In the early days, metal containers were the cheapest and easiest to make, so almost all food was stored in cans. Tin was a particularly soft and easy to mold/shape, and didn’t rust like other options, so most preserved food cans were made of tin.
Things went great for a while, with some foods easily being shipped to places they previously wouldn’t have survived due to long journeys, and families could store food to eat when it wasn’t available fresh.
However, reports of illness around certain foods started to become prevalent. Pickles foods would frequently “go bad” much sooner than other canned foods, and even though the food tasted the same, people would report illness very soon after eating older pickled products. After years of analyzing (crudely) samples of purportedly problematic pickles, scientists finally concluded the preserved foods themselves were fine—it was the cans that were the problem!
They discovered certain food solutions—like pickle brine—could “leach” harmful chemicals from tin, much faster than non-brined foods. As an experiment, they started un-canning recently preserved pickles and putting pickled food in glass containers instead of tin. Jarred pickles tasted exactly the same and were preserved just as well as their canned counterparts, but nobody got sick!
In the end, the conclusion was uncanny and jarring.
Note: this is my first “original” joke (though inspired by lots of other variations). Definitely feel like it’s missing something in the setup and delivery—was going for a “I can’t believe I read that whole thing for a dad-joke level punchline, but feel I may have missed the mark. Welcoming all criticism.