Basically, it boils down to a few simple steps. But knowing why we do these steps is pretty important to your success, I think.
Once cooled to just under 120°F, gently stir in the starter with about 1/4 of the warm milk. The starter will be your favorite brand of PLAIN yogurt clearly labeled "live and active cultures". I like a tangy Greek yogurt, so I started with with a true Greek cultured yogurt. But choose the ones you like, and if you love the result, you can keep reusing it indefinitely. Just store a little bit of each batch for the next.
Relatively simple, right? The incubating part might be a little daunting, but there are ways to make it work. This time, I poured the contents into a 1/2 gallon mason jar, wrapped it in foil and a quilt, and placed it in my oven. I had heated my oven to about 100°F and turned it off before adding my yogurt. It turned out beautifully. Some people who are lucky enough to have an oven light that you can turn on and off like to just leave the light on. The heat from the light bulb in there is apparently enough to maintain a warm environment.
Other options for incubating include placing your container in a cooler and adding a few glasses full of hot water next to your yogurt. Or placing it in a preheated and turned off slow cooker. Or if you're doing it in the Summer, just leave your yogurt in the sun, believe it or not. I liked the oven, though, since it seemed reliable. Of course I prefer my yogurt maker since it's designed to maintain the perfect temperature. So if you love the results, and I think you will, you might want to someday invest in a yogurt maker.
Tools that are necessary or that I recommend:
candy thermometer or digital thermometer with an alarm. I bought mine at IKEA and love it
large, non-reactive, heavy-bottomed pot
cheesecloth or fine muslin
fine mesh strainer (sometimes when you heat up the milk, there will be little pieces. You want to start with a smooth base)
Metal spoon for stirring
large container for incubating (preferably glass. non-reactive, doesn't give off flavor, and see-through!)
Let's get started, shall we?
Homemade yogurt
makes 1/2 gallon, easily halved or doubled
1/2 gallon of good quality, homogenized milk
3 tablespoons (1/4 cup and 2 tablespoons) of your favorite plain yogurt with live and active cultures
- In a large, non-reactive, heavy-bottomed sauce pan or pot, heat the milk over low heat until it reached 180°F (82°C). Don't stir the milk.
- Once heated, let the milk cool to 120°F (48°C). You can speed up this process by placing your saucepan inside a large bowl full of ice water, or transferring your milk into a small bowl that will fit inside a larger bowl full of ice water. Taking care not to get any water into the milk.
- Once the milk has cooled down to 120°F (or a little lower), put the yogurt in the container you will be using to incubate it in. Pouring through a fine mesh strainer to catch any bits or the skin that has formed, pour about 1/4 of your milk into your container with the yogurt. Stir gently with your metal spoon.
- Once incorporated, add the rest of the milk mixture through the strainer as well. Give it another gentle stir, cover, and incubate for 6~24 hours, depending on desired consistency. (Suggested incubation methods above)
- If you want a thick, Greek-style yogurt, line a sieve with a piece of clean, damp cheesecloth or muslin, place it over a bowl and pour in your yogurt. Let it strain for 4~6 hours until desired thickness is reached.