Since You Asked: Add citric acid when canning tomatoes

I was surprised to read in this month's HomeLife magazine story on tomatoes that they are no longer considered a high-acid food and the recommendations for canning have changed. Why did this happen? I've been canning my tomatoes the same way since the 1970s.

— Dave S., Talent

Even if you've been canning tomatoes the same way since the 1970s, Dave, we're betting you haven't grown the same varieties all these decades.

Because most consumers want sweetness in a tomato, newer varieties contain higher ratios of natural sugars to acid, says Carole Evans, Oregon State University master food preserver and president of Jackson County Family Food Education Volunteers.

For that reason, revised recipes for water-bath canning of tomatoes call for the addition of citric acid, either in its natural state or powdered form.

"It requires lemon juice, and it has to be bottled lemon juice," explains Evans, adding that bottled lemon juice guarantees acidity levels.

The standard formula is 1 tablespoon of lemon juice per pint of tomatoes or 2 tablespoons per quart. If using powdered citric acid, 1/4 teaspoon suffices per pint, 1/2; teaspoon per quart, Evans says. Salt can be added for flavor; it has no effect on acidity, she adds.

To be on the safe side, particularly if adding any other food to canned tomatoes, always consult cookbooks or canning guides published in 1988 or more recently. If in doubt, call the Southern Oregon Research and Extension Center at 541-776-7371 and ask to speak to a member of FFEV.

But don't call in the middle of your canning process, Evans says. A certified master food preserver may have to be tracked down at home. And once tomato season hits, they'll be elbow-deep in their own canning.

Send questions to "Since You Asked, A la carte" Mail Tribune Newsroom, P.O. Box 1108, Medford OR 97501; by fax to 541-776-4376; e-mail to

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