You MUST start with fresh milk. As milk ages, the proteins break down and the yogurt will not culture properly. If you had your own cow, it would be great, but start with the freshest milk you can buy. You must also buy a package of store bought yogurt. This is your starter and will add the yogurt culture to your batch. I prefer Stonyfield Farms. You can use any maker’s, but it MUST be labeled “Live and active culture”. I like Stonyfield because they have 6 different cultures and the more beneficial cultures you have in your yogurt, the better gut flora you will have, which aids in digestion. Again, make sure the yogurt you buy is the freshest available. You should have a yogurt maker, but you can make it without it if you do not want to buy one. I bought one off Amazon for under $20 and it holds a quart jar. I will offer a method that uses an alternate method so you can get started right away.
I usually make a quart at a time, so measure out 1 quart of milk. Pour it into a sauce pan. Put the milk on a very low heat and warm the milk until the temperature reaches 190 degrees. Stir the milk a couples in the course of heating it. Make sure you scrape the bottom and sides of the pan to loosen any milk that has started to stick to the pan. Remove from the heat and add about 1/3 cup of sugar. You can adjust this in future batches to your liking. At this point you can add any flavorings, such as coffee (use instant coffee- only about 1 teaspoon) or vanilla. Allow this to cool until it gets below 120 degrees. Take a teaspoon of the store yogurt and put it into a small bowl. Add about an ounce or two of the warm milk and mix together until the yogurt has smoothed out and become more liquefied (this is called tempering). Then add this back to the milk. By doing this, you allow the yogurt to fully mix into the milk and not clump. You will need to strain out the milk mixture to be sure you do not have any scrapings from the bottom of the pan or yogurt clumps. Strain this milk mixture into your quart jar (Glass works better, by the way, because it conducts the heat better than plastic). Place into your warmer and allow this to culture over night or for 8-10 hours. In the morning, put into your fridge and chill to serving temp and enjoy.
Okay, here’s some incidentals.
You don’t have a commercial warmer? Make one! You will need a large stock pot, a heating pad and the quart jar. Put your jar with your cultured milk in the large pot. Wrap the jar with the heating pad, so both are in the pot. Turn on the pad on low and continue recipe.
Wanna try lemon yogurt? Put lemon zest (not any of the white pith) in the milk before you warm it up. The warm milk will draw the lemon oils out of the zest and flavor the milk without curdling it.
Do you like fruit yogurt? Then make plain yogurt and add your favorite jam, preserves or marmelade to the finished yogurt as you serve it.
The longer you keep the milk in the warmer, the more “zip” or twang you will have. You must culture it for a minimum of 8 hours, but at 10, you have more zip to it, although the whole milk will subdue the twang to a great degree.
By bringing the milk to 190 degrees, you are stretching the proteins of the milk out. By under heating them you will create a soupier yogurt, so be sure to heat the milk to get that creamy, thick yogurt.
I used to suggest adding dry milk to the liquid milk to aid in thickening it. From what I have read about dry milk (see Weston A Price), I have altered my thoughts on it. I have experimented with gelatin with pretty good success, but making sure you heat the milk to 190 will alleviate the need for the additives, except maybe in skim and milk alternatives.