2 days total
makes about 24 4-ounce jars
Make tomato paste in the slow cooker - it takes longer but is much less active work. A half-bushel of tomatoes will yield about 2 cases (24 jars) of 4-ounce jars, plus a little bit extra to freeze as 'tomato paste cubes'.
  • ½ bushel (about 25 pounds) ripe paste tomatoes (Roma)
  • citric acid

Tomato paste is, in principle, an easy thing: squish the tomatoes, separate the skins and the seeds, and reduce the resulting pulp until it’s very thick. I have already posted a Roasted Tomato Paste recipe – here’s a version using a slow cooker or two.

wash and quarter the tomatoes

When you wash the tomatoes, you’re not only getting dirt and debris off the outside, but checking each fruit for blemishes or moldy spots. Soft or split tomatoes are fine to use, but cut out any black or spoiled spots. Cut the tomatoes lengthwise in quarters, as they’ll fit through the strainer better.

crush and strain the tomatoes

Follow the directions for your specific strainer. You’ll want the squeezings (the remains) to be as dry as possible – I tend to put them back through the strainer once or even twice, to extract the most pulp that I possibly can. At my house the seeds and skins go into the compost pile, though Joel MacCharles at wellpreserved.ca likes to dehydrate them and use the resulting tomato powder as a seasoning.

cook the pulp in a wide flat slow cooker

When I can tomato paste, I do not use salt or any other additives: only the tomatoes, and when the paste is put in jars, a bit of citric acid. Put the tomato pulp in a slow cooker and use more than one if you’re making a huge quantity. I used two 5-6 quart cookers for a half-bushel of tomatoes, which weighs 25-26 pounds. Set the cooker(s) on HIGH, and cook, covered, at least one hour.

At the end of one hour, check that the tomato pulp is hot – it should be bubbling merrily around the edges. Now the serious reduction can begin. Remove the lids, place chopsticks or wooden spoons across the cookers at each end, then replace the lids on top of the props, leaving about a half-inch of airspace. Don’t leave the lids off entirely, because you need them there to keep the heat in. The airspace of propped-open lids will permit evaporation, so that the tomato pulp becomes thick tomato paste.

NOTE: it’s much better to use wide flat slow cookers for this purpose. You want the largest surface area you can get; a tall narrow slow cooker will take much much longer. 

Cook for 24 hours or so. Fee free to stir occasionally. At the end of 24 hours, you may find you can fit all the pulp into one cooker, and if that’s more convenient for you, do it. Be careful with the hot pulp and cooker insert!

Check the texture of the pulp. If it’s lumpier than you’d like, whiz the tomatoes with an immersion blender to make it uniformly smooth. Continue cooking with the lids propped open until the paste is thick and uniform. It should not separate when mounded on a saucer, and will retain its shape.

put the paste in small jars, add citric acid

Ladle the paste into prepared jars, leaving 1/2 inch headspace. I use 4-oz jars, though according to the National Center for Home Food Preservation, you may use up to 8-oz (half pint) jars. Add citric acid to each jar: ⅛ teaspoon for 4-oz jars, and ¼ teaspoon for 8-oz jars.

seal properly

Place lids and bands on jars. Process in a boiling water bath for 45 minutes. The time is the same for both 4 and 8 ounce jars. Let cool, label, remove bands, and store in a cool dark place.

freeze little cubes

I mentioned that I often need a little teeny bit of tomato paste, so I freeze paste cubes. I like to use a flexible covered silicon ice cube tray so I have a handy supply.


4 Responses

  1. Do I need to actually add the citric acid, or will the tomato paste be fine without it?

    • If you plan to can the tomato paste, then yes, you definitely need the citric acid.

  2. I’ve been clicking on link after link with a great deal of frustration at the terrible state of decay in our use and understanding of simple English. Tomato sauce and tomato paste are TOMATOES, with the possible addition of citric acid, salt, or sugar for taste and preservation. Yet one after another recipe is really mislabeled pasta or pizza sauce. Good stuff, but not what I wanted.
    So far, very little has worked out, but I’m not quitting yet. My gardens have been devoured not by those lovely but pesky deer but by ravenous groundhogs. I live in an old mobile home in central Missouri, all metal, without air, so summer cooking is out. And I’ve yet to figure out a way to can cuz there’s no way my hot plate cooker will boil more than a saucepan of water. Maybe. But I can dehydrate & freeze. So it finally dawned on me I ought to be able to slow cook sauce without adding to heat inside. Can even set it outside since covered. (Was boiling pasta on deck one night when little tree frog lost footing and plopped into the pot – eww)
    And finally, I found your site! Yahoo! Perfect! And I love the format. Simple. Clean. Few distractions. Little relevant tales without a lot of reports on vacations and blah blah blah that have no bearing on the how or why of the recipe. At least so far. I love following links down tasty or informative rabbit trails, but sometimes I wonder where the recipe went. Thank you. Will try this shortly with a small batch of end of season farmers market romas, and plans to box in all my raised beds in 2017. AND to come back and explore this site more thoroughly!

    • First of all, I do hope that you have great success with your outdoor slow cooker – I wouldn’t want a frog in my pot either!

      The design of my site separates the recipes into their own posts, so you might like simply looking through the ‘recipes’ section. If you’re looking for something specific, the search box is labeled ‘find the good stuff’ and works pretty well.

      And lastly – if you find a misspelling or a typo, please let me know so I can correct it! I do try for accuracy, but sometimes pesky errors do creep in. Thanks!

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