Frequently asked questions

What salt percentage should I use for sauerkraut?

2.0% by weight of cabbage is the working default and what Fermentcalc recommends if you do not change the slider. The safe and active range is 1.5%-3.0%; below 1.5% acidification is too slow and the cabbage can spoil before it sours, above 3% the bacteria slow down materially and the kraut takes weeks longer than it needs to. 2.0% gives you a reliable 7-14 day primary ferment at typical kitchen temperature.

What is the difference between dry-salt percentage and brine percentage?

Dry-salt percentage is the salt mass as a percentage of the vegetable mass (used for sauerkraut, kimchi, pepper mash, anything shredded or chopped that releases its own juice). Brine percentage is the salt mass as a percentage of the water mass (used for whole vegetables submerged in liquid — pickles, peppers, garlic, cauliflower). Brine percentages are typically higher (3-5%) because the brine has to do the work that vegetable-released juice does in a dry-salted ferment.

Do I need iodised or non-iodised salt?

Non-iodised. Iodine inhibits the lactic-acid bacteria that drive the ferment and anti-caking agents in standard table salt can cloud the brine and leave deposits. Use pickling salt, kosher salt without anti-caking, or non-iodised sea salt. Fermentcalc assumes non-iodised salt in every calculation.

How does temperature change fermentation timing?

Lactic-acid bacteria roughly double in metabolic rate every 10 °C (Q10 ≈ 2). The site uses that ratio anchored at 68 °F (20 °C) — a ferment at 78 °F finishes about 1.4× faster, at 58 °F about 1.4× slower. This is a first-order approximation; the final tell is taste and pH, not the calendar. The methodology page has the formula and citations.

What is kahm yeast and is it dangerous?

Kahm is a white, sometimes slightly cream-coloured film that forms on the surface of a ferment when it has had air exposure. It is harmless — scoop it off and continue. The taste is musty and unwelcome so try to skim early. Coloured moulds (pink, red, fuzzy green or black) are a different story — those are not kahm and the ferment should be discarded.

How do I know when my ferment is done?

Taste and pH. A finished lacto-ferment is sour and pleasantly tangy, with no remaining raw-vegetable sweetness. With a cheap pH meter or strips, you are looking for pH below 4.6 (the FDA shelf-stability threshold for low-acid foods); most successful ferments end up between pH 3.4 and 4.0. The Fermentcalc timing slider gives you a starting window, but it is a window, not a deadline.

Can I scale a small recipe up to a 5-litre crock?

Yes. Salt percentage is independent of batch size — 2.0% salt on 500 g of cabbage gives the same result as 2.0% on 5 kg. Fermentcalc's batch-scaling pages handle the multiplication for you and suggest vessel sizes (jar, fido jar, ceramic crock) that fit the new total weight. Note that larger batches ferment a little slower at the same temperature because they buffer their own thermal mass — add a day or two to the timing window for big crocks.

Why does the site not cover sourdough, beer, wine, or cider?

Lacto-vegetable fermentation has different safety thresholds, different math, and a different reader profile than yeast-driven cereal or sugar ferments. Mixing them on one site dilutes both. Sourdough is on a sister site; beer, wine, and cider are well covered elsewhere. Fermentcalc stays narrow on purpose.

Are the timings on this site for the primary or secondary ferment?

Primary fermentation only — the active sour-and-bubble phase at room temperature. After the primary phase is done (taste sour, pH below 4.6, bubbling slowed) most ferments go to cold storage where they continue to develop more slowly for weeks or months. The cold-storage stage is not in the calculator; the calculator answers when to move from primary to cold, not how long to keep in cold storage.

What if my kitchen is much colder or hotter than 68 °F?

Use the temperature input — it adjusts the timing window with the Q10 factor described in the methodology. For very cold kitchens (below 55 °F) the ferment will struggle to start at all and you should warm the spot or wait for a warmer season. Very hot (above 80 °F) is fine but expect mushier texture and a sharper, sometimes vinegar-like finish.

Do you store my batches or send me reminders?

No. Fermentcalc is intentionally not a logged-in product. There is no account flow, no batch history, no email collection. Bookmark a result URL if you want to come back to a specific calculation — the URL captures every input and re-renders the same numbers.

Is this site medical or food-safety advice?

No. Fermentcalc is a reference for home fermenters that aligns with published safe ranges (NCHFP, FDA pH 4.6 threshold). If you are fermenting commercially or for an immunocompromised household, you need a process-authority review beyond what this site can give. The methodology page lists the sources we cite.

Question not covered here? Email the contact page address and we will add it.