Yesterday, after struggling to open a glass jar, I resorted to a knife to pry it open. Not for the first time.
Which got me wondering, how do they evacuate the jar, before screwing on the lid?
Another thought, a survey of public science illiteracy, ask: is the lid stuck because it's pressurized, or evacuated? What would be the proportion of replies?
onsdag den 4. januar 2023 kl. 00.54.51 UTC+1 skrev RichD:
they put the lid on while it is hot ...
It's often the polymer layer on the sealing surface or the threads. Turning the jar over and banging it firmly on a countertop will often get it loose.
And of course one can always use the 'blue wrench'. ;)
Cheers
Phil Hobbs
They just top it off with steam instead of air, then as the steam cools it condenses causing a partial vacuum, the steam is often a side-effect of the production process.
You left out "friction" and "glue"
duh! If I didn't sleep through my chem classes, I'd know these things.
That's possible. But in my experience, I always hear a hiss, as air enters.
Indeed, it's an essential part of the process. The food has to be hot enough to be sterile when the lid is put on. That way there's nothing alive inside to make the food go bad.
Sylvia.
The frequently-seen aluminized seal atop catsup bottles etc. is a masterpece of electrical engineering. Plastic bottle, plastic cap, but the seal is an electrical subcircuit, with sticky plastic as output.
On a sunny day (Thu, 5 Jan 2023 12:20:11 +1100) it happened Sylvia Else snipped-for-privacy@email.invalid wrote in snipped-for-privacy@mid.individual.net>:
There are endless series on Smithonian Channel about how food is made in factories. Nice and sometimes huge machines... Satellite dish is all you need. They go into fighter planes and all sort of stuff too.
RichD <r snipped-for-privacy@yahoo.com wrote in news:f3bdb417-cf95-450e- snipped-for-privacy@googlegroups.com:
It is not a full vacuum. Just 'some' negative pressure. The media placed into the hot jar is hot and the air during capping is as well. When it cools, it pulls a "partial vacuum" on the head space in the jar. The same way "Mason Jars" work. I did not believe it was that easy, but it is.
In order to open such a jar, which uses a thick, soft polymer as a gasket material and does not like to readily realease, Turn it upside down and rap it sharply on the ass end with the palm of your hand. If this process worries you, have someone who knows about it show you. It does not take a very hard rap. Anyway, afterward the lid comes off easy. The rap of your hand creates a shock wave that causes a momentary breech of the gasket, freeing it up compared to its long term sealed position.
Things which are packaged cold can be lidded inside a special chamber incorporated into the lidding machine.
Carbonated beverages utilize positive pressure, which they themselves generate in the "head space" of the "pressure vessel" that is a soda bottle.
Lasse Langwadt Christensen snipped-for-privacy@fonz.dk wrote in news:29c0e39a- snipped-for-privacy@googlegroups.com:
Hey! Do you know what the origin for the Ball Drop in New York City on New Years Day is?
Neil DeGrasse Tyson does. Cool little vid about it.
Thanks! Ed
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