Canning Basics: Mason jar myths are rampant on the internet!  

MYTH:  Brand new canning jars fresh out of the box are sterile and do not need to be washed. New jars are not sterile. Before use they should be checked for breakage or manufacturing defects, and then washed. In fact, jars should always be checked and washed right before use (even if they were previously stored away clean).

MYTH:  Canning jars must always be sterilized before canning in them.  Jars need to be sterilized only when the processing time is under 10 minutes. (Find further details on when and how to sterilize jars in our Preserve it Series! )

MYTH:  The flat part of two-piece metal jar lid systems should be boiled before canning.  The sealant used on most metal canning lids changed from rubber latex to plastisol decades ago, at which time the need to boil lids ceased. Boiling can actually damage the plastisol, resulting in seal failures. While it is safe to simmer lids (~180°F) before use, it’s unnecessary and thus a waste of energy. All this said, do check the instructions from the manufacturer for your particular brand of lid for specific handling requirements.

MYTH:  Mayonnaise, pasta, and other similar commercial product jars can be reused for canning.  These types of jars are not designed to be repurposed for home canning, and are not recommended. They may not have the correct tempering to withstand high temperatures or long processing times causing jars to break, and some jar rim sizes can vary slightly, causing seal failures. (That said, some people have had some success reusing commercial jars. For further details, see our food safety poster, Reusing Commercial Product Jars, on our website.)

For further information on canning, visit the National Center for Home Food Preservation (NCHFP) website or contact your local Cooperative Extension Office.

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Last updated July 2025