• Thursday, October 13, 2011

    Meat color is a-changin’!

    Let’s say you bought some steaks or a roast at the grocery store, brought it home and stuck it in the fridge. (Hopefully, stored on a plate on the bottom shelf.) You don’t get around to fixing it (that’s Texan for preparing it) for supper for a day or two. You take it out of the fridge and it has a brownish color. Maybe a few brown spots or maybe the whole thing is just a little browner than it was when you bought it. Has it gone bad? Should you throw it out? It wasn’t cheap, so you hate to throw it out. What to do?
    Check the use-by date. Smell it. Does it smell bad? If it doesn’t smell bad and if you haven’t passed the use-by date, it’s probably ok.

    Why is it brown in my fridge when it was red in the store?
     
    Short answer. It oxidized. Muscle has an ability to prevent (really slow down) oxidation, but that ability runs out with time. Oxidized muscle is brown.
    Long answer. Well, to understand why meat is brown, we need to understand why it was red, first.
    Meat contains lots of proteins. Some are structural (they hold the meat together). Some are for contraction (remember that the meat was originally for moving an animal around). Some proteins hold onto oxygen to help provide the muscle with energy.
    These oxygen-holding proteins are largely responsible for meat color. The main one is called myoglobin. Myoglobin is closely related to the hemoglobin that holds oxygen as it is transported through our blood. Just like we learned in sixth grade science class that blood comes in two colors (red when it is exposed to oxygen in the arteries and blue when the oxygen is gone in the veins), meat pigment comes in those two colors, too. When it is not exposed to oxygen, meat has a purple color. You can see this color right after it is cut. Meat scientists call this ‘deoxymyoglobin’ because the myoglobin doesn’t have any oxygen. If you buy meat that has been vacuum packaged, it will be purplish in color.
    The meat will slowly take up oxygen from the air and turn red. In the meat business, we refer to the time it takes go from purple to red as ‘bloom time’. Most of the meat you buy in the store has been packaged so that the oxygen in the air is available to combine with the myoglobin in the meat. That’s why it is a pretty red color in the store.
    We recently did a research project studying bloom time. This is a picture of some steaks from that study. The ones in the front had just been removed from a vacuum package and were the purplish deoxymyoglobin. The ones in the back had been setting out for an hour, and you can see the bright red color.
    Purple to red… what about brown?
    Ok. So, even though the animal is no longer living, the enzymes in the muscle are still somewhat functional. The enzymes in charge of using oxygen to produce energy will take the oxygen and metabolize it. To do this, the pigment (actually, the iron in the pigment) is oxidized (it loses electrons). When the iron is oxidized, the meat will turn brown.
     In fresh meat, other enzymes can fix the problem by reducing the iron (give it electrons back) and it will turn back to purple. Then, it can grab some more oxygen and produce more energy and the cycle begins again. This really only happens on the surface of the meat where it is exposed to oxygen, so at first, you have a red layer with the purple underneath (everywhere on the meat that is exposed to air will be red. You won’t see the purple unless you cut it). At first, the brown coloring is not around long enough to see. As the process slows with time, a brown layer of pigment will form between the red and purple.


    Eventually, the enzymes will run out completely and the muscle will not be able to fix the oxidized, brown pigment and it will turn completely brown on the surface. That is the brown coloring you see. If you leave it long enough, the oxidation could spread to the fat and cause some off-flavors, but the paying attention to the use-by date should prevent that.
    Here is a picture from a study we conducted. Some steaks were left in retail cases (in our lab) for a week and allowed to turn brown. Then we cut them into little cubes. You can see the completely oxidized brown coloring on the surface and the purple coloring in the middle.

    Just remember to pay attention to the use-by dates on the package and if you don’t cook it by then, freeze it by then.  Use your nose and feel if the meat is slimy. If it’s smelly or slimy, cut your losses and throw it out.

    I also have a video blog about why meat is red.

    40 comments:

    1. Replies
      1. That's a great question. I'm afraid I don't have a good answer. Fresh meat has a tangy, almost-bloody smell, but meat that has spoiled has a more rancid smell. Its very offensive.

        Pathogenic organisms may not produce a smell, but other bacteria do. If spoilage bacteria have had a chance to grow and be smelly, then pathogenic ones may have too.

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    2. Thanks so much. I will not be so wasteful in the future. Very appreciative of your post.

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    3. What about meat that's red on the outside, I go to cut it to repackage it, and I have a ring of brown on the inside, and inside that ring it's red?

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      1. That's a great question! That little ring of brown is from oxidation. The red ring is where the meat is oxygenated, but the oxygen only penetrates so far into the meat. At the border of the red, there is a very low level of oxygen which promotes the formation of the oxidized brown color. The muscle can reduce (or un-oxidize) the meat for a while, but eventually, its ability to do so diminishes. When starts to run out of reduction ability, the brown will form and stay. Eventually, that brown layer will work its way to the surface and make the meat look brown from the outside.

        Hopefully you repackaged it to freeze it because its shelf life is nearing its end when you see that little brown layer. You may only have a day or two left.

        I know this can be confusing. I hope this helps. Its not spoiled, just going through a natural process of oxidizing.

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      2. Thank you very much! This was much more helpful than what Fry's Food & Drug gave me for an explanation.

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      3. And yes, I cut to repackage it to refreeze it.

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    4. I bought Angus stew meat on a Saturday and put it in the back of the refrigerator (which I know to be just below 40 degrees — even in the door our milk is ice cold). On a Thursday mid-morning I went to prepare it when I noticed the Sell By Date was the day before.

      I can't find an expiration (use by) on the meat so I don't know if it's safe to use.

      I am typically very cautious about food, due to a bad case of food poisoning years ago. It's the summer months and so the beef was placed in a zippered club store refrigerator bag at checkout with the rest of the cold food, but it took 35 minutes between the point when I placed the meat in the shopping cart and arrived home thanks to long lines at the club store and one brief stop of less than 10 minutes. The refrigerated bag wasn't used until checkout so I estimate that the meat was in the cart about 14 minutes before it was placed in the refrigerator bag. (In the shopping cart, I cluster the cold items together.)

      Upon arriving home, the meat was placed at the back of the refrigerator. Five days after purchase, I looked but could not find a Use By date (only the aforementioned Sell By date). The meat had gone from bright red in the store to an oxidized color similar to the photos with this post (a dull brown). I opened it up and while I generally have a good nose, I could not smell anything off whatsoever. I did not touch the meat to see if it was slimy but visually it did not look to be changed or smell off in any way. I browned the meat for more than 10 minutes and while I didn't get that characteristic fresh beef fragrance it didn't smell bad, either. By the time I was done it still had no real smell to it at all, either raw or browned. I placed it in a crockpot on high for 6 hours with other ingredients (potatoes, onions, etc.).

      Is this going to be safe to eat? I realize the quality of the flavor will be degraded but I don't want to serve it tonight if it's going to cause illness.

      And with that question, a perhaps you can clarify something for me: Is it true that relying on smell is not a good test because the pathogens responsible for illness don't really produce an odor? I've read conflicting comments on whether or not you can smell the types of bacteria that are responsible for illness.

      Thanks!

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      1. I would use a thermometer and make sure the temperature of your meat reaches 160. Chances are it will reach a much higher temp than that in the crock pot.

        Meat color is generally driven by oxidation. If you get your stew heated good, you should be fine.

        Hope it's tasty.

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    5. Thank you! I appreciate the fast reply. I will use the thermometer as suggested.

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    6. I just opened new pack pork chops family pack of 8. all look good on top; but some discoloration in package where one rested on another. I cooked 4, then I wondered should I eat?
      I don't know if the color was brown, gray, etc. I froze 4, and the discoloration is gone on those. not frozen completely, so I opened to smell. no odor, but do feel "slimy"?? I mean, what is slimy? ok, the date use by is tomorrow. help with advice, please

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      1. Hi. Sorry I'm just getting to this. My internet at home is not great. In the evening, I'm easier to reach through a facebook message or an email.

        The discoloration on the lower chops is caused by the low amounts of oxygen available to them. That doesn't concern my at all.

        I'm not sure what you mean by slimy. Extreme slime can be caused by bacteria, but if they were frozen, I don't think that's what's going on. The moisture and protein can combine and be a little slimy especially if the chops were injected or marinated.

        I would just make sure you cook them to 145 (or 160F if they were injected) and they should be fine. Hope they were good.

        Sorry again about the delay.

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    7. Hey there, I bought some chicken today at the grocery store. Stuff I usually buy. It was packaged today and had a sell buy date of 5 days from now. I noticed it felt rather slimey but rinsed it and cooked it anyway. Figured it was fine. I didn't smell it at all. I cut it up into small pieces and cooked it in coconut oil. A lot of the small pieces cook up kind of grey and were very tough. I tried cutting them apart. Haven't actually eaten it yet. Think it's safe? I'm not sure why it wouldn't be if it was packaged today but I'm worried! Thanks

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      1. Did you make sure that you cooked the chicken to 165F? I'm not worried about it being unsafe if you cooked it to 165.

        I forwarded your question to a poultry scientist friend who does research on poultry quality. Hopefully she will have a better insight into why it looked the way it did.

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    8. I didn't check, they were cut up into bite sized pieces and I don't have a meat thermometer. But there seemed to be a lot of water out of the meat so maybe it had a bit of a boiling effect? I was thinking that might attribute to the grey/tough color and texture.

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      1. You know, I've never cooked in coconut oil, so that may have an effect on the color. Did you go ahead and eat them?

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    9. I haven't tried it. I'm too chicken! Haha!

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      1. Can you take a picture of it and send it to my email? jws09@uark.edu

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    10. Hi there! This may be a dumb question, but now my paranoid self has got me worried. I bought a pack of pork loin yesterday and put it on the fridge. It's use by date is 12/17. Today I took it out to prepare it for the crock pot. I opened the package and it had two pieces folded in half and on the inside of the pieces, it was an off color. Definitely grayish, but I'm not sure about green. Nothing for me to be immediately concerned and the outside was nice and pink. It didn't smell bad or feel slimy so I finished and threw it in the crock pot. Now I'm thinking about it and can't decide whether or not I should eat it tonight for dinner. The uncertainty of not knowing whether it was green is worrying me. I've purchased the same thing before and didn't have this issue. Any suggestions?

      Thank you!

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      1. I wouldn't worry about that color at all. Especially since you didn't notice a smell or any sliminess. When the two pieces were stuck together, it created a situation with low oxygen. That causes the meat to oxidize and turn a brownish-green color. Sometimes you will see the same thing under the label of a package of meat.

        If its cooked all day in the crockpot,it should easily reach a safe temperature of 145 or more. Stick a meat thermometer in it and double check.

        Thanks for the great question!
        Janeal

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    11. Bought a very large exoensive prime grade prime beef 7 days ago. Realized tonight it has been in my trunk since. It has been single digits outside n today high of 40. Car only been in non heated garage at night. No brown spots or smell. Not slimy. One dark blackish spot underneath a fat layer. It does look rather bloody to me. Splurged big time so purchasing another is not an option. Is it okay to still eat?

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      1. I don't know. I don't think I could comfortably tell you it's safe to eat. It may be fine, but I would be very nervous.

        I'm so sorry.

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    12. Ho there last night we went and bought a two pack of thin sliced sirloin for quesadillas. When we opened the pack the part that over lapel were very brown and the inside was a little purple so on both half of them were like this but the other half were not. They were fresh just bought anf did not expire for 4 more days so we cut into the brown part and it was brown and purple threw the hole thing (thickness wise) and it smelt bad. So we cut off the halves that we believed were bad and went ahead and cooked the other halves we thought were good some still had a little brown in the middle. My husband was the only one who ended up eating it and 3 hours later began throwing up continuesly and having sever stomach pains it's been almost 24 hrs nd vomiting has stopped but still in pain. So my question is if u have a steak and only half is bad does that mean that u should throw out all of it and if u didn't could that make you sick?? Thank u hope to hear back soon

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      1. Tiffany, I would contact the store and tell them your story. Sounds like he got some food borne illness. When I worked at a grocery store as a student, if someone came in with a story like that, we tried to make it right. Other stores may not have the same policy.

        For future reference, if part of it smells bad, I would throw it all out.

        I am so sorry that you have had a bad experience. I hope your husband gets to feeling better soon. Be sure to tell the store that he was the only one that ate it and the only one that got sick.

        Take care,
        Janeal

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      2. Yes I did contact the store and they wanted me to bring the meat back I told them I threw the bad meat away but I could try to dig it out they said they would replace it or give me my money back but I had to bring the meat in as crazy as that sounds. Iv cooked steak before that had brown spots and everyone was fine but this was weird because it was all through the thickness and just half of each piece where it was over lapped and once we separated the bad from the red part of the meat the red part we cooked smelt nd felt fine I've never seen it look that bad ever and he is still very sick in the bed he took medicine to atop vomiting but still in pain. But thank you so much for getting back to me so fast iv been disenfecting the whole house because I didn't know if it was the meat or a horrible bug of some sort. So for now on if half is bad it's all bad correct?

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    13. " (Hopefully, stored on a plate on the bottom shelf.) " can you explain this me please. I usually just throw the package in the fridge or freezer. does this mean that's the wrong answer. does on a plate mean covered or uncovered? eeeek, now I feel like I've been getting this wrong for about 40 yrs!! elizabeth

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      1. Sometimes those packages can leak and you don't want meat juice getting all over other foods in the fridge. So I always put fresh or thawing meat on a plate and/or on the bottom shelf of the fridge. If you have lettuce or fresh fruit in the fridge, you are probably going to eat them without cooking them, so you would want to store those things about the meat. The plate doesn't have to be covered.

        I have a whole post about storing food safely called Safety in Knowledge. http://momatthemeatcounter.blogspot.com/2011/09/safety-in-knowledge.html

        Thanks for the great question!

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    14. We just bought a pound of ground chuck. Just a standard one in a black tray and covered in plastic. It's all red, except the part that was right under the label explaining the contents of the package. That part is much darker than the rest of it, but I'm not really sure what I'd call the color. It's like a hint of purple and grey or something. Do you think that the label was just blocking oxygen or something?

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      1. Thats a great question and yes! I think that's exactly what was happening. The label blocked the oxygen some, but not completely and that caused the meat to oxidize and turn it a little brown.

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    15. I purchased a pack of six porkchops and five of them were we're fine thry didn't smell or have discolouration but 1 of them have discolouration and a nasty oder threw out the one but have the rest cooking is that ok?

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      1. I think they are probably ok if you cook them to 145. The outside will get very hot, so any bacteria that might be there will be killed.

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    16. I purchased a meat prder yesterday which came with $50 worth of lean hamburger meat. The burger is extremely dark.. like a chocolate brown/burgundy color.. it smells fine but i am super leery of the color as i have never purchased burger that dark before... thoughts??

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      1. Meat color can be driven by lots of factors. I have a few questions about it.

        Was is frozen? How was it packaged? How lean is it? Did you buy it at a store or order it to be delivered? Is there any way it could have been temperature abused?

        Can you send me a picture to jws09@uark.edu?

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      2. I just emailed you two pictures. I am unsure of tenperature abuse. It is the first time I have personally purchased meat at this local establishment but they sell meat like crazy and are known for their meat orders. I called it in and when we got there, they were putting the order in the box. We live roughly 45 mins away from the city where we got it and we were probably 2 hours shopping after we had picked it up. The meat was however deep in the box under alot of other cold/frozen meat

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      3. Thanks for the pictures. It looks to me like its just deoxymyoglobin. Its just the purpley-red color from not being exposed to oxygen. The surface may be a little oxidized (brown) from a little oxygen leaking in the package. I think it should be just fine. Enjoy!

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    17. To answer ur other questions, it was not frozen when i got it. The packaged date was yesterday, same day i got it and as far as how lean is it? We are in Canada so our hamburger doesn't have the % lean on label.. we have regular, medium, lean and extra lean.

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    18. Hi,

      I just defrosted a pack of pork ribs. While the meat part has a slight freezer burn, it didn't smell funky or slimy. However, the bone part is now very dark, almost black instead of the usual grey. Is this still safe to eat, considering im marinating the ribs?

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      1. Hi Kevin, Sorry for the late reply. I've been out of the office.

        Black bone is not a cause for concern. We actually did research on this when I was a student. The hemoglobin in the bone marrow oxidizes just like the myoglobin in the muscle and it looks dark brown or black. Its perfectly safe to eat. I hope you enjoyed your ribs.

        Janeal

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