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Precautions When Canning Tomatoes

Water-bath canning techniques may no longer be safe.

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 has to say…

… 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.

SAFE & EFFECTIVE!

Canning & Preserving

Canning Supplies

The effective, safe and delicious way to preserve what you grow.

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Whether pickling, making jam or putting up fresh garden produce, Planet Natural has the canning supplies you’ll need — jars, caps, lids, pickling spice — to keep the harvest through the winter and beyond.

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.

17 Responses to “Precautions When Canning Tomatoes”

  1. Holger on October 27th, 2012 at 12:50 am #

    Basic Tomato Sauce Makes 4 cups. Ingredients:1/4 cup extra-virgin olive oil1 Spanish onion, chopped into 1/4-inch dice 4 garlic cloves, peeled and thinly sliced 3 tablespoons chopped fresh thyme leaves, or 1 tablespoon dried 1/2 medium carrot, finely shredded 2 28-ounce cans peeled whole tomatoes, crushed by hand and juices reserved Salt to taste Preparation: In a 3-quart saucepan, heat the olive oil over medium heat. Add the onion and garlic and cook until soft and light golden brown, about 8 to 10 minutes. Add the thyme and the carrot and cook 5 minutes more, until the carrot is quite soft. Add the tomatoes and juice and bring to a boil, stirring often. Lower the heat and simmer for 30 minutes until as thick as hot cereal. Season with salt and serve. This sauce holds one week in the refrigerator or up to 6 months in the freezer.

  2. DeMalkuth on April 23rd, 2013 at 4:05 pm #

    I have never, EVER seen a recipe for canning tomatoes by boiling them for an hour or more….and I learned to can at my grandmother, great aunt and great grandmothers knee! They instructed me to put both salt and lemonjuice (or lime) in with the tomatos…I’ve been canning for years, and have never had a problem…

    • Kevin on August 3rd, 2014 at 8:46 pm #

      I agree.
      If the the lid pops, it’s good.
      If not, it goes in the fridge.
      I’ve canned for over 40 some years.
      Never had a problem.
      There’s way too many opinions and so called Scientific studies out there,
      That try to scare people into thinking that after all these years, we’ve been doing everything wrong.
      So much of it is BS !!!
      Just like humans are responsible for Global Warming.
      Yeah… Right…

      • Anonymous on November 24th, 2014 at 11:09 am #

        Study the science behind it all and make informed choices. We all must consider how we can make changes. Think of others first is what you learned in Kindergarten, right?

    • Cecil Sink on August 5th, 2014 at 6:58 am #

      well that’s great, because when you DO have a problem with botulism, you usually die.

    • Anonymous on July 13th, 2015 at 12:36 pm #

      You’ve got the citric acid in there, as is the way I’ve always canned, 45 min hwb for qts.

    • P. Hickey on August 23rd, 2015 at 5:35 pm #

      Me too. I add a little white Karo to mine too. Granny’s recipe. Never goes bad.

  3. sarah levine simon on October 12th, 2013 at 12:37 pm #

    How about pressure canners. I’ve read that it is necessary to can low acid foods, most vegetables with one.

    • E. Vinje on October 13th, 2013 at 7:31 am #

      Sarah –

      The following is an excerpt from the USDA Complete Guide to Home Canning concerning Food Acidity and Processing Method:

      Whether food should be processed in a pressure canner or boiling-water canner to control botulinum bacteria depends on the acidity of the food. Acidity may be natural, as in most fruits, or added, as in pickled food. Low-acid canned foods are not acidic enough to prevent the growth of these bacteria. Acid foods contain enough acid to block their growth, or destroy them more rapidly when heated. The term “pH” is a measure of acidity; the lower its value, the more acid the food. The acidity level in foods can be increased by adding lemon juice, citric acid, or vinegar.

      Low-acid foods have pH values higher than 4.6. They include red meats, seafood, poultry, milk, and all fresh vegetables except for most tomatoes. Most mixtures of low-acid and acid foods also have pH values above 4.6 unless their recipes include enough lemon juice, citric acid, or vinegar to make them acid foods. Acid foods have a pH of 4.6 or lower. They include fruits, pickles, sauerkraut, jams, jellies, marmalades, and fruit butters.

      Although tomatoes usually are considered an acid food, some are now known to have pH values slightly above 4.6. Figs also have pH values slightly above 4.6. Therefore, if they are to be canned as acid foods, these products must be acidified to a pH of 4.6 or lower with lemon juice or citric acid. Properly acidified tomatoes and figs are acid foods and can be safely processed in a boiling-water canner.

      Botulinum spores are very hard to destroy at boiling-water temperatures; the higher the can- ner temperature, the more easily they are destroyed. Therefore, all low-acid foods should be sterilized at temperatures of 240° to 250°F, attainable with pressure canners operated at 10 to 15 PSIG. PSIG means pounds per square inch of pressure as measured by gauge. The more familiar “PSI” designation is used hereafter in this publication. At temperatures of 240° to 250°F, the time needed to destroy bacteria in low-acid canned food ranges from 20 to 100 minutes. The exact time depends on the kind of food being canned, the way it is packed into jars, and the size of jars. The time needed to safely process low-acid foods in a boiling-water canner ranges from 7 to 11 hours; the time needed to process acid foods in boiling water varies from 5 to 85 minutes.

    • Cecil Sink on August 5th, 2014 at 6:59 am #

      yes, that’s correct.

  4. Jena Reno on April 23rd, 2014 at 9:12 pm #

    So if the lemon juice or citric acid is added, how long would one water bath?

    • Cecil Sink on August 5th, 2014 at 7:01 am #

      depends on the size jar used. if you’re home canning, you really shoulf get “The Ball Blue Book”, and follow it closely.

  5. Quizative on April 23rd, 2014 at 9:22 pm #

    … 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

    This was really confusing.

  6. Cecil Sink on August 5th, 2014 at 7:07 am #

    look folks, grandma’s tomatoes were acid. And they were freash. yours may, or may not be, depending if you grow your own, and use heirloom varieties or not. So grandma’s methods may NOT be safe with modern tomato varieties.

    1) You can buy a good pH meter and learn to use it, and keep it calibrated, and ph test each batch

    2) You can acidify according to lab-proven formula (means someone else has done the above for you)

    3) or you can pressure can.

    4) you can keep doing it “grandma’s way” and hope no one you love dies.

    Your call.

  7. Christine Olinsky on August 5th, 2014 at 7:11 pm #

    Visit the National Center for Home Food Preservation web site or contact your local Extension office for current, tested and safe recipes for home canning and freezing. Using old or untested recipes can have serious, even fatal, consequences.

  8. Tabitha on August 23rd, 2015 at 6:10 pm #

    Will there be signs if there is botulism? Will it not seal or will they stink or something that will clue me in that it’s bad?

  9. Deborah on February 24th, 2018 at 8:05 pm #

    If in doubt, freeze them. I have changed from canning to freezing in freezer bags. One large freezer bag makes a good size spaghetti sauce. I core them first before freezing and I leave on the skins when making the sauce so when they thaw and start heating – it’s really easy to take the skins out of the sauce. Sometimes, I just leave them in.

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