It's that beautiful sound you associate with the canning process: the pop that signifies a proper seal. When canning with two-piece canning lids, the pop can be nearly immediate, happening right when you remove the jars from the boiling water bath. Don't worry, though, if you don't hear your jars popping right away -- it can sometimes take longer, and some jars even seal without a pop.
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Two-Piece Canning Lid Basics
It can take up to an hour or even longer for a canning lid to seal, and jars should be left undisturbed for a full day before you check their closures. When 24 hours have passed, check the lids. Press on the center of the lid -- if it doesn't move, the jar is sealed. If it pops up and down, it is not sealed, and you must refrigerate or reprocess the contents immediately. You can also check the seal by removing the ring and grabbing the lid with your thumb and middle finger. If you are able to pull it straight up, it is not sealed; otherwise a proper seal has been achieved.
Refrigeration of Unsealed Jars
If your canning jars do not pop and form a seal, you have two options: refrigeration and reprocessing. The quickest is to simply place the contents in the refrigerator for use. This is often the best option, as reprocessing requires reheating the contents as well as using a boiling water bath, which leads to a degradation in the finished product. This is most noticeable in products such as pickles that taste best and maintain a good crunch with minimal processing.
Reprocessing of Unsealed Jars
To reprocess unsealed jars, you must redo the recipe, starting by emptying the contents back into a pan to bring the temperature back up to what the recipe requires for canning. Wash, rinse and heat your jars and prepare new lids for canning -- don't try to reuse the ones that didn't seal. Pack the food back into the jars, ensuring you leave the required headspace as indicated in the recipe. Remove air bubbles, wipe down the jar rims and reapply the lids and rings. Process the jars for the entire time indicated in the recipe.
Factors That Affect Seal Closure
If you are continually having problems with seal closure, there may be an issue with your process. Be sure to always use clean, new lids for your canning projects. Take special care to wipe down rims before you place the lids and rings on to provide a flush surface for the lids to seal. When you are done processing your jars, allow them to sit in the canner for five minutes with the heat off to allow excess pressure to stabilize before removing the jars. When you remove the jars from the canner, leave them undisturbed for 24 hours.