To make 1 quart:
- 3 ¾ cups of warm water
- 1 2/3 cups instant nonfat dry milk
- 2 tablespoons store-bought, plain yogurt with active yogurt cultures
To make 2 quarts:
- 7 ½ cups of warm water
- 3 1/3 cups instant nonfat dry milk
- 4 tablespoons store-bought, plain yogurt with active yogurt cultures
In a large pot combine the warm water and the dry milk powder. Stir until it is dissolved. Place your thermometer in the pot and heat the milk mixture over medium low heat until it reaches 180 degrees. (Do not allow the milk to get any hotter than 180 degrees, as it will kill off the yogurt cultures.) Remove the pot from the stove and allow it to cool to 115 degrees. Once the milk has cooled, add the store-bought plain yogurt and stir well. Let the mixture sit for a few minutes and stir again to make sure it is well dissolved.
Pour the mixture into a clean quart jar (or quart sized container). Get out your small cooler and pour 3 quarts of hot tap water into the bottom of it. Set the quart jar with the yogurt in it down in the water in the cooler and cover with a dishcloth. Close the lid of the cooler and set your timer for 4 hours. Do NOT disturb the yogurt during this 4 hours…and do NOT open the cooler to check it. The warm water will keep the yogurt warm as it incubates (gets thick).
After 4 hours has passed, open the cooler and check the yogurt. IMPORTANT: DO NOT STIR THE YOGURT! I stirred my first batch and it all separated! You should be able to tell just by tipping the jar if the yogurt has firmed up. Every batch I have done has firmed up every time after 4 hours. If it HAS firmed up, put a lid on the jar and put in your refrigerator to chill. It is then ready to use! If for some reason after 4 hours that the yogurt has not firmed up, replace the water in the cooler with 3 new quarts of hot water, put your yogurt quart back in, cover, and close the cooler lid again. Check it after another hour or two. Once it has firmed up, then put a lid on the jar and put in your refrigerator to chill. It is then ready to use!
The yogurt will keep 1-2 weeks in your refrigerator.