Eli5, why do Mason jar lids typically come in 2 parts, threads and seal, as opposed to nearly every other commonly used household container?
In: 7899
Home canning in a nutshell:
While you’re preparing the food to be canned (a batch of my jelly, for instance) you put on a large pot of water to boil, with the jars inside to preheat. When you’re ready to pack the jars, you remove them from the hot water, pack in your food being careful to remove any trapped air, and you leave some air space at the top, then you put on the flat lid and just finger tighten the ring.
Once all jars are filled, you put them in the water and boil the jars for several minutes. This accomplishes three things:
1. The boiling heat sterilizes the contents of the jar. Any microorganisms that would cause the food to spoil or would create dangerous toxins, including botulism, is killed.
2. It causes the air inside the jar to expand, and some of it farts out between the seal and the jar.
3. It softens the sealing compound on the rim of the lid, which causes it to conform perfectly to the rim of the jar.
When the jars are removed from the hot water, the air inside cools and contracts, forming a vacuum on the inside, strongly forcing the lid onto the jar, forming a hermetic seal. Everything in side is dead, and nothing alive can get in.
You let the jar cool for awhile, undisturbed, and then remove the rings to inspect the seal. You shouldn’t be able to easily brush the lid off, to declare the contents safe for room temperature storage, the vacuum MUST be strong enough to form a tight seal. With a 1-piece lid, there is no way to perform this inspection; removing the screw thread breaks the seal.
For more information, I recommend reading Ball’s Complete Book of Home Preserving. It gives good, in-depth explanations of home canning technology and technique, as well as hundreds of recipes that have been scientifically verified as safe for canning at home.
Latest Answers