Slow Cooker Tomato Paste

Necessity is the mother of invention. Sometimes you hit a roadblock; something knocks your plans horribly askew. So it was for me this week, when I planned to reduce a half-bushel (25-26 pounds) of tomatoes to thick tomato paste. 

tomatoes in basketsWe had washed, quartered, squished and strained the entire basket, and put the sauce into two large flat hotel-style pans. The pans went into the oven at 425˚F for what was intended to be 4 to 5 hours of reducing.

But the oven stopped working, and wouldn’t start again. (It turns out the electronic board that controls operation just crashed. Crashed hard. I never crashed a stove before.)

Faced with 10-11 quarts of hot tomato pulp and no working oven, I decided to try to make tomato paste in my two large slow cookers. I filled them quite nearly to the brim and set them on HIGH. I laid two chopsticks across the ends of both these long ovals, and rested the lids on top, so there was about a half-inch gap, which I hoped would provide opportunity for evaporation. After an hour or two, I checked the pots, and found moderate bubbling around the edges, but no active boiling. I decided to let them work. It had to be better than stirring a big pot on the stovetop for hours and hours!

24 hours later, I was pleased that there had been no browning or scorching, and the tomatoes had reduced by nearly half. I was able to combine the pulp into just one pot: my largest 6-quart slow cooker. I set the lid on the chopsticks again, and let it continue.

In another 8 hours, the tomato pulp was reduced almost by half again, and was clearly becoming thick. I didn’t like the rough texture, though, so I took my immersion blender, and blitzed the tomato glop into silky smoothness: progress! I tested it: I dropped a spoonful on a saucer, and tilted the saucer.  Darn, clear liquid drained, so it’s still not thick enough!

It was 4 hours later when the tomato paste showed thick enough that a spoonful dropped on a saucer wouldn’t separate at all, and would retain its shape. It took 30 full hours in the slow-cooker on HIGH, with the lid(s) propped up to permit evaporation. I continued as in my original recipe, putting the paste in 4-ounce jars, adding a bit of citric acid, and sealing in a waterbath for 45 minutes.

Good news: you don’t need an oven to make tomato paste. You don’t need to stand over a hot pot and stir so that the tomatoes won’t scorch. You do need patience, though, and a large slow cooker or two. Flat large cookers will work faster than tall ones for this purpose;  the more surface area, the better.  I wish I had taken photos all throughout this process. Next time, I promise I will. 

Result: from a half-bushel of Roma tomatoes, 24 4-ounce jars of slow cooker tomato paste, and the satisfaction of establishing a new easier cooking method to use in the future.


Link to recipe: oven-roasted tomato paste


Link to recipe: tomato paste in the slow cooker

4 Responses

  1. Thank you for the “consistency” test! Love it! When I use the crock pot for paste, I leave the lid off completely – it thickens more quickly.

    • When I use the slow cooker for fruit butters, I prop the lid open with wooden spoons or chopsticks. It keeps up the heat but allows evaporation overnight.

  2. Hi Maurita,

    I’m so excited to try the method above, never having made tomato paste. Might you explain, however, instructions for the first sentence in your second paragraph? “We had washed, quartered, squished and strained the entire basket, and put the sauce…” Would you be kind enough to explain, in more detail, “how” to do this since I’ve never done it?

    Thanks much,

    • Of course. First, there’s a more detailed recipe linked at the bottom of the post, which I’ll also link here: slow cooker tomato sauce recipe. The first step to making tomato paste (or sauce) is to get the good tomatoey stuff, minus the skin and seeds. There are several ways to do this. A hand-crank tomato strainer is a classic. I have one, and used it for many years. As I began to put up more and more sauce and paste, though, I wanted something with more oomph and less work. I now use the fruit/vegetable strainer attachment for my KitchenAid mixer, which does a fantastic job. Whatever strainer you use, you’ll need to quarter the tomatoes before you press them. I hope that’s a full explanation for you, but if you still have questions, do contact me. I’d love to hear how your first tomato paste turns out!

  3. […] And I thought oven tomato paste was good – how about letting your slow cooker do all the work of making tomato paste? […]

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