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Aug 22, 2009 10:38 AM

Pressure Canning Tomatoes: Do I need an acid?

My dude and I bought a pressure canner with the knowledge we could can low acid foods (green beans) and questionably acidic foods (tomatoes) without the use of additional acid such as lemon juice or citric acid. Reading through online lit, the Ball Book and even our Presto canning guide, all recipes (for the pressure canner) use either lemon juice or citric acids. Our question is WHY? It makes no sense to include an additional acid for low acid canning, though we're loath to see our tomato products unpalatable.

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  1. This is a great question. I'm also planning on doing a lot of tomato canning in the next few weeks. A friend of mine just told me that she even cans hers with the water bath method without acids because she knows so many Italians who've been doing it that way for years, and so many vendors at the farmer's market who say the same - that the lemon juice or citric acid changes the taste and is not needed. And that's just in a water bath!

    I'm a little unsure though. I still like to go with the safest method possible. Because I've also read that even canning tomatoes in a pressure cooker requires some kind of added acid. I wonder if any longtime canners have any advice based on their own experiences with tomatoes over the years? Very curious what people think of the great acid or no acid debate when it comes to canning tomatoes...

    5 Replies
    1. re: Pantry Party

      In twenty-plus years of canning, I have NEVER added acid to anything canned in a pressure cooker, and have never gotten sick from a single item canned in a pressure cooker. In my mother's fifty-plus years of canning (using a pressure-canner only), neither has she.

      Pressure canners not only put food under pressure and force air out of the jars, they also super-heat, which is what makes them safer than water-bath canners, which can really only bring the temperature up to boiling. A pressure canner can bring the water in the canner and the contents of the jars up to a much higher temp!

      1. re: LauraGrace

        laura- exactly why i'm confused! isn't the whole point of pressure canning to be able to can w/o the use of acids? hmmm..

        pantry: after figuring out the time it takes to get to pressure (10 minutes) hold pressure (15 minutes) and cool to depressurize (10 minutes), we decided to do our typical waterbath (35 minutes) instead- and add 1/4 tsp. citric acid to each pint jar.

        1. re: sixelagogo

          Oh, interesting. I'd love to find out how you like the taste? Do you think the citric acid will affect it?

          And Laura: Wow. That's exactly what I've heard from other experienced canners. I wonder why the new literature says to add acid in the pressure cooker? ...

          Anyway, six, let us know if you do decide to go the pressure route and how each batch compares in terms of acid and non-acid. I will post about my own tomato canning experiences later this week. Excited!!

          1. re: Pantry Party

            It's bizarre! I wonder the same thing and my suspicious brain says that they're trying to protect themselves against lawsuits from the one freak jar that doesn't seal right and gives a family botulism or something.

            Honestly, what is the point of having a pressure canner if you STILL have to ruin everything with citric acid? I'm going to go ahead and say (in my best Carvey/Bush impersonation, "Not gonna do it, wouldn't be prudent."

        2. re: LauraGrace

          I total agree. There are all kinds of recipes for non acid foods which require no acidification.
          If you are using a water bath it is necessary to use 1 tablespoon per pint or tow for a quart jar.

      2. I don't pressure can--mainly because I don't really like the taste and texture of canned vegetables like corn and green beans. I do can tomatoes, peaches, pickles and jams frequently. I use a water bath canner for these high-acid foods. A few years ago, the government and blue book advice on cannign tomatoes changed with the instruction to add lemon juice or citric acid to tomatoes. I read at the time that it reflected the popularity of new breeds of lower-acid tomatoes, which if processed without additional acid, may not have the correct pH to stave off the development of botulism.

        Since few people know which varieties are low-acid, they just changed it to be safe (the USDA plays it very very very safe--perhaps more than strictly neessary).

        Since I DO know what kind of tomatoes we are growing, I add lemon juice only when I am canning tomato juice made from cherries tomoatoes or tomatoes that I suspect or know are low acid. However, I am young and healthy. I might think twice about serving anything even slightly questionable to the very young, very old or ill.

        I had not heard that they extended the acid thing to pressure canning, but there must have been an instance in real-life or in the lab in which botulism spores survived the heat of the pressure canner. Without enough acid to check it's's reproduction time. And I actually know someone who got botulism (from a commercial tomato product). It is NOT something you want to mess with.

        Clearly, there is a bit of personal preference on how super-safe you want to be. People used to can meat in a water bath. My mother and grandmother used paraffin for jams until the 70s, when they switched to water baths. For me, I can food that I like when canned--not as a hedge for surviving winter.

        You need to be a little knowledgable to make the call. I don't can bruised tomatoes near the end of the season--a little too risky for me--I freeze those instead. But will I eat my neighbors currant preserve put up in reused commercial jars and "sealed" with the slam upside down method--yes I will because 1) with the all the acid and sugar few things (and not the scary B) can grow in it and 2) because it it so damn good!

        In terms of lemon in tomato juice--delish! And just an FYI--fruit often calls for citric acid--this is less for acidity than to prevent browning. I find peaches are better with it than without.

        4 Replies
        1. re: dct

          very interesting indeed...i do think the pressure canned tomatoes+ acid is a hedge, but why? If I can pressure can chicken stock (haven't yet, but can't wait to try...) with NO additional acid (and no inherent acidity) i wonder what's up with tomatoes...hmm...

          also want to add that many of the canned tomatoes I purchase at the store (tuttarossa, del monte) all have citric acid added (this led me to conclude that maybe the acid is added for reasons beyond food safety.) hmm squared...

          1. re: sixelagogo

            The only thing reason I can think of for acidifying in pressure canning tomoatoes is the ubiquity of botulism spores--they are in the soil, just about everywhere. The chance of chicken or other meaty foods having the spores is less than garden produce. Also, tomatoes are often raw packed--so unlike any contaminants in a broth, the nasties aren't killed in a preliminary cooking step. Still, I think it's a case of the USDA suggesting the absolute safest way to do it.

            Citric acid can affect texture as well as acidity--that may be why commercial processors use it.

            1. re: dct

              can you tell me how much red wine per quart and what kind of red wine to you use,I am wanting to can roma's

              1. re: debbi1950

                I use 1 bottle of red wine per 25 pounds of Roma tomatoes.

        2. I just put up 20 quarts of tomato sauce. I've never canned tomato products under pressure, strictly water bath. I add quite a bit of red wine to my sauce, which adds enough acidity to give me confidence. If you're buying tomatoes from a local grower, ask them about the acidity of their product: they will know if it's high acid or low. I do not like the idea of introducing a lemon flavor into my sauce.

          1. Related to this discussion, I've posted the request below on the Cookware board. Please post to the topic if you have a good source.

            pH test kits for home canning tomatoes?

            1 Reply
            1. re: Melanie Wong

              I know many people process everything in a water bath but to destroy bacteria that will allow botulism to grow the water must reach 240 degrees and water bath only reaches 212. Adding acid (whether 2T bottled lemon juice (only bottled not fresh as fresh acidity is variable) or 1/2 t. citric acid per quart will make it less likely that any bacteria that survives can grow...the temp it reaches is the most important thing. No matter what ph you achieve with whatever acid it still needs to be processed correctly at a high enough temp to ensure safety. Water bath is really meant for high acid foods only.

            2. Gardenweb's Harvest forum, a lively place, has a few Master Canners (and great canning recipes in general!). I'd post any questions over there as well. They practice safe canning. I just learned that certain regions, like the Pacific Northwest, has higher levels of botulism spores in the soil, so that is another factor that may have sent the powers that be back to the drawing board, increasing the acids.