1-1½ liter of milk (from cow, sheep, goat, soy or coconut)
Heat the milk to 42°C.
Add starter culture or fresh yogurt and stir thoroughly.
If you use starter culture, dissolve the powder in a small portion of the luke warm milk and add that to the milk.
If you have a yogurt maker, pour the milk into the container and press start.
If you do not use a yogurt maker, pour the milk into a pot or container with lid, cover and place it in an oven at 42°C or wrapped in a towel somewhere it can stay warm, e.g. a boiler room or a thermobox.
Ferment the milk for 6-12 hours if you used a starter culture - or just 4-8 hours if you used fresh yogurt to culture the milk. You can ferment it for longer. The longer it ferments the more acidic it gets.
After fermentation the milk may still appear somewhat thin. Move the container to the refrigerator and let it mature there at least 8 hours. Hereafter, the yogurt is now ready and will stay fresh in the refrigerator for at least a week.
If you are mindful of hygiene, the freshly made soured milk or creme fraiche can be used to culture a new batch, again and again. However, if taste or texture begin to diviate too much from the original - begin again by making a new batch using fresh starter.
Add fresh fruit or marmelade to the soured milk if you wish, but remember first to take out a small portion to culture your next batch!
A gritty texture can sometimes appear if the yogurt is shaken during fermentation or if you have fermented for too long. Try reducing the amount of starter or reduce fermentation time with the next batch.