Thinking of using your own canning recipe? Think again.

The science behind home canning and why it’s important to only use science-based recipes.

I recently had the opportunity to visit the National Center for Home Food Preservation at the University of Georgia, where I learned more about the science of home canning. One thing I learned was that one of the most common errors in home canning is not using a scientifically-tested recipe. This practice is not recommended, and can potentially be deadly.  

So, what does “scientifically-tested” really mean? Imagine researchers in white lab coats working over hot stoves, filling jar after jar with test recipe jams and salsas. It may sound funny, but canning recipes really are developed in lab-like situations set up like a home kitchen, with researchers at the helm. It’s one thing for the product recipe to taste delicious, but it also has to be safe to eat. When a new recipe is being developed one of the main traits being studied is the pH of the product. pH is a measure of the acidity or alkalinity of a substance. Things like lemons, tomatoes and berries are considered “acid foods” and have a pH of less than 4.6 (the scale goes from one to 14, seven being neutral). Foods like squash, beans and meat are “low acid” foods with a pH greater than 4.6. The reason pH is important is because of the bacteria Clostridium botulinum, which is a common microorganism that produces a deadly toxin known as botulism. In high acid foods the C. botulinum spores will not germinate, and thus cannot produce the toxin. These foods can be canned in boiling water through a process called hot water bath canning. Low acid foods, however, need a different type of processing due to the possibility of C. botulinum growth. The spores are destroyed at temperatures of 240 degrees Farenheit or above for specific periods of time. Since that temperature is above the boiling point (212 F at sea level), pressure canning is the method needed to reduce the likelihood of botulism toxin. Some foods, like tomatoes, are close to the borderline pH of 4.6, so acid is added to them (in the form of lemon juice or citric acid) so they can safely be canned in boiling water.

What does any of this have to do with using your own recipe, or a recipe passed down from your great grandmother or a recipe you find online? Many people have created canning recipes and even published them in popular books throughout the world, without ever measuring the pH of their product. Botulism can’t be seen, smelled or tasted, so the best way to prevent food poisoning is to only use recipes that have been rigorously tested by reliable sources and have a known pH.

In addition to pH, the processing time is extremely important to the safety of the finished product. Processing times for canning are based on things like the density of the product and how long it takes to heat that product to the proper temperature throughout the entire jar. Home canners most likely don’t have access to the high-tech equipment to perform those measurements, and thus don’t know with any certainty that their own recipe has been thoroughly processed.

Canning is fun and a great way to enjoy valuable produce year-round, but safe food practices are necessary to prevent foodborne illness. Michigan State University Extension recommends using one of the following approved resources for home canning recipes.

You can also contact your local MSU Extension office for more information on canning and upcoming preservation classes and demonstrations.

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