It’s almost impossible to tell when the food you buy will become “unsafe”
In one episode of the (excellent) podcast 99% Invisible, host Roman Mars and crew examine the expiration date debacle themselves, and find that it is almost scientifically impossible to accurately predict when food you buy may become unsafe to eat. For instance, leaving milk in a hot car the day you buy it will ensure it spoils faster, and colder fridge temperatures can keep a carton of milk longer than others. There are just too many variables to peg a specific day.
They also clear up a long-held medical falsehood: old food almost never makes you sick, contaminated food is what will land you in a hospital bed (or grave). So, these dates, even with fickle dairy items, are not safety precautions. Deli meats, unpasteurized dairy, smoked seafood -- these are the foods that may increase in contamination with time. Graham crackers? Not so much.
Expiration dates signify freshness and taste
...and not some mystical time where your food will "expire." But "freshness" in this case is a nebulous, unspecific parameter.
Once dates on packaging became industry standard, the government began to pursue a uniform system for marking freshness dates. There was zero federal regulation and standardization of dates placed on food. The FDA even attempted to gain some control, but since the labels focused on freshness rather than health, they determined it was not worth their precious time.
Despite these murky details, so many of us believe the dates on our food are ironclad parameters that tell us when our food is safe to consume. Except for my Aunt Linda, who consistently fed me expired yogurt whenever I visit her. As it turns out, she may have the right idea.
Most food companies come to their freshness conclusions by conducting taste tests (yes, seriously)
According to 99% Invisible, a group of testers will subjectively sample food of varying ages and then take a survey. Those results lead to the freshness (or “expiration,” or “best by”) date. So some random tester saying “these waffles taste kind of weird” determines that seemingly concrete but actually very non-scientific expiration date on your food and drink.
And smaller companies, without the budget/time for a taste testing session, will sometimes just estimate (read: make up) their dates. So, if your artisanal, small batch, locally sourced chipotle-infused pickles still taste good a few weeks after they “expire,” it’s no coincidence.