Preparation time : 30 minutes
Incubation : 6–8 hours
4 cups (1 L) milk
1/4 cup (60 mL) skim milk powder
2 tablespoon (30 mL) plain yogurt
1. Sterilize equipment. For best results, don't skip this step! Boil some water in the pot you'll use to heat the milk. Put in any other utensils that will contact the yogurt.
2. Pour milk into the saucepan or top of double boiler. If you are using skim milk powder, whisk it into the milk until has dissolved.
3. Heat milk to 83°C. This is around the time you begin to see steam rise, but before it boils. Heating helps to denature the proteins, so you'll get yogurt that sets well. For even thicker yogurt, turn the heat down low and simmer the milk for 5 minutes.
4. Cool the milk down to 44°C. A quick way to cool your milk down is to place the saucepan with your milk in it (or the top of your double boiler) into a sink filled with cold water. Stir milk until it has cooled. If you don't have a thermometer, check the temperature with your (clean!) finger. If you can count to twenty with your finger in the milk, it's cool enough.
5. Add yogurt and blend it into the milk well.
- Pour the mixture into an incubating container. Here are some possible containers:
- An earthenware bowl that will be covered with a blanket and left in a warm spot in your house—like near your furnace or inside a turned-off oven or microwave.
- A wide-mouthed thermos that has been preheated by pouring hot water into it and letting it stand until you are ready to pour your yogurt mixture into it. Wrap the thermos and leave it in a warm place.
- Preserving jars that have been preheated, as above, filled with yogurt mixture, covered and set on a wire rack or jar rings in a large heavy saucepan. Fill the saucepan with warm water, cover it and set it on the lowest temperature on your stove. Check frequently to make sure that the water stays at the right temperature. Alternatively, you can set small jars on a wire rack in an electric frying pan. Add water to cover the rack, cover the pan, and set the thermostat between off and the lowest possible setting. Check frequently to make sure the water doesn't get too hot.
- An electric yogurt-maker. Just follow manufacturer's instructions.
6. Incubate for 6–8 hours at 40–43°C. The longer the yogurt incubates, the more sour it will taste. If you incubate yogurt overnight, don't worry about setting your alarm just to stop incubation. An extra hour or two in the life of a yogurt isn't much. While the yogurt is incubating, don't disturb it! If yogurt is disturbed, it won't set smoothly.
7. Put the yogurt in the refrigerator. Be gentle. The yogurt will continue to firm up during the first day. Save some of the yogurt as a starter for your next batch. After making a few batches of yogurt, you may need to start with fresh commercial yogurt again.
8. Enjoy your yogurt plain or topped with fresh fruit or muesli.