How do food jar factories put negative pressure into the jar to begin with?
In: 87
Some good comments here about home canning, and how it relies on simple things like thermal expansion and contraction, and the fact that bacteria off-gasses and adds pressure when present. (Basically “germ farts” can break the seal and let product leak out, so a leaky bottle of aunt judy’s tomatoes should be trashed).
But home canners usually use a pressure cooker – water boiled under pressure can get “hotter than boiling”, about 250°f vs. 212°f – so even more safety comes into play, and the environment in the pressure cooker becomes sterile, as does everything in the bottles and the bottles and lids themselves. It’s a very old-school, simple and brilliant solution for a time when a big part of the populace grew some or much of their own food and needed a way to store it long-term; many of those people were probably functionally illiterate (or science-illiterate), so a simple set of steps was needed, that could be taught to your kids. (My mother was born in the 1920’s in an Appalachian shack with no plumbing – she grew cucumbers in our yard and I’ve still never had better pickles than she made every summer).
The metal rings around the top of canning jars aren’t there to seal the jar closed – they’re to *protect the seal* from being knocked loose or chipped free. You just tighten them finger-tight.
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