I was sure that with all the questions and answers we have had about yogurt that this simple question must surely have already been asked. But I couldn't find it.
Making yogurt is simplicity itself.
The goal is to introduce heat-loving (thermophillic) bacteria to milk, keep them warm so that they munch on the lactose in the milk turning it into lactic acid. The acidity and warmth denatures the milk proteins and turns the whole mass into a gel.
The steps may vary a little depending on your equipment and the bacteria that you use.
- Get milk. -- The more fat the better it will taste. Powdered milk can also be added to improve the texture as it will add more protein.
- Get a starter. -- Any commercial yogurt that advertises "live active cultures" will work just fine. Pick a yogurt that you like as the yogurt you make with those cultures will be similar.
- Heat the milk to about 85°C (190°F) for a few minutes. -- This will denature the albumin in the milk which will add to the yogurt structure instead of leaking out with the whey.
- Cool the milk at to between 40°C (110-120°F). -- 55°C (130°F) will kill your starter.
- Mix in the starter.
- Keep the mix warm for 6-10 hours. -- The longer the more acidic and firm it will get. The exact temperature will depend on your starter and equipment. Danon plain yogurt, as a starter, wants to stay at 37°C (100-110°F). My Indian coworker's starter that she brought from India can thrive at almost room temperatures.
"Yogurt makers" can be purchased that simply hold their contents at about 100F. Some people use heating pads. Some people set their oven on low. You can be creative- just don't get hotter than 55°C (130°F) or cooler than 30°C (90°F) or so.
To try it out for the first time I would recommend simply putting your yogurt in a heavy, lidded, container, wrapping in a towel and letting it sit in the turned-off oven for 5-6 hours.
- For a thicker creamier texture you can strain your yogurt. -- After it has fermented to your liking stir it up well, pour it into a piece of muslin in a strainer, and let it drain for a little while. The whey draining off is good for baking. It has some calcium, b12, and a lot of lactose. (If you skipped step 3 it also has a lot of wasted protein).
Making your own yogurt is a fun activity. You get to pick what goes into it so there is no sneaky ingredients and you can make it for a fraction of the cost of commercial. Play around with different starters. Different bacteria will produce yogurt with different qualities and it is interesting to experiment.