Fermented Ketchup

Homemade condiments like fermented ketchup provide another way to take in probiotics, while at the same time eliminating another High-Fructose Corn Syrup-laden food from your diet. They are also a great way to sneak probiotics (good bacteria!) into your kids’ meals.

Bonus points if you make your own paste from fresh tomatoes. If you just don’t have the wherewithal or time to paste your own tomatoes (and it IS a long process!), it would be okay to use organic canned tomato paste. We won’t tell anyone! 😉

Fermented Ketchup

Prep Time 10 minutes
Fermentation Time 7 days
Course condiment
Makes 1 pint


  • 5 lbs. (2.2 kg) fresh San Marzano or other pasting variety tomatoes OR
  • 12 ounces (350g) organic canned tomato paste
  • 1 ounce (30 ml by volume or 1.5 oz/42g by weight) honey
  • 2 garlic cloves
  • 3 fl. oz. (90ml) olive or pickle brine, apple cider vinegar or very ripe kombucha (acidic liquid)
  • 1 tsp. (5ml) fine sea salt
  • ½ tsp. (2.5ml) clove ground
  • 1 tsp. (5ml) allspice ground


Make Paste (from scratch)

  • Wash and remove stems from tomatoes.
  • Make an "X" shaped slit in the skin of the tomatoes at the stem end.
  • Boil water in a medium to large stockpot.
  • A few at a time, drop the tomatoes in for 30-40 seconds. Fish out with a spider or slotted spoon.
  • Immediately put them in a bowl filled with ice water. Then pinch the tomatoes from the non-slit end. The skins will pop off. Set aside in another bowl. Compost or discard skins.
  • Cut tomatoes open and squeeze out gel and seeds. (Reserve for another use).
  • Puree drained tomato flesh in a food processor until mostly smooth (a few lumps is okay).
  • Pour contents into a slow cooker, and cook for 8-10 hours on low heat, stirring occasionally. During this time, most of the juice should evaporate off, and it will take on a darker color. It won't be as thick as canned tomato paste. You can cook longer if you want a thicker paste.
  • Let paste cool.

Mix ingredients (Start here if using tomato paste)

  • Peel and mince garlic finely, or grate using a microplane.
  • Add minced garlic and all remaining ingredients to a pint-size wide mouth or larger jar.
  • Stir contents thoroughly.
  • Tweak with acidic liquid to get the right consistency. There will be a little evaporation during fermentation, so make it a little more runny than you want to have when it's finished.
  • Using a folded towel as a cushion, tap the jar on a countertop or table to get any excess bubbles out of the mixture. Ensure that the top surface is smooth and flat. Wipe down the inside top and neck of the jar to remove any excess, which can collect mold.


  • Cover lid tightly and let ferment at room temperature for 3 to 7 days.
  • When you like the taste, transfer and store in refrigerator. Scrape down sides of jar to reduce chance of mold formation. Lasts at least 6 months in the refrigerator.

8 thoughts on “Fermented Ketchup

  1. Pingback: Grilled Cheese – Meals by Dad

    • Austin Post author

      Most ferments will work without whey (the whey gives it a “kick start”). I would add a few days to the fermenting time if you’re not using whey. Let us know how it goes!

      • Jen

        If I’m not using whey, the sea salt and vinegar will ferment the ketchup?

        • Jen

          Also, where should I buy the whey if I choose to use it? Jimbos?

        • Austin Post author

          Hi Jen,
          Yes, it should still ferment without whey. The whey gives the good bacteria a head-start on fermenting.

          Your best bet is to make your own liquid whey by straining out fresh yogurt or kefir. Here’s a good procedure: http://www.cheeseslave.com/how-to-make-whey/

  2. marykorte

    what do you do about the white stuff on the top? How long will this last in the fridge? How does the flavor compare to conventional ketchup?

    • Austin Post author

      The white stuff is dried whey. You can either mix it in or scoop it off. If there are any off-color spots (blue or black), that’s mold, and you should definitely scoop those off.

      I think it should last about 3 months in the fridge, tightly sealed.

      I think it’s a much more complex flavor, especially with the allspice/cloves combination. More tomatoe-y too!

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