Safe home canning: a practical guide to preserving food

A safe pantry starts with a reliable recipe

Home canning preserves seasonal food. Safety depends on more than a lid that looks indented: acidity, preparation, jar, and heat treatment must follow a researched process for that specific product. Choose a current procedure published by a recognized home-preservation authority.

High-acid and low-acid foods

pH measures acidity. Foods above pH 4.6 are classified as low-acid, including meat, poultry, fish and seafood, milk, and most vegetables. Acid foods have a pH of 4.6 or lower and include many fruits, pickles, sauerkraut, jams, and jellies. Some tomatoes—and figs—can exceed that limit. Follow the exact research-based recipe published by an authoritative source, including any specified acidification. Spores of Clostridium botulinum can survive boiling-water temperatures and produce a dangerous toxin inside a sealed, low-oxygen container. The rule is: use a boiling-water canner for acidic or acidified foods only when a research-based recipe published by an authoritative source directs it; use a pressure canner for low-acid foods, following the validated process for that product. A household pressure cooker or multicooker is not automatically a substitute for a recommended canner.

Do not improvise

Follow the recipe’s ingredients, proportions, preparation, liquid, pack style, headspace, jar size and shape, time, pressure, and canner. Do not add flour, starch, or other thickeners; change vinegar, lemon juice, or vegetable proportions; use a larger jar; or shorten processing. Changes can affect acidity or heat penetration. Altitude matters: water boils at a lower temperature higher up, and pressure settings may need adjustment. Find your local elevation and use the research-based recipe published by an authoritative source’s instructions for that food, jar, and method. Never transfer a table from another product.

Clean handling, jars, and lids

Wash hands, work surfaces, and utensils. Wash and rinse jars; discard any with cracks, chips, or damaged rims. Use home-canning jars and sound lids prepared as their manufacturer directs. Sterilize empty jars when the recipe requires it. Use the stated headspace and wipe the rim before placing the lid; residue can prevent a seal.

Cooling, seals, and storage

Let jars cool undisturbed for 12–24 hours at room temperature; do not tighten bands or press the lid. Then remove bands and check seals as directed. An unsealed jar is not pantry-stable. If you followed a research-based recipe published by an authoritative source and process, consult the specific official instructions for unsealed jars. If the process was improvised or unknown, do not assume the food is safe. Wipe and dry jars, label contents and date, and store them in a clean, cool, dry, dark place away from heat and sunlight. For best quality, aim to use them within a year unless food-specific directions say otherwise. Refrigerate leftovers after opening a safe jar.

Botulism and suspicious jars

Botulinum toxin may leave no visible sign, smell, or taste. Never taste a preserve to check it. Discard it if the process is unknown or incorrect, or if a jar is swollen, leaking, cracked, has a loose or bulging lid, spurts liquid, or contains discolored or moldy food or an unusual odor. Normal appearance does not prove safety. As an additional step before serving, boil home-canned low-acid foods and tomatoes using the published altitude adjustments; this is an additional instruction, not a way to rescue a suspect jar or replace proper processing. Do not open a suspicious sealed jar to smell it or taste the contents. Avoid contact and follow the separate official instructions for disposal of sealed containers and open or leaking jars, including cleanup after contamination. Keep children and pets away.

Vacuum sealing is not canning

A vacuum sealer removes air and closes a bag or container; it does not by itself provide the validated heat treatment needed for a pantry-stable preserve. Do not store food at room temperature just because it was vacuum sealed: refrigerate or freeze it as appropriate, or use a research-based canning recipe and the specified equipment. A visible vacuum in a jar lid does not prove that the food was safely processed.