Ask the Goats: Sterilizing Jars

Ask the Goats is a semi-regular Monday feature in which we, the goats, attempt to answer your questions about growing, making, eating, and preserving food (though you probably don’t need much help with the eating). Send your questions to

Q. Is it really necessary to sterilize the jars for jams? I’ve been making marmalade for many years, and I figure that since the marmalade is almost boiling hot when it goes into the jars, that should do the job. At least, I’ve never had any go bad in the jar.—Ed

A. Weeeeeeeel. It depends. If you’re doing everything else by the book—using a sugar to fruit ratio of at least 1:1, processing your jars for 10 minutes, heating up the lids—it’s highly unlikely that you would have any problems with mold or yeast formation in marmalade unsterilized jars. But those are a lot of ifs.

There are only so many corners that you can cut when canning fruit preserves. You want to reduce the sugar? Fine, but be sure to process the jars for at least 10 minutes. You want to thumb your nose at the USDA and skip processing altogether, like the French? OK, but be sure to use a full 1:1 sugar ratio and sterilized, piping hot jars—and don’t expect the jars to last forever.

The short answer is that you need not sterilize your jars if your processing time is longer than 10 minutes (see the Ball Company’s helpful FAQ for more information). The longer answer is that I often sterilize my jars, both out of habit and because hot jars are less likely than cold jars to break when placed in a boiling water bath. There’s no harm in it, and it doesn’t require any extra energy since you have to boil the water anyway. More importantly, it helps solidify your canning routine so that you’ll automatically remember to sterilize your jars when you really need to.

Long story short: it’s good practice, and harmless, but probably not strictly necessary so long as you’re processing for 10 minutes or more.

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3 comments to Ask the Goats: Sterilizing Jars

  • Stephanie

    For anything that I’m processing for 10 minutes or more, I just heat up the clean jars in my roasting pan in a 220 C oven. I was taught that this is just as good as boiling them. Fact or fiction?

  • And, how about the sterilizing function in the dishwasher? I realize, this is probably the height of laziness. But-I think Barbara Kingsolver mentioned it in her book. I had the canning jar down for a week to sterilize to make preserved lemons and it hasn’t happened. Sad but true, and now my lemons are looking not so tasty, at least for preserving. Sigh. Ironic.

  • Audra, I met you at an SF Blogher discussion a few years ago. Loved that you have a science background which is why I’m posing this question to you! Just made some elderberry flower syrup/cordial. I let it sit on the counter 5 days (1 or 2 more than I probably should have). It had a little surface mold starting to grow. I did put 1.5 tsp citric acid in with 4 cups sugar, about 3 cups water and the flowers. I poured it through a strainer then brought the mixture to a boil for 2 full minutes then let it cool. Do you think that is enough to kill any bacteria? Plan on storing it in the fridge in a mason jar and may freeze a portion. Appreciate your feedback 😉