Food Safety Of Jerky

This product is a nutrient-dense meat that has been made lightweight by drying. A pound of meat or poultry weighs about four ounces after being made into jerky. Because most of the moisture is removed, it is shelf stable – can be stored without refrigeration – making it a handy food for backpackers and others who don’t have access to refrigerators.

Jerky is a food known at least since ancient Egypt. Humans made jerky from animal meat that was too big to eat all at once, such as bear, buffalo, or whales. North American Indians mixed ground dried meat with dried fruit or suet to make "pemmican." "Biltong" is dried meat or game used in many African countries. Our word "jerky" came from the Spanish word "charque."

Drying is the world’s oldest and most common method of food preservation. Canning technology is less than 200 years old and freezing became practical only during this century when electricity became more and more available to people. Drying technology is both simple and readily available to most of the world’s culture.

The scientific principal of preserving food by drying is that by removing moisture, enzymes cannot efficiently contact or react with the food. Whether these enzymes are bacterial, fungal, or naturally occurring autolytic enzymes from the raw food, preventing this enzymatic action preserves the food from biological action.

There are several types of food drying. Two types of natural drying – sun drying and "adiabatic" (shade) drying – occur in open air. Adiabatic drying occurs without heat. Solar drying sometimes takes place in a special container that catches and captures the sun’s heat. These types of drying are used mainly for fruits such as apricots, tomatoes, and grapes (to make raisins).

Drying from an artificial heat source is done by placing food in either a warm oven or a food dehydrator. The main components of an electric food dehydrator include:

• a source of heat;
• air flow to circulate the dry air;
• trays to hold the food during the drying process; and
• mesh or leather sheets to dry certain types of foods.

Illnesses due to Salmonella and E. coli O157:H7 from homemade jerky raise questions about the safety of traditional drying methods for making beef and venison jerky. The USDA Meat and Poultry Hotline’s current recommendation for making jerky safely is to heat meat to 160 °F before the dehydrating process. This step assures that any bacteria present will be destroyed by wet heat. But most dehydrator instructions do not include this step, and a dehydrator may not reach temperatures high enough to heat meat to 160 °F.

After heating to 160 °F, maintaining a constant dehydrator temperature of 130 to 140 °F during the drying process is important because:

• the process must be fast enough to dry food before it spoils; and
• it must remove enough water that microorganisms are unable to grow.

The danger in dehydrating meat and poultry without cooking it to a safe temperature first is that the appliance will not heat the meat to 160 °F – a temperature at which bacteria are destroyed – before it dries. After drying, bacteria become much more heat resistant.

Within a dehydrator or low-temperature oven, evaporating moisture absorbs most of the heat. Thus, the meat itself does not begin to rise in temperature until most of the moisture has evaporated. Therefore, when the dried meat temperature finally begins to rise, the bacteria have become more heat resistant and are more likely to survive. If these surviving bacteria are pathogenic, they can cause food borne illness to those consuming the jerky.

There have been several scientific studies of meat dehydrating and lab tests on jerky samples by the following professionals: Judy Harrison, Cooperative Extension Service, University of Georgia;   Mark Harrison, the Center for Food Safety and Quality Enhancement, Department of Food Science and Technology, University of Georgia; Richard A. Holley, Food Research Institute, Agriculture Canada, in Ontario; and William Keene of the Oregon Health Division. In studies, the meat dehydrated included slices of beef from the round, loin, or flank; corned beef slices; and ground beef formed in jerky presses. Keene examined homemade venison jerky which infected 11 people with E. coli O157:H7.

In a related work, factors affecting the heat resistance of E. coli O157:H7 was the subject of an April 1998 piece by J. Kauer et al., Letters of Applied Bacteriology, Vol. 26, No. 4, page 325.

In the jerky studies, some samples showed total bacterial destruction and other samples showed some bacterial survival – especially the jerky made with ground beef. Further experiments with lab-inoculated venison showed that pathogenic E. coli could survive drying times of up to 10 hours and temperatures of up to 145 °F.

A recent study by the Harrisons and Ruth Ann Rose, also with the University of Georgia, was published in the January 1998 Journal of Food Protection, Vol. 61, No. 1. The authors analyzed ground beef jerky made with a commercial beef jerky spice mixture with and without a curing mix containing salt and sodium nitrite.

Half of the ground beef was inoculated with E. coli O157:H7 before making it into jerky strips and dehydrating it. The authors found that in both the heated and unheated samples, the jerky made with the curing mix had greater destruction of bacteria than jerky made without it. The jerky made with the mix and heated before dehydrating had the highest destruction rate of bacteria.

They concluded, "For ground beef jerky prepared at home, safety concerns related to E. coli O157:H7 are minimized if the meat is precooked to 160 °F prior to drying."

Research findings support what the Hotline has been recommending to callers. Additionally, safe handling and preparation methods must always be used, including:

• Always wash hands thoroughly with soap and water before and after working with meat products.

• Use clean equipment and utensils.

• Keep meat and poultry refrigerated at 40 °F or slightly below; use or freeze ground beef and poultry within 2 days; whole red meats, within 3 to 5 days.

• Defrost frozen meat in the refrigerator, not on the kitchen counter.

• Marinate meat in the refrigerator. Don’t save marinade to re-use. Marinades are used to tenderize and flavor the jerky before dehydrating it.

• Steam or roast meat and poultry to 160 °F as measured with a meat thermometer before dehydrating it.

• Dry meats in a food dehydrator that has an adjustable temperature dial and will maintain a temperature of at least 130 to 140 °F throughout the drying process.

Yes, there are other special considerations when making homemade jerky from venison or other wild game. According to Keene and his co-authors, "Venison can be heavily contaminated with fecal bacteria – the degree varying with the hunter’s skill, wound location, and other factors. While fresh beef is usually rapidly chilled, deer carcasses are typically held at ambient temperatures, potentially allowing bacteria multiplication."

Yes, the process is monitored in federally inspected plants by inspectors of the U.S. Department of Agriculture’s Food Safety and Inspection Service. Products may be cured or uncured, dried, and may be smoked or unsmoked, air or oven dried. The following terms may be on processed jerky products:

• "Beef Jerky" – produced from a single piece of beef.

• "Beef Jerky Chunked and Formed" – produced from chunks of meat that are molded and formed, then cut into strips.

• "Beef Jerky Ground and Formed or Chopped and Formed" – produced from ground or chopped meat, molded and cut into strips. Beef Jerky containing binders or extenders must show true product name (e.g., "Beef and Soy Protein Concentrate Jerky, Ground and Formed").

• "Species (or Kind) Jerky Sausage" – the product has been chopped and may be dried at any stage of the process, and it is stuffed into casings.