1-1½ liter of milk (from cow, sheep, goat, soy or coconut)
1 portion of starter culture
   - or ½ dl fresh plain yogurt

Pot
Thermometer
Yogurt maker
   - or a thermobox, an oven or a warm spot in the house.

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.

Use either
    1  sachet starter culture
or
    1-2 piches starter culture from a glass vial with snap cap.

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. 

Tips:
If you wish a thicker yogurt, heat the milk to 85-90°C, keep this temperature for up to 20 minutes and then quickly cool it to 42°C by using a water bath - always perform this before you add any starter and culture the milk.  

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!

Notes:
Only fresh soured milk or creme fraiche made from heirloom starter cultures (in sachets) are suitable to culture new batches repeatedly. Soured milk or creme fraiche made from non-heirloom starter cultures (in the resealable vials) are not suitable and fresh starter must be used to culture each new 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.