---
title: "Water bath canning: what it means in cooking — Tiny Plates"
description: "Water bath canning preserves high-acid foods like jam, pickles and acidified tomatoes by boiling sealed jars. It is not safe for low-acid foods."
url: "https://www.tinyplates.dev/glossary/water-bath-canning"
---

# Water bath canning

Water bath canning preserves high-acid foods like jam, pickles and acidified tomatoes by boiling sealed jars. It is not safe for low-acid foods.

Also called Boiling water canning, Boiling water bath, Bottling.

Water bath canning means preserving food in sealed glass jars by boiling them, fully covered with water, for a tested time. In the UK it is often called bottling. The heat kills molds, yeasts and most bacteria, and as the jars cool, the lids seal. It is safe only for high-acid foods, with a pH of 4.6 or lower: fruit, jam and jelly, [pickles](https://www.tinyplates.dev/glossary/pickle) made with enough vinegar, and tomatoes with added acid.

## How to do it

1. Use a tested recipe from a reliable source, and do not change the amounts of acid, sugar or vegetables.
2. Put a rack in a large, deep pot or canner. Fill it with water and heat it, to about 60°C (140°F) for raw-packed food or about 82°C (180°F) for hot-packed food.
3. Fill hot, clean jars, leave the right [headspace](https://www.tinyplates.dev/glossary/headspace), remove air bubbles, wipe the rims and put on the lids. Tighten the bands only fingertip-tight.
4. Lower the jars onto the rack. Add boiling water if needed so the water covers the jars by at least 2.5 cm (1 inch).
5. Cover and bring to a full rolling boil. Start timing then, and keep it boiling for the whole time. Add time for altitude as the recipe says.
6. Turn off the heat, take off the lid and wait 5 minutes. Lift the jars out upright and set them on a towel or rack.
7. Leave them undisturbed for 12 to 24 hours, then check the seals.

## How to tell it is done

A sealed lid curves down and does not flex when you press the center. If a jar has not sealed, put it in the fridge and eat it soon, or reprocess it within 24 hours with a new lid.

## Why it works

Boiling at 100°C (212°F) does not destroy the spores of the bacterium that causes [botulism](https://www.tinyplates.dev/glossary/botulism), but acid stops them from growing. That is why tomatoes, which can sit near the limit, need added acid: 1 tablespoon bottled lemon juice or 1/4 teaspoon citric acid per pint (about 500 ml) jar, and double that for a quart (about 1 liter) jar.

## How to store it

Remove the bands, wipe the jars, label them with the date, and store them in a cool, dark, dry place. Use them within a year for the best quality.

## Common mistakes

* Water-bath canning low-acid foods such as plain vegetables, beans, meat or stock. They need [pressure canning](https://www.tinyplates.dev/glossary/pressure-canning).
* Using fresh lemon juice, whose acidity varies, instead of bottled.
* Turning jars upside down to seal them instead of processing them.
* Starting the timer before the water boils hard.

## Related terms

* [Pressure canningPressure canning heats sealed jars to about 116°C (240°F) under steam pressure. It is the only safe home method for low-acid foods such as vegetables.](https://www.tinyplates.dev/glossary/pressure-canning)
* [Sterilize jarsSterilizing jars means heating clean glass jars to kill microbes before you fill them with jam or pickles. Boiling them for 10 minutes is the tested way.](https://www.tinyplates.dev/glossary/sterilize-jars)
* [HeadspaceHeadspace is the empty gap between the food and the lid of a jar or container. The right amount helps canning jars seal and stops frozen jars cracking.](https://www.tinyplates.dev/glossary/headspace)
* [BotulismBotulism is a rare but serious illness caused by a toxin that grows in low-acid, airless food, such as badly home-canned vegetables or garlic in oil.](https://www.tinyplates.dev/glossary/botulism)
* [PickleTo pickle is to preserve food in an acidic liquid, either vinegar or a salty brine that ferments. Quick fridge pickles are ready in an hour or less.](https://www.tinyplates.dev/glossary/pickle)
* [Shelf-stableShelf-stable food can be stored unopened at room temperature, like canned goods, dried pasta and UHT milk. Many of them need the fridge once opened.](https://www.tinyplates.dev/glossary/shelf-stable)

[More in food safety and storage](https://www.tinyplates.dev/glossary/category/food-safety)[Every term from A to Z](https://www.tinyplates.dev/glossary)