The most important factor in deciding whether food should be boiling-water bath or pressure canned is how much natural or added acid is in the food product. On a pH scale, 14 is strongly alkali, with 7 being neutral, below 7 a low-acid food, and 2 a high-acid food. Consumers do not need to test the foods for acidity, but rather use science-based recipes to guide the decision. Foods having natural levels of acid, or those with added acid, making them have a lower pH level to 4.6 or lower can be processed in a boiling-water canner. Foods such as fruit, jams and jellies are high-acid foods, with figs, rhubarb and tomatoes requiring the addition of extra acid such as citric acid, 5 percent vinegar or bottled lemon juice. These foods will have high enough levels of acidity to be safely processed and stored in a sealed canning jar.

Low-acid foods have very little natural acid, with a pH higher than 4.6, such as vegetables, seafood, meats, poultry, as well as soups, stews and meat sauces. These low-acid foods must be processed in a pressure canner to reach high enough temperature to kill any harmful bacterial spores and their toxins. To determine amount of pressure, consult the canning altitude chart at or call your local Extension office.

Foodborne pathogens such as molds, yeast and bacteria may not have a smell or change the consistency of the bottled foods. Never taste a home preserved food to test for safety. Indications of spoilage are a broken seal, mold, gasses released from the bottled food, cloudiness, spurting liquid, bubbles rising in jar after the initial cooling phase, seepage, yeast growth, fermentation, slime or disagreeable odor. Treat all suspect jars as having produced botulinum toxin and handle carefully by placing jars of sealed home-canned food showing signs of spoilage in a garbage bag. Secure the bag closed and place it in the regular trash container or dispose of it at a landfill. Make sure no humans or animals will come into contact with the discarded jars. Contact with botulinum toxin can be fatal whether it is ingested or enters the body through the skin.

As the home food preservation season continues, use science-based recipes. Save those traditional recipes for a scrapbook and update your recipes from Ball at or Interested in a canning app for your smartphone? Download PreserveSmart or Canning Timer.

Julie Buck, EdD, RDN, is a registered dietitian, who is employed as a family and consumer sciences educator at the University of Idaho Extension, Bingham County. She can be reached at 208-785-8060 or