Canning

Canning is a thermal process with a lid, not a vibe of “I boiled it a long time.” NCHFP’s safety page, adapted from USDA AIB 539, exists because Clostridium botulinum can grow in moist, low-acid, low-oxygen food between about 40 °F and 120 °F and produce toxin in days ¹. Spores are ordinary on raw food. Washing does not solve them. The researched process time does.

Acid versus low-acid #

pH 4.6 is the split ¹:

• Acid foods (pH 4.6 or below): most fruits, pickles, sauerkraut, jams, jellies, marmalades, fruit butters. Boiling-water canner, using the tested time for that food and jar size, with altitude adjustment.
• Low-acid foods (pH above 4.6): meats, seafood, poultry, milk, most vegetables. Pressure canner, 240–250 °F. Boiling-water “for hours” is not a substitute; USDA’s comparison is that a true boiling-water process for low-acid food would run on the order of 7–11 hours, which is not how home canners are instructed to work ¹.

Tomatoes and figs can sit near the line; if canned as acid foods they must be acidified with lemon juice or Citric acid ¹. Do not guess a lemon-juice amount. Use the tested recipe.

Acidity explains pH; preserving cares because acidity determines which heat process can control the food.

Jam in a pot is not jam in a pantry #

Cooking Jam to a gel answers pectin, sugar, acid, and concentration. Sealing that gel for the shelf answers heat, headspace, and a tested process. The NCHFP strawberry jam with powdered pectin processes half-pints or pints 5 minutes at 0–1,000 ft, 10 minutes at 1,001–6,000 ft, 15 minutes above 6,000 ft ². Those minutes are not interchangeable with a long-boil no-pectin jam, a reduced-sugar spread, or an invented fruit mix.

Ohio State: all unrefrigerated fruit spreads must be boiling-water processed; paraffin is no longer recommended ³.

Choose a tested process #

Process times for vegetables, meats, and untested jam are food-specific. If two authorities disagree, use the tested process for your country and altitude; do not average them. See Food safety and Strawberry jam (powdered pectin). Fill gaps are Headspace; pickled acid foods are Pickling. Elevation is Canning altitude.