Jar Selection and Preparation
Regular and wide mouth Mason type, threaded, home canning jars with a 2-piece lid including a self-sealing lid and a metal screw band are the best choice. They are available in half-pint, pint, and quart sizes. The standard jar mouth opening is about 2 3/8 inches. Wide mouth jars have openings of about 3 inches, making them easier to fill and empty. With careful use and handling, Mason jars may be reused many times, requiring only new lids each time. When jars and lids are used properly, jar seals and vacuums are excellent and jar breakage is rare. Commercial mayonnaise, salad dressing jars or craft/decorator jars are not recommended for canning because of excessive jar breakage and seal failures.
Do not use cracked jars for processing. Carefully check the jar sealing surface for nicks, chips, and cracks. These will cause unsealed lids, a poor seal, or a poor vacuum. During storage, a poor seal may not maintain the vacuum and spoilage will occur. Before every use, wash empty jars in hot water with detergent and rinse well by hand, or wash in a dishwasher. Detergents may cause unnatural flavors and colors. Scale or hard water films on jars are easily removed by soaking jars several hours in a solution containing 1 cup of vinegar per gallon of water.
Clean jars must also be sterilized if the canning time is less than 10 minutes. To sterilize empty jars, put them right side up on the rack in a boiling water canner. Fill the canner and jars with hot (not boiling) water to 1 inch above the tops of the jars. Boil 10 minutes at elevations of less than 1,000 feet. At higher elevations, boil one additional minute for each additional 1,000 feet elevation. Remove and drain hot sterilized jars one at a time. Use sterile, empty jars for all jams, jellies, and pickled products processed less than 10 minutes. Jars which will be used for processing vegetables, meats, and fruits in a pressure canner need not be pre-sterilized. It is also unnecessary to pre-sterilize jars for fruits, tomatoes, and pickled or fermented foods that will be processed 10 minutes or longer in a boiling water canner.
Lid Selection and Preparation
The common self-sealing lid consists of a flat metal lid held in place by a metal screw band during processing. The flat lid is crimped around its bottom edge to form a trough, which is filled with a colored gasket compound. When jars are processed, the lid gasket softens and flows slightly to cover the jar sealing surface yet allows air to escape from the jar. The gasket then forms an airtight seal as the jar cools.
Buy only the quantity of lids you will use in a year. To ensure a good seal, carefully follow the manufacturer's directions in preparing lids for use. Examine all metal lids carefully. Do not reuse lids because the gasket compound is only good for one canning process. Screw bands can be reused. Old, dented, rusted, or deformed screw bands may not hold the lids securely during processing and should not be used.
Article originally written by Julie Albrecht. Updated and reviewed by Carol Larvick in 2021.