What causes rancidity in fats and oils?

Rancidity in fats and oils primarily occurs due to exposure to air, which leads to the oxidation of unsaturated fats. When fats are exposed to oxygen, a process called oxidation begins, causing the fatty acids to break down and resulting in the formation of off-flavors and off-odors commonly associated with rancid products. This oxidation process can be accelerated by the presence of light and heat, which is why it is essential to store fats and oils in a cool, dark place.

Although high temperature can contribute to rancidity by speeding up the oxidation process, and moisture can create an environment for microbial contamination that affects the quality of fats, the key factor is definitely the exposure to air. Thus, while high temperature and moisture can influence rancidity, it’s the exposure to air that is the primary cause of this chemical degradation in fats and oils.