more closely, referenced their thermometer, or mentioned that it reinforced their 

usual practices. Among the one-fourth of participants who said the food safety instructions 

did not influence their actions during meal preparation, most mentioned that it reinforced 

their usual practices. 

Among the participants who recalled the food safety instructions, about two-thirds of 

participants said the information would influence their actions in the future (64% for T1 and 

66% for T2). When asked whether they would suggest adding other food safety instructions 

to the recipes, about one-third said yes, and suggested adding more information about 

cross-contamination, produce washing, and proper storage. 

Participants in the T2 group were asked additional questions about Kenji Lopez-Alt, the 

celebrity chef featured in the recipes provided to T2 participants, and celebrity chefs in 

general (see Table 3-18). Most participants (81%) had not heard of him prior to the study. 

All T2 group participants were asked whether having the food safety instructions come from 

a celebrity chef influenced how they prepared the meal in the test kitchen. Most (81%) said 

no, with most citing reasons that were coded as “generally follow the recipe anyway” and 
Food Safety Consumer Research Project: 

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“being a celebrity chef does not necessarily equate to expertise in food safety.” Forty-six

percent of T2 participants had seen food safety instructions shared before by celebrity 

chefs. Many participants (81%) said they trusted celebrity chefs to provide information on 

how to cook food safely. Participants shared the following comments:

“Yes. I would say again ... they wouldn’t be where they are if they were 

making people sick. So they should know what they’re doing.”

“So I got to say only like ... I’ll say Rachael Ray and Gordon Ramsay, I 

recognize them.”

“You know, if they made it in their house, and they made it big time in the 

cooking industry, I’d say probably they’re doing ok.”

Table 3-18. T2 Group Participants’ Response to Food Safety Instructions and 

Celebrity Chefs

Question

T2: 

Food Safety 

Recipes+CE 

%

Before today, had you heard of J. Kenji Lopez-Alt or the Food Lab?

Yes 15% (10)

No 81% (55)

Answer unclear 4% (3)

Did having the food safety instructions come from a celebrity chef influence how 

you prepared the meals today?

Yes 19% (13)

Celebrity equals expertise in food safety 69% (9)

No explanation or unclear 31% (4)

No 81% (55)

Generally follow recipe anyway 45% (25)

Celebrity does not equal expertise in food safety 25% (14)

No explanation or unclear 29% (16)

Have you seen this information (i.e., food safety instructions) shared before by 

celebrity chefs? 

Yes 46% (31)

No 46% (31)

Answer unclear 9% (6)

(continued)
Section 3 — Results

3-31

Table 3-18. T2 Group Participants’ Response to Food Safety Instructions and 

Celebrity Chefs (continued)

Question

T2: 

Food Safety 

Recipes+CE 

%

Do you trust the following celebrity chefs to provide information on how to cook 

food safely?a

Yes 81% (55)

No 9% (6)

Answer unclear 10% (7)

Do you ever search for recipes online?

Yes 93% (63)

No 7% (5)

(If yes) When searching for recipes online, do you seek out recipes from celebrity

chefs? (n = 63)

Yes 32% (20)

No 65% (41)

Answer unclear 3% (2)

(If yes) Rate how strongly you agree/disagree with this statement: I follow food 

safety instructions because a celebrity chef endorsed them (n = 20)

Disagree 55% (11)

Neutral 10% (2)

Agree 35% (7)

Number of participants (unless otherwise noted) 68

a Participants were asked about their trust in several specific well-known celebrity chefs, including 

Rachael Ray, Rhee Drummond, Ina Garten, Gordon Ramsey, Jamie Oliver, Martha Stewart, and Jose 

Andres. 

Most participants (93%) have searched for recipes online. Among these participants, 32% 

seek out recipes from celebrity chefs when searching online for recipes. Among participants 

who do seek out recipes from celebrity chefs when searching online (n = 20), over half 

disagreed with the statement "I follow food safety instructions because a celebrity chef 

endorsed them." Participants shared the following comments:

“No, they don’t really wash their hands that much.”

“Not really. Their job is to entertain.”

4-1

4. Conclusion

This section concludes the report by summarizing the key findings from the meal 

preparation experiment and discussing implications for message development that FSIS 

OPACE may want to consider. 

4.1 Impact of Intervention (Control vs. T1 and Control vs. T2)

In 2019, the PFSE (2020) released a Food Safety Style Guide, providing guidance for 

incorporating food safety recommendations and handling instructions for people writing 

recipes. The release of this guidance was due in part to recent consumer research. Maughan 

et al. (2016) assessed whether food safety instructions in recipes improved consumer food 

safety behavior when preparing chicken breasts and ground turkey patties; handwashing 

and thermometer use were significantly improved in consumers who received the recipes 

with food safety instructions compared with those who did not. Participants also stated that 

they were likely to use recipes with food safety instructions in the future if available.

The recipes used for the treatment groups used food safety instructions based on the style 

guide developed by the PFSE. Additionally, the recipes for T2 were endorsed by a celebrity 

chef. The results of this study suggest that the inclusion of food safety instructions in the 

recipes influenced certain food handling behaviors observed in the kitchen as described 

below.

▪ Thermometer use. About 95% or more participants in both treatment groups used 

a food thermometer to check doneness compared with 55% (bratwurst) and 58% 

(hamburgers) of control group participants.

▪ Handwashing before meal preparation. Nearly two-thirds of participants in both 

treatment groups attempted handwashing before meal preparation compared with

44% of control group participants.

▪ Cleaning and sanitizing surfaces. Immediately after handling the chub, 53% of 

T1 participants attempted cleaning/sanitizing of the surface used to prepare the chub

compared with 31% of control group participants. The rate was also higher for T2 

participants (46%), but the difference was not statistically significant.

▪ Cross-contamination. Based on the results of the microbiological analysis, for the 

sink basin the prevalence of contamination was higher for the control group (32%) 

compared with T1 (17%). The prevalence rates for T1 and T2 were also significantly 

different. 

In the post-observation interviews, many participants reported cooking from a recipe, and 

most participants in both treatment groups reported that they noticed the food safety 

instructions in the recipes. 

Inclusion of food safety instructions in the recipes did not appear to influence handwashing 

attempts during meal preparation for required handwashing events, attempting to clean and 

sanitize the surface used to prepare the chub at the end of meal preparation (if not 
Food Safety Consumer Research Project: 

Meal Preparation Experiment on Grilling

4-2

previously cleaned/sanitized), and the prevalence of contamination for the salad lettuce and 

other kitchen surfaces sampled. Also, the inclusion of instructions did not appear to 

influence proper washing of the carrot and apple for the salad (i.e., rubbing under cold 

water), although the rate of attempting washing was higher among the two treatment 

groups compared with the control group.

4.2 Impact of Celebrity Chef Endorsement (T1 vs. T2)

Recognition of the celebrity chef featured in the second treatment group was low (15%). 

Thus, it is not surprising that any differences observed between T1 and T2 were not

statistically significant, with the exception of prevalence of contamination for one surface

(sink basin). About 81% of T2 participants said they trust celebrity chefs (the question 

asked about more mainstream chefs) to provide information on how to cook food safely; 

however, only 35% of participants agreed with the statement “I follow food safety 

instructions because a celebrity chef endorsed them.” Most T2 participants look online for 

recipes, but only 35% said they seek out recipes specifically from celebrity chefs. These 

findings suggest that the addition of a celebrity chef endorsement for food safety 

instructions in recipes may not influence consumers’ food safety behaviors and that 

inclusion of food safety instructions alone may be sufficient to motivate behavior change.

These results highlight the importance of timing in disseminating food safety information to 

consumers. Prompting consumers at the time of meal preparation and as part of the recipe 

positions consumers to follow recommended food safety instructions, even if it is not their 

usual practice. Additionally, the Food Safety Style Guide could serve as a useful reference 

point for media organizations when producing news segments about food safety (e.g.,

including examples of specific safe handling instructions).
R-1

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telephone survey. Journal of Food Protection, 62(8), 921–928.

https://doi.org/10.4315/0362-028X-62.8.921

Keeling, C., Niebuhr, S. E., Acuff, G. R., & Dickson, J. S. (2009). Evaluation of Escherichia 

coli biotype 1 as a surrogate for Escherichia coli O157:H7 for cooking, fermentation, 

freezing, and refrigerated storage in meat processes. Journal of Food Protection, 72, 

728–732.

Kendall, P. A., Elsbernd, A., Sinclair, K., Schroeder, M., Chen, G., Bergmann, V., ... 

Medeiros, L. C. (2004). Observation versus self-report: Validation of a consumer 

food behavior questionnaire. Journal of Food Protection, 67(11), 2578–2586.

https://doi.org/10.4315/0362-028X-67.11.2578

Maughan, C., Godwin, S., Chambers, D., & Chamber IV, E. (2016). Recipe modification 

improves safety practices during cooking of poultry. Journal of Food Protection,

79(8), 1436–1439. https://doi.org/10.4315/0362-028X.JFP-15-468

Montville, R., Chen, Y., & Schaffner, D. W. (2002). Risk assessment of hand washing 

efficacy using literature and experimental data. International Journal of Food 

Microbiology, 73(2–3), 305–13.

Partnership for Food Safety Education. (2020). Safe recipe style guide. 

https://www.saferecipeguide.org/why/

Redmond, E. C., & Griffith, C. J. (2003). Consumer food handling in the home: A review of 

food safety studies. Journal of Food Protection, 66(1), 130–161.

https://doi.org/10.4315/0362-028X-66.1.130

Redmond, E. C., Griffith, C. J., Slader, J., & Humphrey, T. J. (2004). Microbiological and 

observational analysis of cross contamination risks during domestic food preparation. 

British Food Journal, 106(8), 581–597.

https://doi.org/10.1108/00070700410553585

Vasan, A., Geier, R., Ingham, S. C., & Ingham, R. H. (2016). Thermal tolerance of O157 

and non-O157 Shiga toxigenic strains of Escherichia coli, Salmonella, and potential 

pathogen surrogates, in frankfurter batter and ground beef of varying fat levels. 

Journal of Food Protection, 77, 1501–1511.
A-1

Appendix A:

Recipes 

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Appendix A — Recipes 

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Appendix B:

Observation Script

Check-In Script—English

Welcome! My name is _____________ and I’ll be walking you through what you’ll be doing 

as part of our study today.

Today, you will be preparing burgers made from ground beef, brats, and a side salad to help 

us test recipes for a new cookbook.

We will interview you after you finish cooking. The cooking and interview will last no longer 

than 2 hours.

Observation Script (Control and Treatments (not the Guac Group)

Pre-cooking Script

Before we start, I need you to read and sign the consent form.

Please let me know if you have any questions or concerns. 

After Consent Form Is Signed

Today, you will be preparing ground beef burgers, brats, and a side salad.

Please do not eat any of the food or take any home with you. We will interview you after 

you are finished cooking. The cooking and interview will last up to 2 hours.

This is the area where you will be cooking. Here’s the grill for cooking the burgers and brats. 

If you are unfamiliar with this type of grill, here are the instructions. All the available 

utensils and dishes are in these drawers/cabinets. [Note: open a few cabinets and drawers 

and be sure to open the drawer with the thermometer, materials for repackaging, and 

cleaning/sanitizing solution].

The ground beef, brats, and the apples, carrots, and lettuce for the salad are in the 

refrigerator. Here are the recipes (provide formatted recipes). 

Please prepare the burgers and brats first and the salad as the meat cooks. You only need 

to use half of the ground beef today, so please repackage the remaining ground beef as you 

would at home. Materials you may need for repackaging are located here [point] in the 

kitchen.

After you are done cooking, please clean up as you would at home. You can load the 

dishwasher, but please do not turn it on. Also, please do not clean the grill. We will take 

care of that for you.

Feel free to use whatever you need. Please make yourself at home; you are welcome to use 

your phone to listen to music or whatever you usually do when cooking at home. If the 

temperature of the kitchen is not okay, let me know and I can adjust it.

Restrooms are located _______, and in case of an emergency, the exits are _____. The fire 

extinguisher is located ________ and the first aid kit is located _____.

Before you begin, do you have any questions?

If you have any questions or concerns while you’re cooking, I will be in the ___________ 

room.
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[After food preparation]

Now that you have finished the cooking portion of the study, we are ready to begin the 

interview. It should take about 20 minutes to complete. Do you need a break before we 

begin that portion?

Observation Script (Guacamole group)

Pre-cooking Script

Before we start, I need you to read and sign the consent form.

Please let me know if you have any questions or concerns. You will receive a copy of the 

form to take home.

After Consent Form Is Signed

Today, you will be preparing ground beef burgers, brats, a side salad, and guacamole.

Please do not eat any of the food or take any home with you. We will interview you after 

you are finished cooking. The cooking and interview will last up to 2 hours.

This is the area where you will be cooking. Here’s the grill for cooking the burgers and brats. 

If you are unfamiliar with this type of grill, here are the instructions. All the available 

utensils and dishes are in these drawers/cabinets. [Note: open a few cabinets and drawers 

and be sure to open the drawer with the thermometer, materials for repackaging, and 

cleaning/sanitizing solution].

The ground beef, brats, the apples, carrots, and lettuce for the salad, and the cilantro for 

the guacamole are in the refrigerator. The avocadoes, lime juice, and onion for the 

guacamole are here on the counter. Here are the recipes (provide formatted recipes). 

Please prepare the burgers and brats first and the salad and guacamole as the meat cooks. 

You only need to use half of the ground beef today, so please repackage the remaining 

ground beef as you would at home. Materials you may need for repackaging are located 

here [point] in the kitchen.

After you are done cooking, please clean up as you would at home. You can load the 

dishwasher, but please do not turn it on. Also, please do not clean the grill. We will take 

care of that for you.

Feel free to use whatever you need. Please make yourself at home; you are welcome to use 

your phone to listen to music or whatever you usually do when cooking at home. If the 

temperature of the kitchen is not okay, let me know and I can adjust it.

Restrooms are located _______, and in case of an emergency, the exits are _____. The fire 

extinguisher is located ________ and the first aid kit is located _____.

Before you begin, do you have any questions?

If you have any questions or concerns while you’re cooking, I will be in the ___________ 

room.

[After food preparation]

Now that you have finished the cooking portion of the study, we are ready to begin the 

interview. It should take about 20 minutes to complete. Do you need a break before we 

begin that portion? 
C-1

Appendix C:

List of Equipment Provided in Each Test Kitchen

This picture shows one of the test kitchens used for the meal preparation experiment. The 

equipment provided in each test kitchen is listed below.

Kitchenware

Countertop Grill

Skillet

▪ Medium-sized skillet (9–12 inch)

Frying pans (store frying pans in the cabinets)

▪ Small (8 inch) nonstick

▪ Medium or large (10–12 inch)

Saucepans

▪ Small (2–3 quarts)

▪ Medium or large (4–5 quarts)

Knives

▪ Chef’s knife

▪ Paring knife/fruit knife
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Baking dishes

▪ 9 x 13 baking dish (rectangular)

▪ Smaller square, rectangular, or oval baking dish

Utensils

▪ Wooden or plastic stirring spoons (1–2)

▪ Heat-resistant plastic or silicone spatula

▪ Slotted spoon

▪ Ladle

▪ Flat spatula

▪ Cooking tongs

▪ Digital tip-sensitive instant read thermometer

▪ Dry measuring cups

▪ Liquid measuring cup (1 cup)

▪ Measuring spoons

▪ Can opener

▪ Liquid measuring cup (2 cup)

▪ Whisk

▪ Rolling pin

▪ Peeler

▪ Zester/grater

▪ Large cutting boards

▪ Splatter guard

▪ Serving bowl

▪ Serving utensils (serving fork, spoon, and tongs)

▪ Salt and pepper shaker (must be glass)

▪ Garlic and onion powder

▪ Utensil holder

Other essential tools

▪ Small, medium, and large mixing bowls

▪ Colander

▪ Salad spinner
Appendix C — List of Equipment Provided in Each Test Kitchen

C-3

Silverware/dinnerware

▪ Set of spoons, knives, and forks

▪ Dinner plates

▪ Salad plates

▪ Bowls

Cleaning/dishwashing supplies

▪ Kitchen towels

▪ Dish cloths

▪ Hand soap

▪ Dish drain board/dish rack

▪ Paper towels

▪ Sponge

▪ Sponge caddy

▪ Paper towel holder

▪ Apron

▪ Oven mitts

▪ Pot holders

▪ Dishwashing detergent

Cleaning items for under sink

▪ Windex

▪ Clorox bleach

▪ 409 cleaner

▪ Lysol spray

Leftover kit supplies

▪ Ziploc bags (gallon and quart sizes)

▪ Plastic wrap

▪ Plastic containers with lids

Note: Containers must be sanitized between observation events. Ziploc bags and plastic 

wrap must be taken out of retail packaging and placed in kitchen drawers.
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Housekeeping items

▪ First-aid kit

▪ Toolbox

Food

Recipe card

▪ Double-sided, laminated card

Ingredients

▪ 1 pound chub package

▪ Bratwurst

▪ Apples

▪ Carrots

▪ Bagged salad

▪ Onion

▪ Spices
D-1

Appendix D:

Microbiological Methods

D.1 DH5-Alpha Stock Selection and Preparation

In the second year of the annual FSCRP study, NCSU’s microbiology team provided scientific 

justification for using a nonpathogenic Escherichia coli strain, tagged with green fluorescent 

protein (GFP) (E. coli DH5-Alpha), as a surrogate for pathogenic Salmonella in whole 

chicken pieces, with the approval of OPHS. For the grilling study, we used the same 

nonpathogenic E. coli strain as a surrogate for pathogenic E. coli, such as O157, found in 

ground beef and inoculated ground beef packaged in chub-like bags, which was also 

approved by OPHS. A GFP and kanamycin resistance gene were contained in the pBIT 

plasmid that would allow the differentiation of bacterial contamination from improper 

handling of the ground beef and any other naturally present E. coli or kanamycin-resistant 

bacteria. A DH5-Alpha colony with pBIT will fluoresce green under ultraviolet light (UV) and 

be easily identifiable compared with a colony from a bacteria that is naturally occurring and 

not indicating cross-contamination. 

The DH5-Alpha was obtained and frozen in an 80/20 trypticase soy broth kanamycin (30 

ug/mL)/glycerol stock at −80 C. When used for inoculation, one loopful of the frozen stock 

was placed in the appropriate amount of trypticase soy broth with 30 ug/mL of kanamycin 

and mixed. The bacteria was then incubated, shaking overnight at 37°C aerobically. The 

culture was also streaked directly onto trypticase soy agar with kanamycin (TSA Kan30), 

incubated upside down aerobically at 37°C, and visualized under UV light to validate that 

the stock still had an active pBIT plasmid.

D.2 Ground Beef Inoculation

Inoculation was performed by mixing a prepared culture of the surrogate with a specified 

weight of ground beef in a Kitchen Aid mixer. Two pounds of ground beef were used for 

each meal preparation event, and ground beef was inoculated with the surrogate twice a 

week to keep the bacterial concentration high and keep the ground beef within its shelf life. 

The surrogate was cultured overnight, shaking at 37°C in a trypticase soy broth with 

kanamycin. The surrogate was then spun down at 3000 x g for 15 minutes at 4°C. The 

supernatant was then poured off and the pelleted surrogate was resuspended in 0.1% 

buffered peptone water (BPW). Two pounds of ground beef, purchased no more than 24 

hours prior to preparation, were then placed into the mixing bowl of a Kitchen Aid mixer 

with 40 mL of resuspended surrogate and mixed for a minimum of 2 minutes. Ground beef 

was then packaged similarly to commercially available chubs in chub-like bags and sealed 

with a metal hog ring on one end. After packaging, the chubs were transported to the test 

kitchens where they were stored at 4°C and used within 4 days.
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D.3 Inoculation Validation

Periodically, extra ground beef was inoculated on inoculation days to ensure the inoculation 

process remained consistent. This ground beef was not packaged but instead processed for 

enumeration of the surrogate. Following inoculation, a 25-g aliquot of ground beef was 

added to 50 mL of 0.1% BPW and stomached for 1 minute at 260 rpm. The liquid was 

serially diluted and plated on TSA Kan30 and incubated upside down overnight at 37°C 

aerobically. Colonies were counted and visualized under UV light, and an average of the 

surrogate per 1 g of ground beef was determined (consistently 7 log10 CFU/gram of ground 

beef).

D.4 Environmental Sampling and Lettuce Collection

Environmental sampling was performed to assess cross-contamination that occurred during 

meal preparation. Pur-Blue swabs in Letheen broth (World Bioproducts, Libertyville, IL) 

were used to sample the kitchen surfaces, and an aliquot of 25 g of the lettuce from the RTE 

salad was collected in a Ziplock bag for each meal preparation event. Irregular surfaces 

were swabbed entirely, while flat surfaces were swabbed using a 100-cm2template.

D.5 Detection and Quantification of DH5-Alpha on Environmental 

Samples and Lettuce

The environmental samples were analyzed at an NCSU lab within 24 hours. The samples 

were kept at 4°C until they were processed. The outside of the swabs was wiped down with 

ethanol to remove any kitchen surface contamination. The swabs were vortexed for 15 

seconds, and then tenfold dilutions were made for each swab using 9 mL of 0.1% BPW. The 

samples were briefly vortexed to mix, and then 100 uL were plated in duplicate for each 

swab per dilution onto TSA Kan30 plates, and then incubated aerobically upside down at 

37°C for 24 hours. The samples were examined under UV light, and glowing colonies were 

counted as a positive result. The counts were adjusted for total volume and dilution and 

recorded.

For the lettuce sample, 25 g were weighed into a filtered WhirlBag and stomached at 260 

rpm for 1 minute with 50 mL 0.1% BPW. Tenfold serial dilutions were prepared in 9 mL of 

0.1% BPW and vortexed briefly to mix. 100 uL of the dilutions were plated on TSA Kan30 

plates and incubated aerobically upside down at 37°C for 24 hours. The samples were 

examined under UV light, and glowing colonies were counted as a positive result. The 

counts were adjusted for total volume and dilution and recorded.

D.6 Sanitation After Meal Preparation Event

We sanitized the kitchens following meal preparation in accordance with NCSU’s guidelines 

for sanitizing laboratory work surfaces, a requirement of the university, with additional 

requirements because of COVID-19. We applied household bleach diluted to a 10% 
Appendix D — Microbiological Methods

D-3

concentration to hard surfaces with a contact time of 60 seconds before wiping them clean 

with a disposable paper towel. We repeated this step twice for a total of three sanitation 

steps. The efficacy of this sanitation procedure was confirmed during in-lab optimization 

studies and the pilot conducted in the test kitchen. A cleaning validation swab sample was 

also taken at the beginning of all meal preparation observations, and if a cleaning validation 

sample showed signs of remaining contamination on kitchen surfaces, samples for that 

particular observation were excluded from data analysis. All utensils (e.g., knives, cutting 

boards, and bowls) were cleaned in dishwashers.

E-1

Appendix E:

Post-observation Interview Guide

FSCRP YEAR 4

OMB Control Number: 0583-0169

Expiration date: 08/31/2023

Introduction Script

Thank you so much for your time today and allowing us to record your actions while you 

prepared a meal just like you would in your home. Now I would like to ask you a few followup questions that will focus on some of the activities you participated in while in the model 

kitchen. 

Is it okay with you if I record your answers? The recording is confidential and will only be 

used to accurately capture our conversation (allowed recording y/n).

If it is okay with you, I’d like to begin this interview, which will take about 20 minutes. If 

no: Terminate interview.

If yes: Proceed.

Observation Follow-Up (use trigger form for context)

E.1 Handwashing

Did you wash your hands before you started cooking today? Can you tell me why you 

did/did not wash your hands?

Is that something you usually do when cooking at home? Why?

At what other points did you wash your hands when cooking today?

Are there times when you know you should wash your hands, but you do not? Why?

When you touch food, when do you wash your hands? Why those times? [Probe if not 

mentioned: Does the decision to wash your hands vary by the type of food?]

What role do government recommendations play in whether you wash your hands or not?

Has COVID-19 played a role in how often or when you wash your hands? If yes, how?

E.2 Food Thermometer

How did you determine the doneness of the burgers and brats today? [Probe if not 

mentioned: Was it the same or different for the two types of meat? Why?]

Is that how you usually determine doneness of meat when cooking at home? Why?
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[If used thermometer] Do you usually use a food thermometer when grilling at home? For 

which foods? Why? 

[If used thermometer] Why do you use a food thermometer? [Probe if no reason is given for 

using a food thermometer: Is this something your family does? Is it a recommendation you 

saw somewhere?} 

[If used thermometer] How did you check the temperature with the food thermometer? How 

did you insert it into the food?

E.3 Burger Prep/Cooking and Salad Prep

Can you walk me through how you typically make the hamburger patties, transfer them to 

the grill, then off the grill and ready to be served at home? Did you do anything different 

today?

Today we told you what order to cook the foods. If you were grilling out at home, which 

would you do first: grill the meat or make the salad? Why?

E.4 Repackaging Unused Ground Beef

Today we instructed you to use only half of the ground beef and to repackage the remaining 

ground beef. Tell me how you did this today. 

Do you ever buy large quantities of meat or poultry with the plan to use part of it for a meal 

and to store the rest?

Now, let’s assume you purchased a large quantity of ground beef with the plan to use part 

of it for a meal and to store the rest. How would you open the package and separate out the 

meat for use in the meal versus the meat to repackage for storage?

When would you store the ground beef not used for the meal: at the end of meal 

preparation or some other time? (Probe: after coming home from the grocery store in 

advance of when you would actually cook it or during/after meal preparation after you’ve 

separated out what you will cook at that time)

What steps would you take to store the ground beef you were not planning to use at that 

time?

What would you put the unused ground beef in? [Probe if necessary: plastic container, 

plastic or freezer bag, wrap plastic wrap over the chub package, butcher paper, aluminum 

foil] 

How would you clean up after storing the unused ground beef? 

[If not mentioned] What about washing your hands? 

Would you label the unused ground beef in some way? If so, how would you label it and 

why? If not, why not?
Appendix E — Post-observation Interview Guide 

E-3

E.5 Cleaning/Sanitizing 

Can raw brats spread germs to other food in your kitchen? Why? What about other 

surfaces? Why do you think that? 

Assume you were preparing brats at home, can you walk me through how you would usually 

clean up?

[If not mentioned] What about sanitizing, for example, using chlorine bleach or another 

sanitizer? What would you use and how would you use it? 

[If not mentioned before]: Has COVID-19 played a role in how often or when you clean or 

sanitize? If yes, how?

For the meal you prepared today, what else might spread germs?

E.6 Preparation of Guacamole (for the 50 participants not included 

in experiment)

Tell me how you prepared the guacamole from beginning to end.

[If not mentioned] What about washing the avocados before you cut them: is this 

something you did or did not do?

[If yes] Why did you wash them? What were you trying to accomplish? 

[If no] Why didn’t you wash them?

[If yes] How did you wash the avocados? [Probe: rinse under running water, rub with 

hands, scrub with a brush, soak in water] 

[If yes] Did you wash your hands after washing the avocados?

FDA advises consumers to wash their avocados before peeling them. Before today, were 

you aware of the need to wash avocados before cutting them?

[If not mentioned] What about washing the cilantro before you chopped it: is this 

something you did or did not do?

[If yes] Why did you wash it? What were you trying to accomplish? 

[If no] Why didn’t you wash it?

[If yes] How did you wash it? [Probe: rinse under running water, soak in water]

Have you heard of any germs that make people sick associated with avocado or cilantro? [If 

yes] What bacteria?
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E.7 Questions about Intervention—Treatment Groups Only

Do you usually cook from a recipe?

Did you notice the food safety instructions in the recipes today? [If necessary: For example, 

the recipe stated, “Wash hands with soap and water” and “Grill burgers until internal 

temperature reaches 160°F on food thermometer.”]

Have you ever noticed food safety instructions like these in recipes before? Where?

[Treatment Group 1: Instructions with Food Safety Only]

Did the food safety instructions influence how you prepared the meal today? 

[If yes] In what way? [Probe: specific food safety instruction and food]

[If no] Why not? 

Do you think reading food safety practices included in recipes would affect how you prepare 

food at home in the future?

[If yes] In what way? [Probe: specific food safety instruction and food]

[If no] Why not? 

Is there any additional food safety instruction you would add to the recipes?

[Treatment Group 2—Instructions with Food Safety and Celebrity Chef]

Before today, had you heard of J. Ken i Lopez-Alt or the Food Lab? 

[If yes] Have you prepared any of his recipes before?

Did the food safety instructions influence how you prepared the meal today? 

[If yes] In what way? [Probe: specific food safety instruction and food]

[If no] Why not? 

Do you think reading food safety practices included in recipes would affect how you prepare 

food at home in the future?

[If yes] In what way? [Probe: specific food safety instruction and food]

[If no] Why not? 

Is there any additional food safety instruction you would add to the recipes? 

What are your thoughts on having a celebrity chef include food safety instructions in his 

recipes? Have you seen this information shared before by celebrity chefs? 

Did having the food safety instructions come from a celebrity chef influence how you 

prepared the meal today? Why? Does having this information coming from a chef make it 
Appendix E — Post-observation Interview Guide 

E-5

more likely for you to follow it at home? (prompt, information such as “be sure to use a 

thermometer to cook the burgers to 160F)

Would you say that this chef an expert in cooking food safely? 

Rate your level of trust in his ability to provide safe food handling information Likert 1–5, 

five being very high trust, 1 being untrustworthy)

Do you trust the following celebrity chefs to provide information on how to cook food safely: 

▪ Rachel Ray

▪ Rhee Drummond (Pioneer Women)

▪ Ina Garten (Barefoot Contessa)

▪ Gordon Ramsay

▪ Jamie Oliver

▪ Martha Stewart

▪ Jose Andres

Do you ever search for recipes online? 

[If no] Go to Section 1.8 Conclusion

[If yes] When searching for recipes online, do you seek out recipes from celebrity chefs?

[If yes] Which celebrity chefs?

[If yes] How much do you agree with the following statement: I follow food safety 

instructions because a celebrity chef endorsed them. (1 being that you strongly disagree, 7 

being that you strongly agree)

E.8 Conclusion

We mentioned in our recruiting materials that we were interested in testing new recipes. 

However, the specific focus of our study is on food safety and how to prevent food 

poisoning. We purposely did not tell you exactly what our specific research objectives were 

in advance so that we could capture your behaviors in a natural way. In addition, a 

biological tracking agent was in the food to help us track where contamination might occur. 

This biological tracking agent was harmless bacteria called Escherichia coli (E. coli) K12 

DH5-Alpha, it does not pose any health hazard to you, and has been approved for use in 

this study by the Division of EHS and the Institutional Review Board at NCSU. Part of its 

name may sound familiar because it is a harmless cousin of E. coli O157. There are 

hundreds of strains of E. coli, many are needed for our gut system to work correctly and are 

not able to make us ill. E. coli DH5-Alpha doesn’t have the genes that cause disease that E. 

coli O157 does, which is why the second part of their names are different. This makes E. coli

DH5-Alpha non-pathogenic, non-toxic, and safe for humans to handle. You can request to 
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be removed from the study at any time, and if you decide to exit the study at this point, we 

will destroy the recordings of your actions, and you will not be included in the data set.

We want to confirm with you now that you understand the focus of our study and that you 

wish to remain as a participant.

If no: Thank you so much for your time; we will remove your data from our data set and 

destroy any records.

If yes: Thank you for your consent. 

Thank you again for your time and for your participation in our study today. 

Please see the greeter on your way out to receive the $75 gift card and gift.

According to the Paperwork Reduction Act of 1995, an agency may not conduct or sponsor, and a 

person is not required to respond to, a collection of information unless it displays a valid OMB 

control number. The valid OMB control number for this information collection is 0583-0169 and 

the expiration date is 08/31/2023. The time required to complete this information collection is 

estimated to average 20 minutes per response, including the time for reviewing instructions, 

searching existing data sources, gathering and maintaining the data needed, and completing and 

reviewing the collection of information.
F-1

Appendix F:

Screening Questionnaire8

Screen 1

Thank you for your interest in our research study, which is funded by the U.S. Department 

of Agriculture and conducted by researchers from North Carolina State University and RTI 

International. 

According to the Paperwork Reduction Act of 1995, an agency may not conduct or sponsor, 

and a person is not required to respond to, a collection of information unless it displays a 

valid OMB control number. The valid OMB control number for this information collection is 

0583-0169 and the expiration date is 8/31/2023. The time required to complete this 

information collection is estimated to average 8 minutes per response, including the time for 

reviewing instructions, searching existing data sources, gathering and maintaining the data 

needed, and completing and reviewing the collection of information.

Screen 2

If you are eligible for the study on recipe testing, you will be asked to prepare a meal while 

being videotaped and to participate in an interview. The study will last up to 2 hours, and 

you will receive a $75 gift card and a small gift for taking part in the study.

To determine whether you are eligible, you will need to answer a few questions. These 

questions will take less than 10 minutes to complete. Your participation in this study is 

completely voluntary. All of your answers and your contact information will be kept private. 

Please click the “>>” arrows below if you would like to continue.

Question Screens 

1. Have you cooked or worked professionally in a food preparation setting in the past 5 

years?

Yes → Ineligible. Terminate.

No 

2. Have you received any type of food safety training, such as ServSafe, in the past 5 

years?

Yes → Ineligible. Terminate.

No

3. Have you participated in any research studies about cooking in the past 4 years? 

Yes → Ineligible. Terminate.

No

8 Web version shown; a telephone version was also available for people who called in to be screened.
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4. Do you have any children living in your household who are less than 18 years of age?

Yes 

No 

5. Which of the following foods have you cooked outdoors using a grill, barbecue, or other 

cooking tool during the past 6 months?

Vegetables

Fish

Poultry

Steak

Pork (for example, ribs or chops)

Hot dogs

Bratwurst, brats, or Italian sausages

Ground beef burgers → If not selected, ineligible. Terminate.

None of the above

6. Have you purposefully purchased meat or poultry in large quantities with the plan to 

repackage it for cooking at a later date?

Yes 

No 

7. During the past 3 months, about how often did you purchase ground beef that is not 

sold in Styrofoam trays? This type of packaging is sometimes referred to as a chub. 

Chubs are a tube-like package that looks like a sausage with the ends sealed by metal 

crimps or clips.

Never → Go to Question 9.

1 to 3 times 

4 to 6 times 

7 to 12 times 

More than 12 times

8. Why do you purchase ground beef that is not sold in Styrofoam trays (chubs)? Please 

select one or more.

Price

Convenience

Shelf life

Size options

Brand preference (i.e., that’s how the brand you like packages their products)

Other

9. Do you have experience cooking with avocado (cutting and mashing whole avocado)?

Yes 

No → Ineligible for subset. 

10. Do you have experience cooking raw or fresh bratwurst or sausages purchased at a 

meat counter that are not pre-cooked or smoked?

Yes 

No 
Appendix F — Screening Questionnaire

F-3

11. When cooking a food product at home for the first time, how often do you read the 

cooking instructions on the package before you start cooking? 

Always

Most of the time

Sometimes

Hardly ever

Never

12. Which of the following items do you have in your kitchen? (Select all that apply.)

Chef’s knife

Garlic press

Citrus zester

Food thermometer 

Manual can opener

Vegetable peeler

Cheese grater

Wine opener

None of the above

13. Do you identify as ...?

Female

Male

Other

Prefer not to answer

14.Are you ...?

Hispanic or Latino

Not Hispanic or Latino

15. What is your race? Please select one or more.

American Indian or Alaska Native

Asian

Black or African American

Native Hawaiian or Other Pacific Islander

White

16. What is your age? 

Under 18 → Ineligible. Terminate.

18 to 34

35 to 54

55 to 64

65 to 75 → Ineligible. Terminate

76 or older → Ineligible. Terminate
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F-4

17. What is the highest level of education that you have completed? 

Less than high school 

High school graduate or GED

Technical or vocational school

Some college, but did not get a degree 

2-year associate’s degree

4-year college degree

Postgraduate degree 

18.Are you or any members of your household ...? (Select all that apply.)

65 years of age or older

5 years of age or younger

Pregnant

Breastfeeding

Diagnosed with an allergy to any food or food ingredient

Diagnosed with diabetes or kidney disease

Diagnosed with a condition that weakens the immune system, such as cancer, HIV, 

or AIDS; a recipient of a transplant; or receiving treatments, such as 

chemotherapy, radiation, or special drugs or medications to treat these conditions

None of the above 

19. Where did you hear about this study?

Facebook

Twitter

Craigslist

Email from a North Carolina extension program

Sign 

Specify location: __________________________

Other 

Specify location: __________________________

Don’t know

20. Have you knowingly interacted with someone who has been diagnosed with COVID-19?

Yes→ Terminate.

No 

21. Have you been diagnosed with COVID-19 in the past 14 days?

Yes→ Terminate.

No

22. Do you have any (one or more) symptoms of COVID-19 such as cough, fever, 

shortness of breath, chills, muscle pain, new loss of taste or smell?

Yes→ Terminate to Covid Screen

No 
Appendix F — Screening Questionnaire

F-5

23.Are you willing to follow all safety and sanitation procedures while participating in this 

study including wearing appropriate personal protective equipment?

Yes

No → Terminate

24.Check all that apply: 

I am someone with chronic lung disease or moderate to severe asthma

I am someone with a heart condition

I am someone who is immunocompromised. (This can result from cancer 

treatment, bone marrow or organ transplantation, immune deficiencies, 

poorly controlled HIV or AIDS, and prolonged use of corticosteroids and 

other immune weakening medications)

I am someone with a body mass index (BMI) of 40 or higher

I am someone with diabetes or pre-diabetes

I am someone with chronic kidney disease undergoing dialysis

I am someone with liver disease

25. Thank you for taking the time to complete this survey to determine your eligibility for 

this study. We have determined that you are eligible to participate in the study!

Due to the COVID-19 pandemic, there are some additional precautions we must take 

when you participate in the study. Please be on the lookout for an email from our 

research team within a few business days regarding how to prepare to come to your 

study session and what you should expect. 

Yes

No → Terminate.

Contact Screen 1 (if no boxes checked in question 24)

Great! Please enter your name and telephone number so that a study team member can call 

you and schedule an appointment for the Grilling Study at a day and time that works best 

for you and send you text message reminders. The study will last up to 2 hours, and you 

will receive a $75 gift card and a small gift for taking part in the study. Please note that 

additional screening for Covid-19 exposure and symptoms will occur upon arrival which may 

determine you ineligible at that time. If you’d like, you can download a copy of the consent 

form here for your review; you will also receive a paper copy upon arrival.

[ENTER NAME] 

[ENTER TELEPHONE NUMBER]

[Go to Contact Screen 3]

Contact Screen 2 (if ANY boxes checked in question 24)

Great! Please enter your name and telephone number so that a study team member can call 

you and schedule an appointment for the Grilling Study at a day and time that works best 

for you. The study will last up to 2 hours, and you will receive a $75 gift card and a small 

gift for taking part in the study. Please note that additional screening for Covid-19 exposure 

and symptoms will occur upon arrival which may determine you ineligible at that time. If 

you’d like, you can download a copy of the consent form here for your review; you will also 

receive a paper copy upon arrival.
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Please note that you have indicated that because of experiences you may be at risk for 

developing severe illness should you contract COVID-19. Participation in this research 

requires in-person interaction which may result in contracting COVID-19. Precautions 

including physical distancing, wearing PPE and cleaning and disinfection, will be taken to 

mitigate possible transmission of COVID-19; however, you may want to take additional 

personal precautions. 

Contact Screen 3

Please enter your email address so we can send you a confirmation email with directions. 

[ENTER EMAIL ADDRESS; REQUIRE DOUBLE ENTRY FOR VERIFICATION]. 

No Email 

[If no email] Please enter your mailing address. [STREET ADDRESS, CITY, NC, ZIP]

Thank you for your time. A study team member will call you in 1 or 2 days to schedule an 

appointment with you.

If you have any questions about the study or scheduling, you may contact Lisa Shelley at 

919-659-8254. If you have concerns about your rights as a research participant, contact 

North Carolina State University’s Office of Research Protection at 919-515-8754 or via email 

at irb-director@ncsu.edu.

Ineligible/Covid Screen

Thank you for your time. Unfortunately, you are not eligible to take part in our study. Please 

contact your medical provider to discuss your needs. In addition to contacting your medical 

provider, if you are an NC State University employee, use this form to self-report: Employee 

Self-Report Form. If you are an NCSU student, please use this form to report: Student Self 

Report Form. If you are unaffiliated with NC State University, please call your medical 

provider to report symptoms.

Ineligible/Terminate Screen

Thank you for your time. Unfortunately, you are not eligible to take part in our study. Have 

a great day.
G-1

Appendix G:

Observation Rubric for Coding Participant Actions 

in the Kitchen

Notes and Definitions: 

Contaminated hands: Hands that have come into contact with potentially contaminated 

material (raw food, contaminated equipment, touching of face or other parts of body or 

clothing) and that have not been washed according to CDC’s recommended guidelines f or 

proper handwashing.

Elements of handwashing:

▪ Wet your hands with clean, running water (warm or cold), turn off the tap, and apply 

soap.

▪ Lather your hands by rubbing them together with the soap. Be sure to lather the 

backs of your hands, between your fingers, and under your nails.

▪ Scrub your hands for at least 20 seconds.

▪ Rinse your hands well under clean, running water.

▪ Dry your hands using a clean (one use/paper) towel or airdry them.

Source: https://www.cdc.gov/handwashing/when-how-handwashing.html
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For a successful handwashing attempt, all elements should occur in the sequence listed 

above.