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Water bath vs. pressure canning: which one your food needs
Low-acid foods canned incorrectly can grow Clostridium botulinum, which causes botulism. The guidance below summarizes USDA / National Center for Home Food Preservation (NCHFP) positions. Always follow a current USDA-tested recipe for your specific food — never improvise canning times or methods.
There are two home canning methods, and which one you must use is not a preference — it's determined by the acidity of the food.
The pH 4.6 dividing line
Per USDA/NCHFP, the controlling factor is whether a food is high-acid or low-acid, split at pH 4.6:
| Food type | pH | Method (per USDA) |
|---|---|---|
| High-acid | 4.6 or below | Boiling-water bath (or atmospheric steam) is sufficient |
| Low-acid | above 4.6 | Pressure canning is required |
Boiling water (212°F at sea level) can't get hot enough to destroy botulinum spores. Only a pressure canner reaches the ~240°F that USDA-tested processes require for low-acid foods.
Which foods fall where
| Water bath (high-acid) | Pressure canning (low-acid) |
|---|---|
| Most fruits, jams & jellies | All vegetables (green beans, corn, carrots, beets) |
| Pickles & properly acidified relishes | Meats, poultry, seafood |
| Properly acidified tomatoes/salsa | Stocks, broths, soups |
| Most fruit juices | Plain (un-acidified) tomatoes |
Tomatoes sit near the line — USDA recipes call for added acid (lemon juice or citric acid) for safe water-bath processing. And pumpkin/winter-squash purée or mashed has no USDA-tested process — USDA approves only cubed pumpkin, pressure-canned. When in doubt, follow the tested recipe exactly.
Seal checks your method against the USDA tables
Pick a food and Seal tells you the USDA-required method, jar size, and altitude-adjusted time — and warns you if you've chosen water bath for a food USDA requires pressure for. Every number is cited "Per USDA / NCHFP." Pay once, no subscription, works offline.
Sources
This is general education, not a recipe. Always use a current USDA-tested recipe and process for your specific food and equipment.