Now that we are making our own yogurt, I get to taste it in all stages of development. Bacteria are wonderful things. At least the bacteria that inhabit our yogurt are. They create a delicious tang from plain milk.
When I was a youth living in Switzerland, many years ago, I remember my host father tasting and re-tasting a bowl of milk he had fermenting on the kitchen counter. I thought he must have an awfully strange sense of what is edible. But now I like to sample my yogurt even before it has completely fermented and thickened. After coming off the stove and having some of last week's yogurt mixed in as a culture, it goes into a Styrofoam cooler with some jars of hot water. Hours later it is still loose and warm but I love the feel of it when I take a spoonful. Have you ever tried yogurt warm this way?
I'm still refining my yogurt recipe. What seems to work best is a mix of 3 1/4 cups grass-fed whole (cream top) milk and 1/2 cup half-and-half set over gentle heat in a heavy pot. I bring the milk up to just below the boiling point, or past 200 degrees Fahrenheit when the milk is just beginning to foam. This will take about 45 minutes. I then remove the pan from the heat and place it in the sink with cold water to bring the temperature of the milk down to 120 degrees, at which point I mix in about 2 tablespoons of last week's yogurt and pour the mix into a warm quart canning jar. The canning jar goes into a cooler with 2 jars of hot water and sits overnight.
Cooking the milk at a high temperature concentrates the protein and results in a thicker yogurt. The amount of bacteria you put in the milk has no effect on thickness. The yogurt is actually set after a few hours. But I like to give the bacteria more time to create that delicious tang.