Devon and I got a Sous Vide Supreme as a wedding present, and he has been making some pretty damn tasty things with it. Yesterday, I decided to try making some yogurt. The usual technique for cooking with the SVS involves vacuum-sealed bags, since it's a water bath that keeps the food at a consistent temperature indefinitely. It's useful especially for meat and chicken, for keeping them the same consistency throughout. Since vacuum-sealing yogurt is not terribly helpful because we'd need to add the starter later, we put the milk in a plastic resealable container.
We hit two problems: 1) There's always some air in the container, which makes it float, and 2) We didn't have any airtight containers that were the right size, so we had some milk spill into the water. (We saved it before water spilled into the milk.) The first problem ended up being not that big a deal. We tried to weigh it down with a marble mortar initially, but the mortar fell off during the heating. As I'm writing this, I'm kicking myself in the teeth for not thinking of using plastic zipper bags. I'll do that next time. In the end, as long as the container was submerged up to where the milk was, it was fine.
We used the typical method for making yogurt. We heated the water to 185 F and put the container with the milk into the water bath. We left it there for about 20 minutes at that temperature. After 20 minutes, we took it out and put it into an ice bath to bring it back down to 110 F. While it was cooling, we dumped the water in the SVS, refilled it with fresh water and heated that water to 110 F.
When the milk cooled to 110 F, we added the yogurt culture. Adding the culture when the milk is too hot will kill it dead. You can buy starter, but I always use a few tablespoons of plain store-bought yogurt with good results. Buy yogurt with live active cultures, which is just about every yogurt I've ever seen in the store. Make sure it's fresh. Some people add milk powder to make it creamier, but I find this isn't necessarily if you're making whole-milk yogurt.
When the yogurt is back at 110 F, let it sit for between 4 and 8 hours. We let it sit overnight, and we poured off the whey in the morning. It's now firming up in the fridge.
The SVS method is not any easier than doing it on the stove, but it's not any harder, either, and it allows for more control over temperature, which makes me happy.