2 liters of raw milk
100 g of quality yogurt*
* With a high concentration of lactic ferments.
Bring the milk to a boil and let cool to 38-40°C. Pour a small amount of milk into a bowl and add the yogurt (and/or lactic ferments). Whisk well, then pour into the large volume of milk. Mix well.
Distribute the milk in jars of 500 to 900 ml in volume (lidded) or in a large saucepan. Smaller containers will cool too fast. Put the lids and find a way to maintain the temperature of 38°C for at least three hours to activate the lactic fermentation. Wrap in a wool blanket or a warm coat and place this bundle in a warm (next to a heater or on an electric pillow).
The next day (or 5-6 hours later), place the yogurts in the refrigerator. It needs several hours to chill (especially if you have a yogurt maker).
Lately, yogurts are not as rich in starter cultures as those 30-40 years ago. My grandmother used only 1 teaspoon of yogurt for every 2 liters of milk. Whereas, I put 125 g and it is often not enough to make a thick yogurt. So, every 3- 4 rounds, I also add 1 dose of lactic acid bacteria (on sale in the flour, yeast section) and then I use my own yogurt to make new yogurts. A cheaper solution to have starter yogurt cultures is to buy probiotic capsules in the pharmacy. I just empty the capsule into the milk, whisk well and my yogurt is really smooth and thick. The yogurt maker does the rest.