Yogurt making is relatively easy for cooks with a good eye for temperatures and infection control, and the flavor of homemade yogurt can be easily adjusted to meet various tastes. The easiest type of homemade yogurt to create is plain, unflavored yogurt, although flavors can be mixed in after the yogurt is made, or the yogurt can be served with fresh fruit, granola, or other nutritional additions. Homemade yogurt can be made with any type of milk with any fat percentage, although full fat milk will create a more rich, thick final product.
Yogurt has been made for centuries in Turkey and Greece. It is made by mixing Lactobacillus bulgaricus and Streptococcus thermophilus with warmed and cooled milk, held at a temperature to promote growth of these organisms, but not harmful bacteria. The mixture is incubated for eight to 12 hours, and the two organisms digest the lactose in the milk, thickening the milk proteins and producing tangy lactic acid as a byproduct. The end result is yogurt, which can be eaten in a myriad of dishes as well as on its own.
To get started on a batch of homemade yogurt, you will need some equipment. Start by sterilizing containers for the yogurt in a pot of boiling water for ten minutes, leaving the lid on the pot at all times. You will also need a thick bottomed pot to heat the milk in, and an area to incubate the yogurt. If you intend to make homemade yogurt a staple in your household, you may want to consider purchasing a yogurt incubator. Otherwise you can use the oven, a cooler filled with warm water, or your car on a warm day, but be aware that holding the right temperature can be challenging, and will require monitoring. It is also crucial to acquire an accurate thermometer, as you will need to check temperatures frequently.
The first step in making homemade yogurt is warming and sterilizing the milk. Heat milk in a large, thick pot to 180-185 degrees Fahrenheit (82-85 degrees Celsius), stirring frequently to heat it evenly and prevent scalding. Next, allow the milk to cool to 112 degrees Fahrenheit (45 degrees Celsius), and then add a culture. The best culture for homemade yogurt is a batch of plain store bought yogurt, as long as the container says “active cultures” or “live cultures.” Add two tablespoons of yogurt for every quart of milk, stirring the mixture evenly and then pouring it into sterilized containers. Incubate the yogurt containers, holding the temperature between 105-122 degrees Fahrenheit (41-49 degrees Celsius), and do not disturb them. The longer the yogurt incubates, the thicker and tangier it will be.
After approximately eight hours of incubation, the homemade yogurt will be finished, and can be refrigerated for up to two weeks before use. Make sure to set aside a jar to use as a starter for another batch, and use a fresh container of commercial yogurt every five or six batches so that you do not exhaust your culture. If the yogurt smells strange or develops discolorations, discard it. Contaminants can work their way into yogurt even in a very clean kitchen, and it is better to be safe than sorry.