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When raw meat or poultry
is dehydrated at home — either in a warm oven or a food dehydrator
— to make jerky which will be stored on the shelf, pathogenic
bacteria are likely to survive the dry heat of a warm oven and
especially the 130 to 140 °F of a food dehydrator. Included
here is the scientific background behind drying food to make
it safe and the safest procedure to follow when making homemade
jerky.
What is 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."
How Can Drying Meat Make it Safe?
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.
What are the Types of Food Drying?
There are several types of food drying. Two
types of natural drying - sun drying and "adibatic" (shade)
drying - occur in open air. Adibatic 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.
Why is Temperature Important When Making Jerky?
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 and poultry to 165 °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, maintain 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.
Why is it a Food Safety Concern to Dry Meat Without First Heating it to 160 °F?
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 and poultry to 165 °F — temperatures 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 foodborne
illness to those consuming the jerky.
What Research Findings Exist on the Safety of 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."
What are the USDA Meat and Poultry Hotline's Recommendations
for Making Homemade Jerky?
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 to 160 °F and poultry to 165 °F as measured with a food 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.
Are There Special Considerations for Wild Game Jerky?
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."
Is Commercially Made Jerky Safe?
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.
What is the Safe Storage Time for Jerky?
Commercially packaged jerky can be kept 12 months; home-dried jerky can be stored 1 to 2 months.
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Last Modified:
April 5, 2006 |
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