Testing the Seal

A correctly sealed two-piece lid often goes “pop” quite loudly as the jar cools, and later a keen eye can detect that the vacuum created in the sealed jar has caused the lid to be slightly depressed in the center. To test, press each lid center; if the “dome” was still up and now goes down and stays down, the jar is sealed. For a double check, tap each lid with the bowl of a teaspoon: a clear, ringing sound means the seal is complete, while a dull sound indicates an incomplete or doubtful seal. A jar with such a lid should be refrigerated and considered unsealed—use the contents as promptly as you would if they had not been “canned.”