Did you know you can turn a tablespoon of your favorite cultured yogurt into a whole quart? The process is simple, and it requires tools you probably already have in your home. To start, you'll need at least 1 tablespoon plain, unflavored yogurt with live cultures, 1 quart milk (low-fat is fine, but avoid ultra-pasteurized), a quart Mason jar, a cooler, a medium saucepan and a thermometer.
Wash the Mason jar thoroughly. Fill the cooler with hot but not boiling water (about 130 degrees F is best) just up to the neck of the jar. Fill the jar with water to keep it submerged. Cover and set aside.
Pour the milk into the saucepan and put over medium-low heat. Bring the milk to 180 degrees F, stirring constantly to prevent scalding or skin forming on the surface. This re-pasteurizes the milk and eradicates any bacteria that can cause spoilage during development of the culture. Remove from heat.
Place the saucepan in a larger pan full of cold water to bring the temperature down to 110 degrees F, again stirring to cool evenly. Once the milk reaches 110 degrees F, remove the saucepan from the pan of cold water, add 1 tablespoon plain cultured yogurt and stir to combine thoroughly.
Drain the Mason jar. Pour in the heated milk mixture. Cover with a lid, and return the jar to the hot water bath.
Cover the cooler, and let it stand for 8 to 12 hours. Do not move the cooler. You'll get a better texture by allowing the bacteria to do their job undisturbed.
Remove the Mason jar from the water bath. Your yogurt should have a soft, gelatinous set. Cover and store in the refrigerator.
Your yogurt will keep in the refrigerator for at least two weeks, up to a month. Enjoy it as you would store-bought yogurt, with fruit and granola, or in sauces and dips. When you reach the end of your batch, you can repeat the process to create a new one, though you may need to use more starter with each progressive batch.
