NEW INTERVENTIONS AND VALIDATION FOR THE CONTROL OF 

PATHOGENS IN THE PROCESSING OF JERKY 

J.A. Boles, K.I. Neary and K. Clawson 

Montana State University, Bozeman, MT 59717 

Key Words: E. coli O157:H7, Salmonella, Listeria monocytogenes, Jerky 

Introduction 

Jerky is a common ready to eat product that can be purchased at just about any gas 

station, grocery store and small processing facility in the United States. Many small and 

very small plants manufacture jerky. It is important that these small and very small 

plants be able to validate that the product they manufacture is safe and free from 

pathogens. Many of the small processors use smokehouses with minimal controls, 

especially for humidity which are similar to home dehydrators. Faith et al. (1998) 

evaluated ground and formed jerky that had been dried using processes that were similar 

to home style dehydrators. They reported that viability of bacteria was reduced as the 

drying temperature increased and drying time increased. In the past, control of pathogens 

for jerky was due to reduced water activity. Control of most bacteria occurs at water 

activities below 0.90 (Jay, 1986). Calicioglu et al. (2003a) reported a 5 log reduction in 

Escherichia coli O157:H7 inoculated post-drying after 7 days of storage. The water 

activity of the jerky post-drying was between 0.564 and 0.696. Water activity below 0.85 

has been used in other countries to establish safety of jerky (Agriculture and Agri-Food 

Canada, NZFSA). New guidelines from the USDA suggest lowering water activity to 

0.80 to control Salmonella and E. coli 0157:H7 along with processing with high humidity 

at the first of the manufacturing process. 

Listeria monocytogenes has been a new problem that most small processors are now 

dealing with on ready to eat products. Listeria is normally a problem because of post 

processing contamination. Calicioglu et al. (2002) reported that Listeria numbers were 

reduced during the drying process and that the use of acid marinades helped increase this 

reduction. Työppönen et al (2003) observed that traditional processing procedures for 

dried, and fermented and dried sausages were not sufficient to prevent the survival of 

Listeria monocytogenes and Escherichia coli O157:H7. Therefore it is important to 

determine the effect of different water activities on the survivability of select pathogens. 

With the uncertainty of survival of different pathogens in dried products, it is important 

for processors to validate the process they are using to manufacture jerky that is being 

labeled shelf stable. 

Objectives 

1. Determine the survivability of E. coli O157:H7, Salmonella spp. and Listeria 

monocytogenes on whole muscle jerky dried without humidity and stored in a vacuum 

package. 

1 
2. Determine the survivability of E. coli O157:H7, Salmonella spp. and Listeria 

monocytogenes on whole muscle jerky dried with smokehouse dampers closed for the 

first hour of processing. 

3. Determine the survivability of Listeria monocytogenes inoculated post processing on 

jerky treated with a sodium lactate or hot water dip. 

Methodology 

Processing affect on microbial survival 

Beef (semimembranosus muscle) was purchased from a small commercial facility for the 

manufacture of jerky. Meat was tempered at 4oC for 24 h and sliced 6 mm thick. A 

formulation containing beef (89.58% w/w), soy sauce (5% w/w), dextrose (2% w/w), salt 

(1.8% w/w), garlic powder (0.5% w/w), black pepper (0.5% w/w), onion powder (0.4% 

w/w), Cure #1 (0.18% w/w) and sodium erythorbate (0.04% w/w) was used to marinate 

the jerky. Marination was conducted for 20 min in a vacuum tumbler. After marination, 

each slice was inoculated by dipping in a cocktail of pathogens (Salmonella (4 strains S. 

typhimurium 04121V and 0363V, S. abaetebua 0817V and S. choleraesuis 0902V from 

Fisher Scientific, Denver, CO) , 3 x 106; Listeria moncytogenes (4 strains FSL J1-110, 

FSL C1-115, FSL J2-064, and FSL J2-054 from Martin Weidman, Cornell University) 

6.25 x 107 and E. coli O157:H7 (one strain 0617V, Fisher Scientific, Denver, CO) 3.3 x 

107). Three raw slices were tested to determine inoculation level. Jerky was placed on 

racks and dried in an ALKAR smokehouse (Alkar Smokehouses, Lodi WI) at 60°C with 

dampers open and fans running at maximum for the whole drying cycle. To evaluate 

how early damper closure affected survivability dampers were closed for the first hour of 

processing. Samples were taken at 1, 3, 6, 9, and 12 hours of drying to give three slices 

of jerky for each of five storage periods (0, 3, 6, 9, or 12 weeks). Samples from 0 and 1 

hour of drying were not stored. Each sample was tested for microorganism survival 

utilizing selective media. Internal temperature and water activity was also determined. 

Internal temperature was determined using hypodermic thermocouples (Omega 

Scientific, Tarzana, CA) inserted into 6 slices in each of three different full smokehouse 

loads. Water activity was determined with a Series 3 Decagon Aqualab water activity 

meter (Aqualab, Pullman, WA) on two different samples from each jerky slice at each 

drying and storage period. Three jerky slices from different places in the smokehouse 

were analyzed at each storage time for bacterial survival and water activity. 

Post-processing contamination of Listeria monocytogenes 

Beef (semimembranosus muscle) was purchased from a small commercial facility for the 

manufacture of jerky. Meat was tempered at 4oC for 24 h and sliced 6 mm thick. A 

formulation containing beef (89.58% w/w), soy sauce (5% w/w), dextrose (2% w/w), salt 

(1.8% w/w), garlic powder (0.5% w/w), black pepper (0.5% w/w), onion powder (0.4% 

w/w), Cure #1 (0.18% w/w) and sodium erythorbate (0.04% w/w) was used to marinate 
the jerky. Marination was conducted in for 20 min in a vacuum tumbler. Jerky was 

placed on racks and dried in an ALKAR smokehouse (Alkar Smokehouses, Lodi WI) at 

60°C with dampers open and fans running at maximum for the whole drying cycle. After 

drying for 3, 6, 9 or 12 hours slices (30 at each time period) were removed from the 

smokehouse and dipped in a cocktail of Listeria moncytogenes (5.5 x 105

, 4 strains FSL 

J1-110, FSL C1-115, FSL J2-064, and FSL J2-054 from Martin Weidman, Cornell 

University) and allowed to dry for 30 minutes. Samples were then either vacuum 

packaged (10 slices per drying time) and labeled for storage vacuum packaged (10 slices 

per drying time) and dipped in 72oC water for 20 s or dipped in 2% sodium lactate and 

allowed to dry for 30 minutes before vacuum packaging. Samples were stored for 0, 3, 6, 

9 or 12 weeks at 21oC. 

Microbial analysis 

Ten grams of jerky slice per drying time were aseptically transferred into sterile plastic 

bags (Fisher Scientific, Denver, CO). A 90-mL aliquot of 0.1% sterile peptone buffer 

(Difco) was added to each sample bag prior to pummeling with a stomacher for 2 min at 

room temperature. Serial decimal dilutions were made and pour-plated onto each of 

duplicate plates of each agar medium. Three different jerky slices per drying time were 

analyzed at each storage period for processing affects and two slices per drying time per 

treatment were analyzed for post-processing contamination with Listeria monocytogenes. 

Bacteria were enumerated using tryptic soy agar (Difco) plus 0.1% sodium pyruvate 

(TSAP, total plate count), PALCAM agar (Difco) (Listeria monocytogenes), xyloselysine-tergitol 4 agar (Difco) (XLT4, Salmonella), MacConkey sorbitol agar (Difco) 

(SMAC, E. coli) and modified eosin methylene blue agar (Difco) (MEMB, E. coli). 

PALCAM and half of the TSAP plates were incubated at 30oC while the other plates 

were incubated at 35oC. The minimum detection limit was 10 CFU/g. All counts were 

econverted to log CFU/g. When numbers of the pathogen decreased to <10 CFU/g by 

direct plating, the presence/absence of the pathogen was determined by enrichment as 

described by Calicioglu et al. (2003a, b) for Listeria and Salmonella. 

Data were analyzed using the GLM procedure of SAS. The absence of pathogens on 

selective agar was scored as 9 cfu for statistical analysis if there were no colonies on a 

plate. LSMEANS was used to separate means. 

Results & Discussion 

Processing effect on microbial survival 

The internal temperature of jerky slices was similar to the smokehouse temperature after 

three hours of drying (Fig. 1). Calicioglu and co-workers (2003b) reported that the 

internal temperature of jerky slices were similar to the dehydrator temperature after 6 

hours of drying. The difference between these two reports is probably due to increased 

air flow and better temperature control in the smokehouse used in this study when 
compared to the home dehydrator used by Calicioglu et al. (2003b). This variation 

between temperatures also suggests that under drying conditions with no humidity added 

that the processor will need to establish what the internal temperature of a jerky slice is 

going to be under the specific conditions of their smokehouse. 

The total number of colony forming units declined as drying time increased (Fig. 2). The 

total number of E. coli, Salmonella and Listeria also significantly declined as drying time 

increased. Drying of jerky resulted in a 2 log reduction of Listeria after 6 hours of drying 

which increased to a 3 log reduction after 12 hours. Drying of jerky slices inoculated 

with E. coli O157:H7 resulted in a 3 log reduction after 3 hours of drying and a 4 log 

reduction after 12 hours. Drying of jerky slices inoculated with Salmonella resulted in a 

2 log reduction in 3 hours with an increase to 3 log reduction after 6 and 12 hours of 

drying. Albright et al. (2002) reported 2.1 – 2.5 log reductions of E. coli on jerky that 

had been processed in home type dehydrators at 62.5oC. These reductions are similar to 

what was seen in this study. Even after 12 h of drying reduction in pathogens had not 

reached the 5-log reduction and all drying times had surviving bacteria. The largest 

reduction in pathogen load happened within the first 3 hours of processing. There was 

not a drying by storage time interaction. 

After vacuum storage for three weeks there was no Listeria or E. coli recovered from the 

jerky strips (Fig. 3). Furthermore after enrichment there was no Listeria or E. coli 

resuscitated. Salmonella however did survive storage up to 3 and 6 weeks of storage but 

was reduced to below detectable limit after 9 and 12 weeks of storage (Fig. 3). 

Salmonella was recovered after enrichment, but in very low numbers (5 CFU). Survivors 

of all bacteria tested were most often found when the integrity of the vacuum package 

was compromised. Faith et al. (1997) reported a reduction in E. coli in pepperoni stored 

under vacuum at room temperatures. They reported a 1-log reduction after 7 days of 

storage, 3.6-log reduction after 28 days (4 weeks) of storage that increased to 

approximately 5-log reduction (below detection limit) after 60 days of storage (8.5 weeks 

of storage). Additionally, Ihnot et al. (1998) reported that storage under vacuum at 

ambient temperatures was more severe on Salmonella typhimurium DT104 than 

refrigerated storage in pepperoni. Data reported herein suggests that a 5-log reduction 

can be achieved with drying and 6 weeks of vacuum storage. However, Calicioglu et al 

(2003b) reported surviving Salmonella on jerky after 60 days of aerobic storage. 

Information reported herein along with data reported in the literature suggests that 

Salmonella is more resistant to the drying and storage conditions than are Listeria or E. 

coli. 

Water activity was reduced as the drying time increased (Table 1) however at all drying 

times it was low for jerky products. The water activity of jerky slices was reduced from 

0.961 to 0.589 within 3 hours. This is much less than that reported by Calicioglu et al 

(2003b) who reported a reduction in water activity from 0.961 to 0.898 after 4 h of drying 

at 60oC and Albright et al (2002) who reported a reduction in water activity from 0.93 to 

0.90 at 62.5oC in 4 h. Both researchers used home dehydrators for their drying. The 

Alkar smokehouse used in this study resulted in a much more rapid drop of water activity 

then that seen in other reported studies utilizing home-style dehydrators. There is a major 
difference between drying rates of home dehydrators and smokehouses that are used by 

meat processors. It is important to recognize the difference and evaluate the processes 

accordingly. Storage had a significant affect on water activity but the differences were 

not consistent over time and reflect differences in individual slices analyzed along with 

differences due to drying. 

Table 1 Effect of drying and storage on the water activity of jerky 

 Water activity SEM 

Drying Time (hrs) 

0 0.961a 0.012 

1 0.843b 0.012 

3 0.569c 0.012 

6 0.464d 0.012 

9 0.373e

 0.012 

12 0.373e 0.012 

Storage (weeks) 

0 0.445a

 0.008 

3 0.413b

 0.008 

6 0.396b 0.008 

9 0.462a

 0.008 

12 0.393b 0.008 

A significant damper by drying time interaction was observed for bacteria grown on 

MEMB (P = 0.01) and XLT4 (P = 0.0006). Closing of the dampers for the first hour of 

processing resulted in a small significant decrease in E. coli and Salmonella survival that 

carried over to all successive times of drying except for 12 hours of drying (Fig. 4). The 

reduction was approximately 0.4 of a log for all E. coli and Salmonella with a greater 

reduction in total aerobic plate counts (0.7 log; Fig. 5). Salmonella was more susceptible 

to the increased moisture during that first hour of drying than were Listeria and E. coli. 

There was a significant interaction between having the dampers open for the first one 

hour of processing and storage time for survival of Salmonella. This is a result of the 

decreased number of pathogens surviving on the jerky prior to being placed into storage. 

No matter the processing scheme, after 3 to 6 weeks of vacuum packaged storage the 

number of pathogens were below the detectable limit and there were few being 

resuscitated. 

Post-processing contamination of Listeria monocytogenes 

Inoculation of dried jerky by dipping in a solution containing 5.5 x 105 Listeria 

monocytogenes resulted in 2.95 × 104

 per g on the jerky slices. Initially dipping the 

vacuum package in 72oC water for 20 s had a small but significant (P = 0.002) affect on 

Listeria numbers on jerky. A 0.42-log reduction was achieved when compared with no 

treatment. Dipping in sodium lactate did not significantly affect the numbers of Listeria 

on jerky when compared to the control. There was no treatment by drying interaction (P 

= 0.89) but a significant treatment by storage interaction (P = 0.0008) was observed. 

Dipping of packaged jerky in 72oC water for 20 sec resulted in a significantly lower 

number of Listeria surviving after 0 storage than no treatment and sodium lactate dip. 
After 3 weeks of storage water dip was similar to control but had significantly fewer 

Listeria surviving than sodium lactate dipped slices. After 6 weeks of vacuum storage 

the control and water dip had below detectable limits of Listeria surviving. Similarly, 

Calicioglu et al (2003c) reported that Listeria and total bacterial populations decreased or 

were below detection limit after 28 days of vacuum packaged storage. 

Water activity of jerky was significantly affected by treatment (P <0.0001) with jerky 

strips dipped in sodium lactate having a slightly higher water activity than either no 

treatment or water dipping. As expected water activity was reduced (P <0.0001) during 

drying and was significantly different at each drying time evaluated. Storage had a 

significant affect on water activity but the differences were not consistent over time and 

reflect differences in individual slices analyzed along with differences due to drying. 

Table 2 Effect of treatment, drying and storage on the water activity of jerky 

post-processing inoculated with Listeria monocytogenes

 Water activity SEM 

Treatment 

None 0.603b

 0.006 

 Sodium lactate 0.639a 0.006 

Water 0.593b

 0.006 

Drying Time (hrs) 

3 0.739a

 0.007 

6 0.646b

 0.007 

9 0.571c 0.007 

12 0.488d

 0.007 

Storage (weeks) 

0 0.695a

 0.008 

3 0.584b

 0.008 

6 0.612c 0.008 

9 0.613c

 0.008 

12 0.551d

 0.008 

Conclusions 

Drying procedures currently used by most small processors will reduce the number of 

pathogens on the jerky however drying does not reduce the number enough to meet the 5­

log reduction USDA desires. Use of sodium lactate dip (2%) is not as affective as a 20 s 

hot water dip or no treatment in decreasing post-processing inoculated Listeria 

monocytogenes on jerky. Drying and storing in a vacuum package does result in 

reduction of pathogens to below the detectable limit. The cause of the reduction of 

pathogens in storage is not clear. Some will be due to the lowered water activity but 

some may be due to pathogens being injured during drying and not being able to adapt to 

the vacuum packaged atmosphere. As long as the water activity of jerky is below 0.70 

pathogens will not survive vacuum packaged storage at ambient temperature beyond 6 
weeks. More research is needed to determine how high the water activity can be when 

vacuum packaged storage is still affective at reducing microbial numbers. 

References 

Agriculture and Agri-Food Canada, Canadian Food Inspection 94.3(b) 

http://laws.justice.gc.ca./en/M-3.2/SOR-90-288/145394.html 

Albright, S.N., P.A. Kendall, and J. S. Avens. 2002. Effect of marinade and drying 

temperature on inactivation of Escherichia coli O157:H7 on inoculated home 

dried beef jerky. Journal of food Safety 22:155-167. 

Calicioglu, M., J.N. Sofos, J. Samelis, P.A. Kendall and G.C. Smith. 2002 Destruciton of 

acid- and non-adapted Listeria monocytogenes during drying and storage of beef 

jerky. Food Microbiology 19:545-559. 

Calicioglu, M., J.N. Sofos and P.A. Kendall. 2003a. Fate of acid-adapted and nonadapted Escherichia coli O157:H7 inoculated post-drying on beef jerky treated 

with marinades before drying. Food Microbiology 20:169-177. 

Calicioglu, M., J.N. Sofos, J. Samelis, P. A. Kendall and G. C. Smith. 2003b. Effect of 

acid adaptation on inactivation of Salmonella during drying and storage of beef 

jerky treated with marinades. International Journal of Food Microbiology 89:51-

65. 

Calicioglu, M., J.N. Sofos, and P.A. Kendall. 2003c. Influence of marinades on survival 

during storage of acid-adapted and nonadapted Listeria monocytogenes inoculated 

post-drying on beef jerky. International Journal of Food Microbiology 86:283-

292. 

Faith, N.G. N.S. Le Coutour, M.B. A.varenga, M. Calicioglu, D.R. Buege and J.B. 

Luchansky. 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 68oC in a 

home-style dehydrator. International Journal of Food Microbiology 41:213-221. 

Faith, N.G., N. Parniere, T. Larson, T.D. Lorang, and J. B. Luchansky. 1997. Viability of 

Escherichia coli O157:H7 in pepperoni during the manufacture of sticks and the 

subsequent storage of slices at 21, 4 and -20oC under air, vauum and CO2

. 

International Journal of Food Microbiology 37:47-54. 

FSIS / USDA Compliance Guideline for Meat and Poultry Jerky 

http://www.fsis.usda.gov/OPPDE/nis/outreach/models/Jerkyguidelines.htm 

Jay, J.J. (1986) Modern Food Microbiology, 4th ed., Van Nostrand Reinhold, AVI, New 

York, New York. pp 40-41. 

New Zealand Food Safety Authority. Industry Standard 6 Amendment 1 

http://www.nzfsa.govt.nz/animalproducts/meat/meatman/amendments/is6am1.pdf 

Työppönen, S., E. Petäjä and T. Mattila-Sandholm. 2003. Bioprotectives and probiotics 

for dry sausages. 83:233-244. 
E 

Figure 1 Internal temperature of jerky slices during drying at 60oC. 

Jerky Slice Internal Temperature 

0 

10 

20 

30 

40 

50 

60 

70 

le 

degrees C

Top 

Midd 

Bottom 

0 1 3 6 9 12 

Drying time (hrs) 

Figure 2 Effect of drying at 60oC on the survival of E. coli O157:H7, Salmonella spp. 

and Listeria monocytogenes. 

8 

Log 10 (CFU) 

7 

6 

5 

4 

3 

2 

1 

0 

Total 35C 

PALCAM 

MEMB 

SMAC 

XLT4 

Total 30C 

0 1 3 6 9 12 

Drying time (hrs) 
Figure 3 Effect of storage on the survival of E. coli O157:H7, Salmonella spp. and 

Listeria monocytogenes. Log 10 (CFU) 

5 

4.5 

4 

3.5 

3 

2.5 

2 

1.5 

1 

0.5 

0 

0 3 6 9 12 

Lower detection limi

Total 35C 

PALCAM 

MEMB 

SMAC 

XLT4 

Total 30C 

t = 0.95 

Storage (weeks) 
-+-

---

-+-

---

c 

Figure 4 Effect of closing of smokehouse dampers for one hour followed by normal drying on 

the survival of E. coli O157:H7, Salmonella spp. and Listeria monocytogenes (LM). 

Graphs a and b indicates survival of E. coli O157:H7 on jerky recovered on MEMB 

(a) and SMAC (b). Graph c indicates survival of LM on jerky recovered on 

PALCAM and graph d indicates survival of Salmonella spp. on jerky recovered on 

XLT4. 

a 

b 

3 

4 

5 

6 

7 

8 8 

Open 

Closed 

Open

 Closed 

7 

6 

Log 10 (CFU) 

Log 10 (CFU) 5 

4 

3 

2 2 

1 1 

0 0 

0 1 3 6 9 12 0 1 3 6 9 12 

Drying time (hrs) Drying time (hrs) 

d 

8 

7 

3 

4 

5 

6 

Log 10 (CFU) 

7 

8 

Open 

Closed 

2 

1 

0 

Open 

Closed 6 

Log 10 (CFU) 5 

4 

3 

2 

1 

0 

0 1 3 6 912 0 1 3 6 9 12 

Drying time (hrs) Drying time (hrs) 
Figure 5 Effect of closing of smokehouse dampers for one hour followed by normal 

drying on the survival of bacteria (APC) on beef jerky 

0 

1 

2 

3 

4 

5 

6 

7 

8 

Open 

Closed 

Log 10 (CFU) 

0 1 3 6 9 12 

Drying time (hrs) 
-+-

...... 

---

-+-

-+-

...... 

---

-+-

-+- -+-

...... 

--- ...... --- -+- -+-

4 

3 

2 

Log 10 (CFU) 

Figure 6 Interactive effects of drying and storage time on the survival of E. coli 

O157:H7, Salmonella spp. and Listeria monocytogenes (LM). Graphs a and b 

indicate survival of E. coli O157:H7 on jerky recovered on MEMB (a) and 

SMAC (b). Graph c indicates survival of LM on jerky recovered on 

PALCAM and graph d indicates survival of Salmonella spp. on jerky 

recovered on XLT4. 

a b 

5 

5 

4.5 

3 hr drying 

6 hr drying 

9 hr drying 

12 hr drying 

3 hrs drying 

6 hr drying 

9 hr drying 

12 hr drying 

4.5 

4 

3.5 3.5 Log 10 (CFU) Log 10 (CFU) 

3 

2.5 2.5 

2 

1.5 1.5 

1 1 

0.5 0.5 

0 0 

0 3 6 9 12 036 9 12 

Storage (weeks) c d Storage (weeks) 

5 

4.5 

1.5 

2 

2.5 

3 

3.5 

4 

5 

4.5 

3 hr drying 

6 hr drying 

9 hr drying 

12 hr drying 

1 

0.5 

0 

Log 10 (CFU) 

3 hr drying 

6 hr drying 

9 hr drying 

12 hr drying 

4 

3.5 

3 

2.5 

2 

1.5 

1 

0.5 

0 

036 9 12 0 3 6 9 12 

Storage (weeks) Storage (weeks) 

Lower detection limit = 0.95 
-+-

... ---

.... 

Figure 7 Interactive effects of drying and storage on the survival of bacteria (APC) on 

beef jerky 

6 

5 

Log 10 (CFU) 4 

3 

2 

1 

0 

3 hr drying 

6 hr drying 

9 hr drying 

12 hr drying 

Lower detection limit = 0.95 

0 3 6 9 12 

Storage (weeks) 

Figure 8 Effect of storage and sodium lactate or water dip on the survival of postprocessing inoculated Listeria monocytogenes on jerky. 

5 Log 10 (CFU) 3 

2 

a 

a P=0.04 No treatment b Sodium lactate 

a 

Water 

a P<0.001 

b 

b 

P=0.02 

b 

b 

SEM = 0.14 Lower detection limit = 0.95 

0 3 6 9 12 

Storage (weeks) 

4 

1 

0