Fermenting vegetables: sauerkraut, kimchi, pickles

Why

Lactic acid bacteria live naturally on vegetables, tolerate salt and need no air; the right amount of salt, roughly 2–2.5% of the weight for cabbage, draws juice with sugars out of the cells and at the same time holds back spoilage bacteria, so the lactic bacteria gain the upper hand and sour the vegetables with lactic acid. Acidification is the main protection, because harmful microbes do not multiply in finished sauerkraut, but until the acid forms only salt, temperature and submersion protect the vegetables. The vegetables must therefore stay under their juice or a brine the whole time, because in air yeasts, moulds and rot take hold. At 21–24 °C sauerkraut is fermented in 3–4 weeks, at 16–18 °C in 5–6 weeks; below 16 °C fermentation stalls and above 24 °C the cabbage turns soft, as it also does with less than 1.7% salt. A flat white film on the surface is usually kahm yeast, which is skimmed off, whereas fuzzy mould, slimy or rotting vegetables and a putrid smell mean spoilage.

How to do it

• Weigh the salt: 20–25 g per kilogram of trimmed cabbage, ideally pure salt without iodine or anti-caking agent; mix it in evenly and let the cabbage release its juice.
• Pack the cabbage firmly into a jar or crock and weigh it down with a plate and weight or a bag of brine; if juice is lacking, top up with boiled, cooled brine of 30 g salt per litre.
• Ferment in the dark, ideally at 21–24 °C, and two or three times a week check the vegetables are under the surface; above 24 °C they soften and mould more easily.
• Skim off a flat white film with a spoon; if there is fuzzy mould of any size, slime, a putrid smell or rotting vegetables, do not taste the batch and throw it all away.
• Ferment kimchi, cucumbers and other vegetables by a tested recipe with measured salt; kimchi usually only 1–2 days at room temperature and then in the fridge.
• Store fermented vegetables covered in the fridge, where they keep for months; for the pantry they must be canned by a tested method (Home canning and botulism card).

If it goes wrong

Soft sauerkraut that smells clean and sour is edible, just less crunchy; next time salt more accurately and ferment somewhere cooler. Pink sauerkraut that is not slimy is usually caused by yeasts or pigments and is edible. Rinse overly sour sauerkraut briefly and braise it with onion in fat (Braised cabbage and sauerkraut card). Do not taste slimy or rotting sauerkraut, a putrid smell or any fuzzy mould; throw away the whole batch.