Eli5, why do Mason jar lids typically come in 2 parts, threads and seal, as opposed to nearly every other commonly used household container?

Question

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

Answer 1

The seal bit is single-use when canning, where the contents is heated before sealing to kill bacteria which would cause it to spoil. As it cools the pressure goes down which creates suction holding the seal on to the can.

The threaded bit is reusable and can/should actually be removed once the jar is sealed. If the seal is disrupted then you will know as the seal fails, but if you left the threaded bit on then it could reseal and you wouldn’t know the jar was contaminated.