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Food expiration dates are usually determined through a series of tests and trials designed to measure the safety and nutritive value of the food in question. In many places, government regulatory bodies are involved in setting expiration dates, or at least mandating their use. Not all food products have fixed expirations. In general, the only foods that are required to have and display them are infant formulas, which have been shown in numerous clinical trials to lose nutrition over time. Since babies being fed formula typically get all or most of their nutrients from the drink, governments usually see a vested interest in making sure that levels of vitamins and minerals are stable and consistent. Most other foods have “sell by” or “best if used by” dates. These aren’t quite the same as expirations, since in most cases the product can actually be fine for days if not weeks past the noted time. These dates are more often determined not on the food’s inherent nutritive content but on when it is most likely to taste the best and look the freshest. In most instances, the printing of “use by” dates is at the discretion of the manufacturer and isn’t always based on any sound science.
Understanding Food Expiration Generally
There are lots of reasons why foods are printed with expiration dates, though consumer safety is usually at the top of the list. “Expired” foods are typically those that have either lost so much nutrition so as to be harmful, as is the case with many liquid and powdered formulas, or those that are in imminent risk of spoiling and becoming breeding grounds for bacteria, like dairy and meat products.
In general, dates are determined by studying the chemical composition of the food in question and then comparing this with the environmental conditions where the food is likely to be stored. There’s often a lot of testing and experimenting that goes into finding the line between “safe” and “should be thrown away.”
Oversight and Governing Agencies
In the US, the Food and Drug Administration (FDA) oversees the regulation of packaged food and drugs, while the Department of Agriculture (USDA) regulates the production and packaging of fresh meats and produce. Many other countries have parallel systems. The FDA requires an expiration date only on infant formulas, and the USDA requires a label for the packaging date of fresh poultry. Packaging isn’t the same as expiration, but can give consumers a clearer idea about the product’s freshness.
Most all other food and over the counter medication can be labeled with terms such as "best if used by," as opposed to having a clear expiration. The FDA notes that this is because the majority of foods and drugs may spoil if they are kept to long, but they may not, and in most cases they don’t present a serious health danger and shouldn’t be discarded simply on a technicality.
Clinical Studies and Trials
Dates that are printed as true expirations are usually determined based on extensive tests. Researchers try to pinpoint the moment that a food goes from being possibly past its prime to presenting some true threat. These tests are usually carried out by career clinicians and typically go through several iterations.
Understanding “Best By” Labels
It’s much more common to see foods printed with a "sell-by" or “best by” date, though in most cases this is not the same thing as an expiration. Many are actually designed by food manufacturers to force sale and turnover, and can also be used by stores for the same reason. The FDA notes that labels such as "best if used by" refer more to the quality or flavor of the food than its intrinsic quality or nutritive content. Consumers should usually use their best instincts in these cases, and only throw food away that smells, tastes, or looks “off.”
Effect of Packaging
How a food is packaged can also affect its freshness, even if it’s within its window of best use or expiration. Canned foods can typically be stored for up to a year as long as they are stored at a temperature below 75° F (24° C). Dry foods, such as cereals, pastas, and cake mixes, can usually stored up to six months prior to use, but they may spoil faster if they are exposed to moisture, heat, or direct sunlight. Using them even years later may not present any problems, though they may not taste as fresh.