Raw beef turned brown?

What you see: Your raw beef has turned brown in some areas. There may be brown patches on the surface (possibly under stickers) or you might see a layer of brown inside the meat when you cut into it. 
What it is: A biochemical reaction in the meat that happens over time, but can occur within the fresh, safe-to-eat window. The brown color doesn’t mean the meat spoiled.  
Eat or toss: Does the meat otherwise smell and feel fresh? As long as it’s been stored properly and it isn’t sticky, slimy or smelly it should still be fine when cooked to a safe temperature. 

Is raw beef safe if it turns brown?

Many people assume that a bright red color indicates a fresh cut of meat. That’s not exactly true. 

When a cow is slaughtered its meat is actually purplish. If the meat is quickly vacuum packaged it will retain that maroon color. But if the meat is exposed to air for as little as 15 minutes, oxygen will turn its surface a bright, cherry red. The cherry red will eventually discolor to brown when biochemical activity in the meat starts to peter out. 

“It can start discoloring within a few hours,” Liz Boyle, a meat scientist at Kansas State University, told me. “Which is why at the grocery stores they typically grind meat several times a day. They want consumers to see that bright red color.”

According to the USDA, raw cuts of beef keep for three to five days in a fridge that’s 40 degrees Fahrenheit or below; ground beef should be used within one or two days of purchase. So it’s entirely possible for meat still within its fresh window to develop a brown color. 

How long is beef good after it turns brown?

While brown meat can be perfectly fine, and while the color doesn’t indicate the meat is spoiled, it could suggest the meat is a little older. 

So, investigate with your senses. Off odors and sticky and slimy textures indicate that spoilage bacteria have been breaking down the meat’s proteins, potentially ruining the flavor, even if you cook the meat, Boyle told me. (But stickiness you only notice after seasoning your meat probably isn’t a cause for concern. The salt causes little threads of muscle called myofibrillar proteins to search for water, which makes them cling to your hands.)

Pathogenic bacteria—that is, the type that make us sick—don’t typically impart any obvious odor, texture or color changes to the meat. Heating meat to 160 degrees Fahrenheit usually kills them (salmonella and certain strains of e. coli are the top concerns in undercooked beef). Use a food thermometer to check, and for more detailed temperature guidelines, head over to the Partnership for Food Safety Education. 

Beef color behaves differently in vacuum packaging

Without oxygen exposure, vacuum packaged beef will never turn bright red. Over time, it will eventually turn brown. 

“It could take weeks,” Janeal Yancey, a meat scientist at the University of Arkansas, wrote to me in an email. But, she said, a number of variables, including the meat’s age and type, its packaging, and the temperatures it’s exposed to, would influence the actual rate of browning. 

When vacuum-packaged meat spoils, the package puffs up with gases expelled by bacteria. That is your big signal that it’s time to throw it away.

Why exactly does raw beef turn brown? Give me the chemistry!

A protein called myoglobin is the star of the beef color show. 

“Its purpose is to be oxygen storage,” explained Yancey, who writes about meat at Mom At the Meat Counter. “It just holds onto the oxygen for other things to use.”

You may be familiar with how hemoglobin, which is found in blood, goes from dull, dark red to bright red depending on its oxygen status (our blood actually never turns blue–that’s an optical illusion). While hemoglobin courses through arteries and veins, myoglobin inhabits muscle tissue in animals (including us!). When hemoglobin stops by muscles, myoglobin steps up to accept its oxygen. Muscles then use the oxygen to contract and to conduct regular cellular business, like respiration. While muscles stop contracting after slaughter, cellular functions continue. 

Myoglobin consists of a long, tangly bundle of a protein molecule attached to a single iron atom. Oxygen is constantly popping on and off that iron as it fuels the muscle. Depending on its oxygen status, myoglobin changes shape. With each shape shift it reflects light differently, resulting in red, purplish or brown colors. 

Just after slaughter, meat is in the purplish no-oxygen state (which is why vacuum packaged meat is maroonish, as mentioned above). At that point, cellular functions are nearly paused, only proceeding at a very, very slow rate. That is, until oxygen in the air gets together with myoglobin on the meat’s surface. 

“It’s like the oxygen is the gun that starts the race,” Yancey explained. “But if you don’t have the oxygen to start that process like in the vacuum package bag, it’s like it’s waiting at the starting line.”

Once oxygen has kicked off a rush of cellular activity, the meats’ cells use their resources faster. As resources are depleted it becomes harder for the meat to store oxygen in its myoglobin storage tanks. Due to diminished oxygen supplies or free radicals in the neighborhood, the exposed iron on the myoglobin molecule can lose an electron (confusingly, especially amid all our talk of oxygen, losing an electron is known as “oxidation” but doesn’t always involve oxygen). When myoglobin loses that key electron, it turns brown. And that’s when you see your raw steak turning brown.

Why is beef brown underneath stickers and where it touches the tray?

Once oxygen has kicked off a rush of biochemical activity, an environment with some oxygen, but not a lot of oxygen, can actually cause browning to come on the fastest, Yancey said. The oxygen triggers an avalanche of functions, which then demand more oxygen and quickly deplete the limited supply. Before long, myoglobin’s iron atoms lose hope of finding oxygen and each molecule’s vulnerable, exposed electron is snatched up by other functions in the meat or roaming free radicals. Short that precious electron, myoglobin’s shape changes, it reflects light differently, and it looks brown.

That’s why you’re more likely to see brown areas below stickers. While oxygen can travel through the plastic wrap used to seal trays of meat, as soon as some areas are covered by stickers their oxygen supply is cut off.

Parts of the meat that touch the tray are similarly oxygen-deprived and more likely to brown. And, of course, if you stack several trays of meat in the fridge, the areas where they touch will lose oxygen access and will be more likely to turn brown.

All this means that if you see a brown area under a sticker, and your meat has been properly stored in the refrigerator, has no off smells or textures and is still within its fresh window, it’s probably safe and will taste great.  And no, the butcher wasn’t trying to cover up the brown with the sticker!

Why does beef sometimes turn brown just under the surface?

So, we know that the oxygen-rich environment on the surface of the meat causes it to be bright red. Meanwhile, the oxygen-free environment deep within the meat remains purplish in a kind of suspended state; without oxygen its cellular functions proceed very slowly. 

But things get awkward in the liminal space where the red, oxygen-rich outer portion of meat meets the purplish, no-oxygen inner area. There, fast-paced functions are triggered by the small amount of oxygen that’s percolated down from the surface. But the oxygen well quickly runs dry and the meat turns brown.

Yancey said the brown line below the surface usually shows up after the meat has been on display for a few days, though the speed of the reaction depends on the type of meat and how it’s handled. Ground beef changes color the fastest.

Why does frozen meat turn brown? Does thawed meat turn brown faster?

Here at EatOrToss we love our freezer. It keeps food safe for long periods of time and is a great way to reduce food waste. It’s also perfectly fine to stash your meat in the freezer until you’re ready to use it. According to the USDA, frozen raw whole cuts retain their quality for four to 12 months; frozen ground meat should be used in three to four months for peak quality. Here at EatOrToss headquarters we once prepared ground beef that had been in the back of the freezer for more than a year — it was fine.  

But freezing can change raw meat in ways that make browning more likely. For example, freezing damages some of the myoglobin molecules, causing their iron atoms to break off. That free iron can then turn around and nab electrons from myoglobin (the nerve!). Freezing meat can cause fats to break down, releasing free radicals which are also aggressive about grabbing electrons from myoglobin. And, as we know, once myoglobin loses a certain, precious electron on its iron atom, it turns brown. 

All of this is probably why the meat in the image below from EatOrToss reader Jeff S., turned brown. Yancey guessed that it turned brown while it was thawing. 

“I wouldn’t worry about eating or serving that,” Yancey said, noting that, just in case the thawing also led to some off-flavor producing fat oxidation, she’d marinate or heavily season the meat. 

Yancey noted that freezing meat is still a great way to preserve it.

“I don’t want people to be afraid of freezing meat,” she said. “The effects on fat, flavor and juiciness are pretty minimal compared to what freezing can save you in shelf life and waste. I just want them to understand that if meat has been previously frozen, it may not have as pretty a color.”

Before we move on from freezing, just another reminder not to leave your frozen steak or ground beef or anything, really, in the freezer for too long. In addition to the color issues described above, meat frozen for too long can develop freezer burn, which might look like whitish patches or discolored spots on its surface. As long as the meat was properly handled, those areas won’t be unsafe, but they won’t taste good.

Is ground beef spoiled if it turns brown?

Like any red meat, raw ground beef browns over time. The color changes doesn’t necessarily mean the meat has gone bad.

However, ground beef has a shorter shelf life than a cut of meat. The process of grinding the meat accelerates its breakdown. Loose iron and broken down fats can then nab electrons (oxidation), which will turn the meat brown. So, ground beef usually turns brown faster than intact cuts of meat. Since there’s a greater risk of fats oxidizing, the flavor is more at risk. 

“’I’m a little bit more leery on ground beef than I am on whole muscle cuts when it turns brown,” Yancey said. “But if it still smells good and it hasn’t been temperature abused and it’s brown, it’s probably going to be fine.”

She said she wouldn’t buy ground beef like this for fear of off flavors: 

What other factors cause raw beef to turn brown?

As we’ve mentioned above, ground beef and thawing beef are more likely to brown faster. Salt also promotes the biochemical reactions that lead to browning. 

In addition, the type of animal and the animal’s life experiences, including its diet, age and stress level, can impact the balance of chemicals in its tissues and the trajectory and intensity of meat color changes. Older cows, for example, produce more myoglobin. Certain parts of the animal, particularly those used for long, sustained movements, also have more myoglobin than those used for short, quick actions like sprinting or wing flapping. More myoglobin will mean darker meat. (Cool aside: Yancey noted that animals that dive deep or fly high tend to have more myoglobin. So, whale muscle is very high in myoglobin and very dark.)

How meat is packaged and the its storage temperature also impact the speed at which it consumes oxygen and therefore how its color changes over time. Cellular functions happen faster, and use more oxygen, at higher temperatures. Additionally, as noted earlier, vacuum packaging and freezing can have significant impacts on raw meat’s color. 

While a brown color alone shouldn’t be used as an indicator of spoilage, sometimes bacteria produce sulfides and peroxides that can cause beef to look brown. But spoilage bacteria aren’t covert operators. You’ll smell their work and that will be sign enough that the meat is spoiled. 

Can a meat’s color tell you if it’s done cooking?

Many people use color to assess whether meat has fully cooked. Bad idea. 

“Cooked meat color is not a reflection of doneness,” Boyle said. “The only reliable way to know that ground beef is cooked appropriately is to use a meat thermometer.”

Not surprisingly, our friend myoglobin also gives us the colors in cooked beef. Heat denatures it, which means that the tangled protein molecule unfolds and ceases biological functions. The molecule then reflects light differently and the meat looks duller, lighter and, in the case of beef, browner than it did when it was raw. 

But, here’s the thing – myoglobin can denature below or above a food-safe 160 degrees Fahrenheit. So if you rely on color alone, you could end up with undercooked or overcooked meat. 

Where a cut of meat falls on the myoglobin spectrum can influence how quickly it denatures and therefore how quickly it develops a “cooked” brown look. Myoglobin that isn’t carrying oxygen and is still purplish takes longer to brown during cooking. A high pH will “protect” myoglobin, keeping it red after it’s fully cooked. Myoglobin that is already brown, in the oxidized “metmyoglobin” state, denatures and looks “cooked” faster. This is especially problematic in ground beef, which is riskier because pathogens can end up inside the meat, where they’re exposed to less heat.

“The more dangerous situation is when meat browns too early,” Yancey said. “We call this pre-mature browning and you have meat that hasn’t been cooked to a safe temperature that looks done. This is why I always use a meat thermometer.”

Pleased to meat you!