Essential Canning Rules
Follow these rules exactly to ensure food safety and success when canning at home.
- 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 especially prone to harboring harmful microorganisms. They heat food hotter than boiling-water canners. Recipes will specify which type of canner is appropriate. (Learn about high-acid and low-acid foods below.) Learn more about canning equipment.
- Choose the right jars: Use jars made specifically for canning. Don't use glass gars 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 because that can affect the seal. Use the jar size specified in the recipe. Learn more about canning jars.
- Use lids properly: Use the special two-piece lids manufactured for canning. Reuse rings but do not reuse lids, which have a sticky compound that seals the jar. Don't screw on lids 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. Test for sealing on each jar after it has cooled.
- Choose the right recipe: Modern canning recipes are safer than those from even 20 years ago. Foods may be processed longer or hotter. Always use tested recipes from reliable, current sources -- and follow the recipe exactly. Don't alter ingredients. Alterations can compromise food saftey.
- Keep it clean and keep it hot: Keep everyting scrupulously clean. Wash and sterilize jars. Pack hot food into hot jars one at a time -- not assembly-line style. Take only one sterilized jar out of the canner at a time. As soon as it is filled, place it back in the simmering water in the canner.
Boiling-Water Canning BasicsA boiling-water canner
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.
Boiling-Water Canning Step-by-StepRemove canning jars from water with a jar lifter.
- Wash canning jars in hot, soapy water, and rinse them thoroughly. Place washed jars in a boiling-water canner or other deep pot. Cover with hot tap water and bring to simmering over medium heat. Let jars simmer for 10 minutes, then keep them hot in the simmering water until you're ready to fill each one. When you are ready to fill, remove one sterilized jar from the water and place on clean kitchen towel to prevent slipping.
- Most canning racks hold at most seven pint or quart jars, so prepare only as much food as needed to fill your canner at one time. If you have an extra jar or two that won't fit in the canner, refrigerate that jar and eat its contents within 3 days.
- Remove one sterilized jar from the simmering water. Pack food and liquid into the hot jar using a jar funnel.
- Allow the exact amount of headspace recommended by the recipe (use a ruler to measure).
- Release trapped air bubbles by gently working a sterilized nonmetal utensil (such as the one provided in a canning kit) down the jar sides. If headspace changes as bubbles are released, add more hot food or liquid to maintain headspace. Headspace allows food to expand when heated and allows a vacuum seal to form.
- As each jar is filled and assembled, use a jar lifter to place it gently in the canner.
- Be sure that jars do not touch each other, and each time you add a jar, put the canner lid back on.
- When all jars have been added, measure to make sure they are covered by 1 inch of water. If any jar tops are poking out, add some of the extra simmering water ready in your teakettle or other pot.
- Cover the canner and heat the water to a full rolling boil. Begin timing, following your recipe exactly. Check your water occasionally during the processing time, and adjust your burner as necessary to keep water at a steady, gentle boil. If water is boiling so hard that the jars are clinking together, turn it down. If the water has stopped boiling, turn the burner up and stop timing until water returns to boiling.
High-Acid and Low-Acid Foods
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.
More Canning Info
Check out our canning recipes.
Get our pickled recipes.