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Fermenting

Fermenting is a preservation and flavour technique in which microorganisms such as lactic acid bacteria or yeasts transform food. Cabbage becomes sauerkraut or kimchi, milk becomes yoghurt – more durable, more digestible and more intense in flavour.

In fermenting, microorganisms convert sugars and starch into acids, alcohol or gases. The most common in the kitchen is lactic acid fermentation: vegetables are mixed with salt (usually about 2 % of the vegetable weight) and placed in a jar or crock away from air. The naturally present lactic acid bacteria multiply, produce lactic acid and lower the pH so far that spoilage bacteria no longer stand a chance. The result is sour, aromatic and long-lasting.

The process is surprisingly simple: chop the vegetables (cabbage, carrots, radish, cucumbers), salt them, knead vigorously or cover with brine so everything sits under liquid, and let ferment at room temperature. After 3–5 days the sour taste begins; after 1–4 weeks the desired maturity is reached. Then the ferment goes cool into the fridge or cellar, where it keeps for months. Besides vegetables, bread dough (sourdough), milk (yoghurt, kefir), soybeans (miso, tempeh) and tea (kombucha) are also fermented.

Fermenting is for anyone who wants to preserve food, reduce food waste or appreciates complex flavours and probiotic, gut-friendly dishes. In modern fine dining, fermentation is a central tool for new flavour directions (umami, acidity, depth). At home it needs hardly any equipment: a clean jar, salt and patience are enough; a fermentation weight and airlock lid (together often CHF 15–40, no guarantee) make it easier.

What to watch for: cleanliness is crucial, the vegetables must stay fully under liquid (air contact promotes mould), and the salt amount should be right. A white kahm-yeast film is usually harmless and can be skimmed off; fuzzy, coloured mould, on the other hand, means: discard. A pleasantly sour smell is normal, a putrid stench is not.

Example

In autumn a restaurant ferments surplus beetroot and carrots from the region: salted with 2 % salt, they mature for two weeks in a crock into a sour, crunchy vegetable that serves as a side dish through the winter and helps reduce food waste.

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Frequently asked

Is fermented vegetable healthy or dangerous?

Properly fermented vegetables are safe and considered healthy: the lactic acid bacteria act as probiotics and support gut flora. The low pH inhibits harmful germs. It only becomes dangerous with serious hygiene mistakes or if coloured mould grows – then discard. A white kahm-yeast film, by contrast, is harmless.

How long does fermenting take?

Active fermentation starts after 2–3 days. Vegetables are ready after 1–4 weeks depending on taste, sauerkraut often after 3–6 weeks. After that the ferment keeps for many months when stored cool. The warmer the environment, the faster – but also the less controlled – the process.

What is the difference between fermenting and pickling in vinegar?

When pickling in vinegar you add ready-made acid from outside – no fermentation takes place. When fermenting, living lactic acid bacteria produce the acid themselves and form complex aromas and probiotic cultures that vinegar pickling lacks.

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