Have you ever bought an old cardboard tube of salt? The last time I did was in a tropical location. Somehow over the years it had acquired the scent of wet rot, and the relentless cycles of humidity had effectively recrystalized the contents into a rock.

Luckily the packaging had started to biodegrade, too, so it was easy enough to scrape off the fiber fuzz and hammer down the inner salt rocks into something useful. Better than nothing! But I wish I’d been able to buy it by its sell-by.

(Spoken as a skeptic of deadlines of all sorts, and one who routinely ignores food safety. I still think the dates are mostly silly, but that type of instance reminds me why it’s a hard problem: even if you’re not a dastardly wastemonger, choosing the “right” date depends heavily on handling and climate and factors beyond your control—unknowable at production time.)

How do you know this happened as a result of the sellby, as opposed to being improperly stored? The package could get wet at any point.

I suspect it was exactly a function of improper storage (and that it would last forever in a cool dry place).

My broader point, I guess, is that the appropriate date to sell something by depends so heavily on factors unknowable at production time that it’s hard to guess. But also that apparently-shelf-stable goods can in fact degrade.

And I guess that it’s kind of weird and unnatural the way modern industrial packaging/processing have trained us to expect that a given product should be interchangeable with any other until an arbitrary date.

As another poster mentioned, it likely refers to the packaging - either degredation of materials used or the effect that has on the contents (moisture ingress, oxidation, etc).

For salt, that seems somewhat silly, but not enough to make me fundamentally distrust the rationale

Sell by is entirely unrelated to quality though. It's just how often they think they can get away with. Like the recommendation on a box of baking soda... Put it in your fridge and change it every 30 days. No thanks.

Pretty sure that’s the recommendation to deodorize your fridge, not related to the baking soda’s shelf life. The other side of the box says “keep in a cool and dark place”.

It does seem to go “flat” after a few months regardless, even when the expiry date is 2 years in the future.

There’s a whole controversy over this specific issue. For decades they recommended 90 days in the fridge to keep it fresh.

Then they switched to 30 days recommendation to goose sales.

It's not how long they can get away with, it's how long they are willing to listen to complaints about it.

A sell by date makes perfect sense on salt. No packager wants to be responsible for material that sat on someone else's shelf for years and years.

I think it all makes sense when you consider that the sell by date is the date at which they’ll stop accepting responsibility. And the “best before” dates are just guidelines.

I've seen it on vinegar too.