Fermentation Calculators

Salt ratios, brine strengths, timings and batch scaling for kraut, kimchi, kombucha, kefir, miso and the rest. 15 calculators.

Salt percentage is the safety number, and it is the one worth getting exactly right rather than by eye. Lacto-fermentation works because salt suppresses spoilage organisms while letting lactobacillus through, and the window is narrower than most recipes admit. Below about 1.5% by weight of vegetable, soft rot and mould become likely. Above 5% fermentation stalls. Most vegetable ferments sit at 2 to 2.5%, and the percentage is of vegetable plus water together, not of water alone. Measuring salt by tablespoons rather than weight is behind a large share of failed first batches.

Kombucha scales starter liquid with volume rather than treating it as a fixed splash. Starter is what drops the initial pH into a safe range, and an underdosed large batch spends its first days vulnerable. Around 10% by volume is the usual target.

Timings here are ranges tied to temperature, not fixed days. A kraut at 18C and the same kraut at 26C are different projects, and the second can be done in under half the time.