Why You Need To Consider Acidity When Canning Your Own Tomatoes

While canning food at home can be a dauntingly complicated process, it can also be deeply rewarding. Canning your own food helps preserve your favorite fruits and vegetables for a later date and gives you control over the flavor of the ingredients. A wide variety of resources are available with information on how to get started, like the National Center for Home Food Preservation (NCHFP). Plus, learning to can helps carry on a centuries-old tradition first developed in 1810 by French chef and food scientist Nicolas François Appert as a way to preserve food for Napoleon's armies (via IFCA).

However, canning is not without its downsides. A lot of science goes into practice, and a simple mistake can have serious consequences. For example, The Cleveland Clinic explains that improperly canned foods can cause botulism — a food-borne illness caused by a nerve toxin from Clostridium botulinum bacteria. While botulism is rare, it's serious and can lead to hospitalization, paralysis, or even death. According to the CDC, even a small taste of contaminated food can be deadly. Experts recommend seeking immediate medical attention if you experience symptoms, which include difficulty breathing, muscle weakness, and nausea.

NCHFP explains that acid helps inhibit the growth of bacteria, so acidic foods with a pH below 4.6 are the safest to can. Most tomato varieties are acidic enough to can safely, but you should still proceed with caution.

According to Serious Eats, the type of food you can should dictate your process. Foods that are high in acid can be preserved using a boiling water bath canner. However, low acid foods should be tinned with a pressure canner, which does a better job of killing off microbes. The United States Department of Agriculture explains that, when conserving tomatoes, you should add lemon juice or citric acid to the can to ensure the mixture is acidic enough to kill any potential botulism.

Green tomatoes, which are high in acid, are a safe bet, but you should be cautious canning red tomatoes — and never preserve tomatoes from dead vines. Stick to recipes from trustworthy sources, and follow them carefully without changing the ratios or substituting. And as tempting as it is to can your very own salsa recipe, it's not worth the risk.