Essential Canning Rules
Follow these rules exactly to ensure food safety and success when canning at home.
For a boiling-water canner, pack food into canning jars by the raw-pack (cold-pack) or hot-pack method.
Raw Packing: In raw packing, uncooked food is packed into canning jars and covered with boiling water, juice, or syrup.
Hot Packing: In hot packing, food is partially cooked, packed into jars, and covered with cooking liquid. The following guidelines apply to both methods.
In canning, the acidity of foods is critical. High-acid foods are naturally less likely to harbor harmful microorganisms; low-acid foods require either more acid or more heat for safe canning.
High-Acid Foods: These are the simplest to process. Their high acidity levels create a difficult environment for microorganisms and enzymes to thrive, so processing them in the lower heat of a boiling-water canner is safe. High-acid foods have a pH of 4.6 or lower. Lemon juice, lime juice, and vinegar are very acidic. For that reason, most pickles and most salsas are high-acid, even though they may contain foods that are otherwise low-acid, such as green beans and carrots.
Low-Acid Foods: These foods have pH greater than 4.6. Most vegetables are low-acid, as are most soups, stews, and meat sauces. Unless large amounts of an acidic ingredient (such as vinegar) are added, these low-acid foods must be processed in the higher heat of a pressure canner.
Acidity Boosters: Adding highly acidic elements such as lemon juice to low-acid foods greatly broadens the types of foods you can process in a boiling-water canner because they control bacteria that can't thrive in acidic environments. That's why canning recipes for tomatoes, which have a fairly neutral pH, often call for adding a teaspoon of lemon juice. It's also why green beans in a vinegary brine can be processed in a boiling-water canner. Plain green beans, on the other hand, must be processed in the higher heat of a pressure canner.
Timings in most recipes are for altitudes up to 1,000 feet above sea level. Water boils at lower temperatures at higher altitudes, so follow these directions:
Blanching: Add 1 minute if you live 5,000 feet or more above sea level.
Boiling-water canning: Call your county extension service for detailed instructions.
Jellies and jams: Add 1 minute processing time for each additional 1,000 feet.
Sterilizing jars: Boil jars an additional 1 minute for each additional 1,000 feet.