It's not always necessary to sterilize jars before canning.
When canning, sterilizing jars is essential only when processing times are less than 10 minutes. For processing times of 10 minutes or more, pre-sterilization is not required – the jars become sterilized during processing.
Can you pre-sterilize jars anyway? Well sure, it doesn’t hurt anything but you’d really just be expending extra time and energy unnecessarily.
What about increasing processing times to avoid the sterilization step? Yes, that is also acceptable, but not always preferable. For example, some jams and jellies have only 5-minute processing times; if they are made from fruit low in pectin, the gel could be weakened by increasing the processing time.
To recap: Pre-sterilize canning jars only when the processing time is less than 10 minutes.
(And remember, if you live above sea level, make altitude adjustments to the sterilization and/or processing times as necessary.)
Step-by-step process for sterilizing jars
When processing times are less than 10 minutes, canning jars must be sterilized. Here’s how to do so:
To sterilize in a boiling water canner
- fill canner with clean water to cover jars by at least 1”
- place washed jars in an upright position on the rack in the canner
- cover the canner, turn heat to high and bring the water to a full rolling boil
- boil jars for 10 minutes at 0-1000 feet above sea level, plus altitude adjustment if applicable (1 minute for each additional 1000 feet of altitude)
- reduce heat to keep jars warm until ready to fill
- remove jars one at a time, carefully pouring the hot water in the jars back into the boiling water canner
To sterilize in an atmospheric steam canner
- place washed jars in an on the rack in the canner
- place cover on canner with vent hole(s) facing away from you
- turn heat to high and bring canner to the temperature of pure steam (212°F at sea level, as verified by a calibrated thermometer), just as you would when processing filled jars
- heat jars for 10 minutes at 0-1000 feet above sea level, plus altitude adjustment if applicable (1 minute for each additional 1000 feet of altitude)
- reduce heat to keep jars warm until ready to fill
- take off cover directing steam away from you (hot steam is hot!); carefully remove jars one at a time
For further information, visit the National Center for Home Food Preservation (NCHFP) website at or your local Cooperative Extension Office
Brought to you by the UC Master Food Preservers of El Dorado County
Last updated July 2025