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| Color of Cooked Ground Beef as It Relates to Doneness |
The Food Safety and Inspection Service (FSIS) of the U.S. Department of Agriculture (USDA) has
conducted a longstanding consumer education program on safe cooking and handling of meat and
poultry. Proper food safety practices prevent situations that promote bacterial growth,
cross-contamination, and foodborne illness. Thorough cooking destroys bacteria.
FSIS has long advised consumers to use a food thermometer when cooking meat and poultry to ensure
that a temperature sufficient to destroy bacteria has been reached. In June 1997 FSIS expanded this
recommendation to include ground beef patties. Pathogens (including Salmonella and
Escherichia coli O157:H7) die when exposed to heat for a specific amount of time.
Cook all raw ground beef to an internal temperature of 160 °F as measured with a food thermometer.
E. coli O157:H7 is a strain of bacteria that produces a toxin that can cause hemorrhagic
colitis. This illness can develop into an extremely serious condition known as hemolytic uremic
syndrome, which can cause kidney failure, brain damage, strokes, and seizures in young children
and the elderly. E. coli O157:H7 has caused numerous sporadic cases as well as outbreaks
of foodborne disease resulting in illnesses and deaths. This pathogen can survive both refrigerator
and freezer storage. A number of E. coli O157:H7 outbreaks recorded since 1982 have been
linked to undercooked ground beef as the primary source of infection.
The 1993 Western states outbreak of E. coli O157:H7 attributed to undercooked hamburgers
served at a fast-food chain was a turning point. The outbreak sickened hundreds and was responsible
for four deaths. While it was not the first outbreak of foodborne illness that the United States
had experienced, it was a particularly difficult one for the public to accept; many young children
became ill, and the food source was the traditional American hamburger.
In 1994, as a response to the outbreak, the USDA declared E. coli O157:H7 an adulterant
in raw ground beef and initiated a monitoring program for E. coli O157:H7 in raw ground
beef (testing confirmed that contamination occurs sporadically and at low levels). FSIS also
initiated a program to encourage better controls and testing by industry, and required safe
food handling labels on all raw meat and poultry products.
While working with industry to improve the safety of the food supply, FSIS has continued to promote
food safety in the home. Since meat and poultry products can contain harmful bacteria, it is
important that ground beef be cooked thoroughly. Future incidents of foodborne illness may be
prevented if food handlers understand and act on a simple fact: Thorough cooking to an internal
temperature of 160 °F throughout kills E. coli O157:H7.
Many food handlers and consumers believe that visible signs, such as color changes in the food,
are indicators that the food is safely cooked. However, research has shown that color and
texture indicators are not reliable. In particular, a 1995 study done by Kansas State University
(Hunt et al, 1995) found that a sufficient number of ground beef patties were turning brown well
before they reached 160 °F to make color an unreliable indicator of doneness. A consumer who
believes a brown color always means a safe hamburger is taking a chance on foodborne illness.
Unfortunately data show that many consumers either do not own a food thermometer or rarely use one
when cooking ground beef (FDA-CFSAN/USDA, 1998; Koeppl, 1998). Prior to June 1997, consumers who
did not use a food thermometer were advised by FSIS to cook ground beef patties until the center
and the cooked-out juices were no longer pink. Consumers were also advised to look for a firm
"cooked" texture rather than a softer "raw or rare" texture in the
meat.
However, research results raised questions regarding the suggestions for the visual checks for
doneness (Hague et al, 1994; Hunt et al, 1995). Consequently, in June 1997 USDA issued a press
release advising consumers to use a food thermometer when cooking ground beef patties, and not to
rely on the internal color of the meat. Rather, consumers should cook ground beef patties to
an internal temperature of 160 °F as measured with a food thermometer.
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Color as an Indicator of Doneness
FSIS recognizes that there are two paradoxical problems with advice about using the color of
ground beef to test for doneness and guarantee the destruction of pathogens:
- Some ground beef may appear to have lost all pink color before it is fully cooked. If raw ground beef is somewhat brown already, it may look fully cooked before it reaches a safe temperature.
- Some lean ground beef may remain pink at temperatures well above the 160 °F final cooking temperature recommended for consumers.
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Browning Before a Safe Temperature is Reached
Cooked ground beef patties may appear brown before they reach a safe internal temperature.
This is primarily caused by extensive oxidation of the fresh ground beef pigment and can occur,
for example, with prolonged thawing of frozen ground beef, or refrigerator storage of thawed
ground beef.
When ground beef is exposed to air, the ferrous iron in its myoglobin pigment is oxygenated to
form a ferrous iron-oxygen complex. Myoglobin is a purplish-red color in its unoxygenated state,
and becomes red when the iron complexes with oxygen to form oxymyoglobin. This is what gives fresh
beef its red color. But if meat is stored for long periods of time, is stored above proper
temperatures, or is exposed to too much air, the ferrous iron loses an electron to become
ferric iron. The resulting ferric pigment, known as metmyoglobin, is brown.
Consumers associate bright red color with high quality (Lynch et al, 1986) and are frequently
concerned when ground beef appears red on the outside and brown on the inside. Different levels of
oxygenation at different locations inside and on the surface of the meat can account for this
coloration (the grinding process allows air to contact more surface area of the meat). If ground
beef loses contact with the air, as with the inside of the package of ground beef, it will turn
grayish-brown. Likewise, as ground beef is stored, even for as little as one day, it might also
turn prematurely brown (USDA-ARS/FSIS, 1998).
When ground beef is cooked, it changes color from red to pink to brown. If the meat is already
brown, it will not change color during cooking. Recent research has shown some ground beef patties
to look well-done at internal temperatures as low as 131 °F (Hague et al, 1994; Hunt et al,
1995; USDA-ARS/FSIS, 1998).
Raw meat from older carcasses can also be less red or darker in color, and can appear to be
adequately cooked when it is actually still undercooked. When ground beef patties are made from a
mix of older and younger carcasses, it has been found that the patties cooked to 131 °F are
similar in color to patties cooked to 140 °F. Patties cooked to 150 °F have been shown to
be visually indistinguishable from those cooked to 160 °F (Hague et al, 1994).
After reviewing existing research, FSIS initiated its own study to survey the prevalence of
premature browning in cooked ground beef. USDA researchers prepared and cooked patties from ground
beef purchased from various locations across the country. More than 25 percent of the fresh ground
beef patties turned brown prematurely ("prematurely" was defined as before reaching
the safe temperature of 160 °F). USDA research results presented at a May 27, 1998, public
meeting in Arlington, VA, reaffirmed the Agency's advice that color is an unreliable indicator of
doneness. Consumers should use a food thermometer to be sure ground beef patties reach 160 °F
(USDA-ARS/FSIS, 1998).
The USDA researchers found considerable variation both between and within beef patty formulations
in endpoint temperature and color, even when controlled cooking procedures were followed. Therefore,
unless a food thermometer is used when cooking ground beef patties, it is difficult for consumers
to determine whether the patties are thoroughly cooked.
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Persistent Pink Color in Cooked Meat Patties
There are several reasons why ground beef may remain pink at temperatures above 160 °F. This
phenomenon is primarily associated with the pH and the level of pigment in the meat, as well as the
fat content.
Normal fresh muscle has a pH ranging from 5.3 to 5.7. When thoroughly cooked, the myoglobin,
oxymyoglobin, and metmyoglobin pigments of normal meat are converted (i.e. denatured) to denatured
hemichrome, the grey pigment of cooked meat. Meat with a pH of 6.0 or higher can remain pink at
159.8 °F. The rate at which normal muscle pigments change to form the grey denatured hemichrome
is affected by pH. The higher the pH, the longer the cooking time and/or higher the final internal
temperature required for denaturation to be complete (Mendenhall, 1989). A high pH reduces the
amount of myoglobin denatured by cooking, resulting in a pink color rather than the expected grey
cooked color created by denatured hemichrome (Trout, 1989).
A high concentration of pigment also contributes to a red color in cooked meat. Meat coming from
bulls typically exhibits both a higher pH and high concentrations of pigment. Mendenhall (1989)
suggests that when patties are formulated from a mixture of bull meat, chuck, and beef trim with
similar amounts of total pigment, there are significant differences in cooked internal color,
indicating that the pH is responsible. But when pH is held constant, the concentration of total
pigment contributes to the abnormal internal color. It was further shown that when cooked bull meat
(pH 6.2) is compared to a mixture of bull meat, chuck, and trim (pH 6.2), the bull meat patty is
significantly redder due to the higher concentration of pigment.
Most store-purchased ground beef is a mixture of meat from multiple sources (bulls, steers, cows,
heifers) because ground beef is formulated to achieve a very specific fat content. Trimmings from
many sources are combined.
A third factor affecting cooked ground beef color is the amount of fat in beef patties. Low-fat
beef appears to have less conduction of heat than high-fat beef. Consequently, low-fat beef
patties—including those that contain water, oat bran, carrageenan, and/or isolated soy
protein—require longer cooking times and higher cooking temperatures to reach a certain
internal temperature. Furthermore, patties can remain pink even though they have reached internal
temperatures higher than the recommended 160 °F. In some cases, low-fat beef patties have not
only taken longer than expected to reach the targeted end-point temperature but also maintained a
pink color at temperatures of 160° to 165 °F (Berry, 1994; Troutt et al, 1992).
There is considerable variation both between and within beef patty formulations in endpoint
temperature and color even when controlled cooking procedures are followed.
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Advice for Consumers
To avoid foodborne illness, USDA recommends that meat and poultry be cooked thoroughly. Thorough
cooking is most accurately measured by use of a food thermometer. The thermometer should penetrate
the thickest part of the food. For a meat loaf or a casserole, it would be in the center.
Fresh or thawed ground meat should be used quickly, within one day. Consumers should either tightly
wrap and freeze, or store ground beef for no more than one day in a 40 °F refrigerator.
The only way to be sure a ground beef patty is cooked to a high enough temperature to destroy any
harmful bacteria that may be present is to use an accurate instant-read thermometer.
For ground beef patties, a digital instant-read food thermometer may be used toward the end of
the cooking time and inserted at least ½ inch into the thickest part of the patty. If the ground
beef patty is not thick enough to check from the top, the thermometer should be inserted sideways.
If uncertain about the temperature reading, take a reading in a second location.
Cook ground beef to an internal temperature of 160 °F as measured with a food thermometer.
The color of cooked ground beef can be quite variable. At 160 °F, a safely cooked patty may
look brown, pink, or some variation of brown or pink.
When a patty is cooked to 160 °F throughout, it can be safe and juicy, regardless of color.
Eating pink ground beef patties without first verifying that the safe temperature of 160 °F is
reached is a significant risk factor for foodborne illness (Kassenborg et al, 1998; Slutsker et al,
1998).
Consumers should not eat ground beef patties that are pink or red in the middle unless a food
thermometer is used to verify the temperature.
When eating out, ask your server if ground beef patties have been cooked to at least 155 °F for
15 seconds (as recommended by the U.S. Food and Drug Administration Food Code), which is a safe
option for restaurants or food service operations.
Thermometer use to ensure proper cooking temperature is especially important for those who cook
or serve ground beef patties to people most at risk for foodborne illness because E. coli
O157:H7 can lead to serious illness or even death. Those most at risk include young children, the
elderly, and those who are immunocompromised.
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REFERENCES
Berry, B.W. 1994. Fat Level, High Temperature Cooking and Degree of Doneness Affect Sensory,
Chemical, and Physical Properties of Beef Patties. J. Food Science. 59 (1): 10-14, 19.
Cornforth, D.; C.R. Calkins, C. Faustman. 1991. Methods for Identification and Prevention of Pink
Color in Cooked Meat. Reciprocal Meat Conference Proceedings, AMSA 44:53-58.
FDA-CFSAN/USDA-FSIS. 1998. Consumer Food Safety Survey Results. U.S. Food & Drug
Administration, Center for Food Safety & Applied Nutrition, Consumer Studies Branch, Washington, D.C.
Hague, M.A.; K.E. Warren; M.C. Hunt; D.H. Kropf; C.L. Kastner; S.L. Stroda; and D.E. Johnson. 1994.
Endpoint Temperature, Internal Cooked Color, and Expressible Juice Color Relationships in
Ground Beef Patties. J. Food Sci. 59 (3): 465-470.
Hunt, M.C.; K.E. Warren; M.A. Hague; D. H. Kropf; C.L. Waldner; S.L. Stroda; and C.L. Kastner.
1995. Cooked Ground Beef Color is Unreliable Indicator of Maximum Internal Temperature.
Department of Animal Sciences, Kansas State University, Manhattan, KS 66506-0201. Presentation to
American Chemical Society April 6, 1995.
Kassenborg, H.; C.Hedberg; M. Evans; G. Chin; T. Fiorentino; D. Vugias; M. Bardsley; L. Slutsker;
P. Griffin. 1998. Case-Control Study of Sporadic Escherichia coli O157:H7 Infections in
5 FoodNet Sites (CA, CT, GA, MN, OR). Abstract presented at the International Conference on
Emerging Infectious Diseases, March 8-11, 1998, Atlanta, GA.
Koeppl, P.T., Macro International, Inc. 1998. Focus Groups on Barriers that Limit Consumers' Use of
Thermometers When Cooking Meat and Poultry Products. Unpublished report submitted to the Food
Safety & Inspection Service, USDA, Washington, D.C.
Lynch, N.M.; C.L. Kastner; and D.H. Kropf. 1986. Consumer Acceptance of Vacuum Packaged Ground Beef
as Influenced by Product Color and Educational Materials. J. Food Sci. 51 (2): 253-255, 272.
Mendenhall, V.T. 1989. Effect of pH and Total Pigment Concentration on the Internal Color of Cooked
Ground Beef Patties. J. Food Sci. 54 (1): 1-2.
Slutsker, L; A.A. Ries; K. Maloney; J.G. Wells; K.D. Greene; P.M. Griffin. 1998. A Nationwide
Case-Control Study of Escherichia coli O157:H7 Infection in the United States.
J. Infectious Diseases 177:962-6.
Trout, G.R. 1989. Variation in Myoglobin Denaturation and Color of Cooked Beef, Pork, and Turkey
Meat as Influenced by pH, Sodium Chloride, Sodium Tripolyphosphate, and Cooking Temperature.
J. Food Sci. 54 (3): 536-544.
Troutt, E.S.; M.C. Hunt; D.E. Johnson; J.R. Claus; C.L. Kastner; and D.H. Kropf. 1992.
Characteristics of Low-fat Ground Beef Containing Texture-Modifying Ingredients. J. Food Sci.
57 (1): 19-24.
USDA-ARS/FSIS. 1998. Premature Browning of Cooked Ground Beef. Food Safety and Inspection Service
Public Meeting on Premature Browning of Ground Beef. May 27, 1998. USDA, Washington, D.C.
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Last Modified: May 23, 2011 |
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