Tomato Sauce Under Pressure


Yes, yes, yes, I know. The tomato can jam entries should be posted next week, not this. Consider this post a safety intervention.

The most important thing to consider when you’re canning is whether your item is a high-acid or low-acid food. Most food-born pathogens, including yeasts, molds, and most bacteria, can be killed at 212°F. Botulism, on the other hand, that nasty, invisible, food-borne pathogen we’ve all heard so much about, can survive up to somewhere around 238°F. (It’s actually the spores that can survive, but never mind that). But because botulism can’t grow in a high-acid environment, you can still can high-acid foods in a water-bath canner that will never get about 212°F. For low-acid foods, you need the additional heat of a pressure canner, which can take you up to 240°F at 10 pounds of pressure at sea-level. Let me repeat: you can’t get botulism from high-acid foods.

With me so far? Good.

Here’s the thing. Tomatoes aren’t quite a high-acid food. They’re borderline. Older varieties, many heirloom varieties, and most of the varieties that you’re likely to grow at home, frequently are. Newer varieties—particularly the kinds of tomatoes that you tend to find in grocery stores—aren’t necessarily acidic enough. It’s therefore recommended that you add 1 T of lemon juice per pint jar, or 2 T per quart jar, of tomatoes to make them safe for water-bath canning. If you don’t like lemony tomatoes, you can always pressure can them.

Which brings us back to sauce. I’ve seen many, many recipes over the years that say that you can can tomato sauce in a water-bath canner. Many of these are in reputable books that I trust, like Anna Thomas’s The New Vegetarian Epicure. But let’s think about this for a minute. Here you are, taking tomatoes, already a low-acid food. You’re adding olive oil, probably some onions, maybe some garlic, and a handful of herbs. All of these things are low-acid foods. With each one, you’re raising the pH (lowering the acidity) of your product. The more experienced I get in my own canning, the more and more queasy I am about all the people who are going to excitedly put up jars and jars of tomato sauce in a water-bath canner this summer.

The Ball Blue Book does include a version of tomato sauce safe for water-bath canning, but it contains 1 T lemon juice per pint jar and a processing time of 35 minutes (for pints). I can only conclude that if you’re not adding something more acidic than tomatoes (like lemon juice or vinegar) to your sauce, it’s probably not safe for water-bath canning, and certainly not at the 20 minutes usually recommended in non-canning cookbooks. Ergo, you might want to try pressure canning it.

Here’s one version of a meatless tomato sauce appropriate for pressure canning, using the processing times recommended by the National Center for Home Food Preservation.

Canned Tomato Sauce

10 pounds tomatoes, peeled, cored and roughly chopped
1 large onion, chopped
6 cloves garlic, minced
1/4 c. olive oil
A big handful of basil—about a cup or so—chopped
Salt to taste (I use about 1 T kosher)

1) Heat the oil is a large, wide stockpot. The wider the stockpot, the faster your sauce will cook. Sauté the onions and the garlic in the oil until they’re translucent.

2) Add the remaining ingredients and bring to a rapid boil. Turn the heat down to medium and cook until the sauce has reduced by about half. This may take several hours, depending on your stove and your pot. If you want, you can run the sauce through a food mill at some point, but I find that if you cook it long enough, the tomatoes break down on their own.

3) Meanwhile, prepare 4 to 6 pint jars (and maybe a half-pint just in case) and an equal number of lids. Transfer the hot sauce to clean jars and adjust two-piece lids. Process pints for 20 minutes, quarts for 25 minutes at 10 pounds pressure in a steam-pressure canner.

For step-by-step instructions on pressure-canning, please see this post. Please note: I find I get a better seal, and am less likely to lose the contents of my jars, if I wait a long, long time after the pressure’s dropped before opening the lid. Like, hours.

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16 comments to Tomato Sauce Under Pressure

  • I am a big fan of canning tomato juice. I grow the tomatoes in my garden, can them and make soups all winter long with them. I am hosting a “Canning Week Blog Party” the week of Aug. 23-27. We will be posting tips, recipes and have give-a-ways all to encourage and educate other bloggers on canning. I hope you can stop by and join in the fun!!!

  • I am so glad to see this posted. I, too, switched to pressure canning about three years ago and I feel so much better giving away the bounty. I never wanted to give the gift of botulism.

    I do want to make one comment – some heirloom tomatoes are acidic, others aren’t. It’s quite variable. Paste tomatoes have a higher acid – and that’s why they were the ones canned for so many generations. Also, the old standbys like Rutgers seem to have a consistently high acidity.

  • dorisandjilly

    @MrsWheelbarrow That’s fascinating information about Rutgers tomatoes. Do you know if the acidity is affected by climate and/or growing conditions? I tried to hedge the heirloom factor (many…frequently…some), but thanks for making it explicit. Heirloom does not necessarily equal acidic.

  • Amy

    I found this study done by the University of Minnesota food science department. It may be interesting for people to read.

    http://www.extension.umn.edu/distribution/nutrition/dj1097.html

    There is a heading for a section entitled “Tomato Acidity” that outlines which varieties that are unsafe for canning with out pressure due to their too high pH level. I have always added the lemon juice to my tomatoes before water canning and have never really noticed a lemony taste to them.

  • I used to freeze sauce but last year canned it using the recipe in Animal, Vegetable, Miracle and added the lemon juice (as the recipe instructs). I always use roma types for the whole tomatoes. I have pH paper to test jars too.

  • Regarding Rutgers tomatoes, I heard (in my Master Gardener class) someone remark that Rutgers was created for the NJ home canners as a canning tomato. That’s just hearsay, but it makes complete sense to me. So, I don’t think it’s a climate issue. Rutgers isn’t an heirloom variety, per se – it’s just a great old standby that makes great sauce and cans up whole or crushed with little of the water-y-ness that takes away from the fresh taste in a jar.

  • Excellent post. I have been using a pressure canner to do my sauce since 2008 when I started the business. This is the type of information I love to see and hope that Canvolution will be able to use your article to educate new canners. I have only just “met” you via twitter, but I like your style and clarity!

  • dorisandjilly

    Thanks, everybody, for your comments. @Amy: Fascinating article. Did you catch the part where the UMN says that you only need to hold your tomatoes at 15 pounds of pressure for 2 minutes? Suddenly I feel like a very responsible and conservative canner!

  • I have a couple of versions of tomato sauce that I can in the water-bath, based upon the proportions of acid-to-low-acid in “Italian-Style Tomato Sauce” in the Ball Complete. You do add 4 tbsp of lemon juice (to 8 cups tomato puree and almonst 2 cups of non-acid vegetables), but there is really no lemony taste. And none of the recipes contain olive oil; they suggest that you add it for taste prior to serving.

    I agree, that if you have a pressure canner, it is probably easier to be safe with your tomato recipes by canning under pressure; but for those of us who suffer Breakfast-at-Tiffany’s trauma, it’s nice to have the water-bath option. :)

    FWIW, the first year I started canning, tomato sauce was the first thing I canned. I blithely canned my usual recipe, completely clueless as to acid, pH, etc. I was probably lucky that my CSA farm only grows heirloom varieties.. and presumably, the heirlooms that are acidic enough!

  • juliaSB

    Hey Doris and Jilly (and the Goats)
    I’m looking for some confirmation here..
    when I can tomatoes I use a pH meter and adjust w fresh lemon juice or white wine vinegar to 4.2-3. We have unlimited access to lemon trees here so the idea of using bottles is just…you know….
    Does it matter how I get to 4.2 in the finished product..fresh or bottled juice? There has been some real hand waving and ‘oh no you didn’t’ going on in the kitchen..what do you all say?

  • My fiance loves canning our tomatoes but as she just recently got into it, she cans the old way with boiling liquid and cooling in a mason jar. Is pressure that much better? Is it more expensive?

  • dorisandjilly

    Josh: First, the easy part. Pressure canning is a little bit more expensive in that you need a pressure canner. You can get a brand new Presto (you want 23 quarts) for $80, or used for less. Otherwise, the equipment is the same. It’s OK to can tomatoes in a water bath, but you need to add at least 1 T lemon juice per pint jar to ensure proper acidity. Basically, you have a choice between acidified tomatoes in the water-bath, or non-acidified tomatoes in a pressure canner. For more on the difference, see my home canning FAQ.

  • I had never heard about adding a teaspoon of lemon juice if you are water bath canning tomato sauce. Thank you so much for sharing this information! I’m slowing working my way up to using a pressure canner, but I thought I would start with waterbath this year before braving (and investing) in a canner.

  • Homemade tomato sauce is the best! And for us, canning with a pressure canner is the only way to go. We originally started out with a Presto canner that we got used at the local Goodwill (always take a used canner to the county extension office to have them test it if you can for safety!) We loved it so much we moved up to the All American pressure canners (no seals!!!).

    Thanks for the great site.

  • lemon juice?????????? bottled or from fresh lemon?
    1 tablespoon per pint

  • Allan Holtz

    I grow a variety of tomatoes and pressure can maybe 30 or more quarts of sauce per year. I add distilled vinegar, dried mushrooms, dried onion and garlic powder, dried and ground herbs (basil, oregano, marjoram, and parsley), salt, sugar, cornstarch and grape seed oil. I add all of the dry components towards the end of the evaporation/concentration cooking phase with the liquid additives earlier in the cooking. I use a high powered blender (Vitamix) to first puree the raw tomatoes (skin and all). I also add some raw bell peppers and whole onions to the blender. I stop the cooking when the sauce starts to splatter out of the pot and then I stir in the dry stuff to flavor and further suck up the moisture. The cornstarch gives a nice thickened texture, but after pressure canning I notice the texture is no longer as thick. Still tastes great though as a nice nutrient rich cover to lightly cooked vegetables in most of my evening meals. I use a small cooking balance to measure all of the ingredients. I suggest you adjust the amount of all of the non-tomato ingredients I list to your taste.

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