The particulars of the milk you use will determine its consistency. Whole cow’s milk will set up very thick. Low-fat, nonfat, or goat milk will not be as thick. In fact, it might be the consistency of drinkable yogurt. If you prefer thicker yogurt, there are a few things you can do. One is to hold the milk at 180°F for 30 minutes, which will denature some of the whey proteins and cause them to form a thicker gel. Another option is to whisk in ¼ cup dry milk powder for every 1 quart liquid milk before heating it. Finally, you can thicken the yogurt after it has set by ladling it into a colander lined with a flour sack towel and letting it stand until enough whey has drained off for the yogurt to be thickened to your liking.

For this recipe you will need a system for keeping the milk warm as it sets. This can be a small cooler filled with towels. A heating pad or seedling heat mat can be another good option. Insulated containers made specifically for yogurt making are also available, as well as proofing boxes. If you have an immersion circulator, fill a pot or other vessel with water, attach the circulator, and program it to 109°F. When the water is preheated, place the sealed jar of cultured milk in the vessel (the water should completely cover the jar) and let the yogurt set for 5 to 8 hours or until thickened.

Wash a 1-quart wide-mouth glass jar with soap and hot water. Rinse thoroughly, then rinse again with boiling water. Let it dry completely.

Pour into a saucepan or double-boiler:

Heat the milk over medium heat to 180°F, stirring often. If desired, for a thicker yogurt, hold the milk at this temperature, stirring occasionally, for up to 30 minutes. (The easiest way to do this is by using a double-boiler to prevent the milk from scorching.)

Fill the sink with cold water, set the pan of milk in the water bath, and stir constantly until the temperature reaches 118°F. Be careful at this stage because the temperature will drop rapidly, and if the milk gets too cool, it will not set properly.

Stir in:

Stir the milk to disperse the culture, then insulate it using the method of your choosing (see the headnote). After 4 hours, check the milk. If it is not yet ready, check it again in 2 more hours. It may take up to 8 hours for the milk to set. Refrigerate the yogurt.