Ingredient

Kefir

Kefir is milk fermented by a mixed community of bacteria and yeasts, held together in soft, rubbery grains that are strained out and used again. It is thinner than yoghurt, sharper, slightly fizzy, and faintly yeasty — the drink equivalent of a sourdough starter rather than of a set pot.

What makes it different from yoghurt

Yoghurt is made by a small, tidy team: two bacteria, working warm, producing lactic acid and nothing much else. The result is thick, clean and sour in one direction.

Kefir is made by a crowd. The grains hold dozens of species of lactic acid bacteria and several yeasts, living together in a matrix of polysaccharide, and they work at room temperature rather than in a warm cabinet. The bacteria make lactic acid; the yeasts make carbon dioxide and a trace of alcohol; other organisms make acetic acid and aroma compounds.

That is why kefir is thin — the curd is broken up by gas and agitation rather than left to set — fizzy, and much more complex on the nose than yoghurt. It is also why it tastes faintly of bread or beer underneath the sourness, which people either like immediately or have to grow into.

The two kefirs

They share a name and a mechanism and almost nothing else.

Milk kefir

Made with dairy milk and cauliflower-like white grains. Sour, thin, slightly fizzy, drinkable. This is what "kefir" means unqualified.

Water kefir

Made with sugar water and translucent grains, sometimes called tibicos. Light, lightly sweet, properly fizzy, closer to a soft drink than to a dairy product. Often flavoured with fruit or ginger for a second fermentation in a sealed bottle.

Grains, in both cases

Not cereal grains. They are living gel matrices that grow as they work, are strained out of each batch and put straight into the next, and are passed between people rather than bought repeatedly.

Shop-bought kefir

Usually made from a freeze-dried culture rather than from grains, which gives a more consistent and typically milder product. Still a mixed ferment, still fizzy, generally less sharp than home-made.

How to use it

Kefir behaves like a thin, sour, slightly effervescent buttermilk, and that is the shape of every good use for it.

• Drunk cold, plain or with fruit blended in. The most common use and the one it is best at.
• In place of buttermilk in baking. It is acidic, so it reacts with bicarbonate of soda in exactly the same way — soda bread, scones, pancakes and quick breads all take it directly.
• In a marinade for chicken or lamb. The acid and the enzymes tenderise the surface, and the dairy keeps the meat from drying out. This is the same logic as a yoghurt marinade with more acid.
• In cold soups and dressings — a chilled cucumber soup, a herb dressing, a raita-style sauce that needs to pour rather than sit.
• Not in anything that boils. See below.
• Strained overnight through muslin it thickens into a soft, spreadable cheese with a sour, complex flavour. The liquid that drains off is whey and is useful in bread.

Why it splits, and how to stop it

Kefir curdles in a hot pan faster than yoghurt does, for two reasons that stack. It is more acidic, so its casein is already close to the point where it clumps; and it is thinner, with less protein network and no added stabiliser to hold the curds apart once they form.

The fixes are the ones that work for any sour dairy. Take the pan off the heat before it goes in. Temper it — stir some of the hot liquid into the kefir first, then return the lot — so it never meets a temperature shock. Stabilise it by whisking in a little cornflour or plain flour before heating, which gives the proteins something to hang on to. And never let it boil, at any stage, for any length of time.

For a hot dish where none of that is practical, use full-fat yoghurt or crème fraîche instead. Both are far more forgiving, and the extra fat is most of why.

Keeping a culture going

If somebody gives you grains, this is the rhythm. FoodHQ does not publish salt percentages, pH figures or keeping times for home preserving. 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 them 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. Put the grains in fresh milk in a clean jar, roughly the same quantity of milk each time so the pace stays predictable.
2. Cover it so it can breathe but nothing can get in — a cloth and a band, or a loose lid.
3. Leave it at room temperature until it thickens slightly and smells sour. Warm rooms are quick and cold rooms are slow, so go by smell and taste rather than by the clock.
4. Strain the grains out with a plastic or stainless sieve. The finished kefir goes in the fridge; the grains go straight into fresh milk.
5. If you need a break, put the grains in milk in the fridge, where they tick over slowly for a week or two before needing feeding again.
6. Expect the grains to multiply. Give the surplus away, or blend it into a batch, which is what most people do.

Common questions