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Fermented ketchup is a brilliant way to turn a familiar condiment into something more layered. It keeps the sweet-tomato comfort of classic ketchup, but the fermentation adds brightness, depth, and a subtle savoury edge.
This version uses tomato paste for consistency and richness, then ferments with a little active brine from a live ferment, such as fermented cucumber brine, sauerkraut brine, or fermented cabbage and carrot brine.
Makes about 450g
Optional Add-Ons
For a warmer ketchup:
For a fresher version:
For a smoky version:
1. Add the tomato paste, fermented brine, honey or maple syrup, apple cider vinegar, salt, spices, and olive oil if using to a clean bowl. Stir until completely smooth. If the mixture feels too thick, add filtered water little by little until it reaches a spoonable ketchup texture.
2. Spoon the ketchup into a clean glass jar. Leave at least 3cm headspace at the top, as fermentation may create a little pressure. Wipe the rim clean and close the jar loosely. You can also use an airlock lid if you have one.
3. Leave the jar at room temperature for 24–48 hours. Taste after the first day. The ketchup should begin to taste brighter and more rounded. If your kitchen is warm, 24 hours may be enough. In cooler conditions, it may need closer to 48 hours.
4. Once the flavour is where you like it, close the jar properly and transfer it to the fridge. The flavour will continue to settle and develop slowly in the refrigerator.
The finished ketchup should be:
It should not taste aggressively fermented. The goal is a familiar ketchup flavour with more complexity behind it.
Use live, unpasteurised brine from a successful ferment. Vinegar pickle juice from a heat-treated jar will add flavour, but it will not provide the same active fermentation culture.
Always use a clean spoon when serving. Store in the fridge and use within 2–3 weeks.
If it develops mould, an unpleasant smell, or strong pressure build-up, discard it.
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