Companies determine food expiration dates in a variety of ways, depending on the type of food. As of 2015, the only food item required by U.S. federal regulations to be marked with an expiration date is infant formula, so for most other foods, manufacturers are free to set expiration dates at their discretion.
As of 2015, there is no single or universally accepted system for food dating in the United States. However, over 20 states require dating of certain highly perishable foods such as meat, poultry, eggs and dairy products. In the United States, the Food and Drug Administration regulates packaged food and drugs, and the Department of Agriculture oversees the production and packaging of fresh meats and produce. In addition to requiring an expiration date on infant formula, the FDA requires a label identifying packaging date for fresh poultry.
There are typically two methods for dating food – either a best-by date or a sell-by date. A best-by date identifies the date by which food should be consumed for the best quality. A sell-by date identifies the date by which food should be purchased. Sell-by dates are typically determined by the amount of time a food item can keep at a given temperature without losing its nutritional value or developing harmful bacteria. Sell-by dates are ultimately determined by the nature of each specific food, according to the food's specific temperature levels over time.