Heat the fresh milk at 180 to 190 degrees, or to the point that it’s steaming and beginning to form bubbles. The heat alters the milk’s whey proteins and helps create a finer, denser consistency.
Let the milk cool to around 115 to 120 degrees, somewhere between very warm and hot. For each quart of milk, stir in two tablespoons of yogurt, either store-bought or from your last batch, thinning it first with a little of the milk.
Then put the milk in a warm jar or container or an insulated bottle, cover it, and keep the milk still and warm until it sets, usually in about four hours. I simply swaddle my quart jar in several kitchen towels. You can also put the container in an oven with the light bulb on.
Once the yogurt sets, refrigerate it to firm its structure and slow the continuing acid production. To make a thick Greek-style yogurt, spoon it into a fine-mesh strainer or colander lined with cheesecloth, and let the whey and its lactic acid drain into a bowl for several hours. (Don’t discard the whey, whose yellow-green tint comes from riboflavin. It makes a refreshing cool drink, touched up with a little sugar or salt.)
