To ferment the yogurt, it is very important to keep it warm, i.e. around 42°C (108°F). There are several ways to do this using:
A yogurt maker
An oven turned off with light on
A pressure cooker in "yogurt" mode
A cooler filled with hot water bottles
To learn more about these different options, see how to make yogurt without a yogurt maker.
Ingredients
2Lmilk
10gyogurt culture(or 2 tablespoons of homemade or commercial yogurt)
½cuppowdered milk (for thicker yogurt)(or 1 pouch of gelatin (7g))
Steps
Milk Preparation
Pour the milk into the saucepan. If desired, add the powdered milk and mix thoroughly.
Gently heat the milk to 82°/180ºF, or until it boils. Stir from time to time with the wooden spoon to prevent the milk from sticking to the base of the saucepan.
When the milk reaches 82°C/180°F, remove it from heat and let it cool down to 42-44°C/108-112°F. To speed up the process, plunge the saucepan into a sink filled with ice water.
As an option with gelatin: dissolve the gelatin pouch with a little milk in a small bowl, allow it to swell (rise, puff up) and then blend in with the rest of the mixture.
Yogurt Fermentation
Add the starter culture or yogurt to a small amount of warm milk and mix well.
Add to remaining milk. Stir well to distribute the culture in the milk.
Pour the inoculated milk into one or more containers. Close, and place in the yogurt maker or incubator of your choice (oven turned off, pressure cooker, cooler, etc.).
Let it incubate for 4 to 8 hours. Fermentation speed varies according to temperature and incubation method. The longer the incubation, the firmer and sour the yogurt will be.
Rest And Flavouring
Remove the yogurt from the incubator and let it cool down on the counter for an hour.
Place in the fridge for 8 hours, or overnight. Yogurt will thicken as it cools.
Save a few tablespoons of this yogurt for your next recipe.