- 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 (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 as shown in this photo. Add citric acid to each jar: ⅛ teaspoon for 4-oz jars, and ¼ teaspoon for 8-oz jars.
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 bit of tomato paste, so I freeze paste cubes. I like to use a flexible silicon ice cube tray, then remove the frozen cubes and bag them, so I have a handy supply.