Yoghurt

Ingredients

• 1 l milk
• 100 ml yoghurt

Method

Heat the milk to 82°C, then cool it to 45°C. This initial heating fermentation step kills competing bacteria and denatures whey proteins, giving you a smoother set and faster fermentation. The culture you're adding — 100 ml of live yoghurt — needs a clean microbial landscape to dominate. Once cooled, whisk the yoghurt through the milk thoroughly; clumps mean uneven inoculation and patchy results.

Temperature-control is non-negotiable here. 45°C is the sweet spot for Lactobacillus bulgaricus and Streptococcus thermophilus — the two cultures that define yoghurt. Hotter and you'll kill the bacteria; cooler and fermentation crawls or stalls. Use a thermometer. Do not guess. If your milk drifts above 46°C during the incubation, the set will be weak and grainy. If it drops below 40°C, you're looking at 18 hours instead of 12.

Rinse your thermos or insulated container with boiling water to hold temperature steady for the entire ferment. Pour out the water, add the milk, and seal it. The oven with the light on, a turned-off dehydrator, or a cooler packed with warm water bottles all work — anything that buffers temperature swings. Twelve hours is the baseline; taste at 10 hours. You want tang without aggression, and the yoghurt to coat a spoon without breaking. If it's still thin, give it another hour.

Do not open the lid during fermentation. Every peek lets heat escape and disrupts the bacterial colonies mid-work. When the time's up and the yoghurt tastes right — slightly sour, thick enough to hold a shape — chill it immediately. Cold stops fermentation dead and firms the set further. The yoghurt will thicken a little more as it cools, sometimes dramatically. Store in the fridge for up to two weeks, though the live cultures stay vigorous for about five days. Use your finished yoghurt as the starter for the next batch; it'll work four or five times before the culture weakens and you'll need fresh bought yoghurt again.