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This is a list of questions that we get quite often. If you have more to add, please e-mail us with them. Jeff Savell.

• What is "dark cutting beef?"
• What causes the shiny, rainbow appearance on some cured meats?
• Why is the center of ground beef sometimes brown in color?
• Why does ground meat sometimes stay pink when it has been cooked to an adequate temperature?
• What is electrical stimulation?
• What is HACCP?
• Why is thorough cooking so important for ground products such as hamburger?
• What is aging?
• What is the per capita consumption of meat?
• Is Listeria a problem in ground beef?
• Why does jerky sometimes have a white film on it?

A It is where beef is dark red to purple in color.

To understand "dark cutting beef," it is necessary to understand how the bright red color of beef occurs. At death, the muscle attempts to maintain all normal activities. To do so, it must have energy in the form of ATP. To get ATP, it breaks down glycogen through postmortem glycolysis. A by-product of postmortem glycolysis is lactic acid. Lactic acid builds up in the muscle over a 16 to 24 hour period post-slaughter. A normal level of lactic acid (pH of 5.6) in the muscle will cause the meat to be bright cherry-red in color when it is exposed to oxygen for a short time period.

In "dark cutting beef," the animal undergoes long-stress before slaughter. This stress may be from transportation, rough handling, changing weather conditions such as cold fronts, or anything that causes the animal to draw on its glycogen reserves before slaughter. At death, there is limited amount of glycogen available to be converted to lactic acid, the muscle pH will be higher-than-normal (pH of 6.0 or higher), and the color of meat will be darker-than-normal.

"Dark cutting beef" occurs in 1 to 2% of beef carcasses. The percentage will be higher in the fall and winter months, and will be most evident two to three days after a sudden change in ambient temperature, especially if rain and wind accompany the temperature drop. There are different gradients of "dark cutting beef" ranging from slightly dark to very dark purple depending on how much glycogen is depleted in the living animal.

"Dark cutting beef" is used in the foodservice industry rather than the retail industry because of its color. There is no real palatability problem with "dark cutting beef," and this is why it is used in the foodservice industry where the raw product is cooked before the consumer sees it.

For more information:
Producer- and Packer-Related Problems
National Beef Quality Audit -- 1995

A A natural phenomenon in cured meat (and some fresh meat) is the occurrence of iridescence or a rainbow appearance on the cut lean surface. Technically, this is referred to as birefringence. It is caused by the reflectance of light off of muscle proteins, and it is analogous to the color distribution produced by a prism. Muscle proteins are arranged in strands called myofilaments, which are bound together to form myofibrils. Myofibrils are bound together to form muscle fibers, which form together to form muscle bundles and finally whole muscles. When the myofilaments are cut at the appropriate angle, exposing a cross section of the myofilaments, the reflectance of light off the proteins produces the characteristic appearance associated with iridescence.

A In steaks and roasts packaged in overwrap film, the color of the outside of the cut is bright red. Within the cut, it is purple because there is no oxygen to cause the meat to "bloom" (term used in industry to signify the conversion from the purple state to the red state in the presence of oxygen).

In making ground beef, some air is introduced in the grinding process. When ground beef is packaged in overwrap film, plenty of oxygen is available to generate the bright red color of lean on the surface. Because there is some, but not too enough oxygen deep within the product, it causes the meat to turn brown. When the product is allowed to come in contact with oxygen, it usually will bloom to the bright red color like the surface.

For more information:
Metmyoglobin formation in ground beef

Q Why does ground meat sometimes stay pink when it has been cooked to an adequate endpoint temperature?

A Persistent pinkness in cooked ground beef patties is of considerable concern for food service establishments. Consumers view ground beef patties that are pink in the middle as being undercooked and unsafe when, in reality, these patties may be fully cooked and safe to eat. Persistent pinkness can be caused by reducing agents, pH, nitrite contamination, and/or carbon monoxide from gas ovens. Raw beef contains myoglobin, which combines with oxygen to form oxymyoglobin, which has a bright red color. Meat color is regulated (mostly) by a heme ring on the surface of the myoglobin protein. As myoglobin is heated, the protein will denature and unfold allowing oxidation of the iron molecule on the heme ring. Oxidation of the heme iron causes the formation of metmyoglobin, which is a cooked brown color. Reducing agents and the inhibition of oxygen reacting with the heme iron may keep the heme ring from oxidizing thus leaving a pink cooked color.

When the pH value in beef muscle is greater than 6.0, myoglobin is protected from denaturation, leaving oxymyoglobin or a pink color in cooked meats. High pH values may result from long-term stress to live animals prior to harvest, or during quick changes in environmental conditions, especially in the fall and spring. Bull and cow meat may have high pH values, thus cow and bull trimmings may contribute to persistent pinkness.

In addition, nitrite or nitric oxide contamination from water, spices, or processing equipment can also cause nitrosylhemochromagen to form a cured pink color. Incomplete gas combustion in gas-fired ovens may also cause a persistent pink color due to the binding of carbon monoxide or nitric oxide to the heme pigment. Ground beef patties should be heated to 160°F and monitored for proper cooking with a temperature probe rather than relying on color to assure food safety.

Prepared by Pat Mies and reviewed by Jimmy T. Keeton (3/2003).

A It is the application of low (50 to 100 volts) to high (400 to 550 volts) voltage of electricity to freshly slaughtered livestock (applied immediately after slaughter to up to 30 minutes after slaughter) to improve the tenderness of the meat and to cause the color, firmness, and marbling of the meat to be enhanced.

Benjamin Franklin, in 1749, experimented with using electricity to stun turkeys. Rather than stunning the turkeys, the turkeys were given too much electricity and were electrocuted. Franklin found that the meat from these turkeys was more tender. A quote from "The Private Franklin" by Lopez and Herbert, stated that, "Killing turkeys electrically, with the pleasant side effect that it made them uncommonly tender, was the first practical application for electricity."

For more information:
Electrical stimulation pictures
Meat Tenderization

A HACCP stands for Hazard Analysis and Critical Control Point System. It is a system for the prevention of safety problems in food products. It was developed in the 1960s for NASA by the Pillsbury Company as a way to ensure greater safety for the food products used in the Manned Space Program.

In 1996, the Food Safety and Inspection Service of the United States Department of Agriculture mandated HACCP for federal and state inspected meat and poultry plants.

For more information:
International HACCP Alliance
Critical Control Point (CCP) Decision Tree
Modified Critical Control Point Decision Tree
USDA, FSIS

A Within the muscle, there is no bacterial contamination. When muscles are cut into steaks and roasts, bacterial contamination will occur on the cut surfaces. Cooking these cuts on the rare side of "medium" is acceptable because there will be enough heating of the surfaces where bacterial will be present to kill them.

In ground beef, however, the surfaces where the bacterial contamination occurs is spread throughout the product in the grinding process. The only way to be sure that the bacteria are killed is to thoroughly cook the product.

A "Aging," as referred to in the meat industry, is the process where meat becomes more tender as it is stored under refrigeration temperatures. The tenderness improvement comes from the action of naturally occurring enzymes in the meat breaking down the muscle proteins. Meat improves in tenderness very rapidly from day 1 to day 7, less rapidly from day 7 to day 14, and very slowly after day 14.

For most cuts, 14 days of aging is the optimum time necessary to achieve tenderness. For some "white table cloth" hotels and restaurants, longer aging times will be used to maximize tenderness and to enrich flavor.

A For 1997, the per capita consumption of meat was 66.5 pounds of beef, 48.8 pounds of pork, 90.3 pounds of poultry, and 205.6 pounds total. This is reported in pounds of ready-to-cook or retail weight.

For data since 1960:
Per Capita Meat Consumption, 1960-1998

Q Is Listeria a problem in ground beef?

A Listeria is only a problem in ready-to-eat products that will not be heated before consumption and that have a fairly long shelf-life, allowing Listeria to grow to high numbers. Fresh ground beef is not a hazard since the competing microflora slows Listeria growth and the shelf-life is too short for extensive growth. The primary people at risk to Listeriosis is immunocompromised or immune-stressed individuals are susceptible to serious illness from this microorganism.

Q Why does jerky sometimes have a white film on it?

AThis condition may be caused by the following factors:

(Answer provided by Jimmy T. Keeton)