Shelf life is the length of time that food, drink, medicine and other perishable items are given before they are considered unsuitable for sale or consumption. In some regions, a “best before” or “use by” is required on packaged foods. 

Shelf life is different from “expiry date” : the former relates to food quality, the latter to food safety.

The quality of most foods decreases over time and there is the natural need to evaluate for how long these products will maintain its commercial value. In Shelf life testing, one or more quality criteria which constitute sample failure are defined. Sample failure is the condition of the product which exhibits either physical, chemical, microbiological or sensorial characteristics that are unacceptable to the consumer, and the time required for the product to exhibit such conditions is the shelf life of the product. The quality parameters chosen must be monitored periodically for as long as the test is conducted. Normally such tests are conducted lasting at least as long as the required shelf life of the product.

A food that has passed its shelf life is still safe, but optimal quality is no longer guaranteed.

Under some circumstances, the shelf life is critical to health. Shelf life is most influenced by five primary events: light transmission,gas transmission, heat transmission, humidity transmission, or mechanical stresses.