Homemade yogurt: two ingredients and temperatures that must be right
Yogurt is milk and live bacteria, and nothing else. It very nearly makes itself, provided two temperatures are held. The first is 85 °C — heating the milk to it changes the structure of the whey proteins, which is what makes yogurt thick rather than watery; skip this and it comes out noticeably thinner. The second is 42–45 °C, where the bacteria work best. Above 50 °C they start to die, below 35 °C they work very slowly — and that is the only difficulty in the whole recipe.
Your own work in that: 25 min.
- Heating 25 min
- Fermenting 480 min
- Chilling 120 min
Step by step
0 / 5 doneHeat the milk to 85 degrees
Pour the milk into a pan (if using milk powder, whisk it into the cold milk) and heat it slowly, stirring, to 85 °C — this takes about 10 minutes. Small bubbles appear at the edges but the milk must not boil. Hold that temperature 10 minutes, stirring now and then.
Ingredients: 1000 ml whole milk · 3 tbsp natural yogurt
TipThis step makes all the difference to thickness. At around 80 °C and above the whey proteins denature, and only then do they bind water together with the casein. UHT milk has been heated at the factory but still benefits from this stage.
Eighty-five degrees, ten minutes, no boilingCool it to 45 degrees
Stand the pan in a sink of cold water and stir until the milk falls to 42–45 °C. Without a thermometer: a drop on the inside of your wrist should feel clearly warm but not hot — noticeably warmer than a baby's milk, which is at body temperature.
TipAbove 50 °C the yogurt bacteria start to die and the milk may not sour at all. It is the commonest mistake — better to wait a minute longer than to add the starter to milk that is too hot.
Clearly warm, but not hotInoculate with yogurt
Take a cup of the warm milk into a bowl, whisk the yogurt into it until smooth, and only then stir that mixture back into the pan. Yogurt dropped straight into the pan clumps and never disperses evenly.
Ingredients: 1000 ml whole milk · 3 tbsp natural yogurt
TipThe starter yogurt must contain <b>live cultures</b> and be fresh — the closer to its production date, the more live bacteria. Check the label for Lactobacillus bulgaricus and Streptococcus thermophilus.
A cup of milk first, then the whole panKeep it warm for eight hours
Pour into scalded jars, seal, wrap in a thick towel and put them in a cool box, an oven with only the light on, or under a duvet. Leave 8 hours undisturbed. Any movement while it sets breaks the structure that is forming.
TipAn oven with only the light on usually holds 40–45 °C and is the simplest solution. Check with a thermometer the first time — models vary considerably.
Eight hours warm, entirely undisturbedChill and check
After eight hours the yogurt should be set and hold its shape when the jar is tilted. Refrigerate at least 2 hours — it only thickens fully when cold. A little whey on the surface is normal; stir it in or pour it off. Serve with honey.
Ingredients: 3 tbsp milk powder · 2 tbsp honey
It holds its shape when the jar tilts
Before you start
Greek yogurt
Strain the finished yogurt through muslin in a sieve, 4 hours in the fridge. It loses roughly half its volume and becomes thick Greek-style yogurt. What drains off is whey — excellent in pancakes and bread.
Successive batches
Three tablespoons of your own yogurt starts the next batch. After a few generations the culture usually weakens and the yogurt thins — start again from a fresh shop-bought pot.
Too thin
Three causes: the milk never reached 85 °C, the fermenting temperature fell below 38 °C, or the starter was old. Next time, add the milk powder as well — it gives the yogurt more body.
How long it keeps
Two weeks in a sealed jar in the fridge. It grows sourer over time as the bacteria continue working — after ten days it suits cooking better than breakfast.