I learned most of what I know about making yogurt from Maria Lorraine's post at Chowhound. I combined what I learned there with some technical articles and reading tons of other web postings. This recipe is the result of considerable experimentation and has been successfully producing thick delicious yogurt for many weeks.
I'm working by weight using a cheap digital kitchen scale. When I use ounces (oz) below, I mean weight. One fluid ounce of water weighs one ounce but this is not true for other substances. You'll also need an accurate thermometer; I use a Thermopen.
I fortify the milk with additional milk solids by adding Nido Instant Whole Milk. You can usually find Nido in the "Hispanic" section of grocery stores. Don't buy the Infant formula, you want the normal dry milk. They just changed the name to Fortificada. Other people use various brands of dry milk; anything should work as long as it tastes/smells good. Nido is great.
For vanilla flavored yogurt I use:
- 68.9 oz (1/2 fluid gallon) of milk. I use 1% Mapleview milk but any should work.
- 4.5 oz of Nido.
- 5.5 oz of sugar.
- 1 oz of vanilla extract.
I've made lemon by substituting lemon extract for the vanilla.
If you want to make more or less, simply scale the amounts above.
I mix the milk, Nido, and sugar with a stick blender in a 2 quart glass measuring cup. I heat the mixture uncovered in my microwave at full power for intervals of 5, 5, and 4 minutes; stirring after each. Of course, the time depends on your microwave power. Heating the mixture to 180F allows the milk proteins to relax and it kills any microorganisms that might compete with the yogurt culture.
Next I cool the mixture to 115F. Sometimes I just let it slowly cool. Other times I rush things using a bath of ice water in a larger bowl. I don't see any difference in the results.
Next I add the vanilla and yogurt culture (what the technical articles call the innoculum). I bought my initial batch from New England Cheesemaking. I have used both their Y5 "Sweet" culture and the Y1 Bulgarian. I prefer the Y1 for its tarter flavor.
Most articles on the web suggest using store bought yogurt as the starter; that didn't work well for me. I think a good starter is worth the few dollars you pay for it. I only needed one packet because I froze 1/2 ounce portions of the first batch in an ice tray and then transferred them to containers to keep in the freezer. When I'm ready to make yogurt I get out a cube and mix it with a small portion of the cooled milk mixture and add that back to remainder. I recently got near the end of the first batch of 12 cubes so I froze 12 more.
With the starter mixed in I measure 6.5 ounce portions into 8 ounce Ziplock brand plastic containers. I lid them and put them into a 105 degree oven. If your oven does not support settings this low, you'll find a wide variety of alternatives on the web for keeping the yogurt warm.
I leave the yogurt to ferment for 6 to 8 hours. Do not disturb them during this time; I ruined a batch by checking on them too much. When it is ready the yogurt should be firmly set. You can gently test a container by tilting it slightly. The longer you let it ferment the tarter the yogurt will become.
After it is set I move the containers to the refrigerator. The next morning they are ready to eat. They usually have about 1/2 teaspoon of whey on top.
If you stir this yogurt it will become much thinner because you are breaking the matrix that holds it together. Commercial yogurt usually has a stabilizer added to make it hold up to stirring.
This recipe makes 12 servings and we eat them all in a week. I estimate each serving is about 160 calories.