Canning jar lids come in different sizes and types, including self-sealing, glass, and zinc. Jar sizes are identified by the opening size, and rings hold lids in place during canning. Rings do not seal jars, but grommets do. Rubber sealing rings create a vacuum seal as jars cool, and some lids can be reused. Zinc lids with rubber gaskets receive a lower rating due to their tendency to unseal if bumped.
Canning jar lids are available in several sizes to fit a variety of jar styles, including quilted jelly jars and wide-mouth jars. The basic types of lids include the self-sealing lid, glass lid, and zinc lid. Many older canning jars used glass lids in conjunction with rubber gaskets, and many of the modern self-sealing jar lids also employ a rubber ring gasket. The self-sealing lid is popular with modern canners due to its superior sealing capabilities. Some lids and seals are for single use only, while others can be reused.
Home Jar sizes are identified by the size of the opening at the top of the jar. The jar lids are sized to fit the matching sized jars and also the appropriately sized rings. The rings are used to hold the jar lids in place while the jars are used in a water bath or pressure can.
Contrary to typical thinking, rings do not seal preserving jars, as this is the function of jar lids. Grommets are used to hold jar lids just tight enough to keep canned water outside the jar. At the same time, the seals prevent the liquid inside the jar from leaking into the canning water as the jars are heated.
As the temperature inside the jar increases, the rubber sealing ring under the jar lid becomes soft. The seal is formed by a vacuum as the jars begin to cool. Once completely cooled, the rings can be removed from the jars and the lids will remain tightly closed. The flat lids can be removed with a can opener and disposed of, while the jars and rings can be cleaned and reused many times.
The zinc style, one-piece jar lids are placed over the mouth of a jar with a rubber gasket placed between the jar and the lid. The lid is tightened tightly before being placed in the box. Once the canning process has been completed and the jars are removed from the container, the one-piece lids should remain in place on the jars. It is important that the lids are not bumped while the jars are being stored as the rubber seals are easily replaced. Bumps can lead to unsealed jars and spoiled food. For this reason, this style of jar lid receives a lower rating from many home canning experts.
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