Lethality of Commercial Beef Jerky Manufacturing Processes 

1 Lethality of Commercial Whole-Muscle Beef Jerky Manufacturing Processes 

2 Against Salmonella serovars and Escherichia coli O157:H7 

3 

4 Dennis R. Buege1

, Gina Searls1, and Steven C. Ingham2* 

5 

6 University of Wisconsin-Madison 

7 

8 

9 

10 1

Department of Animal Sciences, 2Department of Food Science 

11 

12 Short Title: Lethality of Commercial Beef Jerky Manufacturing Processes 

13 Key Words: beef jerky, Salmonella, Escherichia coli O157:H7 

14 

15 

16 

17 *Corresponding author 

18 University of Wisconsin-Madison, Department of Food Science 

19 1605 Linden Drive 

20 Madison, WI 53706 

21 Phone 608-265-4801, fax 608-262-6872, e-mail scingham@wisc.edu 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 ABSTRACT 

2 Thermal processing used in making whole-muscle beef jerky also involves drying. This 

3 drying may cause enhanced pathogen thermotolerance and evaporative cooling that 

4 reduce process lethality. Several salmonellosis outbreaks have been associated with beef 

5 jerky. In this study, a standardized process was used to inoculate beef strips with 5-strain 

6 cocktails of either Salmonella serovars or Escherichia coli O157:H7, marinade the strips 

7 in pH 5.3 marinade for 22-24 h at 5°C, and then convert the strips to jerky using various 

8 heating/drying regimes. Numbers of surviving organisms were determined during and 

9 after the heating/drying. In some trials, a commercial lactic acid starter culture was also 

10 evaluated as a potential surrogate for the pathogens. The 5-log Salmonella reduction 

11 mandated by the United States Department of Agriculture (USDA), along with a 5-log 

12 reduction in E. coli O157:H7, was best achieved by ensuring that high wet-bulb 

13 temperatures were reached and maintained early in the process (51.7°C or 54.4°C for 60 

14 minutes, 57.2°C for 30 minutes, or 60°C for 10 minutes) followed by drying at 76.7°C 

15 (dry-bulb temperature). Processes that met the USDA guideline with smaller safety 

16 margins were 1) heating and drying at 76.7°C (dry-bulb) within 90 minutes of beginning 

17 the process, 2) heating for successive hourly intervals at 48.9, 54.4, 60, and 76.7°C (dry18 bulb), or 3) heating at 51.7°C (dry-bulb), followed by 76.7°C (dry-bulb) drying started 

19 before product aw was < 0.86. Achieving a > 3.0 log reduction in the starter culture is a 

20 possible standard for validating process lethality. 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 

2 Beef jerky processing, using whole muscle or restructured ground meat, is unique 

3 compared to the processing of other ready-to-eat meat products because heat processing 

4 is intended to attain considerable drying and desired texture and shelf-stability. This 

5 drying may reduce the process lethality against pathogenic bacteria in beef, and outbreaks 

6 of salmonellosis have been linked to the consumption of beef jerky (6). Previous 

7 research has suggested that sub-lethal drying conditions may lead to increased heat8 resistance in pathogens such as Salmonella serovars (7). Furthermore, evaporative 

9 cooling during drying may lessen the effective temperature to which pathogens are 

10 exposed. A possible decrease in lethality related to evaporative cooling on the surface of 

11 cooked beef was noted previously in studies of Salmonella spp. survival during cooking 

12 of beef (2, 8). In fact, Blankenship et al., (1) recommended introduction of steam into the 

13 oven when cooking beef roasts to ensure that adequate lethality against salmonellae was 

14 attained on the roast surface. Evaporative cooling was also noted as a factor contributing 

15 to insufficient thermal lethality in making jerky associated with an outbreak of 

16 salmonellosis in New Mexico in 2003 (11). All of these factors have resulted in 

17 heightened scrutiny of the lethality of the heating and drying steps typically used during 

18 jerky processing. 

19 United States Department of Agriculture (USDA) officials have issued a 

20 compliance guideline for jerky processors (14) that stresses the importance of 

21 maintaining high humidity during thermal processing in order to ensure sufficient 

22 destruction of Salmonella spp. and Escherichia coli O157:H7. However, processors have 

23 had difficulty either complying with USDA guidance or developing and validating 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 adequate alternative processes while still obtaining desired finished product 

2 characteristics. Previously suggested techniques for ensuring adequate lethality included 

3 boiling beef strips in marinade prior to cooking and drying, and oven-heating beef jerky 

4 strips after drying (9, 10). Commercial processors have not widely adopted these 

5 methods, either because of perceived adverse effects on product sensory characteristics or 

6 because of economic or efficiency concerns. Development of validated heating/drying 

7 guidelines for processors of whole-muscle jerky has been further complicated by 

8 variables such as thickness of jerky strips, whether the strips have been marinated and, if 

9 so, the composition and conditions of marination, the type of smokehouse or oven used 

10 for heating/drying, and the weather and altitude at the processing plant. 

11 Presently, the USDA has indicated that a jerky-making process has sufficient 

12 lethality if it results in a 5-log reduction of Salmonella spp. (written communication from 

13 Dr. Paul Uhler, USDA – FSIS, 2005). Furthermore, USDA officials have stated that the 

14 lethality of non-thermal steps in jerky-making, such as marination, can be counted toward 

15 meeting the overall process lethality requirement (Dan Englejohn, USDA – FSIS, 

16 personal communication, 2005). Pre-existing USDA guidance for certain other beef 

17 products specified a 6.5 log reduction in Salmonella spp. (15). The newer 5-log 

18 reduction standard resulted from a USDA draft risk assessment of the impact of different 

19 lethality standards for ready-to-eat meat and poultry products on the incidence of 

20 salmonellosis (13). This risk assessment determined that decreasing the pathogen 

21 reduction standard from 6.5 logs to 5 logs for products such as jerky that do not support 

22 the growth of salmonellae, would have little effect on the incidence of salmonellosis. 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 The first objective of this study was to develop and validate sufficiently lethal 

2 processes for use by commercial jerky manufacturers in heating and drying whole-muscle 

3 beef jerky. In working towards this objective, marination and beef strip thickness were 

4 standardized based on typical industry practice. A standardized smokehouse loading 

5 procedure was used, and ambient weather conditions were noted. 

6 A second objective of this work was to develop a simple method for commercial 

7 processors of whole-muscle beef jerky to evaluate the lethality of new processes. 

8 Because in-plant challenge studies involving pathogenic bacteria are not recommended 

9 for commercial meat processing establishments for safety reasons, and because 

10 laboratory-based challenge studies are neither practical nor affordable for most 

11 processors, we investigated the use of a commercially available lactic acid bacterial 

12 starter culture as a surrogate for Salmonella serovars and E. coli O157:H7. 

13 

14 MATERIALS AND METHODS 

15 Preparation of inoculum. Five-strain cocktails of Salmonella serovars and E. 

16 coli O157:H7 were used to inoculate beef strips prior to jerky processing. E. coli 

17 O157:H7 strains ATCC 43894, 51657, and 51658 were clinical isolates and strain ATCC 

18 43895 was originally from ground beef implicated in an outbreak of food-borne illness; 

19 each of these strains was obtained from the American Type Culture Collection 

20 (Manassas, VA). Strain USDA-FSIS-380-94 was originally from salami implicated in an 

21 illness outbreak and was obtained from the laboratory of Dr. John Luchansky at the Food 

22 Research Institute, University of Wisconsin-Madison. The Salmonella serovars were all 

23 obtained from the laboratory of Dr. Eric Johnson at the Food Research Institute, 

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1 University of Wisconsin-Madison. To obtain a working culture, each strain was cultured 

2 twice successively (from a previously frozen culture) at 35oC for 18-24 hours in Brain 

3 Heart Infusion Broth (BHIB; Difco, Becton-Dickenson, Sparks, MD), streaked to Brain 

4 Heart Infusion Agar (BHIA; Difco), incubated at 35oC for 18-24 hours, examined for 

5 purity, and then stored at 5oC. According to the work of Calicioglu et al. (3 - 5), acid6 adaptation is unlikely to increase pathogen resistance to hurdles involved in beef jerky 

7 processing. Therefore, cultures for inoculation were grown in Brain Heart Infusion broth 

8 (BHIB; Difco, Becton Dickinson, Sparks, MD), a medium containing only a small 

9 amount of glucose that could be metabolized to produce organic acids. To achieve 

10 stationary-phase inoculum cultures, an isolated colony of each strain was transferred from 

11 its working culture plate to 9 mL of BHIB, and incubated at 35oC for 24 hours. To 

12 prepare a 5-strain inoculum cocktail of Salmonella serovars or E. coli O157:H7, the 

13 BHIB culture of each strain was combined into one 50-ml sterile plastic centrifuge tube, 

14 and centrifuged for 12 minutes at 5,000 x g. The supernatant in each tube was decanted 

15 and the pellets were re-suspended with approximately 20 ml of Butterfield’s phosphate 

16 diluent (BPD; Nelson Jameson, Marshfield, WI). A commercial lactic acid bacteria 

17 starter culture, intended for making fermented meat products, was evaluated in several 

18 trials as a surrogate for the pathogens. The starter culture (Formula 100; Trumark, 

19 Linden, NJ) was stored at -20°C. Three different lots of this starter culture were tested 

20 during the study. Preliminary experiments showed that the starter culture was 

21 considerably more thermotolerant than the Salmonella and E. coli O157:H7 strains used, 

22 so a lower inoculum level was used for it. To prepare the starter culture for inoculation 

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1 of beef strips, 0.5 g of culture was added to 99 ml BPD, mixed well, and then diluted 

2 another 100-fold in BPD. 

3 Inoculation of beef strips. Frozen vacuum-packaged beef strips were obtained 

4 from a commercial jerky processor and thawed at 4°C or under running tap water prior to 

5 inoculation. The individual beef strips (5 – 7 mm thick) were placed in a biosafety hood 

6 on aluminum foil that had been previously sanitized with 70% (v/v) ethanol. To 

7 inoculate each strip, 0.4 ml of the undiluted pathogen cocktail or 0.4 ml of the diluted 

8 starter culture was pipetted onto the product surface and distributed as evenly as possible 

9 using a sterile plastic spreader. Aluminum foil was placed over the strips in a tented 

10 manner to minimize the amount of drying during microbial attachment (30 min), after 

11 which strips were turned over and the inoculation/attachment process was repeated on the 

12 other side. For each trial, one group of 9 - 12 beef strips was inoculated with Salmonella 

13 spp., another group of 9 - 12 beef strips was inoculated with E. coli O157:H7, and a third 

14 group of 4 - 6 uninoculated beef strips was used to monitor yield and water activity 

15 throughout thermal processing. In many trials, four additional strips were inoculated with 

16 the starter culture. Initial pathogen levels on inoculated beef strips were approximately 

17 108

 CFU per beef strip and initial starter culture levels were about 104 CFU per beef strip. 

18 Jerky processing. Each group of beef strips was tumbled manually in a closed 

19 zip-lock plastic bag for approximately 5 minutes in a non-acidic (pH 5.3) spice20 containing marinade applied at a level of 15% (w/w; 9.7% water and 5.3% dry 

21 ingredients) intended to result in a pre-processing level of 2% (w/w) sodium chloride, 2% 

22 (w/w) sucrose, and 156 ppm sodium nitrite (w/w) in the meat. Following marination, 

23 strips were held for 22-24 h at 5°C. The next day, strips were arranged on racks placed in 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 the center of a commercial one-truck smokehouse (Model TR2, Vortron, Beloit, WI) for 

2 processing. Pans of water were placed on the lowest rack in the smokehouse and a low 

3 fan speed was used to simulate as much as possible a drying rate consistent with a 

4 smokehouse containing several racks filled with product. The smokehouse dry-bulb and 

5 wet-bulb temperatures were monitored using thermocouples (L#113-1055 P/M, 

6 ThermoWorks, Alpine, UT) and a data logger (Model 92000-00, Barnant Co., 

7 Barrington, IL). Percent relative humidity (%RH) was calculated from the wet-bulb and 

8 dry-bulb temperatures using a slide rule (Alkar, Lodi, WI). In all trials, the product9 internal temperature was measured by inserting a thermocouple probe into the geometric 

10 center of a beef strip. Because insertion of the probe in this location is relatively difficult, 

11 a surrogate product-internal temperature was also obtained by tightly folding a beef strip 

12 once over a thermocouple probe in the majority of the trials. The latter temperature 

13 measurement method is considerably easier, but it was not known at first whether it could 

14 be considered an accurate surrogate for internal beef strip temperature. Smoke was not 

15 applied to the beef strips during processing. Several types of heating/drying processes 

16 were tested (summarized in Table 1). In Type 1-A processes, the dry-bulb temperature 

17 controller was set at 62.8°C (145°F) in the first 15 minutes and then at 76.7°C (170°F) 

18 during the next 15 minutes, with no added humidity. This two-step increase in dry-bulb 

19 temperature was done to simulate the beginning stages of heating a full smokehouse of 

20 moist, ambient-temperature beef strips. Next, humidity (steam or water) was introduced 

21 into the smokehouse via the wet-bulb temperature controller to obtain targeted increases 

22 in wet-bulb temperatures, referred to as “wet-bulb spikes”. The process lethality was 

23 determined for a series of trials conducted using early-process wet-bulb spikes of 51.7°C 

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1 (125°F) for 60 min, 54.4°C (130°F) for 60 min., 57.2°C (135°F) for 30 min., and 60°C 

2 (140°F) for 10 min. Following completion of wet-bulb spikes, no further humidity was 

3 introduced into the smokehouse chamber as the product was further dried at a dry-bulb 

4 temperature of 76.7°C (170°F). To investigate the possible protective or lethal effects of 

5 marinade ingredients, a selected Type 1 process (wet bulb spike of 54.4°C for 60 

6 minutes) was done to products that were marinated either only in water (9.7% initial 

7 product weight gain) or only in the dry ingredients (5.3% initial product weight gain). In 

8 four trials, a Type 1-B process was used (wet-bulb spike of 54.4°C for 60 minutes) in 

9 which the dry-bulb temperature was held at either 65.5°C (150°F) or 87.8°C (190°F) 

10 throughout a 15-minute equilibration period before the wet-bulb spike, the wet-bulb spike 

11 itself, and final drying. Type 2 and Type 3 processes involved rapid (15 minutes) and 

12 slow (90 minutes) increases in dry-bulb temperature to 76.7 °C (170°F) followed by final 

13 drying at a dry-bulb temperature of 76.7°C (170°F). In Type 4 processes, the dry-bulb 

14 temperature was held constant at 51.7°C (125°F) until a desired approximate jerky water 

15 activity was attained, whereupon the dry-bulb temperature was increased to 76.7°C 

16 (170°F) for final drying (no humidity added during the process). In Type 5 processes, the 

17 dry-bulb temperature was held constant at 60, 71.1, or 82.2°C (140, 160, or 180°F) and 

18 no attempt was made to control wet-bulb temperature. Type 6 and 7 processes both 

19 involved sequential 1 hour exposures to dry-bulb temperatures of 48.9, 54.4, and 60°C 

20 (120, 130, and 140°F); in the Type 7 process beef strips were exposed an additional hour 

21 to a dry-bulb temperature of 76.7°C (170°F). In addition to trials in the commercial-scale 

22 smokehouse, a consumer-scale smokehouse (Pragotrade Model TS160, Cabela’s, Sidney, 

23 NE) was used for additional trials testing the relationship between thermally induced 

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1 death of the starter culture surrogate and inoculated pathogens (“consumer-type 

2 process”). Inoculated and uninoculated beef strips were placed on two racks in this 

3 smokehouse, two large (15 cm diameter) Petri dishes containing water were placed on the 

4 floor of the smokehouse, and the dry-bulb temperature was set at either 60 or 70.1°C (140 

5 or 160°F). These trials were done to compare pathogen and starter culture surrogate 

6 survival over a broad range of conditions. In all trials, uninoculated strips were evaluated 

7 at the intermediate sampling point for water activity (measured on-site using an AquaLab 

8 Series 3TE water activity meter, Decagon Devices, Inc., Pullman, WA). In all trials, 

9 additional uninoculated finished beef jerky strips were sent to a commercial testing 

10 laboratory for pH, water activity, % water (forced air oven method, AOAC method 

11 950.46Bb), % protein (Kjeldahl method, AOAC method 991.20.I), and % salt 

12 (potentiometric method, AOAC method 980.25). From these analyses, Moisture: Protein 

13 ratio (MPR), and % water-phase salt values were calculated. 

14 

15 Enumeration of inoculum organisms. The numbers of Salmonella spp. and E. 

16 coli O157:H7 on beef strips were determined prior to marination, after marination (in 21 

17 trials), after the early-process wet-bulb spike in the smokehouse (Type 1 process) or some 

18 other intermediate time (other process types), and following drying when the beef strips 

19 had reached a yield level predetermined to correlate with an average water activity of < 

20 0.90. One beef strip comprised a sample and three samples were analyzed for pathogen 

21 numbers at each sampling time. In several trials, two strips each were analyzed for 

22 starter culture numbers after inoculation and at the end of drying. Each sample was 

23 placed in a whirl pak filter bag (Nasco, Fort Atkinson, WI), BPD (99 ml) was added, and 

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1 the bag contents were stomached for 2 minutes at medium speed (Stomacher 400 

2 Circulator lab blender; Seward) or samples were manually massaged for 1 minute and 

3 shaken for 1 minute. This initial dilution was arbitrarily defined as 10-1. Serial decimal 

4 dilutions were made in BPD as needed. From the initial dilution, 1.0 ml was distributed 

5 for spread-plating among three plates of BHIA. From the original dilution and each 

6 subsequent dilution 0.1 ml was spread on one BHIA plate per dilution. Plates were 

7 incubated at 35°C for 1 h to allow for repair of injured cells, and then overlaid with 

8 MacConkey Sorbitol agar (SMAC; Difco), XLD agar (Difco), or mEnterococcus agar 

9 (mE; Difco) for selective/differential enumeration of E. coli O157:H7, Salmonella 

10 serovars, and starter culture surrogate, respectively. After 20-24 h (E. coli O157:H7, 

11 Salmonella serovars) or 72 h (starter culture surrogate) incubation at 35°C, plates were 

12 examined for typical colonies. For each sampling time, one presumptive colony each of 

13 E. coli O157:H7 and Salmonella was transferred to BHIA, incubated at 35°C for 20-24 h, 

14 and then tested to confirm colony identity. A single plate containing presumptive starter 

15 culture colonies was retained for confirmation tests at each sampling time. Confirmation 

16 tests for the presumptive pathogens were Gram reaction, cellular morphology, oxidase 

17 activity, and biochemical characteristics (API 20E kit, bioMerieux, Hazelwood, MO) for 

18 the pathogens, with an additional O157 latex agglutination test (Oxoid, Ogdensburg, NY) 

19 done to confirm E. coli O157:H7 isolates. Presumptive starter culture surrogate colonies 

20 were evaluated for Gram reaction, cellular morphology, and catalase activity. The log 

21 CFU for a given inoculum organism was calculated for each sample with a mean log 

22 CFU calculated for each sampling time. A value of 9 CFU (0.95 log CFU) was assigned 

23 when no colonies were present for the least dilute plating. 

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1 Weather data. Because outdoor weather conditions, particularly temperature and 

2 relative humidity, were believed to have a potentially important effect on jerky 

3 processing lethality, the dewpoint at noon in Madison, WI, on the day of each trial was 

4 obtained from meteorological archives 

5 (http://www.channel3000.com/weather/index.html). 

6 

7 

8 RESULTS AND DISCUSSION 

9 Finished jerky made in the present study had a pH of 5.6 – 6.1, with 22 of 30 samples 

10 having pH of 5.7 – 5.9. The water activity, MPR, and % water-phase salt varied widely, 

11 as expected, given the range of heating and drying conditions evaluated. When the 

12 normal marination and a Type 1 process were used, the ranges of finished product water 

13 activity, MPR, and % water-phase salt were 0.78 - 0.93, 0.52 – 0.95, and 7.9 – 16.6, 

14 respectively. In contrast, the Type 1 product made with no spices had water activity, 

15 MPR, and % water-phase salt of 0.94 – 0.96, 0.63 – 0.65, and 0.60 – 0.70, respectively. 

16 Type 1 product marinated only with spices had a water activity, MPR, and % water-phase 

17 salt of 0.86 – 0.87, 0.67- 0.68, and 11.1 – 11.5, respectively. Products made using the 

18 normal marination procedure and any of the Type 2 - 7 processes had compositional 

19 values similar to those for Type 1 processes with the exception of product from one Type 

20 2 and three Type 3 processes that had water activity, MPR, and % water-phase salt ranges 

21 of 0.64 – 0.75, 0.41 – 0.66, and 11.2 – 17.1, respectively. It should be noted that in many 

22 trials achieving sufficient lethality, the finished product water activity and MPR were 

23 higher (and the % water-phase salt was lower) than desired for optimum consumer 

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1 acceptance and required in USDA labeling standards (12). However, processors using 

2 the same heating/drying processes could simply extend the drying period to obtain 

3 desired product characteristics. This extended drying would have no adverse effect on 

4 lethality and might, in some situations, increase it. 

5 In 21 trials, pathogen numbers were determined following the 22-24-hour post6 marination refrigerated storage step. Numbers of Salmonella serovars and E. coli 

7 O157:H7 fell by 0.04 – 0.43 and 0.04 – 0.34 log CFU, respectively. We concluded that 

8 this marination step had little lethality, and discontinued post-marination sampling. 

9 Throughout the study, consistent trends in dry-bulb, wet-bulb, product-internal, 

10 and surrogate product-internal (beef strip folded over probe) temperatures were observed. 

11 As shown for a typical Type 1 process (Figure 1), wet-bulb temperature was initially well 

12 below dry-bulb temperature. Product-internal temperature was always similar to the wet13 bulb temperature early in the process and could effectively serve as an estimate of wet14 bulb temperature until later in the process. At some time, though, evaporative cooling of 

15 the strips diminished and the product-internal temperature rose toward the dry-bulb 

16 temperature. It is important to note that throughout the jerky heating/drying process, 

17 product-internal temperature was always close to (within 1°C) or higher than the chamber 

18 wet-bulb temperature. Thus, maintaining the chamber wet-bulb temperature (and thereby 

19 the product temperature) high enough to cause pathogen destruction (ca. 51.7°C/125°F 

20 and higher) can strongly influence process lethality. Early in the heating/drying process, 

21 the surrogate product-internal temperature, measured with a jerky strip folded over the 

22 thermocouple, was often lower than the product-internal temperature because the applied 

23 heat had to pass through twice the thickness of meat in the folded strip. Later in the 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 process, the surrogate product-internal temperature rose above the product-internal 

2 temperature, presumably because the greater meat thickness with the folded strip 

3 diminished evaporative cooling near the thermocouple. By the end of the process, when 

4 little evaporative cooling still was occurring, the two temperatures were the same. The 

5 divergence of the two temperatures by a variable amount during much of the process calls 

6 into question the practice of using the surrogate product-internal temperature for overall 

7 process control or evaluation. However, the surrogate product-internal temperature was 

8 very close to the product-internal temperature early in processing and during the wet-bulb 

9 temperature spikes in Type 1 processes, and could be useful in early-process control or 

10 evaluation. 

11 Earlier research has established the fact that sub-lethal drying can make pathogens 

12 such as Salmonella serovars more resistant to heat (7). This phenomenon was likewise 

13 observed in several early jerky-making trials (data not shown). Therefore, several early14 process wet-bulb temperature spikes were applied to determine the extent of elevated15 humidity heating conditions necessary to achieve desired lethality while maintaining 

16 product quality (Table 2). During the 54.4, 57.2, and 60°C (130, 135, and 140°F) wet17 bulb spikes with concurrent 76.7°C (170°F) dry-bulb temperature, the product-internal 

18 temperature was generally quite similar to the wet-bulb temperature. However, during 

19 the 54.4°C (130°F) wet-bulb spike with a concurrent 87.8°C (190°F) dry-bulb 

20 temperature, the product-internal temperature rose faster than it did during the wet-bulb 

21 spike treatments conducted with 76.7°C (170°F) dry-bulb temperature, and the product22 internal temperature reached at least 5°C higher (Figure 2) than in the latter process 

23 (Figure 1). This more rapid increase in product temperature resulted from faster jerky 

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1 drying at the lower %RH under 87.8°C (190°F) dry-bulb/54.4°C (130°F) wet-bulb 

2 temperature conditions (see % RH values in Table 2). Similarly, when a wet-bulb 

3 temperature spike of 51.7°C (125°F) was applied concurrently with 76.7°C (170°F) dry4 bulb temperature, the %RH was lower than under 54.4°C (130°F) wet-bulb/76.7°C 

5 (170°F) temperature conditions. This lower %RH led to a faster increase in product6 internal temperature and a more rapid achievement of a > 5.0 log reduction in 

7 salmonellae numbers (see first four lines of Table 2). 

8 Presently, the USDA has indicated that a jerky-making process has sufficient 

9 lethality if it results in a 5-log reduction of Salmonella serovars. However, USDA 

10 guidance for certain other beef products specified a 6.5 log reduction in Salmonella 

11 serovars. All tested Type 1 processes (early-process wet-bulb temperature spike 

12 following the standard marination process) resulted in a > 6.4 log reduction in both 

13 pathogens by the end of the complete process (including final drying; Table 2). Three 

14 Type 1 processes achieved a > 5.2 log reduction in Salmonella serovars but caused 

15 smaller decreases in E. coli O157:H7 numbers at the end of the wet-bulb temperature 

16 spike (Table 1). These treatments were 51.7°C (125°F) for 60 min, 57.2°C (135°F) for 

17 30 min, and 60°C (140°F) for 10 min. However, a > 6.4 log reduction of both Salmonella 

18 serovars and E. coli O157:H7 was achieved by the end of drying after each of these 

19 processes. One Type 1 process did not cause a > 5.0 log reduction in either pathogen by 

20 the end of the web-bulb spike but subsequent drying resulted in sufficient overall 

21 lethality. This treatment, wet-bulb temperature of 54.4°C (130°F) for 60 minutes, 

22 resulted in decreases of 3.2 – 3.9 and 2.0 – 2.1 log CFU for Salmonella serovars and E. 

23 coli O157:H7, respectively. By the end of drying after these treatments, reductions of > 

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1 6.9 logs had occurred for both pathogen species. The overall effectiveness of these Type 

2 1 processes appeared to result from the fact that product temperature was controllable via 

3 control of wet-bulb temperature and was increased rapidly to levels at which pathogens 

4 were killed while the beef strips were still moist enough to achieve high lethality. It is of 

5 interest to note that the time for which the wet-bulb temperature was elevated, i.e. the 

6 duration of the wet-bulb temperature spike, was generally shorter than the corresponding 

7 times for the same wet-bulb temperatures listed in USDA guidance (15) for the cooking 

8 of beef. The latter times were 112 minutes at 54.4°C (130°F), 36 minutes at 57.2°C 

9 (135°F), and 12 minutes at 60°C (140°F). By comparison, times used in the present 

10 study were 60, 30, and 10 minutes, respectively. 

11 The dry-bulb temperature during a Type 1 process was found to have a major 

12 effect on process lethality. The application of a wet-bulb temperature spike of 54.4°C 

13 (130°F) for 60 minutes with a concurrent dry-bulb temperature of 65.5C (150°F; Figure 

14 3) reduced Salmonella serovar populations by 4.9 – 5.0 log CFU, but only resulted in 3.2 

15 – 3.6 log reductions in numbers of E. coli O157:7 (Table 2) without further drying. 

16 Subsequent drying at 65.5°C (150°F), however, did lead to overall > 6.7 log CFU 

17 reductions for both pathogens. These final-sampling results were not noticeably different 

18 than results obtained with the same wet-bulb temperature applied with a concurrent dry19 bulb temperature of 76.7°C (170°F), perhaps because pathogen populations following 

20 both types of process had fallen below the detection limit. When the concurrent dry-bulb 

21 temperature was increased to 87.8°C (190°F), though, the wet-bulb temperature spike 

22 caused a > 6.5 log CFU reduction of both pathogens before final drying was even begun 

23 (Table 2). 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to 16 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 Although USDA guidance (14) recommended 90% relative humidity (RH) during 

2 the early heating period in jerky processing, it also stated that such a high humidity may 

3 not be necessary if alternative procedures are validated. In the Type 1-A processes 

4 conducted here using a dry-bulb temperature of 76.7°C (170°F), the calculated RH for 

5 early-process wet-bulb temperature spikes was 27 - 43% RH. When followed by drying 

6 at 76.7°C (170°F), these processes were sufficient to provide > 6.4 log reduction in 

7 numbers of Salmonella serovars and E. coli O157:H7. Taking into account current USDA 

8 expectations for jerky processing lethality, processors using the Type 1 process 

9 conditions employed in this study [achieving 76.7°C (170°F) dry-bulb temperature within 

10 30 minutes and maintaining this temperature throughout processing] could employ any of 

11 the early-process wet-bulb spike treatments listed in Table 1 followed by drying at 

12 76.7°C (170°F) as scientifically validated processes for making safe whole-muscle beef 

13 jerky. 

14 Lethality was compared for several different Type 1 processes at a 

15 common wet-bulb temperature spike time of 60 minutes. The relevant processes were 

16 51.7°C (125°F) or 54.4°C (130°F) wet-bulb temperature spikes with concurrent 76.7°C 

17 (170°F) dry-bulb temperature, and 54.4°C (130°F) wet-bulb temperature spikes with 

18 65.5°C (150°F) or 87.8°C (190°F) dry-bulb temperatures. The 60-minute lethality for 

19 Salmonella serovars for these processes averaged 5.4, 3.5, 4.9, and 6.6 logs, respectively 

20 (Table 2). Corresponding values for E. coli O157:H7 were 4.7, 2.1, 3.4, and 7.1 logs, 

21 respectively. The reason for the highest lethality during the 51.7°C (125°F) wet-bulb 

22 spike (76.7°C dry-bulb temperature) and the 54.4°C (130°F) wet-bulb temperature spike 

23 with 87.8°C dry-bulb temperature (Figure 2) is that both these processes resulted in a 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to 17 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 lower environmental relative humidity, and a more rapid increase in product temperature 

2 to lethal levels early in the process while there was still sufficient product moisture for 

3 enhanced lethality. 

4 Separate trials were conducted with a Type 1-A process to evaluate the relative 

5 importance of the marinade components in achieving desired process lethality. Results 

6 showed that omission of either water or dry ingredients from the marinade led to 

7 somewhat greater reductions in pathogen numbers after a 54.4°C (130°F)/60 minute wet8 bulb temperature spike (Table 2) but comparable lethality after the subsequent drying. 

9 Whole-muscle beef jerky prepared without the addition of salt, however, had a much 

10 higher water activity when trials were completed. We concluded that the choice of water 

11 level in the jerky marinade used in this study (and hence the amount of marinade pick-up) 

12 or the addition of only dry marinade ingredients was not a critical factor in attaining 

13 desired process lethality. 

14 The Type 2 process involving a rapid (15 min) increase in dry-bulb temperature to 

15 76.7°C (170°F) achieved greater pathogen destruction than the Type 3 process in which 

16 dry-bulb temperature did not increase to 76.7°C (170°F) until after 90 minutes (Table 3). 

17 However, both of these processes did result in pathogen reductions exceeding 5.0 log 

18 CFU after drying was completed. An alternative approach that some processors may 

19 elect to use is to initially heat beef strips at the relatively moderate dry-bulb temperature 

20 of 51.7°C (125°F) for a short period of time followed by heating/drying of the strips at a 

21 the relatively high dry-bulb temperature of 76.7°C (170°F). The rationale for this 

22 approach (Type 4 process) is that the short initial heating imparts desirable product 

23 characteristics without increasing pathogen thermotolerance via sublethal stress. As seen 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to 18 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 in Table 4, the success of a Type 4 process depends on beginning the high-temperature 

2 drying when the product water activity is still relatively high. When drying was begun at 

3 a product water activity of 0.72 or 0.81, the reduction in Salmonella serovars was 4.7 log 

4 CFU. Reductions in numbers of E. coli O157:H7 in these trials were 5.4 log CFU, 

5 however. When drying was begun at product water activity of 0.86, 0.87, 0.95, or 0.96, 

6 the reduction in both pathogens was 4.9 – 6.7 log CFU. Although such a process clearly 

7 provided less of a safety margin than using a Type 1 process (wet-bulb temperature 

8 spike), it is likely that short-term heating at a low dry-bulb temperature such as 51.7°C 

9 followed by 76.7°C (dry-bulb temperature) drying could achieve sufficient lethality if the 

10 drying is begun when product water activity is > 0.86. 

11 Heating whole-muscle beef strips at a constant dry-bulb temperature of either 60 

12 or 71.1°C (140 or 160°F) without the addition of humidity (Type 5 processes) did not 

13 achieve USDA-mandated lethality even when product was dried to water activity levels 

14 typical of commercial beef jerky (Table 5). These processes resulted in decreases in 

15 Salmonella serovars and E. coli O157:H7 of 3.8 – 4.7 and 3.9 – 4.0 logs, respectively. 

16 Heating at a constant dry-bulb temperature of 82.2°C (180°F) did result in a reduction of 

17 just over 5 log CFU for both pathogens. The cause of the lower lethality in Type 5 

18 processes can be induced from Figure 4. As can be seen, the wet-bulb temperature and 

19 product-internal temperature remained at sub-lethal levels for long periods of time, 

20 allowing pathogen survival during the drying that took place. The surviving cells 

21 apparently had enhanced thermotolerance during subsequent heating, as previously 

22 described (7). Three Type 5 process trials were conducted on winter days with very low 

23 noon dewpoint temperatures (-11, -12, -14°C) and one trial (60°C/140°F dry-bulb 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to 19 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 temperature) was done in mid-July (noon dewpoint temperature of 20°C). Although it is 

2 possible that using a constant dry-bulb temperature process could attain more lethality 

3 than in the present study if it was employed in very humid weather, we observed no clear 

4 relationship between outdoor dew point and process lethality. We may have mitigated 

5 any weather effects, though, by adjusting process drying times to attain an acceptable 

6 reduction in water activity. Furthermore, our trials were conducted in a climate7 controlled building. Processors with a lower degree of humidity control may need to 

8 adjust process parameters to account for weather extremes. 

9 The Type 6 process that had a slow increase in dry-bulb temperature to a 

10 maximum of 60°C (140°F) did not cause more than a 3 log CFU reduction in pathogens. 

11 In contrast, the Type 7 process which had final 1-hour exposure to dry-bulb temperature 

12 of 76.7°C (170°F) caused > 5 log CFU decreases in pathogen numbers (Table 3). 

13 The starter culture tested in 19 trials as a pathogen surrogate survived the jerky14 making process considerably better than either of the tested pathogens (Table 6). When 

15 the starter culture population was reduced by at least 3.0 log CFU (nine trials), the 

16 populations of both pathogens decreased by at least 5.0 log CFU in eight of the trials. In 

17 the one exception, the E. coli O157:H7 population decreased by 5.0 log CFU and the 

18 population of Salmonella serovars was reduced by 4.7 log CFU. In contrast, when the 

19 starter culture population was reduced by < 3.0 log CFU (10 trials), pathogen populations 

20 were considerably less likely to decrease by at least 5.0 log CFU. Salmonella serovar and 

21 E. coli O157:H7 levels decreased by < 5.0 log CFU in four and three of these trials, 

22 respectively. We conclude that use of this starter culture surrogate with a target lethality 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to 20 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 of at least 3.0 log CFU could be a useful tool for processors validating their whole2 muscle beef jerky processes. 

3 On the basis of our results, we conclude that of the two pathogens studied, E. coli 

4 O157:H7 is better able to survive the heating and drying steps used in making whole5 muscle beef jerky. However, foodborne illness outbreaks linked to beef jerky have 

6 primarily involved Salmonella serovars, so it is prudent for any validation of a jerky7 making process to involve both pathogens. Because our results clearly show the 

8 importance of wet-bulb temperature in achieving mandated lethality, we strongly 

9 recommend that processors buy or make a wet-bulb thermometer for use in processing, or 

10 use a hygrometer to monitor humidity and then use a commercially available slide rule to 

11 determine wet-bulb temperature from known dry-bulb temperature and %RH values. 

12 Reductions in Salmonella serovars and E. coli O157:H7 of > 5.0 log CFU can be 

13 achieved in the production of whole-muscle beef jerky by ensuring that high enough wet14 bulb temperatures are reached and maintained early in the process (Type 1 processes) or 

15 that high dry-bulb temperature heating and drying is done before the beef strip water 

16 activity has fallen below 0.86 (Type 2, 3, 4, and 7 processes). Alternatively, guidance 

17 from USDA (14) has indicated that internal temperatures listed in USDA-accepted 

18 “Appendix A” time/temperature combinations (15) are effectively wet-bulb temperatures. 

19 Processors could consider a process valid in which the smokehouse wet-bulb temperature 

20 and, therefore the product-internal temperature, was at or above a designated level for a 

21 time at least as long as specified in Appendix A. 

22 

23 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to 21 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 ACKNOWLEDGEMENTS 

2 The authors gratefully acknowledge the laboratory assistance of Ryan Algino, Greg 

3 Burnham, Rebecca Engel, Melody Fanslau, Amy Haen, Erica Ready, Erica Schoeller, 

4 and Melissa Talbot. The authors also acknowledge the smokehouse assistance of Ruben 

5 Zarraga. This work was supported by a grant from the United States Department of 

6 Agriculture, Food Safety & Inspection Service. 

7 

8 

9 

10 REFERENCES 

11 1. Blankenship, L.C., C.E. Davis, and G.J. Magner. 1980. Cooking methods for 

12 elimination of Salmonella typhimurium experimental surface contaminant from 

13 rare dry-roasted beef roasts. J. Food Science 45: 270-273. 

14 2. Blankenship, L.C. 1978. Survival of Salmonella typhimurium experimental 

15 contaminant during cooking of beef roasts. Appl. Environ. Microbiol. 35: 1160­

16 1165. 

17 3. Calicioglu, M., J.N. Sofos, J. Samelis, P.A. Kendall, and G.C. Smith. 2003. 

18 Effect of acid adaptation on inactivation of Salmonella during drying and storage 

19 of beef jerky treated with marinades. Int. J. Food Microbiol. 89: 51-65. 

20 4. Calicioglu, M., J.N. Sofos, J. Samelis, P.A. Kendall, and G.C. Smith. 2002a. 

21 Inactivation of acid-adapted and nonadapted Escherichia coli O157:H7 during 

22 drying and storage of beef jerky treated with different marinades. J. Food Prot. 

23 65: 1394-1405. 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to 22 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 5. Calicioglu, M., J.N. Sofos, J. Samelis, P.A. Kendall, and G.C. Smith. 2002b. 

2 Destruction of acid-and non-adapted Listeria monocytogenes during drying and 

3 storage of beef jerky. Food Microbiol. 19: 545-559. 

4 6. Eidson, M., C.M. Sewell, G. Graves, and R. Olson. 2000. Beef jerky 

5 gastroenteritis outbreaks. J. Environ. Health 62: 9-13. 

6 7. Goepfert, J.M., I.K. Iskander, and C.H. Amundson. 1970. Relation of the heat 

7 resistance of salmonellae to the water activity of the environment. Appl. 

8 Microbiol. 19: 429-433. 

9 8. Goodfellow, S.J. and W.L. Brown. 1978. Fate of Salmonella inoculated into beef 

10 for cooking. J. Food Prot. 41: 598-605. 

11 9. Harrison, J.A., M.A. Harrison, R.A. Rose-Morrow, and R.L. Shewfelt. 2001. 

12 Home-style beef jerky: effect of four preparation methods on consumer 

13 acceptability and pathogen inactivation. J. Food Prot. 64: 1194-1198. 

14 10. Nummer, B.A., J.A. Harrison, M.A. Harrison, P. Kendall, J.N. Sofos, and E.L. 

15 Andress. 2004. Effects of preparation methods on the microbiological safety of 

16 home-dried meat jerky. J. Food Prot. 67: 2337-2341. 

17 11. ProMED-mail. 2003. Salmonalla Kiambu, beef jerky – USA (New Mexico). 

18 International Society for Infectious Diseases. Archive no. 20031001.2471. 

19 Available at http://www.promedmail.org. Accessed 21 July 2005. 

20 12. United States Department of Agriculture, Food Safety & Inspection Service. 

21 2005a. Food Standards and Labeling Policy Book. Available at 

22 http://www.fsis.usda.gov/OPPDE/larc/Policies/Labeling_Policy_Book_082005.pd 

23 f. Accessed 11 November 2005. 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to 23 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 13. United States Department of Agriculture, Food Safety & Inspection Service. 

2 2005b. Risk assessment of the impact of lethality standards on salmonellosis 

3 from ready-to-eat meat and poultry products; draft for public review and 

4 comment. 

5 http://www.fsis.usda.gov/PDF/Risk_Assessment_RTE_Salm_Leth_Main.pdf 

6 accessed 21 July 2005 

7 14. United States Department of Agriculture, Food Safety & Inspection Service. 

8 2004. Compliance guideline for meat and poultry jerky produced by small and 

9 very small plants. 

10 http://www.fsis.usda.gov/PDF/Compliance_Guideline_Jerky.pdf. Accessed 4 

11 May 2005. 

12 15. United States Department of Agriculture Food Safety and Inspection Service. 

13 1999. Compliance guidelines for meeting lethality performance standards for 

14 certain meat and poultry products, Appendix A. Available at: 

15 http://www.fsis.usda.gov/oa/fr/95033f-a.htm. Accessed 24 May 2005. 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to 24 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 

2 FIGURE LEGENDS 

3 1. Wet-bulb, dry-bulb, and product-internal temperatures during the manufacture of 

4 whole-muscle beef jerky by a Type 1-A process with a 54.4°C / 130°F, 60-minute 

5 wet-bulb temperature spike. 

6 2. Wet-bulb, dry-bulb, and product-internal temperatures during the manufacture of 

7 whole-muscle beef jerky by a Type 1-B process with a dry-bulb temperature 

8 setting of 87.8°C / 190°F. 

9 3. Wet-bulb, dry-bulb, and product-internal temperatures during the manufacture of 

10 whole-muscle beef jerky by a Type 1-B process with a dry-bulb temperature 

11 setting of 65.5°C / 150°F. 

12 4. Wet-bulb, dry-bulb, and product-internal temperatures during the manufacture of 

13 whole-muscle beef jerky by a Type 5 process with a dry-bulb temperature setting 

14 of 60.0°C / 140°F. 

15 

16 

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Journal of Food Protection 11 November 2005 
1 

2 3 4 5 6 7 8 9 

10 11 12 13 14 15 16 17 18 19 20 21 

Table 1. Summary of heating/drying processes used to make whole-muscle beef jerky. Process Dry-Bulb (Controlled) Wet-Bulb (Controlled) Type Temperature (°C/°F) Time (min) Temperature (°C/°F) Time (min) 1-A 62.8 / 145 15 Not Controlled = NC --- 

76.7 / 170 15 NC --- 

then 76.7 / 170 60 51.7 / 125 60 OR 76.7 / 170 60 54.4 / 130 60 OR 76.7 / 170 30 57.2 / 135 30 OR 76.7 / 170 10 60 / 140 10 

Always followed by 76.7 / 170 varied (to targeted NC ----  final product dryness) 1 – B 62.8 / 145 15 NC --- 

then 65.5 / 150 15 NC 

65.5 / 150 60 54.4 / 130 60 65.5 / 150 varied (to targeted NC --- 

 final product dryness) 

OR 87.8 / 190 15 NC 

87.8 / 190 60 54.4 / 130 60 87.8 / 190 varied (to targeted NC ---- 
Lethality of Commercial Beef Jerky Manufacturing Processes 

1 final product dryness) 2 3 2 62.8 / 145 15 NC --- 4 76.7 / 170 varied (to targeted NC --- 5 final product dryness) 6 7 3 62.8 / 145 90 NC --- 8 76.7 / 170 varied (to targeted NC --- 9 final product dryness) 

10 11 4 51.7 / 125 varied (to targeted aw) NC --- 12 76.7 / 170 varied (to targeted NC --- 

13 final product dryness) 14 15 5 60 / 140 varied (to targeted NC ---- 

16 final product dryness) 17 OR 71.1 / 160 varied (to targeted NC --- 18 final product dryness) 19 OR 82.2 / 180 varied (to targeted NC --- 20 final product dryness) 21 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 6 48.9 / 120 60 NC --- 2 54.4 / 130 60 NC --- 3 60 / 140 60 NC --- 4 5 7 48.9 / 120 60 NC --- 6 54.4 / 130 60 NC --- 7 60 / 140 60 NC --- 8 76.7 / 170 60 NC --- 9 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 2 Table 2. Process lethalitya against Salmonella serovars (S) and Escherichia coli O157:H7 (EC) during Type 1 - A 

3 (wet-bulb temperature spike = WBS; followed by post-spike drying at 76.7°C = PSD) of whole muscle beef jerky4 5 WBS WBS PSD Lethality as determined after Water activity Product6 Temp. Time %RHb time WBS PSD after tempera

7 (°C) (min) (min) S EC S EC WBS PSD WBS 8 Type 1 – A Strips marinated with water and dry ingredients Dry-bulb temperature at 76.7°C during wet-b

9 51.7 60 27 60 5.6 5.6 6.5 6.7 0.87 0.81 60.5 

10 51.7 60 27 60 5.2 3.8 6.4 7.1 0.89 0.78 56.1 11 54.4 60 32 120 3.2 2.0 6.9 7.1 0.93 0.88 54.4 12 54.4 60 32 120 3.9 2.1 6.9 7.0 0.92 0.87 55.0 13 57.2 30 37 120 6.4 2.7 7.0 7.1 ND 0.86 58.3 14 57.2 30 37 90 5.3 3.1 7.0 7.1 0.93 0.90 57.8 15 60 10 43 120 6.2 3.8 7.0 7.2 0.96 0.90 58.9 16 60 10 43 120 6.7 2.2 6.8 7.0 0.96 0.84 60.0 17 Type 1 – B Dry-bulb temperature at 65.5°C during wet-bulb spike 18 54.4 60 56 90 4.9 3.2 6.7 7.1 0.95 0.85 55.6 19 54.4 60 56 150 5.0 3.6 6.9 6.9 0.97 0.91 55.0 20 Type 1 – B Dry-bulb temperature at 87.8°C during wet-bulb spike 21 54.4 60 19 30 6.7 7.3 7.0 7.4 0.93 0.89 66.7 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 54.4 60 19 45 6.5 6.9 7.2 7.1 0.95 0.89 65.0 2 Type 1 – A Strips marinated only with water Dry-bulb temperature at 76.7°C during wet-b3 54.4 60 32 60 5.6 4.9 6.6 6.9 0.98 0.94 55.6 4 54.4 60 32 60 5.4 4.5 6.1 7.0 0.99 0.96 55.6 5 Type 1 – A Strips marinated only with dry ingredients Dry-bulb temperature at 76.7°C during wet-b6 54.4 60 32 90 5.9 3.9 7.1 7.0 0.95 0.87 57.2 7 54.4 60 32 60 5.6 6.9 6.6 7.1 0.93 0.86 58.9 8 a Reduction in log CFU per sample relative to initial pathogen load prior to marination. 9 b Percent relative humidity during wet-bulb temperature spike calculated from wet-bulb and dry-bulb temperatur

10 slide rule. 11 ND = Not Determined 12 13 14 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 Table 3. Process lethality against Salmonella serovars (S) and Escherichia coli O157:H7 (EC) during the type 4, 2 for heating and drying of whole-muscle beef jerky. Processes were 2 = fast come-up [15 minutes to reach dry-bu

3 76.7°C (170°F), followed by drying at 76.7°C], 3 = slow come-up [90 minutes to reach dry-bulb temperature of 7

4 followed by drying at 76.7°C], 6 = 1 hour each at dry-bulb temperatures of 48.9, 54.4, and 60°C (120, 130, and 1

5 each at dry-bulb temperatures of 48.9, 54.4, 60, and 76.7°C (120, 130, 140, and 170°F). No humidity was added 6 chamber during processing. 7 8 Process Lethality (reduction in log CFU)a and product characteristics at 

9 Intermediate Time End

10 

Product 

– internal 

Product 

11 Treatment RHb (min) S EC c aw Temperature (°C) S EC aw Temper12 2 

31 

- 17 60 3.3 2.7 0.95 

13 2 

27 

- 21 60 2.6 1.8 0.96 

14 3 

41 

- 21 90 2.0 1.5 0.97 

15 6 

41 

- 24 120 1.6 1.7 0.92 

16 7 

43 

- 15 180 3.5 2.5 0.94 

17 18 a Reduction in log CFU per sample relative to initial pathogen load prior to marination. 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 

2005 

48.9 6.1 5.6 0.86 

52.8 6.4 6.4 0.91 

46.7 5.5 5.6 0.87 

40.5 2.9 2.7 0.84 

49.4 6.0 5.6 0.89 
Lethality of Commercial Beef Jerky Manufacturing Processes 

1 b Percent relative humidity, change during process (initial value – final value). Values calculated from wet-bulb a

2 temperatures using a slide rule. 3 c Water activity. 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 2 Table 4. Process lethality against Salmonella serovars (S) and Escherichia coli O157:H7 (EC) during the Type 4 

3 whole-muscle beef jerky at a constant dry-bulb temperature of 51.7°C (125°F) to attain a desired water activity f

4 76.7°C (170°F). No humidity was added to the smokehouse chamber during processing. 5 6 Heating Lethality (reduction in log CFU)a and product characteristics at 

7 Time End of heating End of drying 8 

Product 

- internal Cumul. Time 

9 (min) RHb c aw Temperature (°C) S EC (min) aw 

10 240 ND 0.72 47.2 3.3 3.1 300 0.65 11 240 32 – 33 0.81 42.8 3.3 2.7 300 0.75 12 180 30 - 36 0.86 42.8 3.2 2.2 240 0.67 13 270 ND 0.87 45.6 4.3 2.9 330 0.82 14 120 33 - 38 0.95 37.8 1.8 1.7 240 0.83 15 120 35 - 38 0.96 38.9 2.1 1.9 225 0.82 16 

Product 

- intern

Temperature (°

74.4 

70.0 

68.3 

71.7 

67.8 

70.0 

17 a Reduction in log CFU per sample relative to initial pathogen load prior to marination. 18 b Percent relative humidity, change during process (initial value – final value). Values calculated from wet-bulb 

19 temperatures using a slide rule. 20 c Water activity. 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 

2005 
1 

Lethality of Commercial Beef Jerky Manufacturing Processes ND = Not Determined. Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 2005 
Lethality of Commercial Beef Jerky Manufacturing Processes 

1 Table 5. Process lethality against Salmonella serovars (S) and Escherichia coli O157:H7 (EC) during the Type 5 

2 and drying of whole-muscle beef jerky at a constant dry-bulb temperature of 60, 65.5, or 82.2°C (140, 160, or 18

3 was added to the chamber during processing. 4 5 Dry-Bulb Lethality (reduction in log CFU)a and product characteristics at 

6 Temperature Intermediate Time Final Time 7 

Product 

– internal 

Product 

- intern

c 8 (°C) RHb (min) S EC aw temperature (°C) (min) S EC aw tempera

9 60 32 – 24 90 4.3 3.8 0.73 46.7 120 4.2 3.9 0.64 53.9 

10 60 28 - 26 90 1.9 1.6 0.96 42.2 120 3.8 3.9 0.79 52.8 11 71.1 34 - 18 60 4.0 3.3 0.87 50.6 75 4.7 4.0 0.80 59.4 12 82.2 29 - 15 60 5.2 4.6 0.72 64.4 75 5.1 5.6 0.65 72.2 13 14 a Reduction in log CFU per sample relative to initial pathogen load prior to marination. 15 b Percent relative humidity, change during process (initial value – final value). Values calculated from wet-bulb 

16 temperatures using a slide rule. 17 c Water activity. 

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Lethality of Commercial Beef Jerky Manufacturing Processes 

1 Table 6. Comparison of Salmonella serovar (S), Escherichia coli O157:H7 (EC), and starter culture surrogate (S

2 various processes for making whole-muscle beef jerky. 3 4 Process Lethality (reduction in log CFU)a for Finished Sample 

5 Treatment S EC SC 6 7 8 9 

10 11 12 13 14 15 16 17 18 19 20 21 

Consumer 4.4 2.8 2.5 Consumer 4.2 3.0 1.8 1-A 7.0 7.2 3.5 1-B;87.8°C dry-bulb 7.0 7.4 3.2 1-B; 87.8°C dry-bulb 7.2 7.1 3.2 1-B; 65.5°C dry-bulb 6.7 7.1 3.2 1-B; 65.5°C dry-bulb 6.9 6.9 2.8 1-A; spices only 7.1 7.1 3.3 

1-A; spices only 6.6 7.1 2.8 1-A; water only 6.6 6.9 2.7 1-A; water only 6.1 7.0 3.0 2 6.4 6.4 3.4 2 6.1 5.6 2.3 4 4.7 5.4 2.9 4 5.8 5.0 3.2 4 5.8 6.7 2.8 Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 2005 
Lethality of Commercial Beef Jerky Manufacturing Processes 

1 4 4.7 5.4 3.3 2 5 3.8 3.9 1.9 3 6 6.0 5.6 2.6 4 5 a Reduction in log CFU per sample relative to initial pathogen load prior to marination. 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 2005 
t 

f 

t 

1 

Lethality of Commercial Beef Jerky Manufacturing Processes 

1. 

20304050607080 

Tem perature C 

10 30 50 70 90 110 130 150 170 190 210 

Time 

Dry-Bulb Wet-Bulb Product-Internal 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 11 November 2005 

38 
I • 

---0--

1 

Lethality of Commercial Beef Jerky Manufacturing Processes 

2. 

20 30 40 50 60 70 80 90 

Tem perature C 

10 30 50 70 90 110 

Tim e 

Dry-Bu lb Wet-Bu lb Product-Internal 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 2005 
t 

f 

t 

1 

Lethality of Commercial Beef Jerky Manufacturing Processes 

3.

Tem perature C 204060

80

0 

0 50 100 150 200 

Tim e 

Dry-Bulb Wet-Bulb Product-Internal 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 11 November 2005 

40 
I • 

1 

Lethality of Commercial Beef Jerky Manufacturing Processes 

4. 

80 70 60 50 40 30 20 

Tem perature C 

10 30 50 70 90 110 130 150 170 190 

Tim e 

Dry-B u lb Wet-B u lb P ro duct-Interna l 

Buege et al., Lethality of Commercial Jerky Manufacturing Processes. Submitted to Journal of Food Protection 2005