Food Scientist

How are food expiration dates determined?

A reader asked how a food expiration date is determined. What a great question! The answer is both simple and oddly complex. Basically, we get expiration dates by storing a food and waiting to see when the quality starts to go down. That’s right, just let the food sit for a long time and see if it is still good when opened. Sounds easy right? Well, there is a bit more to the process.

The most important thing to remember about expiration dates is that they are just guidelines. If the container has been opened or the seal has been compromised, that food will not last until its expiration date. Also, if the food is kept in harsh conditions (excessive heat, humidity or light) it might not make it to its expiration date. On the other hand, sometimes food can last longer than its expiration date. So use your best judgement when consuming food.

Before getting into the discussion here are some helpful terms:

  • Expiration date: the date when a product will probably not be high quality any more. Some companies use “Best If Used By” instead of “Expiration”.
  • Shelf life: the amount of time between the production of a food and its expiration date.
  • Sell by date: For more parishable products, this is the recommended last day a product should be available for sale.

Expiration dates are determined during storage studies, also known as stability tests. Normally, a company’s Research and Development team will run storage studies on newly developed products. A storage study tests the hypothesis: “Will this food be in good condition after X amount of time?”.

Before starting a storate study, the R&D team determines how long the study should be. They look at how long the shelf life is on similar products, how long the ingredients are supposed to last, what conditions the food will experience during distribution, when they have to report to their boss and/or client and other factors. Once a target shelf life is picked, they set up the storage study.

Background Science

Food ages over time. Aging is a series of chemical reactions that change the nature of the food. In most cases, heat speeds up these reactions and cold slows them down. When food is in sub zero temperatures, the aging process essentially stops. Freezing doesn’t always work though because it damages some foods.

Perishable foods, like milk, have spoilage microorganisms. For these foods, how long the food lasts is mostly related to these microorganisms. The stability tests are slightly different and I’m going to save that discussion for another day.

The Experiment

Prepare the food samples.
It is important that the food comes from the same batch so they are as close to identical as possible.

Label each sample.
Storage studies last anywhere from a couple of months to a couple of years. Can you image how crazy it gets in an area that has samples for several storage studies? It is not pretty. At my work we had two walk-in freezers that were at -20°C(-4°F). My least favorite job was cleaning them out. No one should have to sort through unidentifiable food in a place that cold!

Place the samples in their designated locations.
Normally this includes several environments. A really cold environment is great for control samples. A environment that simulates how the food will normally be stored, like at room temperature or in a refrigerator, is vital to the study. Most studies also include distressing environments such as high humidity, light, and/or high heat. These environments show how the food will hold up in bad conditions.

The distressing environments can also be used as accelerated time tests, since the aging process speeds up in high heat. For example, a sample that sits in 38°C (100°F) for two months could “age” about as much as a sample stored in 25°C(77°F) for six months. Of course, how much faster the aging process happens varies from food to food.


Take samples out and examine them.
Studies are custom designed for their food so what is examined differs from one storage study to the next. Normal items to check are taste, smell, texture, and color. For foods that need additional preparation such as cake mix, instant oatmeal packet, or sports drink powder, the test would include fully preparing the food. Vitamin content  or microbial content might also be tested.

Whenever a sample is taken out, it should be compared side by side with a control sample. Remember, the control sample is fresh or frozen in a temperature so cold that it is similar to a fresh sample. Comparing to a control is the best way to judge how the food changes over time.

Record and report the findings.
Like any good experiment, storage studies have to be well documented. This is imporant for storage studies since they last so long. It is hard to remember findings from a couple months back.


So those are the basics on how food expiration dates are determined. A lot of works goes into that little date.

Photo: Shark15

9 thoughts on “How are food expiration dates determined?”

    1. September 4, 2014 because the standard date format in America is MM/DD/YY which is Month/Day/Year so 09/04/14. In other countries like maybe somewhere in Eurpoe, it might be DD/MM/YY


  1. I do want to know, if consumables after expired, are given a certain grace period, so that, if a food is dated 5-3-017,one can consume it and 5-7-17.?


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