How much salt do I need for fermenting vegetables?

Salt does three jobs in a ferment: it draws water out of the vegetables to make the brine, it holds off the organisms you do not want long enough for the lactic acid bacteria to take over, and it keeps the vegetables firm. Getting the concentration right is most of the difference between a ferment that works every time and one that is a lottery.

Safety

Step by step

1. Work in percentages by weight, not spoons.Salts vary enormously in density — a tablespoon of fine salt weighs roughly twice what a tablespoon of flaky salt does. Scales remove the guesswork entirely and the calculation is trivial.
2. For a dry-salted ferment, weigh the vegetables.Shred and weigh the cabbage or vegetables, multiply by 0.02, and that is your salt in grams. One kilogram of cabbage takes 20g of salt. The vegetables make their own brine when you massage the salt in.
3. For a brined ferment, weigh vegetables and water together.Put the vegetables in the jar, add water to cover, then pour the water off and weigh both. Two per cent of the combined weight is the salt. This is the right method for whole cucumbers, beans, carrot sticks and anything too firm to release its own liquid.
4. Know the working range.1.5% to 3% is the practical band. Around 2% is the everyday default. 2.5 to 3% suits warm weather, a slower and crisper ferment, or anything left to go long. Below 1.5% is where ferments go slimy and unpredictable. Above about 5% the lactic acid bacteria themselves are inhibited and the ferment stalls.
5. Salt more in warm weather.Temperature and salt trade against each other. A ferment at 24°C is much faster and less controlled than one at 17°C, and going up to 2.5 or 3% slows it back to something manageable.
6. Use the right salt.Pure salt without iodine or anti-caking agents — pickling salt, coarse sea salt, or plain rock salt. Iodine can inhibit the bacteria and anti-caking agents cloud the brine. Table salt with additives is the usual reason a first ferment looks murky.
7. Account for water the vegetables bring.Cucumbers, courgettes and radishes are largely water, and that water joins the brine and dilutes it over the first days. This is why brined ferments of watery vegetables often sit at the higher end of the range.

Tips

• Keep a note of the percentage you used on the jar label alongside the date. It turns each batch into information rather than a guess.
• A 2% brine is 20g of salt per litre of water, near enough, which is a useful number to remember for topping a jar up.
• If a ferment tastes too salty at the end, rinse it before serving rather than reducing the salt next time — that solves the taste without touching the safety.

Common mistakes

• Reducing the salt for health reasons — The salt is doing a microbiological job. A low-salt ferment does not simply taste less salty, it behaves differently and is far more likely to go slimy or be colonised by the wrong organisms. Rinse the finished ferment instead.
• Measuring salt by volume — Fine table salt, coarse sea salt and flaky salt differ by a factor of two or more per spoon. A recipe that says 'one tablespoon' means very different things depending on which tub is nearest.

Questions people ask