Canning Calculator
Calculate safe canning processing times.
Canning Details
Higher altitudes require adjustments
Processing Instructions
- • Use tested recipes from reliable sources
- • Inspect jars and lids before use
- • Process full recommended time
- • Check seals after cooling 12-24 hours
How to Use the Canning Calculator
Home canning preserves food by heating jars hot enough and long enough to destroy microorganisms that cause spoilage and foodborne illness. The two main enemies are bacteria (particularly Clostridium botulinum) and mold spores. Botulism is rare but deadly, making proper canning technique absolutely essential. Following tested recipes and processing times from reliable sources prevents these dangers while preserving food safely for months or years.
Food acidity determines which canning method you must use. High-acid foods (fruits, pickles, tomatoes with added acid, jams) can be safely processed in a boiling water bath canner at 212°F. The acid environment prevents botulism bacteria from growing even if a few spores survive. Low-acid foods (vegetables, meats, soups, beans) require pressure canning at 240-250°F because only these higher temperatures kill botulism spores reliably in low-acid environments.
Never process low-acid foods in a water bath canner regardless of how long you boil them. Botulism spores survive boiling water temperatures. Pressure canning uses steam under pressure to reach temperatures high enough to destroy these dangerous spores. Attempting to can green beans, corn, or meat in a water bath canner creates potentially lethal jars that look and smell fine but harbor botulism toxin. Only pressure canning makes these foods safe.
Frequently Asked Questions
Can I use a pressure cooker instead of a pressure canner?
No, pressure cookers and pressure canners are different equipment. Pressure cookers (including Instant Pots) are designed for cooking and don't maintain consistent pressure throughout the large volume needed for canning. Pressure canners are larger, hold multiple jars, and maintain accurate pressure for extended times. Only use equipment specifically labeled as a pressure canner for home canning.
What if my jars don't seal after processing?
Refrigerate unsealed jars immediately and use the food within a few days, just as you would fresh-cooked food. You can also reprocess within 24 hours using a new lid - check headspace, wipe rims carefully, and process again for the full time. After 24 hours, the food quality degrades too much for successful reprocessing. Unsealed jars result from food on the rim, damaged jars, faulty lids, or over-tightened rings.
How long do home-canned foods stay safe?
Properly canned foods remain safe for at least one year, often longer. Quality declines over time - colors fade, textures soften, flavors weaken - but safety remains intact if seals stay vacuum-tight. Store jars in cool, dark places between 50-70°F. Check jars before using by looking for intact seals, clear liquid, normal color, and good odor when opened. Date your jars and use oldest first to maintain best quality.
Why did my jars lose liquid during processing?
Liquid loss (siphoning) happens from several causes: improper headspace, food packed too tightly, fluctuating pressure or temperature, removing jars from canner too quickly, or food not hot enough when packed. Lost liquid doesn't make jars unsafe if seals are good, but exposed food may darken and lose quality. Don't open sealed jars to add liquid - opening breaks the seal and requires reprocessing.
Can I can meat without a pressure canner?
Absolutely not. Meat, poultry, and all low-acid foods require pressure canning to reach temperatures hot enough to kill botulism spores. Water bath canning only reaches 212°F, which is inadequate for these foods. There are no safe alternatives or shortcuts. If you don't have a pressure canner, freeze meat instead of attempting to can it. Botulism poisoning is deadly serious - pressure canning is the only safe method for meat.
Do I need to add lemon juice to tomatoes?
Modern tomato varieties are less acidic than older varieties, making added acid necessary for safe water bath canning. Add two tablespoons of bottled lemon juice or half teaspoon citric acid per quart jar (one tablespoon lemon juice or quarter teaspoon citric acid per pint). Bottled lemon juice has standardized acidity while fresh lemon juice varies. This added acid ensures tomatoes are acidic enough for water bath canning safety.
Water Bath vs Pressure Canning
Water Bath Canning
Pressure Canning
Common Foods Processing Guide
| Food | Method | Pints | Quarts | Headspace |
|---|---|---|---|---|
| Tomatoes (crushed) | Water Bath | 40 min | 45 min | 1/2 inch |
| Jam/Jelly | Water Bath | 10 min | 15 min | 1/4 inch |
| Pickles (whole) | Water Bath | 10 min | 15 min | 1/2 inch |
| Peaches | Water Bath | 25 min | 30 min | 1/2 inch |
| Green Beans | Pressure (10 PSI) | 20 min | 25 min | 1 inch |
| Corn (whole kernel) | Pressure (10 PSI) | 55 min | 85 min | 1 inch |
| Carrots (sliced) | Pressure (10 PSI) | 25 min | 30 min | 1 inch |
| Chicken/Meat | Pressure (10 PSI) | 75 min | 90 min | 1 inch |
Times shown are for sea level. Adjust for altitude using the calculator above.
Critical Safety Guidelines
Never Taste Suspicious Canned Food
Botulism toxin can kill in tiny amounts - smaller than needed to taste. If a jar shows signs of spoilage (bulging lid, spurting liquid when opened, mold, off odor, unusual color), dispose of it safely without tasting. Wrap the jar in plastic bags and throw in outdoor trash where people and animals cannot access it. Wash your hands thoroughly after handling suspect jars.
Process the Full Time
Never reduce processing time, even if jars seal early or the recipe seems overly cautious. Processing times are scientifically tested to ensure heat penetrates to the jar center and kills all dangerous organisms. Starting your timer too early, reducing time to save energy, or assuming your food is safer than test conditions all create potentially deadly jars that look perfectly normal.
Use Current USDA Guidelines
Canning methods and processing times have changed as research reveals safer practices. Recipes from old cookbooks may use outdated methods that aren't safe by current standards. Follow only current USDA guidelines, university extension publications, or recipes from reputable modern canning books. When conflict exists between old family recipes and current science, choose science every time.
Boil Low-Acid Home-Canned Foods Before Eating
Even properly canned low-acid foods benefit from boiling for ten minutes before serving. This extra precaution destroys any botulism toxin that might have developed despite proper canning. High-acid foods don't require this since botulism cannot grow in acidic environments. For extra safety with home-canned vegetables, meats, and soups, boil hard for ten minutes (add one minute per 1,000 feet altitude) before tasting or serving.