[techmind (OP)]

On a few occasions, with meat from more than one supermarket I have observed prepacked refridgerated diced beef turning greeny/grey a day or so after purchase, yet well within its use-by date (eg 5 days within). After less than 24 hours with only minor discolouration I've used the meat with no ill-effects, but a while ago when the meat was badly discoloured a couple of days after purchase we took it back to the store for a replacement.
I've no reason to suspect the domestic fridge was insufficiently cold.


What's going on here? Is the discoloured meat harmful to eat?

[CliffordK]

The grey colored meat is probably no worse to eat than the bright red meat (or visa-versa).

Many stores treat the meat with carbon monoxide which gives it a bright red color, and can make it appear fresher than it actually is.  There have been complaints that this treatment may in fact disguise decay.

If you buy your meat from a smaller butcher, you likely don't get the carbon monoxide treatment, and the meat will discolor quickly without ill effects.

For steaks and similar cuts, make sure the outer layers are thoroughly cooked.  For hamburger and ground meat, make sure it is cooked through the piece.

[evan_au]

The browning is oxidation - reaction with oxygen (a very slow form of the cooking process). By itself, it is not a health hazard.

To reduce oxidation, store the meat hermetically packaged (eg in plastic wrap); this is easier with a lump of steak than with mince (which has been thoroughly exposed to the air during the grinding process). Keeping the temperature lower (eg in the freezer) will slow the reaction even further.

The US Food & Drug Administration has approved CO as a colour-fixer, but the EU has banned it, apparently on the basis that it could disguise unsafe meat.

Many shops use pink-coloured lights to make the meat look fresher; maybe you could wear rose-coloured glasses?

[wolfekeeper]

Are you talking about the rainbow colours you get on meat, or is the green obviously bacterial?

The rainbow colours aren't at all harmful, and can look green, but green from bacteria is something different.

[chris]

We covered the green-meat story earlier this year on the chemistry world podcast;

here's the link to the article it was based on; in that case it concerns bacon, but I suspect something similar is going on:

http://www.rsc.org/chemistryworld/2012/05/mystery-green-bacon-solved

Chris

[evan_au]

If it smells "off", don't eat it!

[wolfekeeper]

Bad idea.

You can't smell botulism or salmonella.

[CliffordK]

Bad idea.

You can't smell botulism or salmonella.

Botulism is an anaerobe, with the primary problem being a toxin buildup in canned goods, not the bacteria itself.  I wouldn't worry about it on your steak.

Salmonella is potentially a problem, along with staph aureus toxin buildup.  Both generally giving unpleasant acute symptoms. 

If you have a steak, cooking the outside will kill a lot of pathogens. 
Hamburger is a bit more of a problem since it is easier for the pathogens to get to the middle of the hamburger, so it needs to be cooked better.

[yapimop]

@techmind hi I have some beef in my fridge and I went to cook it and I noticed that some parts of it were brown and not red like beef is normal what does this mean is it bad or on the turn or quite normal for beef to do this I only brought it Friday and it's well in its sell-by date any help on this would be good as I don't want to cook it for dinner and end up with food poisoning but I don't want to throw it if it's ok I have never come across this before

[Halc]

I don't want to cook it for dinner and end up with food poisoning but I don't want to throw it if it's ok I have never come across this before

If you actually read the replies to this 8 year old topic, the question has nicely been answered. Go ahead and eat your meat. It turns color well before the sell-by date and is edible for some time after it if it has been kept refrigerated.

[paul cotter]

Wolfekeeper, have you ever worked in a microbiology lab?. I have and I can tell you with certainty that some of the worst smells imaginable derive from anaerobic cultures. True that one will not smell botulinum toxin but other bacterial products will stink. Salmonella is aerobic and it's aroma is not quite as bad but still vile.