rancidification

Rancidification is the process of complete or incomplete autoxidation or hydrolysis of fats and oils when exposed to air, light, moisture, or bacterial action, producing short-chain aldehydes, ketones and free fatty acids.

When these processes occur in food, undesirable odors and flavors can result. In processed meats these flavors are collectively known as warmed-over flavor. In certain cases the flavors can be desirable, as in aged cheeses.