Shelf life

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Shelf life is length of time that food can be stored safely. Food cannot be kept forever. After a certain time it may go bad. . Shelf life is also used for drugs, drinks and other things that can go bad or out of date. The words are also used as a metaphor for other things which have been around too long.

In some countries, a best before, use by or freshness date must be put on packaged foods. During this time, if the food is kept under proper conditions the quality of the food does not change. Frozen food that does not remain frozen will go bad earlier, for example. These labels do not guarantee the safety of food. They should only be used as a guide.^[1]

Shelf life is different from expiration date. Shelf life is linked to food quality, expiration date to food safety. Something that has passed its shelf life might still be safe, but quality is no longer guaranteed. In most food stores, shelf life is controlled by using stock rotation. This means moving products with the earliest sell by date to the front of the shelf, so that most shoppers will pick them up first and take them out of the store. Stores can be fined for selling out of date products. Shops may have to mark such products down as wasted, leading to a loss of profit.

Shelf life can be changed by many things: exposure to light, heat, gases (including humidity), mechanical stresses, and contamination by things such as micro-organisms.

Product quality is often modelled using only one parameter, for example the concentration of a chemical substance, a microbiological index, or a physical parameter. Sometimes, the parameter picked is not significant.

The shelf life is an important factor to health. Bacteria are everywhere, and foods left unused too long will often get large amounts of bacteria living in them. It may be dangerous to eat them and lead to food poisoning. The shelf life itself cannot always tell how safe it is to eat a certain item of food. For example, pasteurized milk can remain fresh for five days after its sell-by date if it is refrigerated properly. In contrast, if milk already has harmful bacteria, the use-by dates do not matter.^[1]

For drugs the situation is different. If drugs are used within the expiration date, the manufacturer guarantees that they work as expected. After that date, they may still work, but they are no longer guaranteed. A study done by the U.S. Food and Drug Administration covered over 100 drugs, prescription and over-the-counter. About 90% of them were safe and effective as far as 15 years past their expiration date. Joel Davis, a former FDA expiration-date compliance chief, said that with a handful of exceptions - notably nitroglycerin, insulin and some liquid antibiotics - most expired drugs are probably effective.^[2]

Preservatives and antioxidants may be put into some food and drug products to make their shelf life longer. Some companies use induction sealing and vacuum pouches to add to the shelf life of their products. Some things can be controlled by provisions in the packaging. For example, the amber bottle used for many beers blocks damaging wavelengths of light. Transparent beer bottles do not. Packaging with barrier materials (e.g., (low moisture vapor transmission rate, etc.) extends the shelf life of some foods and pharmaceuticals.

1. ↑ ^{1.0 1.1} "The_Truth_About_Food_Expiration_Dates". Retrieved 2008-09-01.
2. ↑ Cohen, Laurie P. (2000-03-28), "Many Medicines Prove Potent for Years Past Their Expiration Dates.", Wall Street Journal, vol. 235, no. 62, pp. A1 (cover story)