How to make sauerkraut

What you are actually doing

Salt draws water out of shredded cabbage. Within a few hours there is enough liquid for the cabbage to sit under its own brine, and that brine is the whole mechanism: it excludes oxygen, which rules out the moulds and aerobic bacteria that would rot the leaf.

Underneath, the lactic acid bacteria already living on the cabbage are salt-tolerant and do not need oxygen. They eat the sugars in the leaf and produce lactic acid. The jar becomes steadily more acidic and steadily more hostile to everything else.

You are not adding anything. You are creating conditions in which one group of organisms out-competes all the others, and then waiting.

The method

The mechanics, so that a recipe from a reliable source makes sense. FoodHQ does not publish salt percentages, pH figures or keeping times for home fermenting. Those are safety numbers, they are set by a food safety authority rather than by a cookery writer, and the right ones depend on what you are fermenting and where you are. In the UK the Food Standards Agency is the authority — use a recipe from it or from another body with the same standing, and treat this page as the explanation of why that recipe is shaped the way it is.

1. Shred the cabbage finely. Fineness matters — more cut surface releases more juice, faster.
2. Weigh it. Salt is added as a proportion of that weight, and weighing is the difference between a recipe that works and one that does not, because cabbages vary enormously.
3. Add the salt and work the cabbage hard with your hands for several minutes, or salt it and leave it to stand. Wait for it to go limp and wet — you are waiting for liquid, not for a texture.
4. Pack it hard into a jar, pressing out air pockets, until the liquid rises above the solids.
5. Weight it down so nothing floats. A small jar, a sealed bag of brine, or a proper fermentation weight all work. Anything above the brine will mould.
6. Cover it so carbon dioxide can escape but air cannot easily get back in — an airlock lid, or a loose lid burped daily.
7. Leave it somewhere cool and out of direct sun. Taste it from about a week and refrigerate when it tastes right to you.

What normal looks like

Most panic about a first ferment is about things that are supposed to happen.

• Bubbling from day two or three, sometimes vigorous. This is carbon dioxide and it is the sign it is working.
• Cloudy brine. Normal, and it happens to every vegetable ferment.
• A sour, cabbagey smell that gets sharper over days. Pleasantly sour is right.
• The cabbage dulling from bright green to olive or yellowish. Normal.
• Brine rising and sometimes overflowing in the first few days. Stand the jar on a plate.
• A white film on the surface is usually kahm yeast — harmless, and skimmed off. Fuzzy, coloured, raised growth is mould and is a different matter.
• Softening is not normal and usually means too little salt or too warm a spot.

When to stop and when to throw it away

Time

A week for something mildly sour; three to six weeks for a deeply sour kraut. Cooler is slower.

Taste as the test

There is no fixed endpoint. Taste it with a clean fork every few days and refrigerate when you like it.

Kahm yeast

A flat white film. Harmless, skim it off, and it usually means the temperature is too high or something touched the air.

Mould

Fuzzy and coloured — green, black, pink, blue. Discard the batch. Do not scrape it off and carry on.

Smell

Sour is right. Putrid, rotten or cheesy is not. If it smells wrong, throw it away.

Refrigeration

Slows the fermentation almost to a stop. It does not halt it entirely.

Common questions