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Cooking encyclopedia Food science

Fermentation

Controlled microbial transformation of food, and the conditions that keep it controlled.

15โ€“30 ยฐC (59โ€“86 ยฐF)

What it is

Fermentation is the deliberate encouragement of some organisms over others. Lactic acid bacteria, yeasts and certain moulds convert sugars and proteins into acids, alcohol and aromatic compounds, changing flavour, texture and keeping quality.

Why it works

Every traditional ferment works by making conditions that suit the organism you want and not the ones you do not: salt and anaerobic submersion for vegetables, an acid start for dairy, a known culture for soy and grain ferments. As acid builds, the environment becomes progressively more hostile to spoilage. The traditional rules โ€” enough salt, keep it submerged, keep it cool โ€” are the control mechanism, not folklore.

When to use it

Sauerkraut, kimchi, pickles, yoghurt, cheese, bread, tempe, soy sauce, fish sauce, vinegar, cured sausage.

What goes wrong

Too little salt; food above the brine, where moulds grow; wildly warm temperatures, which favour the wrong organisms; scaling a traditional recipe without keeping the salt ratio.

More on this shelf

  • Brining and salt What salt does to meat beyond seasoning it.
  • Caramelisation The breakdown of sugar by heat alone into colour, aroma and bitterness.
  • Carryover cooking Food keeps cooking after it leaves the heat, and large pieces keep going a long way.
  • Collagen and gelatin Why tough cuts become tender and rich with long, moist cooking.
  • Gluten development How two wheat proteins become the elastic network that holds bread together.
  • How heat sets protein Why an egg becomes solid, fish flakes, and meat goes from translucent to opaque.
  • Smoke point The temperature at which a fat starts to break down visibly, and why it matters less than it is said to.
  • Starch gelatinisation The swelling and bursting of starch granules in hot water, which thickens sauces and cooks grains.
  • The Maillard reaction The reaction between amino acids and reducing sugars that browns food and creates hundreds of new flavour compounds.