Follow these basic rules to ensure success.
1. KNOW WHICH CANNER TO USE The boiling-water canner—basically a big pot with a lid and a rack in the bottom—is used for high-acid foods, which naturally resist bacteria growth. Pressure canners are used with low-acid foods and recipes that are prone to harboring harmful microorganisms. They heat food hotter than boiling-water canners. Recipes specify which type of canner to use. (See High-Acid and Low-Acid Foods and Types of Canners for more information.)
2. CHOOSE THE RIGHT JARS Use jars made specifically for canning. Don’t use glass jars from purchased food, even if they look like canning jars. Don’t use jars that look different from the canning jars currently on the market. And avoid jars with chipped edges; that can affect the seal. Use the size jar specified in the recipe because it takes longer to achieve the critical internal temperature in larger jars. (See The Anatomy of a Canning Jar for more information.)
3. USE LIDS PROPERLY Use the special two-piece lids manufactured for canning. Reuse the rings, but do not reuse the lids, which have a special sticky compound that seals the jar. Don’t screw lids on too tightly or they won’t create a vacuum seal. Heat the lids in very hot but not boiling water or the compound won’t seal (check the manufacturer’s directions for preparing lids). Test for sealing on each jar after it has cooled. Press the center of the lid. If the button is depressed and does not make a popping sound, it has sealed properly. Remove and clean the rings before storing canned food. (See for Using Lids and Screw Bands more information.)
4. CHOOSE THE RIGHT RECIPE Always use tested recipes from reliable, current sources—and follow the recipes exactly. Don’t alter ingredients. Alterations can change the acidity and compromise food safety. (See High-Acid and Low-Acid Foods for more information.)
5. KEEP IT CLEAN AND KEEP IT HOT Keep everything scrupulously clean. Wash and sterilize jars. Pack hot food into hot jars one at a time—not assembly-line style. (See Boiling-Water Canning for more information.)
Label jars with contents and date. Include a batch number if you can more than one load in a day (if a jar spoils, you can identify others from the same batch).