There is one caveat; I recommend you get a yogurt machine. At the risk of sounding like a paid yogurt machine salesperson, let me tout the benefits of this device. In order to give your yogurt the proper environment to culture, you will need to keep it at 116 F for eight hours. I tried some makeshift water bath/thermos/in the oven contraptions, but eight hours is a long time and I spent a good portion of that time checking the temperature and adding hot water. And my yogurt didn't even turn out well, it was anemic and thin. Then I got a yogurt machine. It is a really simple device, just a low level electric heat source and a space to put little glass jars on top of it. Fill jars with yogurt, turn it on, then sleep/eat/run errands for eight hours and your yogurt is done.
Yogurt machines were kind of a fad in the 60s, so you might even be able to find an old Salter brand machine in your mom's basement, or at a garage sale. But don't pay too much: my brand new machine with small glass jars (perfect for single servings) was only 20$.
Ingredients:
1 qt. milk (I use a local pasture raised milk that is not ultra-pasteurized.)
2 T. active culture yogurt (or yogurt starter)
Equipment:
2 qt. saucepan
Instant read thermometer
2 small stainless steel bowls
stainless steel spoon
ladle
Funnel (optional)
Clean all equipment. Since you will be actively cultivating bacteria, and keeping your yogurt mix in the heat range that bacteria love most of all, cleanliness is especially important. Make sure all of your utensils and yogurt containers are scrupulously cleaned before you start out.
Heat milk. Pour your milk into a saucepan and place over high heat. Use your thermometer to monitor how hot the milk is. Stir occasionally to prevent scorching. Bring the milk up to 180 F.
Cool milk. Pour hot milk into the smaller of the two stainless steel bowls. You can just cover the milk and leave the milk to cool at room temperature, but I'm always in a hurry so I put it over an ice bath and stir it to bring the temperature down quickly. Once the temperature has dipped down to 116 F you can mix in the yogurt or yogurt starter. Make sure that the yogurt is thoroughly mixed into the milk.
Cultivate yogurt for 6-8 hours. Carefully pour the yogurt into the prepared cups or bowl. I find that using a funnel makes this a tidier operation. Seal containers and turn machine on. Leave for at least 6 hours.
Check for doneness. Most guides say that you want the yogurt to be the consistency of heavy cream, I find that my yogurt will usually thicken more before it is done. Once the yogurt is done, chill and use as you would use storebought yogurt.
Troubleshooting. It is possible to overcook your yogurt, at which point it will break, separating into a thicker curd, and lots of whey. Don't confuse a little whey on top (which is normal) with having overcooked the yogurt. Overcooked yogurt will be obviously thick and without any custard-like smoothness, even after stirring. If you overcook by just a little bit, all is not lost. Strain your yogurt for a day and you will have a wonderful, crumbly yogurt cheese. It is also possible to undercook your yogurt, which will likely mean that your yogurt will be thin. Other reasons that your yogurt could turn out thin would be that you are using a culture that is not active, or that the proper temperature to encourage yogurt cultivation has not been maintained.
Thickeners. The yogurt that I make usually has a beautifully thick consistency without adding any thickeners. But the process has so many variables (milk, temperature, culture) that you might get very different results going through the same process. If you want a thicker texture of yogurt you can experiment with adding thickeners pectin, gelatin or dried milk powder. Add these thickeners when you heat the milk. Or you can always just strain the yogurt afterward which will make the yogurt both thicker and richer.
