Preserve it! Series: Mineral Stains on Pressure Canners aren't Harmful, but Easy to Remove
Mineral deposits on pressure canners can be removed and prevented.
Aluminum pressure canners can become darkened on their insides over time. This discoloration, which is caused by the accumulation of mineral deposits, is not harmful. But should you find it unsightly, it’s fairly easy to remove.
To do so, fill the pressure canner to a level above the darkened area with a mixture of 1 tablespoon of cream of tartar per 1 quart of water. Cover and bring the mixture to a boil, and continue boiling until the dark deposits disappear. Add more cream of tartar if the deposits are particularly stubborn. Then empty the canner, wash it with hot soapy water, rinse well, and dry.
Adding 1 to 2 tablespoons of white vinegar to the water placed in the canner for processing the jars can help reduce mineral deposits if you have hard water.
For further information, visit the National Center for Home Food Preservation (NCHFP) website or contact your local Cooperative Extension Office.
Brought to you by the UCCE Master Food Preservers of El Dorado County
Last updated July 2025