ARIZONA COOP E R AT I V E
E TENSION
College of Agriculture and Life Sciences
AZ1086
Revised 10/08
Time and Temperature
Make a Difference
Bacteria exist everywhere in nature. They are in the soil, air,
water, as well as the foods we eat. Even though most bacteria
will not harm you, some types of bacteria given favorable
conditions can produce sickness in susceptible individuals
including children and the elderly. When bacteria have
nutrients (food), moisture and favorable temperatures, they
grow rapidly and can cause serious illness.
A standard rule, recommended by the U.S. Department of
Agriculture, is to keep hot foods above 140° F and cold foods
below 40° F. Temperatures in between these two are known
as the “Danger Zone”. Outside of the danger zone, it has been
found that above 160° F, heat destroys bacteria. On the other
hand, refrigerating foods below 40° F only slows the growth
of bacteria but does not kill them. Also, freezing stops their
development, but does not destroy bacteria.
Bacteria grow most rapidly in the “Danger Zone”, some
doubling in number in as little as 20 minutes. Also, food
may not be safe to eat if you hold it for more than two hours
at the danger zone temperature range where bacteria can
multiply rapidly. Food can reach the two hour time limit
cumulatively. For example, cooked meat left for one hour at
room temperature, refrigerated, and then left out for another
hour (without proper reheating) is the same as leaving it out for
two consecutive hours. Since refrigerating or freezing cooked
meat does not kill bacteria, these organisms will again multiply
when the meat is put back into the danger temperature zone.
This means that cooked foods should be rapidly cooled in
the refrigerator to less than 40° F and then reheated quickly
to 160° F.
Check your refrigerator and freezer periodically. Keep
your refrigerator at or below 40° F and your freezer at 0° F.
It is also helpful to use a thermometer to make sure of these
temperatures. Always keep your refrigerator and freezer clean
and free from any spoiled food that may contain harmful
bacteria.
Thaw meat and poultry in the refrigerator. Do not thaw
food on the kitchen counter at room temperature. For faster
thawing, place frozen packages in a watertight plastic bag
under cold water and change the water often.
Extra care needs to be given when cooking in the microwave.
Microwaves often cook food unevenly, thus creating hot and
cold spots. Bacteria can then survive and grow in the cold
spots. To prevent this, cover food with plastic wrap or a glass
covering. This produces steam which readily kills bacteria.
Also, to ensure uniform heating, turn the dish or stir dish
contents several times while cooking.
References
Larson Duyff-Roberta, MS, RD, CFCS. The American Dietetic
Association’s Complete Food and Nutrition Guide, 3rd ed.
Wiley and Sons Inc. Publishing, 2006.
U.S. Food and Drug Administration. Food Freshness and
“Smart Packaging. September-October 2002. http://www.
fda.gov/fdac/features/2002/502_food.html
Kendall, P and Diamond, N. Food Safety for Storage and
Quality. Publication No. 9310. Colorado State University
Cooperative Extension, Fort Collins, Colorado, June 2006
USDA 2001. Fact Sheet: Food Product Dating. http://www.fsis.
udsa.gov/Fact_Sheets/Food_Product_Dating/index.asp
Material was originally written by Scottie Misner and Mary
Abgrall, April 1998. Revised by Scottie Misner and Carol
Curtis, October 2008.
Any products, services, or organizations that are
mentioned, shown, or indirectly implied in this publication
do not imply endorsement by The University of Arizona.
ARIZONA COOP E R AT I V E
E TENSION
THE UNIVERSITY OF ARIZONA
COLLEGE OF AGRICULTURE AND LIFE SCIENCES
The University of Arizona
College of Agriculture and Life Sciences
Tucson, Arizona 85721
Scottie Misner, Ph.D., R.D.
Associate Nutrition Specialist
Contact:
Scottie Misner
misner@ag.arizona.edu
This information has been reviewed by university faculty.
cals.arizona.edu/pubs/health/az1086.pdf
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture,
James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona.
The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color,
religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.