Fridge burn?

[cjsmith]

Put a pound of ground beef in a self-defrost freezer and pretty soon it'll be brown around the edges.

Put it in the fridge and sooner or later you'll see a similar brown. I don't think my fridge crosses the freezing point, not since we lost an expensive bottle of insulin to that very thing and messed with the thermostat a tad. Is the blood simply draining out of the tissue? What's going on there?

Comments

[jcgbigler.livejournal.com]

The defrost cycle does bounce the temperature up and down to get rid of the frost build-up, so there could possibly also be some freezing & thawing going on around the edges.

The red in meat is from myoglobin, which stores oxygen in slow-twitch muscle cells. Like hemoglobin, myoglobin has an iron ion that binds the oxygen, and like hemoglobin, myoglobin is red when it's oxygenated.

One of the other common additives is carbon monoxide. CO bonds much more strongly to hemoglobin and myoglobin. When CO gets into our blood, it bonds so tightly that it effectively prevents oxygen from being able to get into the blood, and we asphyxiate. For the same reason, CO bonds more strongly to myoglobin and keeps the meat red even in the presence of oxygen. The CO levels are low enough to not be a health risk, but they can fool you into thinking the meat is a lot fresher than it is.

Of the various descriptions of what's happening as meat turns brown, the one that seems to make the most sense to me is that the red color is from Fe⁺² ions. Fe⁺³ is brown. It would seem that either cooking the meat or exposing it to oxygen will oxidize the Fe from +2 to +3.

[cjsmith.livejournal.com]

You are awesome.

Yeah, freezing/thawing = freezer burn, but I was pretty sure there wasn't freezing/thawing in the fridge. Fe⁺³, huh? Thanks!