09/28/2007

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Chow Line: Canning cherry tomatoes not advised

Writer:

Martha Filipic
filipic.3@cfaes.osu.edu
(614) 292-9833

Source:

Jaime Foster, Human Nutrition

Where can I find how to can cherry tomatoes? I'm having trouble finding guidelines.

There's a good reason you can't find those guidelines: There are none. And if you decide to try it on your own, you need to know that you're taking a risk.

While canning fresh fruits and vegetables may seem like a quaint, home-grown tradition, there's actually a lot of science that goes behind official recommendations. And for good reason: If proper procedures aren't followed, canned foods can spoil due to the presence of microorganisms or because of activity of food enzymes and oxygen, which are naturally present in fresh food tissues.

The biggest threat to the safety of canned foods is Clostridium botulinum. Although the deadly disease caused by these spores, botulism, is rare these days, the actual spores are very common. In fact, most fresh foods have botulinum spores on their surfaces. In a normal environment, the presence of oxygen prevents the growth of these spores and allows you to enjoy eating fresh fruits and vegetables. But once you put that produce into a jar and seal it up, you remove oxygen from the equation, and you lose that protective factor.

The acidity of the food makes a big difference. Botulinum spores can't grow in foods that are high-acid (with a pH of 4.6 or lower). These foods include fruits (except for figs), pickles, sauerkraut, jams and jellies.

Tomatoes used to be classified as high-acid, but in the 1990s, some tomatoes were found to have a pH above 4.6, making them low-acid. To can them using a boiling water canner, they first must be acidified by adding the proper amount of citric acid or lemon juice.

Or, you may can them using a pressure canner, using officially tested time, temperature and pressure, to make sure botulism spores are destroyed during the canning process.

And there's your problem: You can page through the official U.S. Department of Agriculture's Complete Guide to Home Canning (online at http://www.homefoodpreservation.com), and you won't find recommendations for cherry or grape tomatoes. The tests needed for making those recommendations simply haven't been done.

Food safety specialists with Ohio State University Extension recently asked Elizabeth Andress, the director of the National Center for Home Food Preservation at the University of Georgia, for her guidance. If you really want to try to can cherry tomatoes, she said, use the process outlined for tomato halves, but she's not sure you'll be happy with the end product. You can also use them for sauces and juicing, following (of course) the guidelines for acidification for these products.

The bottom line? Neither Andress nor OSU Extension specialists recommend canning whole cherry tomatoes.

Chow Line is a service of Ohio State University Extension and the Ohio Agricultural Research and Development Center. Send questions to Chow Line, c/o Martha Filipic, 2021 Coffey Road, Columbus, OH, 43210-1044, or filipic.3@cfaes.osu.edu.

Editor: This column was reviewed by Jaime Foster, registered dietitian and program specialist for Ohio State University Extension in the Department of Human Nutrition, College of Education and Human Ecology.