Fermentation Brine Calculator

Between 2% and 3% of the total weight of vegetables plus water for most vegetables, with cucumbers needing 3.5% because their dense flesh and intact skin slow salt penetration. For 800 g of vegetables in 600 g of water at 2.5%, that is 35 g of salt. The critical detail is the basis: percentages must be taken against vegetables and water together, not against the water alone.

Total weight, and the difference is large enough to matter for safety. Vegetables are roughly 90% water themselves and the salt equalises across the whole jar within a day, so salting only against the added water leaves the real concentration far below the target. With 400 g of vegetables in 600 g of water at 2.5%, the water-only method gives 15 g against 25 g by total weight, and the effective jar concentration is only 1.48% — under the 2% working minimum.

Below 4.6, which is the threshold under which Clostridium botulinum cannot grow. A healthy vegetable ferment crosses it within 48 to 72 hours and settles between 3.5 and 4.0 as it matures. If a ferment has been at room temperature for three days and the pH has not dropped below 4.6, something has gone wrong and it should not be treated as shelf stable.

Not really, and this is the most common misunderstanding about fermentation. Salt does two limited jobs: it draws water out of the vegetables to form brine, and it gives salt-tolerant lactobacillus a competitive advantage over spoilage organisms for the first day or two. After that the lactic acid those bacteria produce does all the actual preservation by dropping the pH. The salt is a starting condition; the acid is the preservative.

Down to about 1.5%, with caution. Below that, lactobacillus loses its competitive advantage, spoilage organisms and pectin-degrading enzymes get a foothold, and the texture goes soft even when the batch does not outright fail. If you want lower salt, ferment cooler, keep the batch small, keep everything strictly submerged and taste more often. Do not go below 1.5% simply to reduce sodium — most of the salt stays in the brine and is discarded anyway.

Above about 5%, lactobacillus itself begins to stall and the ferment slows dramatically or never really starts. You get salty vegetables rather than fermented ones, the pH does not drop, and without that pH drop the preservation mechanism is missing. Some traditional preparations do use much higher salt — preserved lemons at 10%, olives at 8–10% — but they work by osmotic preservation over months rather than by rapid acidification.

Weigh it if you can, because salts differ by more than two to one in density. A teaspoon holds 6.0 g of fine table salt, 4.8 g of Morton coarse kosher and only 2.8 g of Diamond Crystal. A recipe written in teaspoons and made with the wrong salt can land at half or nearly double the intended concentration, which is the difference between a good ferment and a failed one.

Sources genuinely disagree, and it is worth saying so rather than picking a side. The traditional advice is to avoid iodised salt because iodine is antimicrobial and may inhibit the bacteria you want. Several experienced fermenters report no measurable difference at the concentrations found in table salt. The better documented complaint is anti-caking agents, which cloud the brine without harming the ferment. Plain non-iodised salt sidesteps the whole argument.

Almost certainly Kahm yeast, which appears as a flat, wrinkled, matte white film across the surface. It is harmless, though it gives a musty off-flavour if left, so skim it off and make sure everything stays submerged. What you must not ignore is fuzzy mould, particularly in blue, green, black or pink. That means discarding the whole batch rather than scooping out the visible part, because mould hyphae penetrate far deeper than what you can see.

It depends on the vegetable and the temperature. Kimchi and pickled radish take 3 to 7 days, cucumbers 3 to 7, carrots 5 to 10, sauerkraut 3 to 6 weeks and whole garlic cloves 3 to 5 weeks. Temperature moves all of these substantially: at 80°F a ferment runs perhaps 40% faster but comes out softer and less complex, while at 60°F it takes half as long again and stays notably crisper.

Usually too little salt, too warm a fermentation, or pectin-degrading enzymes from the blossom end of the cucumber. Trim a slice off the blossom end before packing, use 3.5% salt rather than the 2% that suits leafy vegetables, and ferment somewhere cool. Tannins help too — a grape, oak or bay leaf in the jar is a traditional and genuinely effective firming trick.

Yes, without exception. Lacto-fermentation is anaerobic, and anything sitting above the surface is exposed to oxygen where moulds and aerobic yeasts thrive. Use a glass weight, a smaller jar, a folded outer cabbage leaf or a brine-filled bag. If the level drops, top up with brine mixed at the same percentage rather than plain water, which would dilute the jar and weaken its protection.