© Noel Hendrickson/Getty Images
Mike Pomranz
June 22, 2017

As the discussion over food waste has grown in recent years, the expiration dates put on products have increasingly come into the crosshairs. What do things like “sell by,” “use by” or “best if used by” really mean? Who comes up with these dates and how? Will I die if I eat old bagged lettuce or will I just end up with a gross but edible salad?

The site The Conversation specifically set out to explain all the different ways these dates are decided on. Of course, no one set method exists, which is part of the problem. Instead, brands will pick from a number of different processes. Some are highly scientific: “Microbial challenge studies” will actually add a pathogenic microorganism to a food, and then researchers will try to mimic the conditions that product will withstand all the way to a customer’s home, testing the product along the way. “Mathematical modeling tools” are also scientifically-based, using the results of previous challenge studies to extrapolate out a products shelf life.


Some testing methods are more straightforward. A “static test” simply puts the product under the same conditions it would face in the real world, with samples taken periodically as the food sits. The process can also be accelerated by placing the food in chambers controlling conditions like temperature and oxygen, meaning a company doesn’t have to wait ten years before determining that whatever it makes will be good until 2026.

But labeling can be even more basic than that. “Smaller companies may list a date on their product based on the length of shelf life they have estimated their competitors are using, or they may use reference materials or ask food safety experts for advice on the date to list on their product,” assistant professor of food safety Londa Nwadike writes. Somewhere out there, some company is probably just taking a solid guess.

The biggest takeaway is that not only does the method used to determine these dates vary wildly, but how we should interpret that information does too. Even if a company does do a fancy microbial challenge study on their product, the date it stamps on the package isn’t the date after which you’ll get sick anytime you eat it. Unfortunately, the diligence still falls on consumers.

As far as I can tell, the safest and least confusing way to deal with these dates is to just eat everything as fast as possible

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