The technique I use to make yogurt requires a heating pad to keep the milk at or about 110° F during the 7-8 hour incubation period. But in the years that I have had the site on the web, I have heard from many visitors that do not have a heating pad, and do not wish to purchase one. A hot-plate will work, but even less people seem to have one of those anymore. Food dehydrators are enjoying a renaissance of sorts, and work perfectly for making yogurt. But they are on the expensive side, and most people still don't have one. Many readers have asked me if they can use their crockpot to make yogurt. It turns out that the answer is yes.
Now I should note that I do not own a crockpot (or slow-cooker) myself, but I have borrowed one for potlucks and family get togethers. They are really handy for keeping food hot, and for long, slowly cooked dishes. Thus the generic name, slowcooker. But if you have every used one, you know that they heat up and cool down very slowly. This is fine for a pot roast or some chili, but not what you want when making yogurt. So I am suggesting a process where you still heat the milk to 185° F on your stovetop, and use the crockpot solely for the incubation period.
As a quick review, to make yogurt you heat the milk to 185° F on your stove top using a double-boiler technique. Then you cool it down quickly to 110° F in a cold water bath. They you add 2-3 Tbs. of plain yogurt as a starter, and keep it at or about 110° F for 7-8 hours. If you know at what setting your crockpot will hold liquid at 110° F, then it makes an ideal incubator. The easiest way to do this, without wasting any milk, is to experiment with water. Use a thermometer and a half a gallon of water and figure out the setting that will hold this temperature while covered.
The next time you go to make a batch of yogurt, start off by first getting your crockpot up to this 110° F setting using some water. After you have heated the milk on the stovetop to 185° F, and then cooled it to 110° F, empty the water from your crockpot and put the 110° F milk in its place. Add your 2-3 Tbs. of starter culture to the milk and stir it in well. Then cover your crockpot and leave it at the 110° F setting for 7-8 hours. It will hold a nice even temperature and you will be able to reproduce your results every time. Then you can adjust the incubation period to your thickness/tartness preferences. Remember, the longer you let it incubate, the thicker it will get. But it will be more tart as a result.
So if you have been wondering if you can make yogurt in a crockpot, the answer is absolutely yes.