Water-bath canning is a safe way to preserve many fruits, jams, jellies, pickles, and other high-acid foods. The catch is simple: you must start with a current, tested recipe and follow it exactly. The boiling-water process is not suitable for plain vegetables, meat, poultry, seafood, or other low-acid foods.
This guide explains the method without giving one-size-fits-all processing times. The correct time depends on the food, jar size, pack style, elevation, and recipe. Use the exact table published with your tested recipe.
What foods can you process in a water-bath canner?
Acidity determines which canning method is safe. Foods with a pH of 4.6 or lower can generally be processed in boiling water when a research-tested recipe calls for it. Low-acid foods above pH 4.6 require pressure canning.
Common water-bath projects include:
- Whole or cut fruit prepared from a tested recipe
- Jams, jellies, and fruit spreads
- Pickles and relishes with the specified amount of vinegar
- Acidified tomatoes when the recipe includes bottled lemon juice or citric acid
- Salsa made from a tested formula with no unapproved ingredient changes
Do not judge safety by taste. A food can taste tart and still fall outside the safe range. Use a recipe from the National Center for Home Food Preservation, USDA, a university Extension program, or another source that publishes laboratory-tested home-canning directions.
Equipment you need
- A boiling-water canner or deep pot with a fitted lid and rack
- Canning jars made for home food preservation
- New two-piece lids and undamaged screw bands
- A jar lifter, canning funnel, bubble remover, and clean towels
- A timer and an elevation-adjusted, tested recipe
The pot must be deep enough to keep the jars covered by at least 1 to 2 inches of briskly boiling water during the entire processing time. The rack keeps jars off the bottom and allows hot water to circulate.
Before you fill the first jar
- Read the full recipe. Confirm the food, jar size, headspace, processing time, and elevation adjustment before heating anything.
- Check every jar. Discard jars with cracks, chips, or rough rims. Wash jars, lids, bands, tools, and work surfaces.
- Keep jars hot. Hot food going into a cold jar can cause thermal shock. Follow the recipe’s directions for preheating and sterilizing jars.
- Prepare the canner. Add enough water to cover the filled jars, then begin heating it while you prepare the food.
- Prepare the food exactly as directed. Do not change the vinegar strength, alter the ratio of vegetables to acid, thicken the product, or enlarge the jar size.
How to process jars in a boiling-water canner
- Fill one hot jar at a time, leaving the headspace listed in the recipe.
- Remove trapped air bubbles when directed. Recheck headspace and add more product or liquid if needed.
- Wipe the rim with a clean, damp cloth. Place the lid on the jar and tighten the band only to fingertip tight.
- Place the filled jar upright on the canner rack. Keep jars separated.
- Lower the rack and cover the canner. Keep at least 1 inch of water above the jar tops, or 2 inches when processing longer than 30 minutes.
- Bring the water to a full rolling boil. Start the timer only when the boil is steady.
- Keep the canner covered and maintain the boil for the entire time. Add boiling water if the level drops.
- If the water stops boiling, bring it back to a rolling boil and restart the full processing time.
- At the end, turn off the heat, remove the lid carefully, and wait 5 minutes before lifting the jars, following the National Center for Home Food Preservation’s boiling-water canner instructions.
- Move jars straight up with a jar lifter. Set them upright on a towel with space between them. Do not retighten bands or press the lids.
Adjust processing time for elevation
Water boils at a lower temperature as elevation rises, so boiling-water recipes require extra processing time above specified elevations. Check your actual elevation and use the adjustment table that accompanies the tested recipe. Do not guess from the nearest city’s elevation.
How to check seals and store jars
Leave the jars undisturbed for 12 to 24 hours. Then remove the screw bands and check each seal according to the lid maker’s directions. The center of a sealed lid should stay down when pressed.
Label sealed jars with the product and date. Store them without the bands in a clean, cool, dark, dry place. For best quality, plan to use properly canned food within about a year, unless the tested guidance for that product says otherwise.
If a jar fails to seal, refrigerate it and use it promptly, freeze it in a suitable container, or reprocess it within the time allowed by a current tested source using a new lid and the complete original processing time.
Mistakes that can make water-bath canning unsafe
- Using an untested blog, social post, AI-generated recipe, or family recipe without a validated process
- Reducing vinegar, lemon juice, or citric acid
- Adding extra low-acid ingredients to salsa, relish, or sauce
- Using a jar larger than the recipe allows
- Starting the timer before the water returns to a full boil
- Using open-kettle canning, oven canning, dishwasher canning, or simply vacuum-sealing a hot jar
- Assuming a sealed lid proves the food was processed safely
A vacuum seal only shows that the lid is attached. It does not prove that the food reached a safe temperature or that the recipe contained enough acid.
When to discard a jar
Do not taste food from a jar that is unsealed, leaking, spurting, moldy, foamy, discolored, or smells unusual. A bulging lid is another warning sign. When in doubt, keep people and animals away from the food and follow the disposal guidance from the National Center for Home Food Preservation.
A safer way to choose a canning recipe
Start with the food you want to preserve, then find a current tested recipe. Confirm that your jar size and ingredients match it. Write down your elevation adjustment before you begin. That short check prevents most of the improvisations that cause trouble later.
For low-acid vegetables, broth, soup, meat, poultry, or seafood, use a tested pressure-canning process instead. The University of Minnesota Extension food-preservation hub and the National Center for Home Food Preservation both provide research-based directions.
