Preserved through dehydration, jerky is a nutritious shelf-stable product that has been enjoyed for generations. On January 6, 1999, the USDA-FSIS final rule for the implementation of the pathogen reduction performance standards for Salmonella became effective for small and very small meat and poultry processors. Under these rules, establishments producing ready-to-eat beef and poultry products were required to achieve 6.5 and 7.0 log10 reductions, respectively, of Salmonella spp. “Log” stands for logarithm, which is the exponent of 10. A log reduction refers to one decimal reduction or a 90 percent reduction in numbers of recoverable bacteria in food. In other words, a 1.0 log10 reduction reduces the number of bacteria by 90 percent; a 2.0 log10 reduction reduces the number by an additional 90 percent, and so on.
In the fall of 2003, the United States Department of Agriculture’s Food Safety and Inspection Service (FSIS) became concerned that processors were not effectively heat-treating jerky to kill pathogenic bacteria. Numerous jerky producers were only using the moisture-protein-ratio (MPR) to determine if the jerky was adequately dried. Jerky must have an MPR of 0.75:1 to meet the standard of identity for jerky. Standard of identity does not relate to processing a product safely. It ensures that a product contains a specific composition and that the name of the food reflects that composition. It defines what may be in the food and what cannot be in the food using the prescribed name.
The MPR of 0.75:1 does not necessarily verify that the proper water activity (Aw) was attained to control pathogen growth. Water activity measures the amount of available water for microbial growth and should not be confused with the relative humidity of a cooking system. Relative humidity is a measurement of how much moisture is in the air. To prevent pathogen growth after safe processing, jerky should have a water activity <0.85, which can inhibit growth of important bacterial pathogens, including Salmonella spp., Listeria monocytogenes, Staphylococcus aureus, and Escherichia coli O157:H7.
To enable small jerky processors to manufacture a safe product this publication has referenced several sources for determination of an adequate lethality treatment on jerky. During processing, a lethality treatment must be included to control, reduce, or eliminate the biological hazards identified in the processor’s Hazard Analysis and Critical Control Point (HACCP) program. Additionally, FSIS requires processors to heat jerky with humidity prior to dehydrating. Cooking and drying times and temperatures alone are not considered a lethal process. Without humidity the product will dry, and bacteria can become more heat resistant. To produce the required 6.5 log10 reduction of Salmonella in cooked beef products, processors may refer to Appendix A of the Compliance Guidelines for Meeting Lethality Performance Standards for the Production of Certain Meat and Poultry Products (http://www.fsis.usda.gov/OPPDE/rdad/FRPubs/95-033F.pdf). To achieve the 7.0 log10 reduction of Salmonella in cooked poultry products, processors may refer to the recently published Time-Temperature Tables for Cooking Ready-to-Eat Poultry Products (http://www.fsis.usda.gov/OPPDE/rdad/FSISNotices/RTE_Poultry_Tables.pdf).
The important steps that processors should use to prepare jerky that is microbiologically safe are listed below.
1) Strip preparation
- Wash hands thoroughly with soap and hot water for at least 20 seconds before and after handling raw meats.
- Clean work surfaces, avoid cross contamination of raw and cooked meat.
- Use clean equipment and utensils.
- Keep all meat or poultry refrigerated (<40ºF).
- Always thaw frozen meat in the refrigerator, not at room temperature.
- Slice whole muscles or reform ground meat into uniform strips.
- Soak meat in water and selected seasonings of choice.
- Marinate meat in the refrigerator.
- Do not save and reuse marinade.
- Do not combine poultry and beef during marinating.
3) Lethality Step (Required by FSIS)
If the jerky is heated in an adequately humid environment and the internal temperature of the jerky strips reaches the appropriate temperature for the corresponding time, the process would be valid. Regardless of the final internal temperature, adequate humidity should be incorporated during the heating process. If Appendix A in the Compliance Guidelines for Certain Ready-to-Eat Meat and Poultry Products is used, a 90 percent relative humidity must be achieved during the heating stages to an instantaneous internal temperature of 160ºF. The American Association of Meat Processors has compiled several smokehouse schedules in a Special Report Jerky Compliance Guidelines – Compliance vs. Guidance – (http://www.aamp.com/regulatory/documents/ValidatingtheSafetyofYourJerkyProcess.pdf) to help processors comply with these compliance guidelines. Establishments may use alternative lethality processes. FSIS will only accept alternative lethality processes as being valid if they prove to have an effective log reduction through research or supporting documentation. Some examples of these processes are in Table 1.
|Table 1: Research on alternative lethality processes for meat and poultry jerky|
|Ground beef inoculated with L. monocytogenes and S. typhimurium||Cured and heated in mechanical convection oven to 160ºF||No||140ºF for 6 hr in dehydrator||0.69||Salmonella reduced 4.9 logs and Listeria reduced 3.2 logs||Harrison, JA, Harrison, MA, Ruth, AR, 1997|
|Beef jerky strips inoculated with E.coli O157:H7||Heated in dehydrator at 125ºF, 135ºF, 145ºF, 155ºF||No*||10 hr, 9 hr, 7 hr, 4.5 hr in dehydrator||N/m**||All processes produced at least a 5 log unit reduction||Buege, D, 2004|
|Beef loin strips inoculated with E.coli O157:H7, L. monocytogenes and S. typhimurium||Heated in marinade on a hot plate to 160ºF||Yes||140ºF for 10 hr in dehydrator||N/m**||Reduction of 5.0, 5.6 and 5.9 log units for E.coli O157:H7, L. mono. and S.typhimurium, respectively||Harrison, JA, Harrison, MA, 1996|
|Meat and poultry strips and reformed jerky||Heat in 90% relative humidity to 160ºF||Yes||140ºF until acceptable Aw is attained||<0.85 or 0.70 if exposed to air||Salmonella spp. reduced 6.5 –7.0 logs||USDAFSIS, 2004|
|*These studies did not incorporate humidity which is now a necessary part of the lethality step.|
To achieve a 90 percent relative humidity during heating, FSIS suggests the following:
- Close the oven dampers. This provides a closed system and prevents moisture loss.
- Place a wide, shallow pan of hot water in the oven. A high water temperature translates to more humidity being introduced during the heating stage. If no evaporation occurs, this would indicate that a relative high humidity was not maintained in the oven.
- Preheat the jerky to 160°F in the marinade or another solution, such as water, before placing it in the oven. This will provide an immediate reduction of greater than 5 log10 of Salmonella spp. and E. coli O157:H7. The times and temperatures listed in Appendix A in the Compliance Guidelines for Ready-to-Eat Meat and Poultry Products could also be used for preheating.
Following the lethality step, the product has to be dried to comply with the MPR standard and stabilized to ensure the control (prevent the growth) of pathogens. A meat product with a Aw <0.85 is usually considered shelf stable and not able to support the growth of microorganisms. Jerky in contact with air should have a Aw <0.70 to control mold growth. If the water activity is greater than 0.70, additional control measures such as vacuum packaging or the incorporation of a pillow pouch package or gases to exclude oxygen should be used to prevent mold growth.
Sanitation Standard Operating Procedures (SSOPs) for the processing facility should ensure that the product is properly handled to prevent contamination.
Monitoring the Process
1) Meat temperature
A calibrated food thermometer should be used to validate that the jerky reached the appropriate internal temperature. An example of thermometer calibration to 32ºF is shown in Figures 1a, 1b, and 1c. The thermometer should be placed lengthwise in the jerky to measure the internal temperature of the jerky. Cutting a strip of jerky large enough for a thermometer to completely fit in it should suffice (Figure 2). Since a thicker strip takes longer to heat up, the thinner strips will have reached the appropriate internal temperature needed for safe processing. Internal temperature could be measured during the whole process, but it is critical to measure it towards the end of heating to ensure the proper temperature was reached.
2) Relative humidity
A calibrated wet-bulb thermometer should be placed in the oven to measure relative humidity during the lethality step. This can be constructed by wrapping a wet, moisture-wicking cloth around a dry bulb thermometer (Figures 3a and 3b). To ensure an accurate wet-bulb temperature the cloth encompassing the wet-bulb thermometer needs to be in constant contact with the pan of water during the heating cycle. Use a wet-bulb thermometer in combination with a dry-bulb thermometer to calculate the relative humidity. The use of a wet bulb thermometer is especially important for production at high altitudes or areas of low humidity. A wet- and dry-bulb temperature difference greater than 4.5ºF will result in a relative humidity less than the required 90 percent.
3) Water Activity
Product samples should be collected during the drying process to evaluate how fast the jerky is drying, but especially at the end to ensure that the proper Aw has been reached for stabilization. Collecting several finished product samples (2.0 to 3.0 grams each) and analyzing them with an approved water activity instrument will allow processors to evaluate the jerky stabilization. For a fee, processors can send their samples to an analytical food laboratory for measurement if they do not have a method to measure water activity.
Additional Pathogen Interventions
Regardless of the intervention, a lethality step is still mandatory. Antimicrobial treatments before or after marinating have produced greater pathogen reductions than heating alone. Applying a 5 percent acetic acid dip before marinating can decrease the bacterial load. As an additional precaution, reheat the dried product in a 275°F oven for 10 minutes after the initial heating and drying cycle. This has the potential to further reduce Salmonella levels by approximately 2 logs from the level of reduction achieved during the initial heat step.
- Following strip preparation and marinating, a lethality step must be included in jerky HACCP plans.
- The lethality step must be validated to achieve 6.5 and 7.0 log10 reductions to meet the lethality performance standards for Salmonella spp. in beef and poultry. Other pathogens that should be considered reasonably likely to occur and be addressed are Listeria monocytogenes, Staphylococcus aureus, and E. coli O157:H7.
- FSIS suggests heating the strips in 90 percent relative humidity to an internal temperature of 160ºF. Alternative lethality steps will be accepted provided they are valid for producing a sufficient log10 reduction for the pathogens of concern.
- Following the lethality step, the strips need to be dehydrated to meet the product’s MPR and to reduce the Aw <0.85 to inhibit pathogen growth. If the product is in contact with air, the water activity needs to be <0.70 to prevent mold growth.
Association of Food and Drug Officials. 2004. Guidance for Processing Beef Jerky in Retail Operations. Available at: http://www.afdo.org/afdo/upload/BeefJerky.pdf.
Buege, D. 2004. Validating the Safety of Your Jerky Process. Available at: http://www.aamp.com/regulatory/documents/ValidatingtheSafetyofYourJerkyProcess.pdf.
Calicioglu, M., Sofos, J.N., Samelis, J. Kendall, P.A., and Smith, G.C. 2003. Effects of acid adaptation and modified marinades on survival of postdrying Salmonella contamination on beef jerky during storage. Journal of Food Protection 66(3):396-402.
Faith, N.G., Le Contour, N.S., Alvarenga, 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 degrees C in a home-style dehydrator. International Journal of Food Microbiology 41:213-221.
Harrison, J.A., Harrison, M.A., Rose-Morrow, R.A., and Shewfelt, R.L. 2001. Home-style beef jerky: effect of four preparation methods on consumer acceptability and pathogen inactivation. Journal of Food Protection 64(8):1194-98.
Harrison, J.A., and Harrison, M.A. 1996. Fate of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella typhimurium during preparation and storage of beef jerky. Journal of Food Protection 59(12):1336-1338.
Harrison, J.A., Harrison, M.A., and Ruth, A.R. 1997. Fate of Listeria monocytogenes and Salmonella species in ground beef jerky. Journal of Food Protection 60(9):1139-1141.
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. Journal of Food Protection 67(10): 2337-2341.
United States Department of Agriculture-Food Safety and Inspection Service. 2004. Compliance guideline for meat and poultry jerky produced by small and very small plants. USDA-FSIS, Washington, D.C. Available at: http://www.fsis.usda.gov/PDF/Compliance_Guideline_Jerky.pdf.
Wenther, Jay B. 2004. Special Report Jerky: Compliance Guidelines – Compliance vs. Guidance –. American Association of Meat Processors. Available at: http://www.aamp.com/regulatory/documents/AAMPSpecialReport_000.pdf.
Virginia Cooperative Extension materials are available for public use, reprint, or citation without further permission, provided the use includes credit to the author and to Virginia Cooperative Extension, Virginia Tech, and Virginia State University.
Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg.
May 18, 2011