Precautions When Canning Tomatoes

Canning TomatoesFor years, we canned tomatoes and homemade tomato sauce the way grandma taught us: using the water bath method. This involved packing sterilized jars with hot (cooked) fruit or tomatoes and boiling for a designated amount of time, usually an hour or more for tomatoes. That’s not true anymore. In this age of increasing food contamination, you don’t want anything bad to come out of your kitchen. What could happen? Listen to what Renee R. Boyer, Assistant Professor, Food Science and Technology, Virginia Tech; Julie McKinney, Project Associate, Food Science and Technology, Virginia Tech…

… high-acid foods prevent the growth of spores of the bacterium Clostridium botulinum, which can’t be killed by boiling. Foods with a pH more than 4.6 allow the spores to grow. If spores of C. botulinum are allowed to grow, toxin will form, and consumption of C. botulinum toxin is deadly. Symptoms from the consumption of this toxin develop within six hours to 10 days and include double and blurred vision, drooping eyelids, slurred speech, difficulty swallowing, and muscle weakness. Paralysis of breathing muscles can cause a person to stop breathing and die unless mechanical ventilation is provided.

Didn’t mean to scare you. But this is serious business. Take precautions.

The water bath method is considered safe for acidic fruits with a pH of 4.6 or less (few vegetables fall in this category unless their pickled, like beets). Tomatoes are often right on that acid-enough line, or falling on either side of it. Some of the more recently developed strains of tomatoes are low-acid. You can’t safely tell by looking — or tasting — to see if your tomatoes are acidic enough acidic or not. Grandma taught us to can tomatoes right off the vine. This was good advice. Tomatoes that have sat around for a day or two or more tend to lose their acid. Bruises and other damage also reduce a tomato’s acidity. These should not be canned. Late season tomatoes, stressed from shorter days and cooler temperatures, also tend to be less acidic. What do you do if you don’t want them to go to waste?

The answer? Increase the acidity in the jar by adding citric acid or lemon (or lime) juice. A tablespoon of bottled lemon juice or 1/4 teaspoon of citric acid per pint should do it. Don’t like the acidic taste this leaves? Add just a touch of sugar to each. Then proceed as usual (scroll down for specific instructions on canning tomatoes) , keeping everything clean and hot just the way grandma did.

Special care should be taken when canning homemade tomato sauce or salsa. The many other ingredients added to sauces and salsa decreases the tomato’s acidity further. You may love your particular home recipe for sauces and salsa, but it’s most likely not appropriate for safe canning. Use recipes, like this one, recommended for canning. Be safe! You grandmother would want you to.

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