I've been getting milk from the farm for eight months. I've been making yoghurt from it for about seven and a half. When I started getting raw milk I was still buying yoghurt at the store. It soon dawned on me that I could make my own yoghurt. My thinking was that such delicious milk must be able to be transformed into delicious yoghurt. It turns out I was right, although it took me a little while to get consistently good results.
The first time I tried to make yoghurt I didn't have a thermometer, an incubator, or any experience. I had the thought, though, that it could be done. So it was that I heated a half-gallon of milk until it was warm to the touch, stirred in some store-bought yoghurt with active cultures, poured the mixture into canning jars and left them in the the half-bathroom with an electric heater overnight. The results were not spectacular. I ended up with slightly thick-ish sour milk. Surprisingly, I wasn't discouraged.
The next day I ordered myself a Yogourmet Multi II yoghurt maker. I think "maker" is a bit of an overstatement, though. I prefer to think of it as an incubator. In any case, it is a great little machine that keeps my milk and bacteria at the optimal temperature for turning milk into yoghurt. I also got myself a thermometer.
Seven months later, I have my process down.
First a note about starters. I used to order the Yogourmet starter culture, but find that using half a cup of store-bought yoghurt that has active cultures works just as well. It also allows you to somewhat control the texture of your yoghurt. I find that the finished product mimics the texture of the starter yoghurt. I use Butterworks whole milk yoghurt because it's local to Vermont. It also has a silky texture and a nice tang that translate well into the finished product. I can also recommend Seven Stars whole milk yoghurt, for all you Pennsylvanians. I tried using some of my own yoghurt as a starter, but found that it didn't work very well. The resulting yoghurt was grainier than I like, although the flavor was still good. I'm not sure why, but my thought is that the other bacteria in the raw milk took over, overpowering the 'intentional' bacteria from the store-bought yoghurt.
I start by putting a half-cup of the starter yoghurt into a Pyrex measuring pitcher. Knowing the jar in which I incubate my yoghurt doesn't fit quite a half-gallon of milk, before I heat the milk I decant some of it into this little crystal pitcher that came from my grandmother's house. (It holds the exact amount that doesn't fit in the jar.) I then heat the milk, stirring it constantly, until it reaches 110 degrees Fahrenheit. To keep the bacteria from getting too much of a fright, I ladle some of the hot milk into the starter yoghurt and stir it up, making sure there are no lumps. I then add the mixture to the pot and stir it in. I pour the milk into the jar, pop it into the Yogourmet, which I have filled to the line with warm water, plug her in, and wait at least eight hours. The whole process, including dishes takes less than ten minutes.
On the other end of the eight or so hours (it doesn't really seem to matter how long you leave it, whithin reason), I strain my yoghurt to make it a bit thicker. I put two pieces of cheesecloth in a colander and the colander in a bowl. I pour the warm yoghurt into the colander and let it sit until it reaches the desired thickness. If I want a runnier yoghurt I leave it for between 40 minutes and an hour, if I want it thicker I leave it longer. Reaching the thickness of Greek yoghurt takes quite a while, a couple hours or so. At this point the yoghurt is kind of lumpy so I tend to whisk it until it is smooth. Once smooth, I pour or ladle it into a quart jar and refrigerate it before using it for anything. I don't know how long it keeps because it's always gone within three days.
What I like about making yoghurt is that it takes almost none of your time and the result is amazing. I find my yoghurt to be far tastier than any store-bought yoghurt I've tried. It's just so rewarding to transform good milk into perfect yoghurt. Making yoghurt has become a routine for me--it's no longer a hassle, just a normal part of every-other day.