-

Final Report (June 2005 to October 2006) 

Jerky Validation for Small and Very Small Meat and Poultry Businesses 

EXECUTIVE SUMMARY 

Thermal Process for Jerky Provides Proper Lethality for Controlling Pathogens 

Getty, K.J.K., Boyle, E.A.E., Roberts, M.N, and Lonneker, S.M. 

Department of Animal Sciences and Industry and Food Science Institute 

Kansas State University, Manhattan, KS 

USDA/FSIS issued a Compliance Guideline that provides jerky processing parameters 

for controlling pathogens. The Guideline was aimed at providing additional processing 

information for small and very small processors of jerky. The objectives of this study were: 

Phase 1) to develop a survey tool and collect information relative to manufacturing equipment, 

processing techniques, ingredients and end item characteristics typical of jerky products 

produced by small and very small manufacturers primarily in Kansas, Nebraska, Missouri, and 

Wisconsin and Phase 2) to determine the effects of typical thermal processing temperatures and 

times on reducing E. coli O157:H7 and Salmonella in chopped and formed beef jerky. 

Phase 1: Development of a four-page survey tool was a coordinated effort between 

Kansas State University and the University of Wisconsin, with input from the University of 

Nebraska. It contained questions directed at detailing equipment, ingredients and processing 

techniques used in jerky manufacture to gain very specific information providing up to 168 data 

points. 

Of the 78 plants contacted, 37 contributed surveys for a 47% response rate. Of these, 33 

plants contributed 61 product samples. Analytical results of product samples revealed a mean aw 

of 0.74 (SD 0.10); mean NaCl of 6.85% (SD 2.5%); and mean pH of 5.85 (SD 0.33). Some key 

results garnered from the survey include thermal processing extremes and nearly a complete lack 

of relative humidity instrumentation. These ranged from processing jerky at 51.6°C for 45 min 

followed by 3°C increases every 45 minutes to reach an oven temperature of 62.8C maximum, to 

processing jerky at 93.3°C for 6-7 h. Perhaps the single most important finding is the depth of 

variability within this industry. The survey tool provided the means to quantify some of the 

extremes in this variability and in that way will serve as a pivotal source of information for 

developing challenge studies. 

Phase 2: A thermal process was validated to determine its ability to control pathogens 

during the production of chopped and formed all-beef jerky. A mixture of E. coli O157:H7 or 

Salmonella spp. was added to raw batter (ca. 7.0 log10 CFU/g). Jerky strips were placed on 

screens and put into a smokehouse. Jerky strips were sampled throughout processing and 

reductions of E. coli O157:H7 or Salmonella populations were determined. Greater than or equal 

to 5.0 log10 CFU/g reductions were seen for both pathogenic populations after 45 min of 

processing at dry bulb temperatures of 55.6°C and relative humidity (R.H.) at <10%, followed by 

45 min with dry bulb temperatures at 77.8°C and R.H. at <10%. However, product was dried 

further at 77.8°C for an additional 3.25 h to achieve moisture-to-protein ratios of approximately 

0.75:1 and water activity levels of < 0.70 characteristic of shelf stable jerky. At the end of the 

thermal process, approximately 7.2 log10 CFU/g reductions of both E. coli O157:H7 and 

Salmonella spp. were observed, thus meeting USDA/FSIS validation guidelines for being 

1 
deemed safe and shelf stable. A reviewed short paper of this study is available on the web at at 

www.asi.ksu.edu/cattlemensday. This 

APPLICATION TO SMALL PROCESSORS 

The information from the survey indicated that small processors of jerky have varied processing 

parameters/methods and need to have more control of their processes. It also determined that 

there are limited means to incorporate humidity into their smokehouses. In addition, although 

processors stated various product parameters (salt, pH and water activity levels) these levels 

were inconsistent with our testing results. The results indicate a need to education small 

processors about jerky processing parameters and the need to have routine analysis of product 

completed. 

From the preliminary studies it was determined that even at higher water activity levels for 

kippered beef effective log reductions were achieved for controlling E. coli O157:H7 and 

Salmonella spp. More research is needed to further substantiate the data. In the validation study, 

it was also determined that at low (<10%) relative humidity levels greater than 5 log reductions 

of E. coli O157:H7 populations and greater than 6.5 log reductions of Salmonella spp. were 

observed when chopped and formed jerky was dried to <0.70 water activity level and a 0.75:1 

moisture-to-protein ratio was achieved. This is helpful information to small processors that may 

not be able to achieve high relative humidity levels in their smokehouses. 

Although we tested a less expensive water activity meter (Pawkit, Decagon, Pullman, WA) that 

was approximately $400, we did not get consistent results compared to a standard water activity 

meter (Model CX2, Aqualab, Pullman, WA). Decagon is coming out with a new hand held 

water activity meter and has recognized that differences have been observed. This new model 

may be more adequate in analyzing water activity levels and should be tested. Some suggestions 

would be to have small processors send samples to universities labs for testing periodically to 

determine that low water activity levels and 0:75:1 moisture-to-protein ratios are being met for 

their jerky products. 

OTHER ACTIVITIES 

The Survey Phase of the study will be developed into a manuscript and submitted to either Meat 

Science or Journal of Muscle Foods. 

The M.S. thesis chapter on the Validation Phase of M.N. Roberts thesis will be developed into a 

manuscript and submitted to the Journal of Food Protection. In addition, funds have been 

secured to conduct additional validation research on chopped and formed jerky. 

2 
 

STATUS OF ANY NEW PUBLICATIONS OR TRAINING MATERIALS BEING 

DELIVERED OR FINALIZED 

1. A poster presentation was given at 51st Intl. Cong. Meat Sci. Tech. in Baltimore, MD in 

August of 2005. The reference and text and poster presentation follows. 

2. In addition, the M.S. graduate (Lonneker) conducting the survey phase also completed a M.S. 

report focused on processing parameters for controlling Salmonella species and Escherichia coli 

O157:H7 in jerky products. The report has been completed and an abstract is provided. 

Principle investigators Boyle and Getty served as committee members with Dr. Melvin Hunt 

serving as the major advisor. 

3. The preliminary studies and the validation part of the jerky project are the main focus of a 

M.S. thesis by Michelle N. Roberts. She will be defending her thesis in December 2006. The 

chapter on the preliminary studies is included. 

4. The validation study of the project was reported in a progress report form at the Annual Food 

Safety Consortium Meeting in Fayetteville, AK in October 2006. The reference and text 

follows. 

5. The validation study is also being reported in a Cattleman’s Day Report published by Kansas 

State University in March 2007. A submitted report is included. 

6. The validation study was also the main chapter in Michelle N. Roberts’ M.S. thesis. Both a 

copy of the thesis abstract and the chapter on validation is included. 

7. References for Michelle N. Roberts’ M.S. thesis is included to support the Chapter on 

Preliminary Studies and the Chapter on Validation Study. 

3 
1. Lonnecker, S.M., Boyle, E.A.E., Getty, K.J.K., Buege, D.R., Ingham, S.C., and Searls, G.A. 

20005. Determination of baseline product characteristics and production methods in small and 

very small jerky plants. 51st Intl. Cong. Meat Sci. Tech. Baltimore, MD (see paper below). The 

poster copy is also attached. 

DETERMINATION OF BASELINE PRODUCT CHARACTERISTICS AND 

PRODUCTION METHODS IN SMALL AND VERY SMALL JERKY PLANTS 

S.M. Lonnecker1

, E.A.E. Boyle*1, K.J.K. Getty2, D. R. Buege3, S.C. Ingham4, G.A. Searls4 

1 Department of Animal Sciences and Industry, and 2 Food Science Institute, Kansas State 

University, Manhattan, KS; 3 Department of Animal Sciences, and 4 Department of Food 

Science, University of Wisconsin, Madison, WI 

Key Words: Jerky, water activity, salt concentration, jerky production 

Introduction 

Jerky products have long been a popular meat based food in the United States. For much 

of its history, these products have enjoyed production with minimal supervision or intervention 

by regulatory entities. However, in the light of a jerky related Salmonellosis outbreak during 

October 2003, new scrutiny has been turned to jerky production nationwide. The USDA FSIS 

(2004) response to this outbreak was the issuance of the “Compliance Guideline for Meat and 

Poultry Jerky Produced by Small and Very Small Plants,” which provide thermal processing 

guidelines, humidity requirements and end product recommendations that may be applied to any 

jerky production scenario. The USDA did not stop with simply issuing these new guidelines. In 

Spring 2004, USDA solicited proposals to conduct research focused on providing small and very 

small manufacturing plants a means for validating their HACCP plans, specifically by achieving 

a 6.5 log reduction in pathogenic microorganisms. In order to develop validation studies, there 

was a need to determine the current state of the jerky industry in these facilities. 

Objectives 

The objective was to develop a survey tool and collect information relative to 

manufacturing equipment, processing techniques, ingredients and end item characteristics typical 

of jerky products. The targeted segment of the jerky industry were small and very small 

manufacturers primarily in Kansas, Nebraska, Missouri, and Wisconsin. This information will 

be used as a baseline for the design of lethality challenge studies in whole muscle and ground 

and formed jerky. 

Methodology 

Development of a four page survey tool was a coordinated effort between Kansas State 

University and the University of Wisconsin, with input from the University of Nebraska. It 

contained questions directed at detailing equipment, ingredients and processing techniques used 

in jerky manufacture to gain very specific information providing up to 168 data points. Surveys 

were mailed to 78 small and very small manufacturers of jerky that were identified through state 

meat processing associations, state and federally inspected plant lists and internet resources such 

as state or county health department listings. The packet mailed to processors included a cover 

letter, the four page survey, and a request to provide four samples of each jerky product they 

manufactured for complimentary NaCl, pH and water activity (aw) analysis. Approximately one 

month after surveys were mailed, a follow-up telephone call was made to processors who had not 

4 
yet returned the completed survey. In some cases, another copy of the survey was sent to 

processors if the first copy had been misplaced. 

Survey data were compiled and means generated for quantitative data. Qualitative data 

were compared to determine if consensus existed among industry practices. Jerky samples that 

were returned with surveys were stored in original packaging at ambient temperature for up to 

two weeks before analysis. All lab analyses were done by KSU or UW, with one exception. 

NaCl analyses for jerky samples received by UW were done at KSU or a commercial lab. All 

samples were pulverized in a blender (Waring Blender 700 Model 33BL79, Waring Products 

Division, New Hartford, CT) with a 10 cm blending cup by two 30 sec bursts, pausing for 120 

sec between bursts to help minimize heat buildup. Water activity was measured at ambient 

temperature using an AquaLab Series 3 TE (Decagon Devices, Pullman, WA), using standard 

seven ml disposable sample cups. Measurement of pH was based on a 10 g sample of pulverized 

sample material, blended with 110 ml distilled, deionized water for two min in a stomacher 

(Seward Stomacher 400 laboratory blender, Seward Medical, London, UK) and tested 

immediately with a pH meter (Accumet Portable model AP61 Fisher Scientific, Fair Lawn, NJ). 

NaCl content was determined using Quantab® titrators for chloride (0.05-1.0% NaCl, Hach 

Company, Loveland, CO), using five g pulverized sample material combined with 45 ml 

distilled, deionized water according to manufacturers instructions. Resulting measurements were 

plotted against one another and mean and standard deviation determined for each of the three 

parameters, by species and as a full lot. Results from whole muscle versus formed products were 

not separated. Upon completion of all analyses, each plant received their individual results 

plotted against results for all plants. Anonymity of plant results was maintained on all but their 

own sample data. 

Results & Discussion 

Of the 78 plants contacted, 37 contributed surveys for a 47% response rate. Of these, 33 

plants contributed 61 product samples. Analytical results of product samples revealed a mean aw 

of 0.74 (SD 0.10); mean NaCl of 6.85% (SD 2.5%); and mean pH of 5.85 (SD 0.33). Specific 

results broken down by species are shown in Table 1. Some key results garnered from the 

survey include thermal processing extremes and nearly a complete lack of relative humidity 

instrumentation. These ranged from processing jerky at 51.6C for 45 min followed by 3C 

increases every 45 minutes to reach an oven temperature of 62.8C maximum, to processing jerky 

at 93.3C for 6-7 h. Perhaps the single most important finding is the depth of variability within 

this industry. The survey tool provided the means to quantify some of the extremes in this 

variability and in that way will serve as a pivotal source of information for developing challenge 

studies. 

The survey instrument revealed that approximately 56% of all product produced is the 

whole muscle type and 44% is ground or chunked and formed. Total plant output was not 

requested nor reported. NaCl concentration in mixes ranged from 1% to more than 85%, and 

pickup of wet marinade ranged from 3% or less to 100%. 

Survey results further revealed that 34 of 37 manufacturers (92%) used only a 

smokehouse for thermal processing, 3 of 37 (8%) used a commercial oven and one manufacturer 

(3%) used both a smokehouse and an oven for thermal processing. Within the thermal 

environment, nine manufacturers determined the wet bulb temperature to yield relative humidity 

and only one employed a relative humidity instrument. However, 35 of 37 manufacturers 

claimed they are able to control humidity. Controls employed are closing the dampers (35%), 

5 
steam injection (8%), direct addition of water (8%), placing a pan of water in the house (3%) or a 

combination of these methods (43%). All respondents who claimed a combination of these 

methods used steam as one component, indicating that 51% of these manufacturers are using 

steam injection to increase their humidity. Manufacturers reported an average of 44% cooked 

yield. 

Ingredients used in the production of jerky may be grouped into two broad categories, 

those with a functional purpose besides flavor and those added solely for flavor. Functional 

ingredients found included sodium nitrite, sodium erythorbate, lactic acid, and potassium 

sorbate. Thirty-two of 37 respondents (86%) indicated the use of sodium nitrite, however only 

15 (41%) also indicated the use of sodium erythorbate as a cure accelerator. Those 

manufacturers not using a cure accelerator reported time spans ranging from 45 min (wet 

marinade) up to 7 d (dry cure) between the time seasonings are added until the drying process is 

begun. Only five (14%) manufacturers reported the use of potassium sorbate for mold inhibition 

and one (3%) reported using lactic acid to acidify the product. Ingredients used for their 

seasoning properties included soy sauce (62%), vinegar (8%), worcestershire sauce (16%) and 

tabasco sauce (5%). Lesser used ingredients included pineapple juice, teriyaki sauce, apple 

cider, garlic salt, and char oil (3% each). 

Respondents indicated a variety of packaging methods were employed including vacuum 

(78%), no vacuum (32%), and gas flush (14%). Storage, distribution, and marketing were 

variable as well, with 32% reporting refrigerated storage, 3% frozen and 5 of 13 (38%) reported 

shelf-stable storage and distribution. However, examination of package markings upon receipt 

of samples indicated that 12 of 13 (92%) of sample packages lack any precautionary handling 

markings, and may be interpreted as shelf-stable. 

Conclusions 

In the Midwest, slightly more than half of the jerky produced by small and very small 

facilities that responded to the survey was whole muscle, while slightly less than half was ground 

and formed or chunked and formed. Jerky aw and pH among different species was similar. NaCl 

levels among species may be similar, however an insufficient number of turkey samples were 

tested to conclude this similarity. This data provides sufficient correlation to proceed with 

lethality studies around aw 0.74, NaCl 6.85% and pH 5.85, with additional study around upper 

and lower limits of each parameter in combination to determine any synergistic affect between 

parameters. 

Survey results confirmed the hypothesis that there is widespread variability in thermal 

processing and most other production methods from one manufacturer to another. Variables 

included processing time and temperature, processing environment relative humidity and method 

employed to control humidity. Extremes in thermal processing provide useful baselines under 

which to proceed with lethality studies. Challenge studies at thermal extremes, in the presence 

of mean product characteristics, can provide inactivation or protective effects for targeted 

microorganisms. 

The survey revealed that, while a significant proportion of the industry has instituted the 

use of sodium nitrite into their product, many manufacturers may not be realizing any functional 

properties of this ingredient. Fifty-three percent of those using nitrite are not using a cure 

accelerator to speed the curing process. Among this group of products, product is allowed a 

lower limit of 45 minutes for the curing reaction to occur. With 86% of the industry using cure, 

6 
 

 

 

 

 

challenge studies should be conducted with cure for most iterations, and without cure in a 

comparative study at the mean level of product and thermal processing conditions. 

Slightly less widespread use of acidic ingredients are used in jerky production. 

Ingredients such as vinegar (pH 2.41), worcestershire sauce (pH 3.50), soy sauce (pH 4.83) and 

tabasco sauce (pH 3.20) are used by some manufacturers as flavor additives, primarily as a 

constituent of a wet marinade process. The pH of a marinade mixture and length of time held in 

marinade prior to thermal processing should be considered in a challenge study. 

Packaging methods employed throughout the industry varied slightly with most 

manufacturers using vacuum packs or modified atmosphere packaging to extend shelf-life by 

preventing oxidation or mold growth. The use of potassium sorbate as a mold inhibitor was 

limited. One consideration in a challenge study would be the impact of packaging and 

subsequent shelf life on pathogen lethality during storage. 

References 

USDA, FSIS. Compliance guideline for meat and poultry jerky produced by small and very small plants. 

2004. Available at http://www.fsis.usda.gov/pdf/compliance_guideline_jerky.pdf, accessed on 15 Feb 05. 

Tables and Figures 

Table 1. Mean NaCl content, aw and pH of whole muscle, ground and formed, and chunked and 

formed jerky by species from 33 primarily Midwestern companies. 

Species % NaCl SD1 Aw SD pH SD 

Beef 6.90% 2.54% 0.74 0.10 5.86 0.32 

(n=28) (n=49) (n=49) 

Pork 7.58% 2.42% 0.71 0.09 5.87 0.35 

(n=5) (n=6) (n=6) 

Turkey 3.73% - 0.77 0.09 5.82 0.46 

(n=1) (n=4) (n=4) 

Buffalo 4.95% - 0.79 0.08 5.52 0.16 

(n=1) (n=2) (n=2) 

 Maximum for all Products 11.54% 0.90 6.60 

 Minimum for all Products 2.10% 0.51 5.00 

1 Standard deviation 

7 
 

 

 

 

 

 

 

 

 

 

POSTER: DETERMINATION OF BASELINE PRODUCT CHARACTERISTICS AND 

PRODUCTION METHODS IN SMALL AND VERY SMALL JERKY PLANTS 

S.M. Lonnecker1, E.A.E. Boyle1, K.J.K. Getty1, D. R. Buege2, S.C. Ingham2, G.A. 

Searls2 

1Kansas State University, Manhattan, KS, and 2University of Wisconsin, Madison, WI, 

USA 

Conclusions 

 Beef jerky lethality studies designed to apply to survey respondents should target aw 0.74. 

NaCl 6.90%, and pH 5.86. 

 There is widespread variability in thermal processing and production methods across 

manufacturers. Challenge studies at thermal extremes, in the presence of mean product 

characteristics, would provide inactivation or protective effects for targeted microorganisms. 

 With 86% of the industry using cure, challenge studies should be conducted with cure for 

most iterations, and without cure in a comparative study at the mean level of product and 

thermal processing conditions. 

 The pH of a marinade mixture and length of time held in marinade prior to thermal 

processing should be considered in a challenge study. 

 Packaging methods employed throughout the industry varied slightly, with most 

manufacturers using vacuum packs or modified atmosphere packaging to extend shelf-life by 

preventing oxidation or mold growth. One consideration in a challenge study would be the 

impact of packaging and subsequent shelf life on pathogen lethality during storage. 

Objective 

Develop a survey tool and collect information from small and very small manufacturers primarily 

in Kansas, Nebraska, Missouri, and Wisconsin relative to manufacturing equipment, processing 

techniques, ingredients and end item characteristics typical of jerky products to form a baseline 

for the design of lethality challenge studies in whole muscle and ground and formed jerky. 

Introduction 

 In light of a jerky related Salmonellosis outbreak during October 2003, USDA FSIS 

scrutinized jerky production methods in the U.S. 

 USDA FSIS issued “Compliance Guideline for Meat and Poultry Jerky Produced by Small 

and Very Small Plants,” which provided thermal processing guidelines, humidity requirements 

and end product recommendations that may be applied to any jerky production scenario. 

 In Spring 2004, USDA solicited proposals to conduct research focused on providing small 

and very small manufacturing plants a means for validating their HACCP plans, specifically by 

achieving a 6.5 log reduction in pathogenic microorganisms. 

 To develop validation studies, there was a need to determine the current state of the jerky 

industry in these facilities. 

Materials & Methods 

 Developed a four page survey tool in conjunction with University of Wisconsin and 

University of Nebraska. 

 Questions directed at detailing equipment, ingredients and processing techniques used in 

jerky manufacture to gain very specific information providing up to 168 data points. 

8 
 

 

 

 

 

 

 Packet mailed to 78 small and very small jerky processors included a cover letter, four page 

survey, and a request to provide four samples of each jerky product they made for 

complimentary NaCl, pH and aw analysis. About one month after surveys were mailed, a 

follow-up telephone call was made to processors who had not yet returned the completed 

survey. 

 Survey data were compiled and means generated for quantitative data. Qualitative data 

were compared to determine if consensus existed among industry practices. 

 NaCl content was determined using Quantab® titrators for chloride (0.05-1.0% NaCl, Hach 

Company, Loveland, CO), using five g jerky combined with 45 ml distilled, deionized water. 

 aw was measured at ambient temperature using an AquaLab Series 3 TE (Decagon 

Devices, Pullman, WA). 

 pH was determined on 10 g jerky blended with 100 ml distilled, deionized water and 

measured with a pH meter (Accumet Portable model AP61 Fisher Scientific, Fair Lawn, NJ). 

Results 

 Of 78 plants contacted, 37 contributed surveys for a 47% response rate. Of these, 33 

plants contributed 61 product samples. 

 Whole muscle jerky produced by 33 plants, ground/chunked and formed jerky produced by 

26 plants. 

9 
 

 

 

 

Results (continued) 

Equipment Used for 

Jerky Processing: 

34 (92%): use 

smokehouse 

3 (8%): use commercial 

oven 

1 (3%): use 

smokehouse and oven 

Relative Humidity 

Measurement: 

9 (24%): determine wet 

bulb temperature 

1 (3%): use relative 

humidity instrument 

35 (95%): claim they are 

able to control relative 

humidity 

Relative Humidity 

Techniques Used: 

13 (35%): close dampers 

3 (8%): steam injection 

3 (8%): direct addition of 

water 

1 (3%): place pan of water 

in house 

16 (43%): combination of 

these methods 

Thermal Processing 

Schedule Extremes: 

93.3°C smokehouse for 

“entire process” 

51.7°C for 45 minutes, 

followed by 2.2°C increase 

every 45 minutes to 62.7°C 

(max) 

Common Ingredients 

Used: 

28 (86%): sodium 

nitrite 

15 (41%): sodium 

erythorbate 

5 (14%): potassium 

sorbate 

23 (62%): soy sauce 

3 (8%): vinegar 

6 (16%): 

worcestershire sauce 

2 (5%): tabasco 

sauce 

Ingredient Addition 

Method: 

45 products marinated 

16 products dry addition 

18 products tumbled 

2 are vacuum tumbled 

1 injected before 

tumbled 

4 soaked before and 

after tumbled 

Packaging Type Used 

for Jerky: 

29 (78%): vacuum 

12 (32%): no vacuum 

5 (14%): gas flush 

Table 1. Mean NaCl content, aw and pH of whole muscle, ground and formed, and 

chunked and formed jerky by species from 33 primarily Midwestern companies. 

Species % NaCl SD1 aw SD pH SD 

Beef 6.90% 

(n=28) 

2.54 

% 

0.74 

(n=49) 

0.10 5.86 

(n=49) 

0.32 

Pork 7.58% 

(n=5) 

2.42 

% 

0.71 

(n=6) 

0.09 5.87 

(n=6) 

0.35 

Turkey 3.73% 

(n=1) 

- 0.77 

(n=4) 

0.09 5.82 

(n=4) 

0.46 

Buffalo 4.95% 

(n=1) 

- 0.79 

(n=2) 

0.08 5.52 

(n=2) 

0.16 

Maximum for all Products 11.54% 0.90 6.60 

Minimum for all Products 2.10% 0.51 5.00 

10 
 type or 

shelf stability. 

Figure 1. Target aw versus actual aw in nine jerky samples, relative to packaging 

0.65 

0.7 

0.75 

0.8 

0.85 

0.9 

Refrigerated 

Shelf-Stable 

Shelf-Stable 

Shelf-Stable 

Shelf-Stable Shelf-Stable 

MAP 

Vac/No-vac 

MAP 

Packaging or Shelf Stability Characteristics 

aw

Tar get 

Actual 

11 
2. Lonnecker, S. M. 2005. Variables affecting lethality of Escherichia coli O157:H7 and 

Salmonella species in whole muscle or formed jerky products. M.S. report, Kansas State Univ., 

Manhattan (abstract follows). 

ABSTRACT 

In light of several foodborne outbreaks related to jerky products, manufacturers have 

found themselves in the spotlight of heightened scrutiny by regulatory entities and the consumer 

public. Industry has found regulations changing and an immediate need to carefully review 

processing methods and formulations. Regulatory and industry officials have also found that 

very little scientific information exists that can be directly applied to this jerky products. 

The intent of this review is to present direct and indirect scientific information that can be 

applied to jerky manufacturing schemes, from formulation through thermal processing for the 

production of a safe product. Studies reviewed in this thesis demonstrate processing methods or 

ingredients that directly affect lethality of Salmonella spp. and Escherichia coli O157:H7. 

Some key findings of this review include evidence that sodium chloride or fat can support 

pathogenic survival, evidence on the effect of water activity on lethality and post-processing 

growth and the remarkable and often unanticipated effect solutes can have, not only on available 

nutrients but on the osmotic environment surrounding microorganisms. Discussion also focuses 

on the use of an acid or alkaline environment to reduce pathogen populations and a brief 

discussion of packaging methods and environments that can introduce storage and distribution 

concerns. 

While specific heat processing schedules are beyond the intended scope of this document, 

variables that should be considered during thermal treatments are discussed in great detail. 

These variables include: concepts behind the thermal death of microorganisms, types of heat 

transfer in gas, liquid and solid media, mass transfer effects and the importance of relative 

humidity during heat treatment. 

This report will provide information that might be implemented not only by industry 

officials looking for a better understanding of their products or HACCP validation, but also by 

academia in developing scientific data and further research of relevance to jerky or similarly 

processed products. Still another potential use is by regulatory officials seeking evidence 

supporting guideline development or enforcement strategies. 

12 
3. Roberts, Michelle N. Evaluation of thermal processing parameters in production of chopped 

and formed beef jerky for controlling Escherichia coli O157:H7 and Salmonella species. Chapter 

on Preliminary Studies. M.S report, Kansas State Univ., Manhattan (December 2006) Coadvisors: Getty, K.J.K. and Fung, D.Y.C. and Committee member: Boyle, E.A.E. 

PRELIMINARY STUDIES 

NOTE TO READERS: The preliminary studies are a collection of small research studies to 

develop jerky processing parameters, a process schedule, and inoculation procedures for 

incorporating microorganisms into the raw jerky batter. These studies were not designed for 

obtaining process validation information. Therefore, the results presented here should not be 

used as verification or validation information for determining lethality of jerky processing 

schedules. 

Introduction 

The United States Department of Agriculture Food Safety and Inspection Service 

(USDA/FSIS) has published Compliance Guidelines for the Production of Jerky. The guidelines 

were issued in part to a 2003 Salmonella kiambu outbreak being linked to the consumption of 

jerky produced by a New Mexico firm, resulting in the recall of 22,000 lbs. of jerky (FSIS, 

2003). The guidelines require that processors achieve a water activity level of <0.70 (FSIS, 

2004). In addition, FSIS’s standard of identity for jerky is a moisture-to- protein (MPR) ratio of 

0.75:1 (AAMP, 2004; Compliance Guideline, 2004). FSIS performance standards for ready-toeat meat and poultry products, according to a 2001 proposed rule, require that processes achieve 

a 5.0 log CFU/g reduction of Escherichia coli O157:H7 and a 6.5 log CFU/g reduction of 

Salmonella spp. 

The basic objectives of the preliminary studies were: 1) to determine if a hand-held jerky 

strip dispenser with nozzle would produce a product similar to commercial jerky; 2) to evaluate 

the effectiveness of typical smokehouse schedules for producing commercially chopped and 

formed all-beef jerky to an appropriate water activity level of <0.70 and a MPR of 0.75:1; 3) to 

determine how many strips would be needed to fill the smokehouse to capacity; and 4) to 

determine inoculum levels needed to achieve greater than 7.0 log CFU/g of E. coli O157:H7 or 

Salmonella spp. in raw chopped and formed jerky. Six preliminary studies were conducted and 

the objectives, materials and methods, and results and discussion of each study are discussed. 

Preliminary Study 1 

Objectives 

1. To determine if a hand-held jerky strip dispenser with a nozzle would produce a product 

similar to finished commercial jerky product. 

2. To evaluate the effectiveness of a typical smokehouse schedule for producing 

commercially chopped and formed all-beef jerky. 

13 
Materials and Methods 

Meat Batter Preparation 

Fresh chopped and formed all-beef jerky batter (-5°C), was obtained from a commercial 

processor, immediately frozen at –15 ± 2°C for 1 to 2 weeks and then tempered overnight at 4°C 

and used the following day. A 0.907 kg (2 lb) batch was used for testing purposes. 

Raw jerky batter was transferred to a manual jerky strip dispenser with a 0.19 cm (3/16”) 

by 0.19 cm (3/16”) nozzle (Model Nbr. H6253, Grizzly Industrial, Inc., Bellingham, WA). 

Strips were placed on polyscreen sheets (Excalibur, Sacramento, CA) with four strips per sheet. 

Each strip was approximately 17.78 cm (7”) long with width and depth similar to size of the 

nozzle. Strip-filled sheets were placed on the seven-smokehouse trays and the trays were placed 

on a smokehouse cart. Once loaded, the smokehouse cart was placed in a commercial 

smokehouse (Alkar Model 450-UA, Alkar, Lodi, WI) and thermally processed (Table 1). 

Sampling Times 

Heat-treated samples were taken at four different times throughout the process [end of 

Stages 6, 7, 8, and 9] (Table 1). Four strips were taken randomly throughout the smokehouse for 

each sampling time. 

Water Activity (aw) 

Water activity was measured on all samples collected at the different sampling times. A 

sample consisted of four combined strips. A composite sample was prepared by finely chopping 

the four strips. Duplicate readings were taken. A water activity meter (Pawkit, Decagon, 

Pullman, WA) measured water activity. Readings were recorded when the stabilized icon was 

displayed. 

Results and Discussion 

Finished strips were approximately 1.27 cm (1/2”) by 0.26 cm (1/10”) by 10.16 cm (4”). 

This was too small compared to typical commercial jerky strips having dimensions of 

approximately1.91 cm (3/4”) by 0.32 cm (1/8”) by 15.24 cm (6”). It was determined that a 

larger nozzle would be needed to account for shrinkage during the drying process and to produce 

a more typical commercial jerky product. 

Water activity for samples collected at the end of stage 6, 7, and 8 ranged from 0.76 to 

0.71. Final water activity, taken at the end of stage 9, was 0.70 (Table 1). Typical water activity 

for jerky products should be < 0.70 to ensure lack of microbial growth (FSIS, 2004). A jerky 

product with a water activity of less than 0.85 is usually considered shelf stable and would not 

support the growth of pathogenic microorganisms. A water activity of < 0.70 is suggested for 

the stabilization of jerky product that is to be in contact with air as this water activity level 

inhibits mold growth (AAMP, 2004). 

14 
 

 

 

 

Table 1. Thermal processing schedulea

, sampling times, and water activity levels for chopped 

and formed beef jerky. 

Stage 

Dry Bulb 

(D.B.) 

(°C) 

Wet Bulb 

(W.B.) 

(°C) 

Percent 

Relative 

Humidity 

(R.H.) Time 

Sampling 

Time 

Water 

Activity 

0b Raw 0.94 

1 23.9 23.9 90 30 min 

2 43.3 32.2 68 30 min 

3 54.4 32.2 60 30 min 

4 65.6 35.0 48 30 min 

5 68.3 35.0 14 30 min 

6 71.1 40.6 14 30 min End of stage 0.76 

7 71.1 37.8 29 30 min End of stage 0.72 

8 76.7 37.8 21 30 min End of stage 0.71 

9 76.7 35.0 13 30 min End of stage 0.70 

10 76.7 35.0 <10 30 min a

The smokehouse has an automated damper system and the ability to inject steam humidity as 

needed to control humidity. The blower was not turned on and the dampers were set on 

automatic to allow for effective control of humidity. 

b

Stage 0 = raw meat batter. 

Preliminary Study 2 

Objective 

1. To determine if a larger nozzle for the jerky strip dispenser would yield a more typical 

commercial size jerky strip. 

Materials and Methods 

The same procedures were used for meat batter preparation as described in Preliminary Study 

1. However, a larger nozzle of 0.64 cm (1/4”) by 2.54 cm (1”) nozzle (Model Nr. LEM468D, 

Allied Kenco, Houston, TX) was attached to the jerky strip dispenser. The sampling times were 

the same as Preliminary Study 1 and are also defined in Table 2. In addition, water activity 

levels were measured in a similar manner. 

Results and Discussion 

Finished strips were approximately 1.91 cm (3/4”) by 0.32 cm (1/8”) by 15.24 cm (6”). 

This was comparable to typical commercial jerky strips having dimensions of approximately 

1.27-1.91 cm (1/2-3/4”) by 0.32-0.64 cm (1/8-1/4”) by 15.24-20.32cm (6-8”). Therefore, the 

larger jerky nozzle allowed for a correct amount of raw product to meet finished product 

dimensions due to shrinkage during processing. 

Due to larger product dimensions, water activity levels at the end of stages 6, 7, and 8 

ranged from 0.84 to 0.78 and were approximately 0.4 points higher than for products sampled at 

the same time in Preliminary Study 1. Final water activity for final product, at end of stage 9, 

was 0.74 (Table 2). Typical water activity for jerky products should be < 0.70 to ensure lack of 

15 
 

 

 

 

microbial growth (FSIS, 2004). The current processing schedule would need to be altered in 

order to dry the product sufficiently to achieve the desired water activity < 0.70. 

Table 2. Thermal processing schedulea

, sampling times, and water activity levels for chopped 

and formed beef jerky. 

Stage 

Dry Bulb 

(D.B.) 

(°C) 

Wet Bulb 

(W.B.) 

(°C) 

Percent 

Relative 

Humidity 

(R.H.) Time 

Sampling 

Time 

Water 

Activity 

0b Raw 0.94 

1 23.9 23.9 90 30 min 

2 43.3 32.2 68 30 min 

3 54.4 32.2 60 30 min 

4 65.6 35.0 48 30 min 

5 68.3 35.0 14 30 min 

6 71.1 40.6 14 30 min End of stage 0.84 

7 71.1 37.8 29 30 min End of stage 0.80 

8 76.7 37.8 21 30 min End of stage 0.78 

9 76.7 35.0 13 30 min End of stage 0.74 

10 76.7 35.0 <10 30 min a

The smokehouse has an automated damper system and the ability to inject steam humidity as 

needed to control humidity. The blower was not turned on and the dampers were set on 

automatic to allow for effective control of humidity. 

b

Stage 0 = raw meat batter. 

Preliminary Study 3 

Objectives 

1. To test a different smokehouse schedule that is more typical of a commercial jerky 

process. 

2. To determine how many strips are needed to completely fill the smokehouse to its 

capacity. 

3. To determine the finished weight of strips for sampling purposes. 

Materials and Methods 

The same procedures were used for meat batter preparation as described in Preliminary Study 1. 

However, the raw jerky product was separated into one 1.814 kg (4 lb) batch. Sampling times 

differed from those listed in Preliminary Studies 1 and 2 in order to test the different smokehouse 

schedule used in this study. Heat-treated samples were taken at eleven different times 

throughout the process [end of Stages 6, 7, 8, 10 and at thirty minute intervals throughout Stage 

12] (Table 3). Four strips were taken randomly throughout the smokehouse for each sampling 

time. Water activity was performed in the same manner as in Preliminary Studies 1 and 2. 

16 
-

Results and Discussion 

Finished strips were approximately 1.91 cm (3/4”) by 0.32 cm (1/8”) by 15.24 cm (5.5”). 

This was comparable to typical commercial jerky strips having dimensions of approximately 

1.27-1.91 cm (1/2-3/4”) by 0.32-0.64 cm (1/8-1/4”) by 12.70-20.32cm (5-8”). Two finished 

strips weighed approximately 27 g. According to the USDA/FSIS Microbiology Laboratory 

Guidebook (1998) a typical sample size for microbial analysis is 25g. Therefore, two strips 

could be used to represent a “sample” in future studies. The 1.814 kg (4 lb) batch made 

approximately 56 strips and filled 1/3 of the smokehouse. In order to get results typical of a 

smokehouse running at full capacity, a 5.442 kg (12 lb) batch would need to be used for future 

studies. 

Final water activity for final product, at the end of stage 12 was 0.65 (Table 3) which is 

below the suggested FSIS requirement of < 0.70 (FSIS, 2004). Water activity reached the 

desired level 1.5 h into stage 12, so the schedule could be modified to end at this time. 

17 
 

 

 

 

 

 

 

 

 

 

 

 

 

Table 3. Thermal processing schedulea

, sampling times, and water activity levels for chopped 

and formed beef jerky. 

Stage 

Dry Bulb 

(D.B.) 

(°C) 

Wet Bulb 

(W.B.) 

(°C) 

Percent 

Relative 

Humidity 

(R.H.) Time 

Sampling 

Time 

Water 

Activity 

0b Raw 0.95 

1 55.6 N/A 72 14 min 

2 55.6 37.8 84 16 min 

3 55.6 43.3 43 14 min 

4 77.8 43.3 78 16 min 

5 77.8 48.9 78 14 min 

6 77.8 48.9 78 16 min 

End of 

stage 0.89 

7 77.8 48.9 78 14 min 

End of 

stage 0.85 

8 77.8 48.9 78 16 min 

End of 

stage 0.86 

9 77.8 48.9 78 14 min 

10 

77.8 48.9 

78 16 min 

End of 

stage 0.81 

11 77.8 48.9 78 14 min 

End of 

stage 0.78 

12 77.8 N/A 78 3h 

30 min 

into stage 

12 0.76 

1 h into 

stage 12 0.73 

1.5 h into 

stage 12 0.69 

2 h into 

stage 12 0.68 

2.5 h into 

stage 12 0.66 

3 h into 

stage 12 

(End) 0.65 a

The smokehouse has an automated damper system and the ability to inject steam humidity as 

needed to control humidity. The blower was not turned on and the dampers were set on 

automatic to allow for effective control of humidity. 

b

Stage 0 = raw meat batter. 

18 
Preliminary Study 4 

Objectives 

1. To determine the amount of inoculum needed for both E. coli O157:H7 and Salmonella 

spp. to achieve > 7.0 log CFU/g in raw batches of product. 

2. To determine the effectiveness of the smokehouse schedule for controlling E. coli O157:H7 

and Salmonella spp. inoculated batches of commercially prepared chopped and formed allbeef jerky batter. 

3. To analyze the moisture-to-protein ratios (MPR) in finished jerky product. 

Materials and Methods 

Confirmation of Cultures and Presumptive E. coli O157:H7 and Salmonella spp. Colonies

 All E. coli O157:H7 cultures were originally obtained from the American Type Culture 

Collection (ATCC 43894, ATCC 43889, ATCC 43890, ATCC 43895) (Rockville, MD) and the 

United States Department of Agriculture/Agricultural Research Service (USDA 380-94) 

(USDA/ARS, Athens, GA). All Salmonella spp. cultures were originally obtained from ATCC 

[ATCC 35640 (Salmonella abaetetuba), ATCC 4931 (Salmonella enteriditis), ATCC 13076 

(Salmonella enteriditis), ATCC 15060 (Salmonella enteriditis), ATCC 13311 (Salmonella 

typhimurium). Cultures arrived in commercial bead form and were kept in an -80°C freezer in 

the KSU Food Safety and Security lab. 

Confirmation 

All cultures and presumptive E. coli O157:H7 and Salmonella spp. colonies taken respectively 

from, phenol red sorbitol agar (PRSA; Becton Dickinson, Franklin Lakes, NJ) and xylose lysine 

desoxycholate agar (XLD; Becton Dickinson, Franklin Lakes, NJ) plates from raw and heattreated samples were streaked, using a sterile loop (Fisher Scientific Inc, Pittsburgh, PA) onto 

tryptic soy agar (TSA; Becton Dickonson, Franklin Lakes, NJ) and incubated at 37oC for 24 h. 

Typical colonies were used to inoculate API 20E biochemical identification test strips 

(bioMerieux Vitek, Inc., Hazelwood, MO) and Enterotubes (Becton Dickinson, Franklin Lakes, 

NJ). 

Preparation of Bacterial Culture 

A five-strain cocktail of E. coli O157:H7 as described above and a separate five-strain 

cocktail of Salmonella spp. as describe above were prepared. For inoculum preparation of each 

pathogen strain, one loopful of each culture was transferred into 9 mL of tryptic soy broth (TSB; 

Difco) and incubated at 35oC for 18-24 h. Four mL of each culture suspension was then 

transferred to a sterile bottle (Nalgene, Rochester, NY). Two separate bottles resulted with one 

containing 20 mL of E. coli O157:H7 and one containing 20 mL of Salmonella spp. 

19 
 

 

 

Meat Batter Preparation and Inoculation 

Fresh chopped and formed all-beef jerky batter was obtained from a commercial 

processor, immediately frozen for 1 to 2 weeks and then tempered overnight at 4oC and used the 

following day. The product was separated into three 1.814 kg (4 lb) batches. To the control 

batch, 15 mL of sterile deionized water was mixed evenly into the meat batter and stored at 4oC 

until stuffing and enumeration. To a separate batch, 15 mL of the E. coli O157:H7 five-strain 

inoculum was intermittently pipetted drop-wise over the batter surface and massaged with gloved 

hands until thoroughly mixed into the jerky batter. The batter was stored at 4oC until stuffing 

and enumeration. This procedure was repeated with the last batch of batter, however, 15 mL of 

the Salmonella spp. five-strain inoculum was added instead. 

Raw jerky batter (control followed by inoculated batches) was transferred to a manual 

jerky gun (Model Nbr. H6253, Grizzly Industrial, Inc.) with a 0.64 cm (1⁄4”) by 2.54 cm (1”) 

jerky nozzle (Model Nr. LEM468D, Allied Kenco, Houston, TX). Strips were placed on 

polyscreen sheets (Excalibur, Sacramento, CA) with eight strips per sheet. Each strip was 

approximately 17.78 cm (7”) long. Strip filled sheets were placed on smokehouse trays in a way 

as to prevent potential cross contamination (Table 4). This allowed elimination of the possibility 

of competitive exclusion between E. coli O157:H7 and Salmonella spp. Once loaded, the 

smokehouse cart was placed in a commercial smokehouse (Alkar Model 450-UA, Alkar, Lodi, 

WI) and thermally processed (Table 5). 

E. coli O157:H7 and Salmonella spp. Enumeration 

One mL of the E. coli O157:H7 inoculum was enumerated using duplicate phenol red 

sorbitol agar (PRSA; Difco) plates. One mL of the Salmonella spp. inoculum was enumerated 

using duplicate xylose lysine desoxycholate agar (XLD; Difco) plates. Six 1:10 dilutions of each 

inoculum were made using 0.1% peptone water (PW; Difco) and then spread plated onto their 

corresponding media in duplicate. 

Raw inoculated samples were taken from the inoculated jerky batter to determine the 

initial inoculum level of the product. Heat-treated samples were taken at five different times 

[end of Stages 6, 7, 8, 10, and at end of Stage 12] (Table 5). At each sampling time, two samples 

of each of the three batches were taken. A sample comprised of two strips. Control samples 

were used for proximate analysis, pH, and water activity analysis. The inoculated samples were 

used for E. coli O157:H7 and Salmonella spp. enumeration. 

Raw and heat-treated samples were prepared by weighing 25 g in filtered stomacher bags 

to which 225 mL of PW diluent was added. The samples were pummeled in a stomacher 

(Stomacher Mix 1 Lab Blender, Microbiology International, Frederick, MD) for 1 min and six 

serial 1:10 dilutions were prepared using 9 mL 0.1% peptone blanks. Dilutions were spread 

plated in duplicate onto PRSA for E. coli O157:H7 inoculated samples and XLD plates for 

Salmonella spp. inoculated samples. For samples taken at the end of the cycle, a 1:10 dilution 

was spread-plated (0.25) onto four plates in duplicate, allowing for a sample detection limit of 1 

log cfu/g. 

pH Analysis 

The pH was measured on control samples (2) by weighing 25 g of sample into a filtered 

stomacher bag and adding 225 mL PW and stomaching for 1 min. A pH meter (Corning 

Pinnacle 530 pH Meter, Corning, NY) was used to measure pH. The pH readings were recorded 

when the stabilized icon was displayed (Table 5). 

20 
 

 

Water Activity (aw) 

Water activity was measured on control samples. Two samples were taken per treatment. 

Each sample was from a different set of two combined strips. Duplicate readings were taken. A 

water activity meter (Pawkit, Decagon, Pullman, WA) was used to measure water activity. 

Readings were recorded when the stabilized icon was displayed (Table 5). 

Proximate Analysis 

Samples for proximate analysis were taken from non-inoculated raw control, end of 

Stage 10, and End of Stage 12 (final) product samples (Table 5). Two fifty gram samples of raw 

inoculated batter, two samples containing two jerky strips each from 1.5 h into Stage 12, and two 

samples containing two finished jerky strips were vacuum packaged, and placed in frozen 

storage (-80oC) prior to analysis. Samples were prepared by freezing in liquid nitrogen and 

pulverized in a Waring Blender. Moisture (AOAC 985.14) and fat (AOAC 985.15) were 

determined by a rapid microwave solvent method (CEM, Matthews, NC, U.S.A.). Protein was 

determined by the LECO method (AOAC 990.03) and salt was analyzed by a volumetric method 

(AOAC 935.47). 

Results and Discussion 

Finished strips were approximately 1.91 cm (3/4”) by 0.32 cm (1/8”) by 15.24 cm 

(5.5”). This was comparable to typical commercial jerky strips having dimensions of 

approximately 1.27-1.91 cm (1/2-3/4”) by 0.32-0.64 cm (1/8-1/4”) by 12.70-20.32cm (5-8”). 

For all E. coli O157:H7 inoculated jerky strips, initial raw batter populations were 5.58-to 5.89 

log CFU/g on PRSA. For Salmonella spp. inoculated jerky strips, initial raw batter populations 

ranged from 5.08 to 5.40-log CFU/g on XLD (Table 5). For samples taken at the end of stages 6, 

7, 8, and 10, E. coli O157:H7 and Salmonella spp. ranged from <3 to <5-log CFU/g on all media. 

Plating was not low enough to catch the dilution. End of Stage 12 product microbial populations 

were consistently <1 log CFU/g on all media (Table 6). 

The dilution factor was not low enough to visibly detect growth on stages 6, 7, 8, 

and 10, so reductions could not be adequately determined. A > 4.24 log CFU/g reduction of both 

Salmonella spp. and E. coli O157:H7 was observed on the end product. Due to the inoculum 

level not being high enough and the detection limit not being low enough, this process was 

inadequate at determining reduction levels mandated by USDA/FSIS. Therefore, inoculation 

levels would need to be increased and the detection level lowered to adequately determine log 

reductions. 

Moisture content for control raw product was approximately 51.6% for raw 

product and ranged from 28.4 to 30.05% for final product. Final product moisture levels fall 

within the typical range of percent moisture levels for jerky, which is 28-30% (Ricke and Keeton 

1997). Protein content for control raw product was approximately 17.0% for raw product and 

ranged from 27.6 to 28.6% for final product (Table 5). The moisture-to-protein ratio (MPR) 

ranged from 0.99 to 1.08 for the final product. This ratio is not in compliance with the guideline 

of an MPR at <0.75:1 that is needed for product to be labeled as jerky (Compliance Guideline, 

2004). This product falls within the < 2.03:1 and >0.76:1 MPR range that is typical of kippered 

beef (AAMP, 2004). The product MPR would need to be driven lower to be labeled as “jerky”. 

21 
Raw batter pH values ranged from 6.1 to 6.4. Final pH range for all products was 

6.1 (Table 5). This falls within the typical pH range of 5.3-6.6 for jerky products products 

(Lonnecker, 2005; Buege, 2005). This range is of particular concern as it easily supports the 

growth of gram-negative bacteria. For example, E. coli O157:H7 can grow at pH levels <4.4, 

while some Salmonella spp. can grow at pH levels as low as 3.8 (AAMP, 2004). 

Final water activity range for all final products was approximately 0.72 (Table 5). Which 

is slightly higher than the suggested FSIS level of < 0.70 to ensure lack of microbial growth 

(FSIS, 2004). Therefore the smokehouse schedule would need to be modified in order to achieve 

a water activity of < 0.70 to inhibit microbial growth. 

Table 4. Order of placement in smokehouse for control (C), E. coli O157:H7 (E), and Salmonella 

spp. (S) jerky batches. 

C E S 

C E S 

C E S 

C E S 

C E S 

C E S 

C E S 

22 
Table 5. Thermal processing schedulea, sampling times, mean water activity levels, mean pH values, and mean p

chopped and formed beef jerky. 

Stage 

Dry 

Bulb 

(D.B.) 

(°C) 

Wet 

Bulb 

(W.B.) 

(°C) 

Percent 

Relative 

Humidity 

(R.H.) Time 

Sampling 

Time 

Water 

Activity pH 

Percent 

Moisturec 

Percent 

Protein 

0b Raw 0.95 6.23 51.6±0.17 17.0±0.13 

1 55.6 N/A 72 14 min 

2 55.6 37.8 84 16 min 

3 55.6 43.3 43 14 min 

4 77.8 43.3 78 16 min 

5 77.8 48.9 78 14 min 

6 77.8 48.9 78 16 min 

End of 

stage 0.88 6.26 

7 77.8 48.9 78 14 min 

End of 

stage 0.84 6.21 

8 77.8 48.9 78 16 min 

End of 

stage 0.84 6.29 

9 77.8 48.9 78 14 min 

10 

77.8 48.9 

78 16 min 

End of 

stage 0.83 6.21 32.1±0.37 25.1±1.07 

11 77.8 48.9 

78 

14 min 

12 77.8 N/A 78 1.5 h 

End of 

stage 0.72 6.06 29.2±1.15 28.1±0.74 

aThe smokehouse has an automated damper system and the ability to inject steam humidity as needed to control humidity. 

turned on and the dampers were set on automatic to allow for effective control of humidity. 

bStage 0 = raw meat batter. cRanges are due to duplicate sample 

23 
(This page has been left blank due to formatting). 

24 
 

 

Table 6. E. coli O157:H7 and Salmonella spp. populationsa (log CFU/g) at seven 

sampling times during production of chopped and formed beef jerky. 

Stage/Sampling 

time 

Media 

PRSA XLD 

Raw 5.7±0.22 5.2±0.23 

Stage 6 <5 <5 

Stage 7 <4 <4 

Stage 8 <3 <3 

Stage 10 <3 <3 

1.5 h into stage 

12 

<1.48 <1.48 

End of stage 12 <0.48 <0.48 a

Populations are an estimate based on the detection limits. 

Preliminary Study 5 

Objectives 

1. To determine if the addition of 29 mL of an E. coli O157:H7 or Salmonella spp. 

inoculum to a 1.814 kg (4 lb) batch of raw jerky batter would allow for >7.0 log 

CFU/g. 

2. To determine if the addition of the exhaust fan at a high blower speed for the first 

part of the smokehouse cycle would drive down water activity levels and the 

moisture-to-protein ratio (MPR). 

3. To evaluate if a different water activity meter would give more reliable aw levels. 

Materials and Methods 

The same procedures were used for meat batter preparation as in Preliminary 

Study 4, however, 29 mL of sterile deionized water was added to the control batch and 29 

mL of the two (E. coli O157:H7 or Salmonella spp.) inoculums were added to their 

respective batches. Only the control batch was used to produce strips to undergo the 

thermal process. E. coli O157:H7 and Salmonella spp. enumeration were done in a 

similar fashion, however, only the inoculum and raw samples were enumerated in order 

to determine the inoculum level in the raw product. The sampling times were the same as 

in Preliminary Study 3 and are defined in Table 7. One sample, comprised of two strips, 

was taken randomly throughout the smokehouse for each sampling time. Samples were 

used for water activity and proximate analysis. The pH levels were not measured in this 

study. 

Water activity was determined as described in Preliminary Study 4, however; only 

the one sample was analyzed (Table 7). A different water activity (Model CX2, Aqualab, 

Pullman, WA) was used. Proximate analysis was conducted in a similar fashion; 

however, one sample of product was taken 1.5 h into stage 12 and at the end of stage 12 

(Table 8). 

25 
Results and Discussion 

Finished strips were approximately 1.91 cm (3/4”) by 0.32 cm (1/8”) by 13.97 cm (5.5”). 

This was comparable to typical commercial jerky strips having dimensions of 

approximately 1.27-1.91 cm (1/2-3/4”) by 0.32-0.64 cm (1/8-1/4”) by 12.70-20.32cm (5-

8”). For E. coli O157:H7 inoculated batter, initial raw populations were 9.02-log CFU/g 

on PRSA. For Salmonella spp. inoculated jerky strips, initial raw batter populations were 

7.95-log CFU/g on XLD. These levels are high enough to provide detection of the 5-log 

reduction of E. coli O157:H7 and the 6.5-log reduction of Salmonella spp. proposed by 

the USDA/FSIS, provided that the detection limit is lowered from that described in 

Preliminary 4. This could be achieved by adding 50 mL of peptone diluent to a 25 g 

sample instead of 225 mL. 

Moisture content was 27.63% 1.5 h into stage 12, and 23.43% for final product. 

This is lower than the typical moisture content for beef jerky, which ranges from 28 to 

30% (Ricke and Keeton 1997). Protein content was 28.90% 1.5 h into stage 12, and 

30.34% for final product (Table 7). The moisture-to-protein ratio was 0.77 for final 

product. This ratio is not in compliance with the guideline of an MPR of < 0.75:1 needed 

for product to be labeled as “jerky” (Compliance Guideline, 2004). Therefore, the MPR 

would need to be driven lower for the product to be considered jerky. 

Water activity for final product was 0.71 (Table 7). Typical water activity for 

jerky products should be < 0.70 to ensure lack of microbial growth (FSIS, 2004). The 

smokehouse schedule would need to be modified to achieve a < 0.70 water activity level. 

This could be achieved by employing the exhaust fan for a longer period of time 

throughout the smokehouse cycle in order to efficiently dehydrate the product. 

26 
Table 7. Thermal processing schedulea, sampling times, and water activity levels for chopped and formed beef je

Stage 

Dry Bulb 

(D.B.) 

(°C) 

Wet Bulb 

(W.B.) (°C) 

Percent 

Relative 

Humidity 

(R.H.) Time Sampling Time 

Water 

Activity 

Percent 

Moisture 

Percen

Protei

0b Raw 0.94 

1 55.6 N/A <10 14 min 2 55.6 37.8 <10 16 min 3 55.6 43.3 <10 14 min 4 77.8 43.3 <10 16 min 5 77.8 48.9 <10 14 min 6 77.8 48.9 55 16 min End of stage 0.95 

7 77.8 48.9 65 14 min End of stage 0.89 8 77.8 48.9 78 16 min End of stage 0.84 9 77.8 48.9 78 14 min 

10 77.8 48.9 78 16 min End of stage 0.82 11 77.8 48.9 78 14 min End of stage 0.79 12 77.8 N/A 78 3h 30 min into stage 

12 0.81 

1 h into stage 12 

0.77 

1.5 h into stage 12 

0.79 

27.63 28.90 

2 h into stage 12 

0.74 

2.5 h into stage 12 

0.73 

3 h into stage 12 

(End) 

0.71 23.43 30.34 

aThe smokehouse has an automated damper system and the ability to inject steam humidity as needed to control humidity. 

on high for the first 1.5 h of the cycle and the dampers were set on automatic to allow for effective control of humidity. 

bStage 0 = raw meat batter. 

27 
 

Preliminary Study 6 

Objectives 

1. To evaluate the effect of using the same schedule as Preliminary Studies 4 and 5, 

but lengthening the cycle by 2 h accompanied by the addition of the exhaust fan on 

medium speed for the first 1.5 h of the cycle and increased to high speed for the 

duration of the cycle. 

Materials and Methods 

The same procedures were used for meat batter preparation as were used 

in Preliminary Study 5, however, only one 1.814 kg (4 lb) batch was dispensed into 

strips. Sampling times differed from those listed in Preliminary Study 5 in order to 

represent the different smokehouse schedule used in this study. Heat-treated samples 

were taken at fifteen different times throughout the process [end of Stages 6, 7, 8, 10 and 

at thirty minute intervals throughout Stage 12] (Table 8). One sample, comprised of two 

strips, was taken randomly throughout the smokehouse for each sampling time. Samples 

were used for water activity and proximate analysis. The pH levels were not measured in 

this study. 

Water activity was determined as described in Preliminary Study 4, however; only 

the one sample was analyzed (Table 8). A different water activity (Model CX2, Aqualab, 

Pullman, WA) was used. Proximate analysis was conducted in a similar fashion; 

however, one sample of product was taken 4.5 h into stage 12 and at the end of stage 12 

(Table 9). 

Results and Discussion 

Finished strips were approximately 1.91 cm (3/4”) by 0.32 cm (1/8”) by 12.70 cm 

(5”). This was comparable to typical commercial jerky strips having dimensions of 

approximately 1.27-1.91 cm (1/2-3/4”) by 0.32-0.64 cm (1/8-1/4”) by 12.70-20.32cm (5-

8”). Moisture content was 21.83% 4.5 h into stage 12, and 21.02% for final product. This 

is lower than the typical moisture content for beef jerky, which ranges from 28 to 30% 

(Ricke and Keeton, 1997). Protein content was 29.04% 4.5 h into stage 12, and 30.13% 

for final product (Table 9). The moisture-to-protein ratio was 0.71 for final product. 

This ratio is in compliance with the guideline of an MPR of < 0.75:1 needed for product 

to be labeled as “jerky” (Compliance Guideline, 2004). 

Water activity for final product was 0.69 (Table 8). Typical water activity for 

jerky products should be < 0.70 to ensure lack of microbial growth (FSIS, 2004). This 

cycle successfully produced product meeting the appropriate MPR and water activity 

levels. 

28 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 8. Thermal processing schedulea

, sampling times, and water activity levels for 

chopped and formed beef jerky. 

Stage 

Dry Bulb 

(D.B.) (°C) 

Wet Bulb 

(W.B.) (°C) 

Percent 

Relative 

Humidity 

(R.H.) Time Sampling Time 

Water 

Activity 

0b Raw 0.94 

1 55.6 N/A <10 14 min 

2 55.6 37.8 <10 16 min 

3 55.6 43.3 <10 14 min 

4 77.8 43.3 <10 16 min 

5 77.8 48.9 <10 14 min 

6 77.8 48.9 <10 16 min 

End of stage 

0.88 

7 77.8 48.9 <10 14 min 

End of stage 

0.87 

8 77.8 48.9 <10 16 min 

End of stage 

0.86 

9 77.8 48.9 <10 14 min 

10 

77.8 48.9 

<10 16 min 

End of stage 

0.82 

11 77.8 48.9 <10 14 min 

End of stage 

0.84 

12 77.8 N/A <10 3h 

30 min into stage 

12 

0.81 

1 h into stage 12 

0.74 

1.5 h into stage 12 

0.77 

2 h into stage 12 

0.79 

2.5 h into stage 12 

0.73 

3 h into stage 12 

0.73 

3.5 h into stage 12 

0.71 

4 h into stage 12 

0.73 

4.5 h into stage 12 

0.71 

5 h into stage 12 

(End) 

0.69 a

The smokehouse has an automated damper system and the ability to inject steam humidity as 

needed to control humidity. The blower was turned on medium for the first 1.5 h of the cycle and 

bumped up to high for the duration of the cycle. The dampers were set on automatic to allow for 

effective control of humidity. 

b

Stage 0 = raw meat batter. 

29 
 

 

 

Table 9. Proximate analysis of control chopped and formed beef jerky samples. 

Sampling 

time 

Percent 

Moisture 

Percent 

Protein MPR 

Percent 

Fat 

4.5 h into 

Stage 12 21.83 29.04 .75:1 29.74 

End of 

Stage 12 21.02 29.70 .71:1 30.13 

Conclusions 

After conducting six preliminary studies, appropriate processing parameters were 

developed that allowed for the production of a typical commercial chopped and formed 

all-beef jerky to an appropriate water activity level of < 0.70 and a MPR of 0.75:1. 

Inoculum methods were developed that allowed for a greater than 7.0 log CFU/g of E. 

coli O157:H7 or Salmonella spp. in raw chopped and formed jerky. Appropriate dilution 

levels were determined for appropriate enumeration and detection of both pathogens 

throughout the smokehouse schedule. The processing parameters and microbial methods 

developed from the preliminary studies will be used for a comprehensive validation 

study. 

30 
 

 

 

4. Roberts, M.N., Getty, K.J.K., and Boyle, E.A.E. 2006. Control of Escherichia coli 

O157:H7 and Salmonella spp. in chopped and formed beef jerky. Annual Meeting 

Proceedings, Food Safety Consortium, University of Arkansas, Oct. 1-3. CD format. 

CONTROL OF ESCHERICHIA COLI O157:H7 AND SALMONELLA SPP. 

IN CHOPPED AND FORMED BEEF JERKY 

M.N. Roberts, K.J.K. Getty and E.A.E. Boyle 

Department of Animal Sciences & Industry and Food Science Institute 

Kansas State University, Manhattan, KS 66506 

SUMMARY AND IMPLICATIONS 

USDA/FSIS issued “Compliance Guideline for Meat and Poultry Jerky Produced 

by Small and Very Small Plants,” that provides processing parameters for controlling pathogens 

such as Escherichia coli O157:H7 and Salmonella spp. The objective of this study was to 

determine the effects of typical thermal processing temperatures and times on reducing E. coli 

O157:H7 and Salmonella spp. in chopped and formed beef jerky. Initial raw batter E. coli 

O157:H7 and Salmonella spp. populations were approximately 7.3 log cfu/g. When the 

smokehouse dry bulb (D.B.) temperature was 55.6oC and relative humidity (R.H.) was 

approximately 10% for 44 min followed by 77.8oC D.B. and R.H. at approximately 10% for 46 

min, 5 log reductions were observed for both E. coli O157:H7 and Salmonella spp. 

populations. However, an additional heating/drying phase of 3 h with smokehouse D.B. at 77.8oC 

was required to achieve a moisture-to-protein ratio (MPR) of 0.77:1, which is slightly higher than 

the 0.75:1 MPR as required by USDA/FSIS for jerky products. Furthermore, additional heating 

of 3.5 h was needed to achieve Salmonella spp. log reductions of 6.5 as required by 

USDA/FSIS, which resulted also in MPR values of 0.45:1 and water activity levels of 0.59. 

INTRODUCTION 

In 2003, the New Mexico 

Department of Health linked an outbreak of 

Salmonellosis with consumption of beef 

jerky (Smelser, 2004). Due to the increasing 

commonality of foodborne illness associated 

with dried meats, in 2004, USDA/FSIS 

published the Compliance Guideline for 

Meat and Poultry Jerky Produced by Small 

and Very Small Plants, which addresses the 

issues of how to obtain proper lethality, and 

how to verify proper drying (USDA/FSIS 

2004 and Sindelar, 2005). Small meat 

processors that produce jerky products must 

validate that their processes achieve a 5-log 

reduction of E. coli O157:H7 and a >6.5-log 

reduction of Salmonella spp. (Sindelar, 

2005). Therefore, the objective of this study 

was to determine the effects of typical 

thermal processing temperatures and times 

on reducing E. coli O157:H7 and 

Salmonella spp. in chopped and formed beef 

jerky. 

MATERIALS AND METHODS 

Experimental Design: Two 

treatments, consisting of an E. coli O157:H7 

inoculated batch and a Salmonella spp. 

inoculated batch were studied. A control 

batch was also prepared. A replication 

consisted of both inoculated batches and a 

control batch placed in the smokehouse 

simultaneously. The study consisted of 

three replications. Due to potential crosscontamination from pathogens and potential 

smokehouse location variations of 

temperatures, the smokehouse cart was 

divided in thirds from side-to-side for the 

two treatments and control. Each batch was 

31 
 

 

then placed in a different location for each 

replication (Table 1). 

Confirmation of Cultures and 

Presumptive E. coli O157:H7 and 

Salmonella spp. Colonies: All E. coli 

O157:H7 cultures were originally obtained 

from the American Type Culture Collection 

(ATCC 43894, ATCC 43889, ATCC 43890 

ATCC 43895) (Rockville, MD) and the 

United States Department of 

Agriculture/Agricultural Research Service 

(USDA 380-94) (USDA/ARS, Athens, GA). 

All Salmonella spp. cultures were originally 

obtained from ATCC [ATCC 35640 

(Salmonella abaetetuba), ATCC 4931 

(Salmonella enteriditis), ATCC 13076 

(Salmonella enteriditis), ATCC 15060 

(Salmonella enteriditis), ATCC 13311 

(Salmonella typhimurium). Cultures arrived 

in commercial bead form and were kept in 

an -80oC freezer in the KSU Food Safety 

and Security Lab. 

Confirmation: All cultures and 

presumptive E. coli O157:H7 and 

Salmonella spp. colonies taken respectively 

from, phenol red sorbitol agar (PRSA) and 

xylose lysine desoxycholate agar (XLD; 

Difco) plates from raw and heat-treated 

samples were streaked, using a sterile loop 

(Fisher Scientific Inc, Pittsburgh, PA) onto 

tryptic soy agar (TSA; Difco) and incubated 

at 37oC for 24 h. Typical colonies were 

used to inoculate API 20E biochemical 

identification test strips (bioMerieux Vitek, 

Inc., Hazelwood, MO) and Enterotubes 

(Becton Dickinson, Franklin Lakes, NJ). 

Preparation of Bacterial Culture: 

A five-strain cocktail of E. coli O157:H7 as 

described above and a separate five-strain 

cocktail of Salmonella spp. as describe 

above were prepared. For inoculum 

preparation of each pathogen, one loopful of 

each culture was transferred into 9 mL of 

tryptic soy broth (TSB; Difco) and incubated 

at 35oC for 18-24 h. Six mL of each culture 

suspension was then transferred to a sterile 

bottle (Nalgene, Rochester, NY). Two 

separate bottles resulted with one containing 

30 mL of E. coli O157:H7 and one 

containing 30 mL of Salmonella spp. 

Meat Batter Preparation and 

Inoculation: Fresh chopped and formed allbeef jerky batter was obtained from a 

commercial processor, immediately frozen 

for 1 to 2 weeks and then tempered 

overnight at 4oC and used the following day. 

The product was separated into three 1.814 

kg (4 lb) batches. To the control batch, 29 

mL of sterile deionized water was mixed 

evenly into the meat batter and stored at 4oC 

until stuffing and enumeration. To a 

separate batch, 29 mL of the E. coli 

O157:H7 five-strain inoculum was 

intermittently pipetted drop-wise over the 

batter surface and massaged with gloved 

hands until thoroughly mixed into the jerky 

batter. The batter was stored at 4oC until 

stuffing and enumeration. This procedure 

was repeated with the last batch of batter, 

however, 29 mL of the Salmonella spp. fivestrain inoculum was added instead. 

Raw jerky batter (control followed 

by inoculated batches) was transferred to a 

manual jerky gun (Model Nbr. H6253, 

Grizzly Industrial, Inc.) with a 0.64 cm (1⁄4”) 

by 2.54 cm (1”) jerky nozzle (Model Nr. 

LEM468D, Allied Kenco, Houston, TX). 

Strips were placed on polyscreen sheets 

(Excalibur, Sacremento, CA) with eight 

strips per sheet. Each strip was 

approximately 13 cm (5”) long. Strip filled 

sheets were placed on smokehouse trays 

with order varying per replication (Table 1). 

Once loaded, the smokehouse cart was 

placed in a commercial smokehouse (Alkar 

Model 450-UA, Alkar, Lodi, WI) and 

thermally processed as discussed in Table 2. 

E. coli O157:H7 and Salmonella 

spp. Enumeration: One mL of the E. coli 

O157:H7 inoculum was enumerated using 

duplicate phenol red sorbitol agar (PRSA; 

Difco) plates. One mL of the Salmonella 

spp. inoculum was enumerated using 

duplicate xylose lysine desoxycholate agar 

(XLD; Difco) plates and XLD plates with a 

thin agar layer of trypic soy agar (TALXLD; Difco). Six 1:10 dilutions of each 

inoculum were made using 0.1% peptone 

water (PW; Difco) and then spread plated 

onto their corresponding media in duplicate. 

32 
 

 

 

 

 

 

Raw inoculated samples 

were taken from the inoculated jerky batter 

to determine the initial inoculum level of the 

product. Heat-treated samples were taken at 

six different times [end of Stages 6, 7, 8, 10, 

and 1.5 h into Stage 12, and at the End of 

the Stage 12] (Table 2). At each sampling 

time, four strips of each of the three batches 

were taken. Control samples were used for 

proximate analysis, pH, and water activity 

analysis. The inoculated samples were used 

for E. coli O157:H7 and Salmonella spp. 

enumeration. 

Raw and heat-treated 

samples were prepared by weighing 25 g in 

filtered stomacher bags to which 50 mL of 

PW diluent was added. The samples were 

pummeled in a stomacher (Stomacher Mix 1 

Lab Blender, Microbiology International, 

Frederick, MD) for 1 min and two serial 

1:10 dilutions were prepared using 9 mL 

0.1% peptone blanks. Dilutions were spread 

plated in duplicate onto PRSA for E. coli 

O157:H7 inoculated samples and XLD and 

XLD plates with a thin agar layer of trypic 

soy agar (TAL-XLD; Difco) for Salmonella 

spp. inoculated samples. The 1:10 dilution 

allowed for a 1.48 log cfu/g detection limit 

for samples taken at Stages 6, 7, 8, 10, and 

1.5 h into Stage 12. For samples taken at the 

end of the cycle, a 1:10 dilution was spreadplated (0.25) onto four plates in duplicate, 

allowing for a sample detection limit of 0.48 

log cfu/g. 

Enrichment: Heat-treated samples 

were enriched by adding 50 mL modified E. 

coli medium (mEC; Difco) to 25 g of E. coli 

O157:H7 inoculated samples and by adding 

50 mL of Preuss Broth (Preuss; Difco) to 25 

g of Salmonella spp. inoculated samples 

taken at the End of Stage 12. After 

incubation at 37oC for 24 h, the samples 

were streaked onto PRSA for E. coli 

O157:H7 inoculated samples and XLD and 

TAL-XLD for Salmonella spp. inoculated 

samples. Plates were incubated at 37oC for 

24 h and observed for typical colonies. 

pH Analysis: The pH was 

measured on control samples (2) by 

weighing 25 g of sample into a filtered 

stomacher bag and adding 50 mL PW and 

stomaching for 1 min. A pH meter (Corning 

Pinnacle 530 pH Meter, Corning, NY) was 

used to measure pH. The pH readings were 

recorded when the stabilized icon was 

displayed. 

Water Activity (aw): Water activity 

was measured on control samples. Two 

samples were taken per treatment. Each 

sample was from a different set of two 

combined strips. Duplicate readings were 

taken. A water activity meter (Model CX2, 

Aqualab, Pullman, WA) was used to 

measure water activity. Readings were 

recorded when the stabilized icon was 

displayed. 

Proximate Analysis: Samples for 

proximate analysis were taken from noninoculated raw control, 1.5 h into Stage 12, 

and End of Stage 12 (final) product samples. 

Fifty grams of raw sample, two jerky strips 

from 1.5 h into Stage 12, and two finished 

jerky strips were vacuum packaged, and 

placed in frozen storage (-80oC) prior to 

analysis. Samples were prepared by 

freezing in liquid nitrogen and pulverized in 

a Waring Blender. Moisture (AOAC 

985.14) and fat (AOAC 985.15) were 

determined by a rapid microwave solvent 

method (CEM, Matthews, NC, U.S.A.). 

Protein was determined by the LECO 

method (AOAC 990.03) and salt was 

analyzed by a volumetric method (AOAC 

935.47). 

RESULTS AND DISCUSSION 

For all E. coli O157:H7 

inoculated jerky strips, initial raw batter 

populations ranged from 7.3 to 7.4 log cfu/g 

on PRSA. For Salmonella spp. inoculated 

jerky strips, initial raw batter populations 

ranged from 7.1 to 7.5 log cfu/g on both 

XLD and TAL-XLD media (Table 3). For 

samples taken at the end of Stages 6, 7, 8, 

and 10, E. coli O157:H7 populations ranged 

from <1.48 (detection limit) to 2.68 log 

cfu/g on PRSA and Salmonella spp. 

populations ranged from <1.48 to 2.08 log 

cfu/g on both XLD and TAL-XLD. By 1.5 

h into Stage 12, populations for both 

pathogens were consistently <1.48 log cfu/g 

on all media. In addition, End of Stage 12 

33 
 

 

product populations were consistently <0.48 

log cfu/g on all media (Table 3). 

All sampling times indicate 

a > 5.0 log cfu/g reduction of E. coli 

O157:H7 as required by USDA/FSIS with 

the most consistent reductions occurring at 

the end of Stage 7 to the End of Stage 12 

(Figure 1). A > 6.5 log cfu/g reduction of 

Salmonella spp. as mandated by 

USDA/FSIS was observed 1.5 h into Stage 

12 and at the End of Stage 12. For End of 

Stage samples, log reductions for both E. 

coli O157:H7 and Salmonella spp. were well 

above those mandated by USDA/FSIS. 

Enrichment results for 

samples from 1.5 h into Stage 12 and End of 

Stage 12 samples showed negative 

confirmation for all samples tested, 

confirming the likelihood that pathogens are 

dead as opposed to heat-injured. Thus 

indicating 7.0 log cfu/g reductions of both 

pathogens. 

Moisture content for control 

raw product ranged from 52.4 to 56.0% and 

15.1 to 19.8% for final product. Protein 

content for control raw product ranged from 

16.0 to 17.0% for raw product and 34.19 to 

37.66% for final product (Table 4). Salt 

contents for control raw product ranged 

from 2.2 to 2.3% and from 4.2 to 5.2% for 

final product. The moisture-to-protein ratio 

ranged from 0.40 to 0.58 for final product. 

This ratio is in compliance with the 

guideline of an MPR <0.75:1 needed for 

product to be labeled as jerky (Compliance 

Guideline, 2004). 

Raw batter pH values 

ranged from 6.0 to 6.2. Final pH range for 

all products was 5.1 to 5.3 (Table 5). It 

should be noted that a lowered pH was not a 

determining factor for the reduction of E. 

coli O157:H7 or Salmonella spp. 

Final water activity range 

for all final product was 0.570 to 0.625 

(Table 5). Typical water activity for jerky 

products should be < 0.70 to ensure lack of 

microbial growth (FSIS, 2004). 

REFERENCES 

New Mexico Department of Health. 

2004. Outbreak of Salmonellosis Associated 

with Beef Jerky in New Mexico, 2004. New 

Mexico Epidemiology Report. Vol. 2004, 

Nbr. 3 

Food Safety And Inspection Service 

(FSIS). 2004. Compliance guideline for 

meat and poultry jerky produced by small 

and very small plants. 

http://www.fsi.usda.gov/PDF/Compliance_ 

Guideline_Jerky.pdf (accessed July 27, 

2006). 

Sindelar, Jeff. 2005. Understanding 

the New FSIS Guidelines Associated With 

the Manufacture of Jerky. Kansas Meat 

Processors Association 2005 Annual 

Convention. 

34 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 1. Order of placement in smokehouse for control (C), E. coli O157:H7 (E), and 

Salmonella spp. (S) jerky batches. 

Replication #1 Replication #2 Replication #3 

E S C C E S S C E 

E S C C E S S C E 

E S C C E S S C E 

E S C C E S S C E 

E S C C E S S C E 

E S C C E S S C E 

E S C C E S S C E 

Table 2. Thermal processing schedule and sampling times for chopped and formed beef 

jerky. 

Stage 

Dry Bulb (D.B.) 

(oC)a Time 

Blower 

Speed Exhaust Fan Sampling Time 

1 55.6 14 min Medium Yes 

2 55.6 16 min Medium Yes 

3 55.6 14 min Medium Yes 

4 77.8 16 min Medium Yes 

5 77.8 14 min Medium Yes 

6 77.8 16 min Medium Yes End of stage 

7 77.8 14 min Fast Yes End of stage 

8 77.8 16 min Fast Yes End of stage 

9 77.8 14 min Fast Yes 

10 77.8 16 min Fast Yes End of stage 

11 77.8 14 min Fast Yes 

12 77.8 5 h Fast Yes 1.5 h into stage 

End End of stage 12 a

The smokehouse has an automated damper system and the ability to inject steam 

humidity as needed to control humidity. Percent relative humidity remained at <10 throughout the 

entire smokehouse cycle. 

Table 3. E. coli O157:H7 populations (log CFU/g) recovered on PRSA and Salmonella 

spp. populations recovered on XLD and TAL-XLD at seven sampling times during 

production of chopped and formed beef jerky. 

Media 

Stage/Sampling 

time 

PRSA XLD TAL-XLD 

Raw 7.3±0.1a 7.2±0.1ax 7.3±0.1ax 

Stage 6 2.3±0.4b 1.7±0.1bx 1.9±0.2bx 

Stage 7 2.0±0.3c 1.7±0.3bx 1.9±0.1bx 

Stage 8 1.8±0.2d 1.7±0.1bx 1.8±0.1bx 

Stage 10 1.6±0.0e 1.6±0.0cx 1.7±0.0bx 

Stage 12 (1.5 h into 

stage) 

<1.48f <1.48dx <1.48cx 

End of stage 12 <0.48g <0.48ex <0.48dx 

a-fIndicates significant differences in a column within the heating process. x

 Indicate significant differences between XLD and TAL-XLD counts for that sampling 

period. 

35 
 

 

 

 

- - - ~ 

- _ ,... -- -- -- ~- - ,- - ~ - ,-

- - ,_ - ~ - ,_ 

- - ~ - ~ -

,,,,,,, ,,,,,,,, 

-C ~ - ~ - ~ - ~ 

=L - - 111111 ,-

I -

• ~ 111111 - I ,-

-

8 

7 

6 

5

Log cfu/g Reductions 4 

3 

PRSA 

XLD 

TAL-XLD 

2 

1 

0 

Stage 6 Stage 7 Stage 8 Stage 10 Stage 12 

Thermal Stages 

End 

Figure 1. E. coli O157:H7 log CFU/g reductions on PRSA and Salmonella spp. 

reductions on XLD and TAL-XLD media at seven sampling times during production of 

chopped and formed beef jerky. 

Table 4. Proximate analysis means and standard deviations of control chopped and 

formed beef jerky samples. 

Sampling time Percent Moisture Percent Protein MPR Percent Fat Percent Salt 

Raw 53.7±1.4 16.5±0.4 3.25:1 17.4±1.8 2.2±0.0 

Stage 12 (1.5 h) 24.8±1.5 32.0±0.9 0.77:1 24.5±1.4 4.3±0.3 

End of Stage 12 16.8±2.2 36.2±1.4 0.46:1 25.6±1.4 4.5±0.5 

1

Moisture-to-protein ratios. 

Table 5. pH and water activity means and standard deviations of control chopped and 

formed beef jerky samples. 

pH Value Water Activity 

Raw 6.1±0.1 0.936±0.02 

Stage 6 6.0±0.0 0.846±0.01 

Stage 7 6.0±0.1 0.829±0.02 

Stage 8 6.0±0.0 0.843±0.02 

Stage 10 6.0±0.1 0.819±0.02 

Stage 12 (1.5 h) 5.7±0.1 0.670±0.02 

End of Stage 12 5.2±0.1 0.594±0.02 

36 
-

6. Roberts, Michelle N. 2006. Evaluation of thermal processing parameters in production 

of chopped and formed beef jerky for controlling Escherichia coli O157:H7 and 

Salmonella species. Abstract and Chapter on Validation Study. M.S report, Kansas State 

Univ., Manhattan, KS. Co-advisors: Getty, K.J.K. and Fung, D.Y.C. and Committee 

member: Boyle, E.A.E. 

ABSTRACT 

Due to a 2003 salmonellosis outbreak being linked to consumption of beef jerky 

produced by a New Mexico Firm, United States Department of Agriculture/Food Safety 

and Inspection Service (USDA/FSIS) issued, “Compliance Guideline for Meat and 

Poultry Jerky Produced by Small and Very Small Plants.” The objectives of this study 

were: 1) to conduct preliminary studies to determine proper processing parameters for 

producing typical commercial jerky, 2) to determine the effects of typical thermal 

processing temperature/time combinations on reducing E. coli O157:H7 and Salmonella 

spp. in chopped and formed jerky, and 3) to determine whether xylose lysine 

desoxycholate (XLD) alone, or thin agar layer (TAL-XLD) method incorporating 

selective media (XLD) and nonselective media (TSA) would provide a better detection of 

injured cells. Both E. coli O157:H7 inoculated and Salmonella spp. inoculated raw jerky 

batter (ca. 7.0 log10 CFU/g) was dispensed into 2.54 cm by 0.64 cm by 15.24 cm strips. 

Strips were processed for 6.75 h and heat treated samples were collected at six different 

sampling times. Greater than or equal to 5.0 log10 CFU/g reductions were seen for both 

pathogenic populations after 45 min of processing at dry bulb temperatures of 55.6°C and 

relative humidity (R.H.) at <10%, followed by 45 min with dry bulb temperatures at 

77.8°C and R.H. at <10%. However, product was dried further at 77.8°C for an additional 

3.25 h to achieve moisture-to-protein ratios of approximately 0.75:1 and water activity 

levels of < 0.70 characteristic of shelf stable jerky. Salmonella spp. counts on XLD and 

TAL-XLD were similar (p > 0.05) throughout the whole process. At the end of the 

thermal process, approximately 7.2 log10 CFU/g reductions of both E. coli O157:H7 and 

Salmonella spp. were observed, thus meeting USDA/FSIS validation guidelines for being 

deemed safe and shelf stable. 

37 
CHAPTER IV 

EVALUATION OF THERMAL PROCESSING PARAMETERS IN 

PRODUCTION OF CHOPPED AND FORMED BEEF JERKY FOR 

CONTROLLING ESCHERICHIA COLI O157:H7 AND SALMONELLA SPP. 

Introduction and Objectives 

In 2003, the New Mexico Department of Health (NMDOH) linked an outbreak of 

Salmonellosis, which impacted 26 individuals, with consumption of beef jerky. This 

outbreak, caused by a rare strain, Salmonella Kiambu, resulted in the recall of 22,000 lbs. 

of beef jerky (FSIS, 2003). Due to the increasing commonality of foodborne illness 

associated with dried meats, in 2004, the United States Department of Agriculture/Food 

Safety and Inspection Service, published “Compliance Guideline for Meat and Poultry 

Jerky Produced by Small and Very Small Plants,” which addresses the issues of how to 

obtain proper lethality, and how to verify proper drying (Sindelar, 2005; FSIS, 2004). 

According to this publication, jerky processors must meet the performance 

lethality for Salmonella, a reduction of > 6.5 log10 CFU/g. However, more recent 

literature acknowledged by the USDA/FSIS demonstrates that a 5.0 log10 CFU/g 

reduction of both Salmonella spp. and E. coli O157:H7 will now be accepted as 

indication of a “safe” product (FSIS, 2001; Uhler, 2005; Ingram, 2006). The Compliance 

Guideline outlines specific thermal processing parameters, such as humidity and wet bulb 

settings for jerky processors to utilize in order to achieve proper reductions. 

Validation and challenge studies have recently become very important as a means 

to determine whether or not individual thermal processes are capable of producing a safe 

product. Researchers at many universities have conducted studies on both restructured 

and whole-muscle jerky processed in both home-style dehydrators, as well as commercial 

smokehouses (Harrison and Harrison, 1996; Harrison, et al., 1996; Faith, et al., 1998; 

Buege, et al., 2006). 

Prior to conducting a validation study, six preliminary studies were conducted to 

determine proper processing parameters in order to obtain typical commercially prepared 

chopped and formed beef jerky. The objectives of the validation study were to determine 

the effects of typical thermal processing temperatures and times on reducing E. coli 

O157:H7 and Salmonella spp. in chopped and formed beef jerky and to determine 

whether xylose lysine desoxycholate (XLD) alone, or thin agar layer (TAL) method 

utilizing XLD with a thin top layer of Tryptic Soy Agar (TSA) would provide a better 

detection of injured cells. 

Materials and Methods 

Experimental Design: 

Two treatments, consisted of an E. coli O157:H7 inoculated batch and a 

Salmonella spp. inoculated batch, as well as control batches of jerky were prepared. A 

replication consisted of both inoculated batches and a control batch placed in the 

smokehouse simultaneously. This study consisted of three replications. 

38 
 

Confirmation of Cultures and Presumptive E. coli O157:H7 and Salmonella spp. 

Colonies: 

E. coli O157:H7 cultures used in this study were originally obtained from the 

American Type Culture Collection (ATCC 43890, ATCC 43894 and 43895; Rockville, 

MD), and Centers for Disease Control and Prevention (KSU-01 and KSU-02; CDC, 

Atlanta, GA). Salmonella spp. cultures were originally obtained from the ATCC (ATCC 

4931, ATCC 35640, ATCC 13076, and ATCC 13311), and United States Department of 

Agriculture/Agricultural Research Service (USDA 15060; USDA/ARS, Athens GA). 

Salmonella spp. cultures included, three strains of Salmonella enterica subsp. enterica 

serovar Enteriditis, one strain of Salmonella enterica subsp. enterica serovar Abaetetuba, 

and one strain of Salmonella enterica subsp. enterica serovar Typhimurium. E. coli 

O157:H7 isolate ATCC 43894 was obtained from a human who experienced hemorrhagic 

colitis. ATCC 43895 was isolated from raw ground beef implicated in a case of 

hemorrhagic colitis. Isolates ATCC 43890, KSU-01 and KSU-02 were obtained from 

humans with E. coli O157:H7 infections. S. Enteriditis isolates ATCC 4931, ATCC 

13076, and USDA 15060 and S. Typhimurium isolate ATCC 13311 were obtained from 

humans experiencing salmonellosis, while S. Abaetetuba isolate ATCC 35640 was 

obtained from creek water in Zaiman, Argentina. 

For confirmation, all cultures and presumptive E. coli O157:H7 and Salmonella 

spp. colonies taken respectively from, phenol red sorbitol agar (PRSA; Difco, Detroit, 

MI) with 1% sorbitol (Fisher Scientific, Pittsburgh, PA) and xylose lysine desoxycholate 

agar (XLD; Remel, Lenexa, KS) plates from raw and heat-treated samples were streaked, 

using a sterile loop (Fisher Scientific Inc, Pittsburgh, PA) onto tryptic soy agar (TSA; 

Remel) and incubated at 37oC for 24 h. Typical colonies were used to inoculate API 20E 

biochemical identification test strips (bioMerieux Vitek, Inc., Hazelwood, MO) and 

Enterotubes (Becton Dickinson, Franklin Lakes, NJ). 

Preparation of Bacterial Culture: 

A five-strain cocktail of E. coli O157:H7 (ATCC 43890, ATCC 43894, ATCC 

43895, KSU-01 and KSU-02) and a separate five-strain cocktail of Salmonella spp. 

(ATCC 4931, ATCC 35640, ATCC 13076, ATCC 13311, and USDA 15060) were 

prepared. For inoculum preparation, one loopful of each culture was transferred into 9 

mL of tryptic soy broth (TSB; Difco) and incubated at 35°C for 18-24 h. Six mL of each 

culture suspension was then transferred to a sterile bottle (Nalgene, Rochester, NY). Two 

separate bottles resulted with one containing 30 mL of E. coli O157:H7 and one 

containing 30 mL of Salmonella spp. One mL of each separate inoculum was saved for 

inoculum enumeration. 

Meat Batter Preparation and Inoculation: 

Fresh chopped and formed all-beef jerky batter containing: 83% lean beef, 

dextrose, flavorings, beef stock, salt, soy, corn protein, smoke flavoring, and curing 

agents was obtained from a commercial processor, immediately frozen for 1 to 2 weeks 

and then tempered overnight at 4oC and used the following day. The product was 

separated into three 1.814 kg (4 lb) batches. 

To the control batch, 29 mL of sterile deionized water was mixed evenly into the 

meat batter and stored at 4oC until stuffing and enumeration. To a separate batch, 29 mL 

39 
of the E. coli O157:H7 five-strain inoculum was intermittently pipetted drop-wise over 

the batter surface and massaged with gloved hands until thoroughly mixed into the jerky 

batter. The batter was stored at 4oC until stuffing and enumeration. This procedure was 

repeated with the last batch of batter; however, 29 mL of the Salmonella spp. five-strain 

inoculum was added instead. 

Raw jerky batter (control followed by inoculated batches) was transferred to a 

manual jerky strip dispenser (Model Nbr. H6253, Grizzly Industrial, Inc.) with a 0.64 cm 

(1⁄4”) by 2.54 cm (1”) jerky nozzle (Model Nr. LEM468D, Allied Kenco, Houston, TX). 

Strips were placed on polyscreen sheets (Excalibur, Sacremento, CA) with eight strips 

per sheet. Each strip was approximately 2.54 cm (1”) by 0.64 cm (1/4”) by 15.24 cm 

(6”). Strip filled sheets were placed on smokehouse trays with order varying per 

replication (Table 10). Once loaded, the smokehouse cart was placed in a commercial 

smokehouse (Alkar Model 450-UA, Alkar, Lodi, WI) and processed, using a typical 

commercial thermal processing procedure as discussed in Table 11. 

Table 10. Order of placement in smokehouse (three replications) for control (C), E. coli 

O157:H7 (E), and Salmonella spp. (S) jerky batches. 

Replication 1 Replication 2 Replication 3 

E S C C E S S C E 

E S C C E S S C E 

E S C C E S S C E 

E S C C E S S C E 

E S C C E S S C E 

E S C C E S S C E 

E S C C E S S C E 

40 
 

 

 

 

 

Table 11. Thermal processing schedule1 and sampling times for chopped and formed beef 

jerky. 

Stage 

Dry Bulb 

(D.B.) 

(oC) Time 

Blower 

Speed Sampling Time 

1 55.6 14 minMedium 

2 55.6 16 minMedium 

3 55.6 14 minMedium 

4 77.8 16 minMedium 

5 77.8 14 minMedium 

6 77.8 16 minMedium End of stage 

7 77.8 14 minFast End of stage 

8 77.8 16 minFast End of stage 

9 77.8 14 minFast 

10 77.8 16 minFast End of stage 

11 77.8 14 minFast 

12 77.8 5 h Fast 1.5 h into stage 

End End of stage 12

1

The smokehouse has an automated damper system and the ability to inject steam 

humidity as needed to control humidity. Percent relative humidity remained at <10% 

throughout the entire smokehouse cycle. The exhaust fan was activated during the entire 

cycle. 

E. coli O157:H7 and Salmonella spp. Enumeration: 

Phenol red sorbitol agar (PRSA) plates were used for enumeration of E. coli 

O17:H7 inoculated samples, while typically prepared XLD plates and plates containing 

25 mL XLD with a 14 mL top layer of TSA (TAL-XLD) were used for the enumeration 

of Salmonella spp. inoculated samples (Wu and Fung, 2003). One mL of the E. coli 

O157:H7 inoculum was enumerated using duplicate PRSA plates. One mL of 

Salmonella spp. inoculum was enumerated using duplicate XLD and duplicate TAL-XLD 

plates. Six serial 1:10 dilutions of each inoculum were made using 0.1% peptone water 

(PW; Difco). Dilutions were then spread plated onto their corresponding media in 

duplicate. 

Raw inoculated samples were taken from the inoculated jerky batter to determine 

the initial inoculum level of the product. Heat-treated samples were taken at six different 

times [after Stages 6, 7, 8, 10, 1.5 h into Stage 12, and at the end of the cycle]. At each 

sampling time, two samples (comprised of two strips) were taken from each of the three 

batches. Control samples were used for proximate analysis, pH, and water activity. The 

inoculated samples were used for E. coli O157:H7 and Salmonella spp. enumeration. 

Two strips from each raw and heat-treated sample were cut into small pieces and 

combined together. Twenty-five gram samples were deposited into filtered stomacher 

bags to which 50 mL of PW diluent was added. The samples were pummeled in a 

stomacher (Stomacher Mix 1 Lab Blender, Microbiology International, Frederick, MD) 

for one min and two serial 1:10 dilutions were prepared using 9 mL 0.1% PW blanks. 

Dilutions were spread plated in duplicate onto PRSA for E. coli O157:H7 inoculated 

samples and XLD and TAL-XLD for Salmonella spp. inoculated samples. 

41 
A 1:3 dilution allowed for a 1.5 log10 CFU/g detection limit for samples pulled at 

the end of Stages 6, 7, 8, 10, and 1.5 h into Stage 12. For samples taken at the end of the 

cycle, a 1:3 dilution was spread-plated (0.25) onto four plates in duplicate, allowing for a 

sample detection limit of 0.5 log10 CFU/g. All media was incubated at 37°C for 24 h. 

E. coli O157:H7 and Salmonella spp. Enrichment: 

Heat-treated samples were enriched by adding 225 mL of modified E. coli 

medium (mEC; Difco) containing sodium novobiocin (Sigma Chemical Co.; St. Louis, 

MO) to 25 g of E. coli O157:H7 inoculated samples and by adding 225 mL of Preuss 

broth (Preuss; Difco) to 25 g of Salmonella spp. inoculated samples taken 1.5 h into 

Stage 12, and at the end of the cycle. All samples were stomached for 1 min. After 

incubation at 37°C for 24 h, the enriched samples were streaked onto PRSA for E. coli 

O157:H7 inoculated samples and XLD and TAL-XLD for Salmonella spp. inoculated 

samples. Plates were incubated at 37°C for 24 h and observed for typical colonies 

(PRSA-colorless colonies; XLD/TAL-XLD-black colonies). Presumptive colonies were 

then confirmed using API 20E test kits and Enterotubes. 

pH and Water Activity (aw): 

The pH level was measured on raw and heat-treated control samples (2) by 

weighing 25 g of sample into a filtered stomacher bag and adding 50 mL PW and 

stomaching for 1 min. A pH meter (Corning Pinnacle 530 pH Meter, Corning, NY) was 

used to measure pH. Readings were recorded when the stabilized icon was displayed. 

Water activity was measured on raw and heat-treated control samples. Two 

samples were taken per treatment. Each sample was from a different set of combined 

strips. Duplicate readings were taken. A water activity meter (Model CX2, Aqualab, 

Pullman, WA) was used to measure water activity. Readings were recorded when the 

stabilized icon was displayed. 

Proximate Analysis: 

Samples for proximate analysis were taken from non-inoculated raw control, 1.5 h 

into Stage 12, and End of Stage 12 (Final) product samples. Fifty grams of raw sample, 

two jerky strips from 1.5 h into Stage 12, and two finished jerky strips were vacuum 

packaged and placed in frozen storage (-80°C) prior to analysis. Samples were prepared 

by freezing in liquid nitrogen and pulverized in a Waring Blender. Moisture (AOAC 

985.14) and fat (AOAC 985.15) were determined by a rapid microwave solvent method 

(CEM, Matthews, NC, U.S.A.). Protein was determined by the LECO method (AOAC 

990.03) and salt was analyzed by a volumetric method (AOAC 935.47). 

Statistical Analysis: 

The experimental design was a strip-split plot and data were analyzed using 

PROC MIXED in SAS Version 9.0 (SAS Institute, 2002). The fixed effects were media 

types, sampling time, and bacteria types along with all combinations of these effects. 

The random effects were replication, replication by sampling time by bacteria type, 

replication by sampling time, and replication by bacteria type. Significant interactions (p 

< 0.05) were sampling time by bacteria type and media type. LS Means were used to 

compare sampling time by bacteria type and media type. Least significant differences 

42 
 

 

 

(LSD) were used to compare LS Means of sampling times, bacteria types, and media. 

Proximate analysis, pH, and water activity mean values and standard deviations were 

calculated by Microsoft Excel. 

To determine statistical differences between pathogen counts at different 

sampling times, duplicate plate counts were averaged. For product pulled at the end of 

Stages 6, 7, 8, 10, and 1.5 h into Stage 12, when duplicate plate counts had no colonies, 

they were assigned a log10 CFU/g value of 0.8. This assumed that the actual value was 

between zero and the detection limit, 1.5 log10 CFU/g. Similarly, for samples pulled at 

the end of the smokehouse cycle, when duplicate plate counts had no colonies, they were 

assigned a log10 CFU/g value of 0.3, which assumed that the actual value was between 

zero and the detection limit, 0.5 log10 CFU/g. However, for determining log reductions 

only the detection limit will be used as a value. 

Results and Discussion 

E. coli O157:H7 and Salmonella spp. Enumeration and Enrichment: 

Initial levels of the five-strain inoculum of E. coli O157:H7 and Salmonella spp. 

averaged on PRSA, XLD and TAL-XLD respectively, over three populations, were, 9.3, 

9.0 and 9.2 log10 CFU/g. There were no statistical differences (p > 0.05) between the two 

media types used to enumerate inoculum level of Salmonella spp. Initial level of 

bacterial populations in raw inoculated meat was similar (p > 0.05) for both pathogens 

with raw batter counts ranging from 7.2 to 7.4 log10 CFU/g on PRSA and 7.1 to 7.4 log10 

CFU/g on XLD and TAL-XLD (Table 12). When product reached Stages 6, 7, 8, and 10, 

counts ranged from <1.5 (detection limit) to 2.7 log10 CFU/g on PRSA. During these 

stages, populations recovered for E. coli O157:H7 were consistently decreasing (p < 

0.05). For XLD and TAL-XLD, Stages 6, 7, 8, and 10 achieved similar (p > 0.05) 

recoveries with counts ranging from 1.4 to 2.1 log10 CFU/g. 

When processed at dry bulb temperatures as high as 55.6°C (132°F) for 45 min 

followed by dry bulb temperatures of 77.8°C (172°F), and with relative humidity levels at 

< 10%, > 5.0 log10 CFU/g reductions (Figure 1) of both pathogen populations were seen 

in as little time as 1.5 h (Stage 6) into the 6 h and 45 min cycle, meeting guidelines 

suggested by USDA/FSIS. At all sampling times, internal product temperatures leveled 

out at 78.9°C (174°F), meeting the USDA/FSIS recommendation of heating jerky product 

to an internal temperature of 71.1°C (160°F), also noted as a temperature that eliminates 

bacterial growth (FSIS, 2000). Although the appropriate log reductions were achieved by 

the end of Stage 6, product was dried further in order to meet Compliance Guideline 

recommendations suggesting that a water of activity of < 0.70 be met in order for jerky to 

be considered shelf stable, as well as the USDA/FSIS requirement of a moisture-toprotein ratio (MPR) of < 0.75:1. 

43 
 

 

,... _ 

-- - - --

I I I I I 

Table 12. Mean E. coli O157:H7 populations (log10 CFU/g) recovered on PRSA and 

mean Salmonella spp. populations recovered on XLD and TAL-XLD at seven sampling 

times during production of chopped and formed beef jerky. 

Stage/Sampling time 

Media 

PRSA XLD TAL-XLD 

Raw 7.3±0.1a 7.2±0.1ax 7.3±0.1ax 

Stage 6 2.3±0.4b 1.7±0.1bx 1.9±0.2bx 

Stage 7 2.0±0.3c 1.7±0.3bx 1.9±0.1bx 

Stage 8 1.8±0.2d 1.7±0.1bx 1.8±0.1bx 

Stage 10 1.6±0.0e 1.6±0.0bx 1.7±0.0bx 

Stage 12 (1.5 h into 

stage) 

<1.48f <1.48cx <1.48cx 

End of stage 12 <0.48g <0.48dx <0.48dx 

a-f Indicates significant differences in a column within the heating process. 

xy Indicates significant differences between XLD and TAL-XLD counts for that sampling 

period. 

8 

7 

ions

6 

CFU/g Reduct 5 

4 

3 

PRSA 

XLD 

TAL-XLD 

Log10 

2 

1 

0 

Stage 6 Stage 7 Stage 8 Stage 

10 

Thermal Stages 

Stage 

12 

End 

Figure 1. Average log reductions (log10 CFU/g) for chopped and formed beef jerky 

inoculated with either E. coli O157:H7 or Salmonella spp. 

By 1.5 h into Stage 12, there were no populations recovered for any of the 

pathogens, with counts reported as < 1.5 log10 CFU/g (detection limit). At the end of the 

44 
cycle, finished product counts were consistently <0.5 log10 CFU/g on all media types 

(Table 12) averaging final reductions of > 6.5 log10 CFU/g for both E. coli O157:H7 and 

Salmonella spp. (Figure 1), meeting Appendix A lethality performance standards for 

Salmonella spp. (FSIS, 1999) and guidance specified by USDA/FSIS stating that > 5.0 

log10 CFU/g reductions of both E. coli O157:H7 and Salmonella spp. are indicative of 

safe jerky processes (FSIS, 2001; Uhler, 2005). 

Enrichment results for samples from 1.5 h into Stage 12 and end product samples 

showed negative confirmation for all 24 samples tested, confirming the likelihood that 

pathogens were dead as opposed to being heat-injured. Thus, indicating an even greater 

reduction of approximately 7.2 log10 CFU/g for both pathogens. 

Results indicate that high humidity, such as the > 90% relative humidity stated in 

the Compliance Guideline, is not necessarily needed to achieve appropriate log10 

reductions. This is important as resentment towards the Compliance Guideline is due to 

the fact that many small and very small processors argue that their equipment is not 

capable of achieving the specified high humidity levels (AAMP, 2004). 

Other research in which similar results as ours were obtained include a study 

conducted by Faith, et al. (1998), in which home dehydrators were used to process E. coli 

Ol57:H7 inoculated, restructured jerky. Batches of inoculated strips were dried at several 

different temperature/time combinations, with no added humidity. Results indicated 5 

log10 CFU/g reductions for jerky processed at lower dry bulb temperatures, such as 52°C 

(125°F) when processed for longer periods of time, i.e., 8-10 h, and when processed at 

higher dry bulb temperatures, such as 68°C (155°F) for shorter periods of time, i.e., 4-6 h. 

In addition to this, a study by Buege et al. (2006), in which a commercial 

smokehouse was used to process whole-muscle beef jerky inoculated with Salmonella 

serovars and E. coli O157:H7 showed that while processing parameters with wet bulb 

spikes, resulting in increased humidity, produced > 5.0 log10 CFU/g reductions of both 

pathogens, a four-hour drying cycle processing at 48.9oC (120F) for 60 min, 54.4oC 

(130oF) for 60 min, 60oC (140oF) for 60 min, and 76.7oC (170oF) for 60 min, without 

added humidity, was also capable of achieving sufficient reductions. 

Although TAL-XLD was generally able to recover > 0.1 log10 CFU/g more than 

XLD, results were not significantly different (p > 0.05) for samples collected at all 

sampling times. Although these results do not necessarily support the supposition that 

the thin agar layer (TAL) method recovers a greater portion of heat-injured cells than 

selective media alone, other research has provided evidence to support this theory. 

In a 2001 study by Wu and Fung, the thin agar layer (TAL) method was used to 

enumerate four heat-injured foodborne pathogens including, E. coli O157:H7, Listeria 

monocytogenes, Salmonella typhimurium, and Yersinia enterocolitica. One mL of 

pathogen cocktail was added to peptone water (PW) that had been preheated to 55°C. 

The suspension was then heated for ten minutes in a shaking water bath at 55°C. After 

heating, the suspension was immediately cooled to room temperature (25°C) and 

enumerated on both TAL agar plates and pathogen-selective agar plates. Results showed 

TAL to have significantly greater (p ≤0.05) recovery of all five pathogens than pathogenselective media alone. 

45 
 

 

pH and Water Activity (aw): 

Raw batter pH values ranged from 6.0 to 6.2. Final pH range for all products was 

5.1 to 5.3 (Table 13). This falls below the typical pH range of 5.3-6.6 for jerky products 

(Lonnecker, 2005; Buege, 2005). This range is of particular concern as it easily supports 

the growth of gram-negative bacteria. For example, E. coli O157:H7 can grow at pH 

levels < 4.4, while some Salmonella spp. can grow at pH levels as low as 3.8 (AAMP, 

2004). 

Although > 5 log10 CFU/g reductions were achieved at the end of Stage 6, water 

activity levels ranged from 0.833 to 0.859. These values did not consistently fall under 

the level of < 0.85, which excludes most pathogenic growth. Product was dried further in 

order to achieve a water activity of < 0.70 which excludes mold growth, deeming the 

product shelf stable. Water activity 1.5 h into Stage 12 ranged from 0.619 to 0.692, 

while water activity range for all final products was 0.570 to 0.625 (Table 13). These 

values fall within the level of < 0.70 suggested by FSIS to ensure lack of microbial 

growth (FSIS, 2004). 

Proximate Analysis: 

The FSIS’s standard of identity for jerky is a moisture-to-protein ratio (MPR) of < 

0.75:1 (FSIS, 2004). For all final products, MPR was approximately 0.46:1. This ratio is 

in compliance with the FSIS standard. At 1.5 h into Stage 12, the MPR was 

approximately 0.77:1. Although product pulled at this time cannot be considered jerky, 

it does fall within the range of < 2.03:1 and > 0.76:1 typical of a kippered beef product 

(AAMP, 2004). With >5 log10 CFU/g reductions were clearly met at this point, 

processors producing kippered beef could use this thermal process as well to produce safe 

product. 

Moisture content ranged from 52.3 to 56.0% for raw product and ranged from 

14.6 to 19.0% for final product. Final product moisture levels fall below the typical 

range of percent moisture levels for jerky, which is 28-30% (Ricke and Keeton, 1997). 

Protein content for control raw product ranged from 16.1 to 16.9% and ranged from 34.8 

to 37.6% for final product. Salt contents for raw treatments were approximately 2.2% 

and from 4.0 to 5.0% for final product (Table 13). These levels fall within the typical salt 

range for jerky which is 3.7 -11.4% (Lonnecker et al. 2005). 

Although product pulled at the end of the cycle clearly met the requirements 

typical of shelf-stable jerky, product pulled at this point may lack pleasing palatability 

characteristics, as moisture and protein levels were below those typical of jerky. In order 

to achieve a more pleasing product, end product should be pulled between 1.5 h into 

Stage 12 and at the end of Stage 12. By keeping the MPR closer to 0.75:1 and the water 

activity as close to 0.70, a processor will also have decreased product costs, as water is an 

inexpensive ingredient. Jerky produced with these parameters will also be safe from a 

microbial standpoint. 

46 
Table 13 . pH and water activity means and standard deviations of control chopped and formed beef jerky 

times. Stage/Sampling Time 

pH Value Water Activity 

Percent Moisture 

Percent Protein MPR 

Percent Fat 

Percent Salt 

Raw 6.1±0.1 0.936±0.016 53.7±1.4 16.5±0.4 3.25:1 17.4±1.8 2.2±0.0 

Stage 6 6.0±0.0 0.846±0.013 Stage 7 6.0±0.1 0.829±0.024 Stage 8 6.0±0.0 0.843±0.021 Stage 10 6.0±0.1 0.819±0.017 

Stage 12 (1.5 h) 5.7±0.1 0.670±0.032 24.8±1.5 32.0±0.9 0.77:1 24.5±1.4 4.3±0.3 

End of Stage 12 5.2±0.1 0.594±0.020 16.8±2.2 36.2±1.4 0.46:1 25.6±1.4 4.5±0.5 

47 
Conclusions 

The thermal process used in the production of chopped and formed beef jerky resulted in 

approximately 7.2 log10 CFU/g reductions for both E. coli O157:H7 and Salmonella spp for 

product collected at the end of the process. No statistical differences were observed for 

Salmonella spp. counts on XLD and TAL-XLD. Reductions of > 5.0 log10 CFU/g were achieved 

for both pathogenic populations after 45 min of processing at dry bulb temperatures of 55.6°C 

and relative humidity (R.H.) at < 10%, followed by 45 min with dry bulb temperatures at 77.8°C 

and R.H. of < 10%. However, product was dried further at 77.8°C in order to achieve moistureto-protein ratios of < 0.75:1 and water activity levels of < 0.70 characteristic of a 

microbiologically safe, shelf stable jerky. With achievement of > 5.0 log10 CFU/g reductions for 

both pathogenic populations, according to USDA/FSIS guideline, this process produced product 

considered safe and shelf-stable. 

48 
 

 

7. Roberts, Michelle N. Evaluation of thermal processing parameters in production of chopped 

and formed beef jerky for controlling Escherichia coli O157:H7 and Salmonella species. 

References Chapter. M.S report, Kansas State Univ., Manhattan (anticipated December 

2006) Co-advisors: Getty, K.J.K. and Fung, D.Y.C. and Committee member: Boyle, E.A.E. 

REFERENCES 

Aberle, E.D., Forrest, J.C., Gerrard, D.E., and Mills, E.W. 2001. Principles of Meat Science, 4th 

ed. Kendall/Hunt Publishing Co. Dubuque, IA. pp. 191-193. 

Ahmed, N.M. and Conner, D.E. 1994. Evaluation of various media for recovery of thermallyinjured Escherichia coli O157:H7. J. Food Prot. 58:357-360. 

Ahmed, N.M., Conner, D.E., and Huffman, D.L. 1995. Heat-resistance of Escherichia coli 

O157:H7 in meat and poultry as affected by product composition. J. Food Science. 60(3): 

606-610. 

Alkar. 2006. Online Alkar Manual. http://www.alkar.com/service manual.htm. [accessed 

October 2005]. 

American Association of Meat Processors (AAMP). 2004. The Jerky Journal. American 

Association of Meat Processors. Elizabethtown, PA. pp. 1-225. 

Arthritis Society. 2006. Reiter’s Syndrome. 

http://www.arthritis.ca/types%20of%20arthritis/reiters%20syndrome/default.asp?s=1. pp. 1-

9. [accessed November 2006]. 

Bagi, L.K. and Buchanan, R.L. 1993. Preservation of Listeria monocytogenes and other 

pathogenic foodborne bacteria on silica gel. Lett. Appl. Microbiol. 17:37-39. 

Buchanan, R.L. and Doyle, M.P. 1997. Foodborne disease significance of Escherichia coli 

O157:H7 and other enterohemorrhagic E. coli. Food Technol. 51(10):69-76. 

Buege, D. 2005. Personal communication regarding ongoing research. University of Wisconsin. 

Buege, D.R., Searls, G., and Ingham, S.C. 2006. Lethality of commercial whole-muscle beef 

jerky manufacturing processes against Salmonella serovars and Escherichia coli O157:H7. J. 

Food Prot. 69(9): 2091-2099. 

Buzby, J.C., Roberts, T., Jordan Lin, C.T., and MacDonald, J.M. 1996. Bacterial Foodborne 

Disease: Medical Costs and Productivity Losses. Food and Consumer Economics Division. 

Agricultural Economic Report No. 741. Economic Research Service, USDA. pp. 14-21. 

Washington DC. 

49 
Calcioglu M., Sofos, J.N., Samelis, J., Kendall, P.A., and Smith, G.C. 2002. Inactivation of acidadapted and nonadapted Escherichia coli O157:H7 during drying and storage of beef jerky 

treated with different marinades. J. Food Prot. 65:1394-1405. 

Centers for Disease Control and Prevention (CDC). 1995a. Outbreak of Salmonellosis associated 

with beef jerky-New Mexico. MMWR 44(42):785-787. 

Centers for Disease Control and Prevention (CDC). 1995b. Escherichia coli O157:H7 outbreak 

linked to commercially distributed dry-cured salami-Washington and California, 1994. 

MMWR 44:157-159. 

Centers for Disease Control and Prevention (CDC). 1996. Outbreak of Trichinellosis associated 

with eating cougar jerky-Idaho. MMWR 45:205-206. 

Centers for Disease Control and Prevention (CDC). 1997. Outbreaks of Escherichia coli 

O157:H7 infection and cryptosporidiosis associated with drinking unpasteurized apple 

cider-Connecticut and New York, October, 1996. MMWR 46:4-8. 

Centers for Disease Control and Prevention (CDC). 1998. Plesiomonas shigelloides and 

Salmonella Serotype Hartford infections associated with a contaminated water supplyLivingston County, New York, 1996. MMWR 47(19): 394-396. 

Centers for Disease Control and Prevention (CDC). 2000. Outbreak of Escherichia coli O157:H7 

infection associated with eating fresh cheese curds-Wisconsin, June 1998. MMWR 284:911-

913. 

Centers for Disease Control and Prevention (CDC). 2002a. Outbreak of Salmonella serotype 

Kottbus infections associated with eating alfalfa sprouts-Arizona, California, Colorado and 

New Mexico, February-April 2001. MMWR 51(01): 7-9. 

Centers for Disease Control and Prevention (CDC). 2002b. Multi-state outbreaks of Salmonella 

serotype Poona Infections associated with eating cantaloupe from Mexico-United States and 

Canada-2000-2002. MMWR 51(46): 1044-1047. 

Centers for Disease Control and Prevention (CDC). 2004. Escherichia coli O157:H7. CDC. 

http://www.cdc.gov/ncidod/dbmd/diseaseinfo/escherichiacoli_g.htm. pp. 1-5 [accessed 

October 2006]. 

Centers for Disease Control and Prevention (CDC). 2005a. Salmonellosis. CDC. 

http://www.cdc.gov/ncidod/dbmd/diseaseinfo/Salmonellosis_g.htm. pp. 1-4. [accessed 

August 2005]. 

50 
 

Centers for Disease Control and Prevention (CDC). 2005b. Outbreaks of Salmonella infections 

associated with eating roma tomatoes-United States and Canada, 2004. MMWR 54(13): 325-

328. 

Centers for Disease Control and Prevention (CDC). 2006. Update on multi-state outbreak of E. 

coli O157:H7 infections from fresh spinach, October 6, 2006. CDC. 

http://www.cdc.gov/foodborne/ecolispinach/100606.htm. pp. 1-2. [accessed November 

2006]. 

Center for Profitable Agriculture (CPA). 2005. Value-added projects-project highlights-9. 

http://cpa.utk.edu/level2/projecthighlights/projhigh-9.htm. pp. 1-4 [accessed November 

2006]. 

Ceylan, E. and Fung, D.Y.C. 2004. Antimicrobial Activity of Spices. Kansas State University. 

pp. 5-7. 

Cheville, A.M., Arnold, K.W., Buchrieser, C., Cheng, C.M., and Kaspar, C.W. 1996. rpoS 

regulation of acid, heat, and salt tolerance in Escherichia coli O157:H7. Appl Environ 

Microbiol. 62(5): 1822-1824. 

Clavero, M.R.S. and Beuchat, L.R. 1996. Survival of Escherichia coli O157:H7 in broth and 

processed salami as influenced by pH, water activity, and temperature and suitability of 

media for its recovery. Appl Environ Microbiol. 62(8):2735-2740. 

D’Aoust, J.Y. 1997. Salmonella species. Ch. 8 in Food Microbiology: Fundamentals and 

Frontiers, 1st ed, Doyle, M.P., Beuchat, L.R., and Montville, T.J. (Ed.), pp. 171-187. ASM 

Press, Washington DC. 

Doyle, M.P. and Schoeni, J.L. 1984. Survival and growth characteristics of Escherichia coli 

associated with hemorrhagic colitis. Appl Environ Microbiol. 48(4): 855-856. 

Doyle, M.P. and Schoeni, J.L. 1987. Isolation of Escherichia coli O157:H7 from retail fresh 

meats and poultry. Appl Environ Microbiol. 53(10):2394-2396. 

Doyle, M.P., Zhao, T., Meng, J., and Zhao, S. 1997. Escherichia coli O157:H7. Ch. 10 in Food 

Microbiology: Fundamentals and Frontiers, 1st ed, Doyle, M.P., Beuchat, L.R., and 

Montville, T.J. (Ed.), pp. 171-187. ASM Press, Washington DC. 

Environmental Protection Agency (EPA). 2006. E. coli O157:H7 in Drinking Water. 

http://www.epa.gov/safewater/ecoli.html. pp. 1-5. [accessed October 2006]. 

Faith, N.G., LeCoutour, N.S., Avarenga, M.B., Calicioglu, M., Buege, D.R., and Luchansky, J.B. 

1998. Viability of Escherichia coli O157:H7 in ground and formed beef jerky prepared at 

levels of 5 and 20% fat and dried at 52, 57, 63, or 68°C in a home-style dehydrator. Int J 

Food Microbiol. 41: 213-221. 

51 
Feng, P. 1995. Escherichia coli serotype O157:H7: Novel vehicles of infection and emergence of 

phenotypic variants. Emerg Infect Dis. 1:47-52. 

Food and Drug Administration (FDA). 2006. Salmonella spp. Bad Bug Book. 

http://vm.cfsan.fda.gov/`mow/chap1.html. pp. 1-5. [accessed June 2006]. 

Food Safety and Inspection Service (FSIS). 1996. FSIS Recall Cases: 1996. 

http://www.fsis.usda.gov/OA/recalls/recdb/rec1996.htm. pp. 1. [accessed November 2006]. 

Food Safety and Inspection Service (FSIS). 1998a. Microbiology Laboratory Guidebook. 

http://www.fsis.usda.gov/Science/Microbiological_Lab_Guidebook/index.asp. pp. 1-3. 

[accessed April 2006]. 

Food Safety and Inspection Service (FSIS). 1998b. Safe Storage of Meat and Poultry: The 

Science Behind It. 

http://dwb.unl.edu/Teacher/NSF/C10/C10Links/www.fsis.usda.gov/oa/pubs/storage.htm. pp. 

1-7. [accessed November 2006]. 

Food Safety and Inspection Service (FSIS). 1999. Appendix A-June, 1999. Appendix A: 

Compliance guidelines for meeting lethality performance standards for certain meat and 

poultry products. http://www.fsis.usda.gov/OA/fr/95033F-a.htm. pp. 1-4. [accessed 

September 2005]. 

Food Safety and Inspection Service (FSIS). 2000. Food Safety of Jerky. 

http://www.fsis.usda.gov/oa/pubs/jerky.htm. pp. 1-5 [accessed August 2005]. 

Food Safety and Inspection Service (FSIS). 2001. 9 CFR Parts 301, 303, et al. Performance 

Standards for the Production of Processed Meat and Poultry Products; Proposed Rule. 

http://www.fsis.usda.gov/OPPDE/rdad/FRPubs/97-013P.pdf. pp 1-48. [accessed September 

2006]. 

Food Safety and Inspection Service (FSIS). 2003. New Mexico firm recalls beef jerky for 

possible Salmonella contamination. http://www.fsis.usda.gov/OA/recalls/prelease/pr051-

2003.htm. pp. 1-3. [accessed March 2006]. 

Food Safety and Inspection Service (FSIS). 2004. Compliance Guideline for Meat and Poultry 

Jerky Produced by Small and Very Small Plants. 

http://www.usda.gov/PDF/Compliance_Guideline_Jerky.pdf. pp. 1-7. [accessed May 2006]. 

Food Safety Research Information Office. 2005. A focus on Salmonella. USDA. 

http://www.nal.usda.gov/fsio/research/fsheets/fsheet10.htm. pp. 1-8. [accessed September 

2006]. 

52 
Frenzen, P.D., Drake, A., Angulo, F.J., and The Emerging Infections Program FoodNet Working 

Group. Economic cost of illness due to Escherichia coli O157:H7 nfections in the United 

States. J Food Prot. 68:2623-2630. 

Glass, K.A., Loeffelholz, J.M., Ford, J.P., and Doyle, M.P. 1992. Fate of Escherichia coli 

O157:H7 as Affected by pH or Sodium Chloride and in Fermented, Dry Sausage. Appl 

Environ Microbiol. 58(8): 2513-2516. 

Harrison, J.A. and Harrision, M.A. 1996. Fate of Escherichia coli O157:H7, Listeria 

monocytogenes, and Salmonella typhimurium during Preparation and Storage of Beef Jerky. 

J. Food Prot. 59:1336-1338. 

Harrison, J.A., Harrison, M.A., and Rose, R.A. 1997. Fate of Listeria monocytogenes and 

Salmonella Species in Ground Beef Jerky. J. Food Prot. 60:1139-1141. 

Harrison, M.A., Singh, R.K., Harrison, J.A., and Singh, N. 2006. Antimicrobial Intervention and 

Process Validation in Beef Jerky Processing. University of Georgia. pp. 1-19. 

Ingham, S. 2006. Personal Communication regarding jerky validation. University of Wisconsin. 

Jay, J.M. 2000. Modern Food Microbiology. 6th ed. Chapman and Hall, New York. 

Kang, D.H. and Fung, D.Y.C. 1999a. Thin Agar Layer Method for Recovery of Heat-injured 

Listeria monocytogenes. J Food Prot 62(11): 1346-1349. 

Kang, D.H. and Fung, D.Y.C. 1999b. Application of thin agar layer method for recovery of 

injured Salmonella typhimurium. Int J Food Microbiol. 1999: 000-000 

Karmali, M.A., Steele, B.T., Petric, M., and Lim, C. 1983. Sporadic cases of hemolytic-uraemic 

syndrome associated with faecal cytotoxin and cytotoxin-producing Escherichia coli in 

stools. Lancet. i:619-620. 

Kenneth Todar University of Wisconsin-Madison Department of Bacteriology (Todar). 2005. 

Salmonella and salmonellosis . Todar’s Online Textbook of Bacteriology. 

http://textbookofbacteriology.net/salmonella.html. [accessed October 2006]. 

Leyer, G.J., Wang, L., and Johnson, E.A. 1995. Acid adaptaion of Escherichia coli O157:H7 

increases survival in acidic foods. Appl Environ Microbiol. 61(10):3752-3755. 

Lonnecker, S. 2005. Variables affecting lethality of Escherichia coli O157:H7 and Salmonella 

Species in whole muscle or formed jerky products. M.S. Report, Hale Library. Kansas State 

University. pp. 41-48. 

53 
Marchello, M.J. and Garden-Robinson, J. 1999. Jerky Making: then and now. 

http://www.ag.ndsu.edu/pubs/yf/foods/fn580w.htm. [accessed November 2006]. 

Martin, M.L., Shipman, L.D., Wells, J.G., Potter, M.E., Hedberg, K., Wachsmuth, I.K., Tauxe, 

R.V., Davis, J.P., Arnoldi, J., and Tilleli, J. 1986 Isolation of Escherichia coli O157:H7 from 

dairy cattle associated with two cases of haemolytic uremic syndrome. Lancet II:1043. 

Mattick, K.L., Jorgensen, F., Legan, J.D., Lappin-Scott, H.M., and T.J. Humphrey. 2000. 

Habituation of Salmonella spp. at Reduced Water Activity and Its Effect on Heat Tolerance. 

Appl Environ Microbiol. 66(11): 4921-4925. 

Mendonca, A.F., Amoroso, T.L., and Knabel, S.J. 1994. Destruction of Gram-Negative FoodBorne Pathogens by High pH Involves Disruption of the Cytoplasmic Membrane. Appl 

Environ Microbiol. 60(11): 4009-4014. 

Midura, T.F., Nygaard, G.S., Wood, R.M., and Bodily, H.L. 1972. Clostridium botulinum Type 

F: Isolation from Venison Jerky. Appl Microbiol 24:165-167. 

New Mexico Department of Health (NMDOH). 2004. Outbreak of Salmonellosis Associated 

with Beef Jerky in New Mexico. New Mexico Epidemiology Report. 2004(3):1-4. 

Nummer, B.A., Harrison, J.A., Harrison, M.A., Kendall, P., Sofos, J.N., and Andress, E.L. 2004. 

Effects of Preparation Methods on the Microbiological Safety of Home-Dried Meat Jerky. J 

Food Prot 67:2337-2341. 

Noveir, M.R. and Halkman, A.K. 1999. A Study on Selective Broths and Agar Media for the 

Isolation of Escherichia coli O157:H7 Serotype. Department of Food Engineering. Ankara 

University. pp 459-464. Ankara, Turkey. 

Pearson, A.M. and Gillett, T.A. 1996. Processed Meats, 3rd ed. Chapman and Hall, New York. 

Rangel, J.M., Sparling, P.H., Crowe, C., Griffin, P.M., and Swerdlow, D.L. 2005. Epidemiology 

of Escherichia coli O157:H7 outbreaks, United States, 1982-2002. Emerg Infect Dis. 

http://www.cdc.gov/ncidod/EID/vol11no04/04-0739.htm. pp. 1-14. [accessed November 

2006]. 

Reed, C.A. 1995. Challenge Study-Escherichia coli O157:H7 in fermented sausage. Letter to 

plant managers; April 28, 1995. USDA, FSIS, Washington, DC. 

Ricke, S.C. and Keeton, J.T. 1997. Fermented meat, poultry, and fish products. Ch. 33 in Food 

Microbiology: Fundamentals and Frontiers, 1st ed., Doyle, M.P., Beuchat, L.R., and 

Montville, T.J. (Ed.), pp. 610-628. ASM Press, Washington DC. 

54 
Roman, J.R., Costello,W.J., Carlson,C.W., Greaser, M.L., and Jones, K.W. 2001. The Meat We 

Eat, 14th ed. Interstate Publishers, Inc., Danville, IL. pp. 734-735. 

Salt Institute (SI). 2006. Salt in Food. http://www.saltinstitute.org/53.html. [accessed November 

2006]. 

Sigma-Aldrich. 2006. Preuss Broth. Sigma Aldrich Corporation. 

http://www.sigmaaldrich.com/preussbroth.html. [accessed May 2006]. 

Sindelar, J. 2004. Jerky Guidelines Past, Present, and Future. Iowa State University. pp. 1-6. 

Spondylitis Association of America (SAA). 2006. Ankylosing Spondylitis (AS). 

http://www.spondylitis.org/about/as.aspx. pp. 1-3. [accessed November 2006]. 

Stoltenberg, S. K., Getty, K.J.K., Thippareddi, H., Phebus, R.K., and Loughlin, T.M. 2006. Fate 

of Escherichia coli O157:H7 during production of snack sticks made from beef or a 

venison/beef fat blend and directly acidified with citric or lactic Acid. J Food Scie. 71:228-

235. 

Su, C. and Brandt, L.J. 1995. Escherichia coli O157:H7 infection in humans. Annal. Int. Med. 

123(9):698-707. 

Uhler, P.M. 2004. Questions about Compliance Guidelines. Letter to Dr. Dennis Buege; 

May 7, 2004. USDA, FSIS, Washington, DC. 

Uhler, P.M. 2005. Lethality Performance Standard for Samonella in Regards To Jerky 

Processing. Letter to Dr. Dennis Buege; 2005. USDA, FSIS, Washington, DC. 

United States Department of Agriculture (USDA). 2005. Food Standards and Labeling Policy 

Book. http://www.fsis.usda.gov/OPPDE/larc/Policies/Labeling_Policy_Book_082005.pdf. 

pp. 83-84. [accessed April 2007]. 

Waterman, S.R. and Small, P.L.C. 1998. Acid-Sensitive Enteric Pathogens Are Protected From 

Killing Under Extremely Acidic Conditions of pH 2.5 When They Are Inoculated Onto 

Certain Food Sources. Appl Environ Microbiol. 64(10): 3882-3886. 

Wu, V.C.H., Fung, D.Y.C., Kang, D.H., and Thompson, L.K. 2001. Evaluation of thin agar layer 

method for recovery of acid-injured foodborne pathogens. J Food Prot. 64:1067-1071. 

wu, v.c.h. and fung, d.y.c. 2001. evaluation of thin agar layer method for recovery of heat-injured 

foodborne pathogens. J. Food Safety. 66:580-583 

55 
Wu, V.C.H. and Fung, D.Y.C. 2003. Simultaneous recovery of four heat-injured foodborne 

pathogens from a four-compartment thin agar layer plate. J Food Scie. 68(2): 646-648. 

Zimbro, M.J., and Power, D.A. (Ed). 2003. MacConkey sorbitol agar. Difco and BBL Manual. 

BD Diagnostic Systems, pp. 340-341. Becton, Dickinson and Company, Sparks, MD. 

56 
6. Roberts, M.N., Getty, K.J.K., and E.A.E. Boyle. 2006 Thermal Process for Jerky Provides 

Proper Lethality for Controlling Pathogens. Kansas State University Cattleman’s Day Report 

2007. Available at www.asi.ksu.edu/cattlemensday. 

NOTE TO READERS: This report contains specific information about processing times and 

temperatures and is the most appropriate document to use for validation. It was reviewed by two 

meat scientists and is in layman’s language that is easily understood by small and very small 

processors. It can also be easily accessed from the web at www.asi.ksu.edu/cattlemensday under 

Publications and then pages 122-124 of Beef Cattle Research 2007. 

Beef Cattle Research — 2007 

THERMAL PROCESS FOR JERKY PROVIDES PROPER LETHALITY FOR 

CONTROLLING PATHOGENS 

M. N. Roberts, K.J.K. Getty, and E.A.E. Boyle 

Introduction 

In 2003, the New Mexico Department of 

Health linked an outbreak of Salmonellosis 

with consumption of beef jerky. Due to the 

increasing commonality of foodborne illness 

associated with dried meats, in 2004 

USDA/FSIS published the Compliance 

Guideline for Meat and Poultry Jerky 

Produced by Small and Very Small Plants, 

which addresses the issues of how to obtain 

adequate lethality and verify adequate drying. 

Small meat businesses that produce jerky 

products must validate that their processes 

achieve a 5-log reduction of E. coli O157:H7 

and a > 6.5-log reduction of Salmonella. The 

objective of this study was to determine the 

effects of thermal processing temperatures and 

times on reducing E. coli O157:H7 and 

Salmonella in chopped and formed beef jerky. 

Experimental Procedures 

Meat Batter Preparation and 

Inoculation. Fresh chopped and formed allbeef jerky batter was obtained from a 

commercial processor. The product was 

separated into three 4-lb batches. Two 

treatments, consisting of an E. coli O157:H7-

inoculated batch and a Salmonella-inoculated 

batch, were prepared by adding an E. coli 

O157:H7 five-strain inoculum or Salmonella 

five-strain inoculum and thoroughly mixing 

into the jerky batter. A control batch was 

prepared by adding sterile deionized water 

into the meat batter. 

Batter was extruded using a manual jerky 

gun with a 1/4-inch by 1-inch nozzle onto 

polyscreen sheets and then thermally 

processed in a commercial smokehouse (Table 

1). A replication consisted of both inoculated 

batches and a control batch placed in the 

smokehouse simultaneously. Three 

replications were conducted. 

E. coli O157:H7 and Salmonella 

Enumeration. Raw inoculated samples were 

taken from the inoculated jerky batter. Heattreated samples were taken at six different 

times (end of stages 6, 7, 8, 10; 1.5 hours into 

stage 12; and at the end of the stage 12; Table 

1). Population levels of E. coli O157:H7 and 

Salmonella were determined for both raw and 

heat-treated samples. In addition, heat-treated 

samples with counts below the detection limit 

were tested for a positive or negative level of 

either E. coli O157:H7 or Salmonella. 

57 
Water Activity (aw), pH, Proximate 

Analysis, and Salt. Water activity and pH 

levels were determined on control samples. 

Samples for proximate analysis (moisture, fat, 

and protein) and salt content were taken from 

the non-inoculated raw control batch 1.5 hours 

into stage 12 and at the end of stage 12 (final). 

Results and Discussion 

For all E. coli O157:H7- and 

Salmonella-inoculated jerky strips, initial raw 

batter populations ranged from 7.3 to 7.4 log 

cfu/g and 7.1 to 7.5 log cfu/g, respectively. 

When the product reached stages 6, 7, 8, and 

10, E. coli O157:H7 populations ranged from 

less than 1.48 (detection limit) to 2.68 log 

cfu/g and Salmonella counts ranged from less 

than 1.5 to 2.1 log cfu/g. By 1.5 hours into 

stage 12, counts were consistently less than 

1.5 log cfu/g on all media. End-product E. 

coli O157:H7 and Salmonella populations 

were consistently <0.5 log cfu/g. 

There was ≥ 5.0 log cfu/g 

reduction of E. coli O157:H7 at all sampling 

times as required by USDA/FSIS, with the 

most consistent reductions being after stage 7. 

A ≥ 6.5 log cfu/g reduction of Salmonella, as 

mandated by USDA/FSIS, was seen in stage 

12 and at the end of the cycle (Figure 1). End 

product populations for both E. coli O157:H7 

and Salmonella show reductions well above 

those mandated by USDA/FSIS. 

Samples from 1.5 hours into 

stage 12 and end-product samples showed 

negative populations for both E. coli O157:H7 

and Salmonella for all samples tested, 

confirming the likelihood that pathogens are 

dead as opposed to heat-injured. 

Moisture content ranged from 

52.4 to 56.0% for raw product and 15.1 to 

19.8% for the final product. Protein content 

ranged from 15.9 to 17.0% for raw product 

and 34.2 to 37.7% for the final product. Salt 

contents for raw products ranged from 2.2 to 

2.3% and from 4.2 to 5.2% for final product. 

The moisture-to-protein ratio ranged from 0.4 

to 0.6 for the final product. This ratio is in 

compliance with the requirement of an MPR 

less than 0.75:1 needed for the product to be 

labeled as “jerky”. 

Raw batter pH values ranged 

from 6.0 to 6.2. The final pH range for all 

products was 5.1 to 5.3. It should be noted 

that a lowered pH was not a determining 

factor for the reduction of E. coli O157:H7 or 

Salmonella populations. 

Water activity range for all 

final products was 0.570 to 0.625. According 

to the USDA/FSIS Jerky Compliance 

Guidelines, water activity for jerky products 

should be 

≤ 0.80 to ensure lack of microbial growth. 

Implications 

A thermal process for producing chopped 

and formed jerky provided proper lethality to 

control pathogens such as E. coli O157:H7 

and Salmonella and provides a process that 

will produce safe jerky for consumers. 

58 
0 

1 

2 

3 

4 

5 

6 

7 

8 

Stage 

6 

Stage 

7 

Stage 

8 

Stage 

10 

Stage 

12 

End 

Thermal Stages 

Log cfu/g Reductions

E. coli O157:H7 

Salmonella 

Figure 1. E. coli O157:H7 log CFU/g Reductions and Salmonella Reductions at Six 

Thermal Stagesa

 during Production of Chopped and Formed Beef Jerky. a

Times and dry bulb smokehouse temperatures for thermal stages: stage 6 – 44 min at 132oF 

and 46 min at 172oF, stage 7 – 44 min at 132oF and 1 hour at 172oF, Stage 8 – 44 min at 132oF and 1 

hour 16 min at 172oF, stage 10 – 44 min at 132oF and 1 hour 46 min at 172oF, stage 12 – 44 min at 

132oF and 3 hours 30 min at 172oF, End – 44 min at 132oF and 7 hours at 172oF. 

59 
 

 

 

 

Table 1. Thermal Processing Schedulea and Sampling Times for Chopped and Formed Beef 

Jerky 

Dry Bulb Cumulative Times and 

(D.B.) Blower Temperatures at Each 

Stage (oF)a Time Speed Sampling Time Sampling Time 

1 132 14 min Medium 

2 132 16 min Medium 

3 132 14 min Medium 

4 172 16 min Medium 

5 172 14 min Medium 

44 min at 132oF and 

6 172 16 min Medium End of stage 46 min at 172oF 

44 min at 5132oF and 

7 172 14 min Fast End of stage 1 h at 172oF 

44 min at 132oF and 

8 172 16 min Fast End of stage 1 h 16 min at 172oF 

9 172 14 min Fast 

44 min at 132oF and 

10 172 16 min Fast End of stage 1 h 46 min at 172oF 

11 172 14 min Fast 

44 min at 132oF and 

12 172 5 h Fast 1.5 h into stage 3 h 30 min at 172oF 

44 min at 132oF and 

End End of stage 12 7 h at 172oF 

a

The smokehouse has an automated damper system and the ability to inject steam as needed 

to control humidity and the exhaust fan was running during the whole process. Percent relative 

humidity remained at less than 10% throughout the entire smokehouse cycle. Blower speed: 

Medium=788.8 ± 52.7 ft/min and fast speed = 1141.5 ± 111.9 ft/min. 

60