When & How to Sterilize Canning Jars

A few days ago, I read an article in one of the country's most famous cooking magazines (affiliated with a very famous television network), trying to explain how to can tomatoes. It was riddled with errors – none of which were going to lead to food poisoning, thank goodness. But it was yet another reminder that as canning gains popularity again, there’s an awful lot of misinformation out there.

One area that many, many canners seem to find confusing is when to sterilize jars.

Why Sterilize Canning Jars?
The only reason to sterilize canning jars before canning is if the processing time is very short. Otherwise, the jars and their contents will be perfectly sterilized during the processing time - assuming you're using an approved recipe from Ball or the National Center for Home Food Preservation. (All canning recipes here at Proverbs 31 Woman are from one of these sources.)

When to Sterilize Canning Jars 
It is only necessary to sterilize canning jars before filling them if the processing time is under 10 minutes. Very few things fall into that category: Some jellies, jams, marmalades, and similar preserves, and perhaps some pickles in smaller jars, for example.

Anything that is processed more than 10 minutes is put in clean, hot jars that don’t need sterilizing first.

Jars in the Canner Aren't Sterile
Some people think if they put their jars in the canner and turn on the heat, making the water hot (and perhaps even simmering), they are sterilizing the jars. This is not true. This keeps the jars warm before filling them - which is necessary in order to prevent jars from breaking - but the jars aren't actually getting sterilized. (There are other ways to keep jars warm, too, including in a clean sink of hot water and in a dishwasher that has a hot "drying" temperature. I do not recommend keeping them hot in the stove, since this can lead to temperature fluctuations that can make jars break.)

How to Sterilize Canning Jars
There are people who recommend sterilizing canning jars in the oven or the dishwasher, but the only safe way to get them sterile is to boil them. Here’s how:

1. Fill your canner with water so it comes at least 2 inches above the tops of the jars. Be sure there is a rack in the bottom of the canner.

2. Add the canning jars and bring to a boil. Boil for 10 minutes.

3. Now just leave the jars in the canner until you are ready to fill them. (Don’t take them out of the canner and let them air dry.)

It’s that simple!

1 comment

  1. Huh. I thought I was doing that right, but, nope! Thankfully, I don't think anything I can has a processing time of less than 15 minutes because I'm barely over the altitude threshold to push me into adding that extra 5 minutes. :)