Chemical deterioration

Whole grain cracker rancidity – An example with GC-MS comparisons of complaint samples to normal samples

https://danharring54.blogspot.com/2023/10/chemical-changes-observed-in-spoiled-or.html

Metallic flavor in milk: during processing the fat can become oxidized. Some of the 8, 9, and 10 carbon scission or cleavage products with double bonds have unusual odors (e.g. cucumber, mushroom, metal). 1-octen-3-one in particular has an unusual metallic note. It is more noticeable (has a lower flavor detection threshold) in reduced fat milk, because there is less milkfat to cover up the taste of the breakdown products. This is different from canned milk (or dairy plants with rusty pipes), which have a measurable increase in iron.

https://danharring54.blogspot.com/2022/08/metallic-flavor-in-milk.html

Color degradation

Oxidation of fats/oils, polymerization, hydrolytic breakdown

Terpene degradation. (primarily Monoterpenes)

Polymerization, dimerization, resin formation, texture change, darkening, clumping, protein denaturation

Hydrolysis