According to Serious Eats, warmed flavor (WOF) is caused by the breakdown of polyunsaturated fatty acids (PUFAs) in the cell membranes of meat, poultry and fish. During the cooking process, the meat cells begin to break down, allowing fat to enter the muscle for tender, juicy results. However, cell breakdown also releases iron molecules, which react with oxygen, and the aforementioned PUFAs.
This creates free radicals and unstable atoms that damage cells as part of disease and aging, according to Medical News Today. They process the fatty acids in the meat, giving it an appetizing aroma, although Serious Eats points out that the meat is still safe to eat at this stage. If it were spoiled meat, it would have a strong sour smell. According to Serious Eats, WOF is worse in poultry and fish because they have higher PUFA concentrations than beef or pork.
To reduce WOF in cold-cut chicken and turkey, many companies process the meat with phosphates and vacuum pack it while still hot. Phosphates neutralize free iron molecules and a vacuum seal keeps oxygen out to prevent a chemical reaction. There’s not much you can do to prevent WOF in a home kitchen, but follow the advice of the pros and try to limit your meat’s exposure to oxygen from the moment it comes off the heat. As soon as you’ve served everyone, pack your leftovers in airtight, heat-resistant containers.