Rancidity of oils and fats is a factor which can immediately reduce the sale price of these products to customers in the food and cosmetics industries. Oils which remain stable over longer periods of time are more highly valued as they lead to a higher quality end product. Rancidity is a natural process which occurs as fats and oils age and oxidize, and can be delayed or even stopped by addition of antioxidants at the right time.
Determination of rancidity is possible in several ways (e.g., measuring the acid number or peroxide value), though these tests only give information about the current state of the product, with no indication about the remaining shelf life. One analytical method that can measure this time span until spoilage is the Rancimat method, which artificially ages the samples to determine whether antioxidants may be needed to help manufacturers get the full value from their oils.