How to sterilize canning jars

First: do you actually need to?

This is the part most guides bury. Jars do not always need sterilizing. When the food will be processed for 10 minutes or longer, the processing itself does that work — the jars only need to be clean and hot. Sterilizing them first is a redundant step that heats your kitchen and delays your batch.

In practice this means jams and jellies with short processing times often need sterilized jars, and almost everything else does not. Check your recipe's processing time before you decide.

The method

1. 1Wash the jars in hot soapy water and rinse well. Sterilizing is not a substitute for washing.
2. 2Check every rim. Run a finger around the sealing surface. Any chip or nick and the jar is out — it will not seal.
3. 3Stand the jars upright on a rack in a deep pot. Not directly on the base, where they can crack.
4. 4Cover with water by at least an inch, making sure the jars fill with water so they do not float or tip.
5. 5Bring to a full boil and boil for 10 minutes. Add 1 minute for every additional 1,000 feet of altitude — see altitude adjustment.
6. 6Leave the jars in the hot water until you fill them. A sterilized jar that cools on a counter for twenty minutes is no longer doing what you sterilized it for, and a cold jar can crack when filled with hot food.
7. 7Lift one out at a time with the jar lifter, empty the water back into the pot, and fill it immediately.

The dishwasher method

A dishwasher with a sanitize or heated cycle is an excellent way to wash jars and keep them hot, and for the many recipes that do not require sterilizing, it is the easiest option — run the cycle so it finishes as you are ready to fill.

Where recipes call for sterilized jars specifically, use the boiling method above unless your dishwasher documents a sanitizing cycle you are confident meets that requirement. The boiling method is unambiguous and it takes ten minutes.

Do not sterilize jars in the oven

Dry oven heat is a different thing from wet heat and does not achieve the same result at the same temperature. It is also hard on the glass: canning jars are not designed for dry oven heating, and the risk of thermal shock when a hot dry jar meets hot wet food is real. Oven sterilizing is not part of any tested canning process and we would not do it.

What about the lids?

Guidance on lids has changed over the years and current manufacturer instructions generally do not require boiling — clean and warm is enough, and prolonged boiling can be hard on the sealing compound. Follow the instructions on the box of lids you actually bought, since that is the guidance for that product. Screw bands need no treatment beyond being clean and dry.

Keeping jars hot without sterilizing

• In the canner water as it heats. The most efficient method — they are already where they need to be.
• In a dishwasher on a heated cycle, timed to finish when you are ready.
• In a sink of very hot water, topped up as it cools.
• Not in the oven, for the same reasons as above.