Saturday 18 August 2012

Keep Tomatoes Safe and Tasty

Posted at 7:41 AM

Tomato plants are beginning to yield, and with the new crop comes a new activity: home canning. But whether you’re canning whole tomatoes, homemade ketchup, pasta sauce or anything in between, adding acid to canned tomato products is a must, according to University of Wisconsin-Extension Family Living Agent Jackie

“Tomatoes can be preserved by canning, drying, freezing or pickling,” says Carattini.
“And when foods are home-canned, the safety depends primarily on the amount of acid
in the product.” Though tomatoes are usually considered a high-acid food, food safety
researchers now know that the pH (acid) levels of tomatoes and other fruits can vary
greatly because of many factors, including climate, soil, cultivar variety and ripeness.
Because of this variation in acid levels, the United States Department of Agriculture
recommends adding acid to all home-canned tomato products.

Carattini warns that improperly canned foods are dangerous to consume. “Foods
canned with too little acid may allow the bacteria that cause botulism to grow in the jars,
producing a deadly neurotoxin,” Carattini says.

Adding acid to home-canned tomatoes is one way to help prevent botulism. “The rule is
½ teaspoon of citric acid or two tablespoons of bottled lemon juice for every quart of
tomatoes,” Carattini says. “The acid can be mixed into the tomatoes or added to the jar
directly before filling with product.” Using vinegar is also an option (five percent acetic
acid at four tablespoons per quart), but because vinegar will affect the flavor, it may not
be the best choice for things like plain canned tomatoes or tomato juice. And be sure to
use bottled lemon juice, not fresh-squeezed, for the assurance that your home-canned
tomatoes will be safe and tasty, Carattini says.

There are a few other important safety tips Carattini recommends keeping in mind when
home-canning tomatoes and other fruits and vegetables. “When choosing tomatoes to
can, do not use tomatoes that are overripe or have bruises, cracks or insect damage,”
she says. “Tomatoes growing on dead or frost-killed vines are also unsafe, because
these fruits will have lower acidity.” It is also unsafe to add thickening agents like flour
and starch to tomato products before canning. Carattini instead recommends thickening
things like tomato sauce and soup immediately before serving.

Carattini also recommends using current, research-tested recipes for all home canning.
“Just because a recipe is in print, doesn’t mean it’s safe for you and your family,” she
says. “Canning recommendations have changed dramatically over the last 15 years, so
if you are using recipes that date before 1994, it’s a good idea to set those aside and
find an up-to-date recipe that has been tested for safety.” It is also important to make
sure all canning equipment, such as boiling water or pressure canners, are in good
working order.

More information on adding acid to canned tomatoes is available here:
Cooperative Extension Publishing also has several publications on canning tomatoes
and general canning safety available at

For specific home canning questions, contact your county Cooperative Extension office:

Jackie Carattini
Family Living Agent
UW Extension, Marathon County
212 River Drive, Suite 3
Wausau, Wisconsin 54403


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