How to Test pH of Food for Canning

Test the acidity of your batch for water bath canning to ensure that you are meeting the requirements for high acid foods.

Reader Contribution by Ilene White Freedman
Updated on July 20, 2022
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by Adobestock/lawcain

Learn how to test pH of food for canning in a water bath to ensure that you are meeting the requirements for high-acid foods. This is an educational tool and not a license to change lab-tested recipes. 

Canning guide books, such as the Ball Blue Book Guide to Canning, warn canners that they must carefully follow lab-tested recipes in order to ensure safety against botulism. The recipes are tested for proper acidity levels and stability during shelf life. It has always bugged me that the books say, “Trust us, follow our recipe, and you’ll be fine.” Oh, and otherwise the results could be fatal.

So I did something bold, something that Ball would surely not recommend. I bought a litmus paper pH testing kit. I use Whatman litmus paper test strips.

Food Acidity Basics

Water bath canning sterilizes jars of high acid food for a stable shelf life. The water bath boiling kills off the organisms that create mold and fungus, but it is not enough to kill off botulism. That is alright, because botulism cannot survive in the high acid environment anyway. So it is important to water bath process only foods with a high acidity (a pH under 4.7) that are not at risk for botulism. Foods that could harbor botulism — low acid foods with a pH of over 4.7 — must be pressure-canned to kill off any botulism-creating spores. Tomatoes teeter near the unsafe zone, up to 4.5, so lemon juice is added to bring the numbers down. Adding spices and additional ingredients to a jar of tomato puree can increase the pH to those unsafe numbers. Following tested recipes is important to help you steer clear of unsafe acidity levels.

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