When meat turns brown in the fridge, it’s not necessarily an indication that it has gone bad. This is because color change depends on a variety of factors, including oxygen exposure and treatments during processing or packaging. Here is a look at the reasons meat changes color and whether you can use color to determine whether it’s safe to eat.
- Most of the color change comes from the oxidation state of myoglobin, a compound similar to hemoglobin found in muscle.
- Deep purple-red, red, pink, and brown are natural colors of myoglobin. Meat that is one or more of these colors usually is fine.
- Meat that is bad has a gray or green color, a sticky or slimy exterior, a bad odor, and/or puffy packaging from gases released by decay.
- The expiration date is a guideline. Under improper storage conditions, meat goes bad before its date. Similarly, frozen meat lasts past its date.
Myoglobin and Its Oxidation States
The main reason meat turns brown is because it contains myoglobin. Myoglobin is a protein responsible for transporting oxygen in muscle tissues. Like the hemoglobin in blood, it undergoes color changes in response to oxygen:
- Deoxymyoglobin: In a reduced state, myoglobin appears purplish red. This is the color of the interior of a large piece of meat or the color of vacuum-sealed meat.
- Oxymyoglobin: In fresh meat, muscle is oxygenated and the iron in myoglobin is in its +2 oxidation state, which makes the molecule appear red. But, packaging meat in a controlled atmosphere or treating it with additives also turns it pink or red.
- Metmyoglobin: Further oxidation of iron in myoglobin to the +3 oxidation state turns meat brown. The brown color often comes from exposure to air in the refrigerator. Cooking also oxidizes iron and turns meat brown.
Reasons Meat Turns Brown or Changes Color
Myoglobin is only part of the story. Meat changes color for a variety of reasons, while remaining safe to eat:
- Oxidation of Myoglobin: This protein reacts with oxygen to change color.
- Presence of Other Chemicals: Nitrites and other chemicals affect the color.
- Lighting: Exposure to natural or artificial light change the color. Colored light alters the perceived color, but ultraviolet exposure alters molecules and actually changes their color.
- Aging Process: The aging process of meat often causes color alterations.
- Maillard Reaction: The Maillard reaction browns meat, usually in connection to heating.
Other Chemicals That Change Meat Color
Additives to meat or to packaging sometimes change meat color.
- Nitrites: Nitrites turn meat pink. They are a common additive used for curing meat.
- Erythorbate or Ascorbic Acid (Vitamin C): As additives, these compounds stabilize the color of cured meat.
- Nitric Oxide: Nitric oxide yields a bright red color in cured meats.
- Artificial Coloring: Some companies add color to make meat appear fresher.
- Modified Atmosphere Packaging (MAP): MAP utilizes specific gases to maintain a red or pink color. Examples include carbon monoxide (CO), carbon dioxide (CO2), and oxygen (O2). These gases also extend shelf life, but only up to a point.
Colors of Meat and Indications of Safety
So, can you tell whether meat is safe based on its color? Not entirely, but there are certain colors that are usually safe and ones to avoid.
Red or Purple-Red
For the most part, red or pink is the color of fresh meat. But, meat packed in a carbon monoxide atmosphere can appear “fresh” up to a year! Don’t use color as your only indicator of freshness.
- Fresh Meat: Ideally, any shade of red indicates that the meat is freshly cut.
- Safety: Usually safe for consumption if handled and stored properly.
Brown
Brown raw meat doesn’t look particularly appetizing, but it’s not a cause for concern. Usually it just means part of the meat has been exposed to either oxygen (air) or heat.
- Oxidation: Often occurs due to exposure to air.
- Safety: Not an indication of spoilage unless accompanied by other signs. For example, if a package of refrigerated ground beef has a brown exterior and a pink interior, it’s perfectly okay.
Green or Other Unusual Colors
Green or gray raw meat colors come from the appearance of bacteria, mold, or other unpleasant organisms. Don’t eat rotting meat.
- Contamination: May indicate spoilage or presence of harmful bacteria.
- Safety: Not safe for consumption.
How to Identify Bad Meat
Color is one indicator of meat freshness, but check these other signs too:
- Smell: An off or sour odor is a clear indication of spoilage.
- Texture: Discard raw meat that has a slimy or sticky surface.
- Expiration Date: Always check the packaging date and expiration date.
- Taste: If you cook the meat and it tastes bad or “off”, throw it out.
References
- Fraqueza, M.J.; Barreto, A.S. (Sep 2011). “Gas mixtures approach to improve turkey meat shelf life under modified atmosphere packaging: the effect of carbon monoxide”. Poultry Science. 90 (9): 2076–84. doi:10.3382/ps.2011-01366
- Henchion, Maeve; McCarthy, Mary; Resconi, Virginia C.; Troy, Declan (November 2014). “Meat consumption: Trends and quality matters”. Meat Science. 98 (3): 561–568. doi:10.1016/j.meatsci.2014.06.007
- La Storia, A.; Ferrocino, I.; et al. (2012). “A combination of modified atmosphere and antimicrobial packaging to extend the shelf-life of beefsteaks stored at chill temperature.” Int J Food Microbiol. 158(3):186-94. doi: 10.1016/j.ijfoodmicro.2012.07.011
- Lawrie, R.A.; Ledward, D A. (2006). Lawrie’s Meat Science (7th ed.). Cambridge: Woodhead Publishing Limited. ISBN 978-1-84569-159-2.
- McGee, H. (2004). On Food and Cooking: The Science and Lore of the Kitchen. New York: Scribner. ISBN 0-684-80001-2.