How to make yoghurt

Why the milk is heated first

Heating milk before culturing does two things. It reduces competing organisms, which matters. But the bigger effect is on texture: heating denatures the whey proteins so they join the casein network as it sets, giving a thicker, firmer, less watery yoghurt.

Milk that has been cultured without that step still sets, but it is thinner and more prone to separating. This is why almost every yoghurt method begins by scalding the milk and then cooling it.

The second temperature — the incubation — is the one the bacteria care about. Too cool and they work slowly or not at all; too warm and they are killed. Exact figures are worth taking from a reliable source rather than from memory.

The method

Heat, cool, culture, wait. FoodHQ does not publish salt percentages, pH figures or keeping times for home fermenting. 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 it 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. Heat the milk gently, stirring, until it is steaming and just about to simmer. Do not let it boil over.
2. Cool it until it is comfortably warm rather than hot. A clean finger held in it should be comfortable — but use a thermometer and a reliable recipe if you want to be accurate.
3. Stir in a few spoonfuls of live yoghurt with active cultures, or a sachet of starter. Whisk it into a little of the warm milk first so it disperses.
4. Pour into a clean jar or bowl, cover, and keep it warm and undisturbed for several hours — a yoghurt maker, a thermos, a warm airing cupboard, or a wrapped bowl in a switched-off oven with the light on.
5. Do not move or stir it while it sets. Disturbance breaks the gel and gives a grainy result.
6. Check after four hours. It is done when it has set and tastes pleasantly sour. Longer gives a tarter, firmer yoghurt.
7. Refrigerate. It firms up further as it chills.

Making it thicker

• Strain it. Line a sieve with muslin and let it drip in the fridge for a few hours. This is Greek-style yoghurt, and longer straining gives labneh.
• Heat the milk longer, holding it hot for twenty minutes or so, which denatures more whey protein.
• Add milk powder to the milk before heating, which raises the solids.
• Use whole milk rather than semi-skimmed. Fat contributes to the perception of thickness.
• Do not disturb it while setting. Moving the container breaks the gel.
• Keep the whey that drips out — it is useful in bread, smoothies, or for cooking grains.
• Save a few spoonfuls of each batch as the starter for the next. It weakens after several generations and then needs refreshing.

Notes

Whole or semi-skimmed

Both work. Whole milk gives a richer, thicker result.

UHT milk

Works, and needs no heating stage since it has already been heat-treated.

Starter strength

A few spoonfuls is plenty. More starter does not give a faster or better set.

Timing

Four to twelve hours. Longer is tarter and firmer.

Whey

The liquid that separates or strains out. Useful rather than waste.

Common questions