How do I make sauerkraut at home?

Sauerkraut is the simplest ferment there is: cabbage, salt and time. The salt selects for lactic acid bacteria that are already on the leaves, and they convert sugars to lactic acid, which drops the pH below the level anything harmful can grow at. That acid is the entire safety mechanism, so the technique exists to give those bacteria the conditions they need and nothing else.

Safety

What you'll need

• A firm white or red cabbage
• Pure salt without anti-caking agents or iodine
• Digital scales
• A large bowl and a wide-mouthed jar
• A fermentation weight, or a small water-filled bag

Step by step

1. Take the outer leaves off and keep one.Reserve one clean outer leaf. It is the cheapest fermentation weight there is — folded and tucked over the top of the shredded cabbage, it holds the loose shreds under the brine.
2. Shred it finely and evenly.2 to 3mm on a mandoline or with a big knife. Fine shreds release liquid readily and pack down tight; chunks trap air pockets and take much longer.
3. Weigh the cabbage and calculate the salt.2% of the cabbage weight is the standard — 20g of salt per kilogram of shredded cabbage. Weigh it; do not use a spoon. Use pure salt, since anti-caking agents cloud the brine and iodine can inhibit the bacteria.
4. Massage until it makes its own brine.Salt over the cabbage in the bowl, then squeeze and pound it with your hands for five to ten minutes. It will go limp and a pool of liquid will collect. That liquid is the brine — you are not adding water.
5. Pack it down hard into the jar.A fistful at a time, pressed down firmly with a fist or a wooden spoon to drive out air. Pour every drop of the liquid from the bowl in after it. Leave 2 to 5cm of headspace, because it rises in the first few days.
6. Get everything under the brine and weight it.The liquid should rise above the cabbage when it is pressed. Lay the reserved outer leaf over the top, then a glass weight or a small freezer bag part-filled with brine. If there is genuinely not enough liquid after an hour, top up with brine made at 2% salt — never plain water, which dilutes the salt.
7. Cover loosely and leave it somewhere cool.A lid resting on, an airlock lid, or a cloth and a band. 16 to 20°C suits it — warmer ferments faster and softer, colder is slower and crisper. Stand the jar on a plate; it will overflow in the first few days.
8. Watch it through the stages.Days one to three: bubbles, a rising brine level, a smell that is faintly cabbagey. Days three to ten: active bubbling, the brine goes cloudy, the colour dulls from bright to olive, and the smell turns sour and pickled. After two weeks: bubbling slows, the smell settles.
9. Burp it daily if the lid is on.Unscrew, let the gas out, screw back down. A tightly sealed rigid jar with an active ferment in it can build real pressure. An airlock lid does this for you.
10. Refrigerate when it tastes right to you.One week gives a mild, crunchy kraut; four weeks gives a sour, soft one. Once it is where you want it, seal it and put it in the fridge, where it keeps for months and continues to change very slowly.

Tips

• Caraway seeds, juniper berries, dill or shredded apple all work in a kraut, added at the packing stage. Add nothing that brings much water with it.
• Warmth is the main variable. In summer a kraut can be done in five days; in an unheated winter kitchen it can take five weeks.
• Red cabbage makes a spectacular magenta kraut and behaves identically.
• Save a little of the brine when the jar is finished — it is a good starter splash for the next batch and it is excellent in a salad dressing.

Common mistakes

• Using less salt to make it healthier — The salt is what selects for the right bacteria and holds off the wrong ones while the acid builds. Below about 1.5% the ferment goes slimy and unreliable, and above about 3% it stalls. Two per cent by weight is the target.
• Topping up with plain water when there is not enough brine — It dilutes the salt concentration in the whole jar, which is the one thing keeping the ferment on track. Make up 2% brine separately and use that.
• Sealing the jar tight and leaving it for a fortnight — Carbon dioxide has nowhere to go. At best the jar overflows in the cupboard; at worst a glass jar under pressure is a hazard. Burp it or use an airlock.

If it doesn't work

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