How this calculator works
Salt selects which microbes grow in a vegetable ferment. Lactic acid bacteria tolerate salt and produce acid, while many spoilage organisms and pathogens do not, so a brine of about 2 to 3 percent salt by water weight lets the wanted fermentation run and keeps the unwanted ones down. The percentage here is measured against the water alone, which is the usual way a brine is written. A dry salt method, where salt is rubbed into shredded cabbage and the salt is measured against the vegetable weight, uses a slightly lower figure for the same effect because the cabbage releases its own water. Use non iodised salt: iodine can slow the bacteria. The real safety check is the finished pH, which should be 4.6 or lower, and keeping the vegetables under the brine stops mould growing on exposed pieces.
Formula
salt = brine share x water mass. water mass = salt / brine share, with one litre of water taken as 1000 g. brine share = salt / water mass. salt per litre = brine share x 1000. A 2.5 percent brine is 25 g of salt in 1 L of water, and a 3 percent brine is 30 g in 1 L.
Worked example
For 2 L of water at the 2 percent brine used for cabbage and leafy greens, salt = 0.02 x 2000 = 40 g. For cucumbers at 3 percent and 1.5 L of water, salt = 0.03 x 1500 = 45 g. Working backwards, 30 g of salt at 2.5 percent needs 30 / 0.025 = 1200 g of water, or 1.2 L. A mix of 50 g of salt in 2 L of water is 50 / 2000 = 2.5 percent.
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Frequently asked questions
Should the percentage be based on the water or on the vegetables?
A brine is normally written against the water, which is what this page does. The dry salt method rubs salt into the vegetables and measures it against their weight. Choose one method and follow its numbers; mixing the two conventions gives a much weaker or much stronger brine than intended.
Is 5 percent too salty?
It is at the top of the working range. Up to 5 percent is used for warm weather, long storage or soft vegetables, but the ferment slows and the finished vegetable is salty. Above about 8 percent the salt preserves rather than ferments. Start at 2 to 3 percent unless your recipe says otherwise.
Why does the page mention pH?
Salt slows the wrong microbes but does not stop all of them on its own. The acid produced during fermentation is what makes the vegetables safe. A finished ferment should test at pH 4.6 or below, and a ferment that smells wrong, grows fuzzy mould or never turns acidic should be discarded.
Which salt should I use?
Use plain non iodised salt, such as pickling salt or coarse sea salt, and weigh it. Crystal sizes differ so much that a tablespoon of one salt can weigh nearly twice as much as a tablespoon of another. Iodised salt can also slow the bacteria.