I learned an easy way to make yogurt when I had dinner at the home of a friend from India. Since yogurt takes the bite out of a hot and spicy meal, it was part of most dinners, and my friend liked to serve it fresh and warm.
To make yogurt, you will need a six-pack cooler, hot water, one or two glass or plastic 1-quart containers (I use Ball jars or 1-quart, store-bought yogurt containers), a saucepan, a wooden spoon or spatula, milk, and about 1 tablespoon of prepared yogurt per quart of milk.
Heat to boiling as much milk as you want to turn into yogurt. As soon as it begins to boil, remove from heat. Let it stand until cool enough to comforably hold your fingertip in the milk without burning it. I could get scientific and give you a temperature range, but the finger method was good enough for my friend, Olivia, so it's good enough for me. As long as the milk doesn't get downright cool, anything from lukewarm to warm will nurture the yogurt culture just fine.
Use a plastic or wooden spoon to place about 1 tablespoon of yogurt into each 1-quart container. This can be from a previous batch of homemade yogurt or you can use store-bought yogurt as long as it contains active cultures. Look at the label carefully. "Made with" active cultures isn't always the same as "contains" live, active cultures! Plain yogurt works best as a starter, but flavored and sweetened yogurt will also work in a pinch. The exact amount of yogurt you use doesn't really matter. More will give a firmer product, less will make a creamier yogurt.The trick here is to avoid using metal implements to handle the yogurt. I don't know why, but metal does something to disrupt the bacterial cultures-the lactobacillus acidophilus, bifidus, l. casei, and l. reuteri-and the yogurt doesn't set well.
When the milk has cooled to a finger-tolerant level, pour it into the prepared containers. Do not stir. Place the containers into a six-pack cooler and fill the cooler with hot tap water (hot enough to hand-wash dishes without scalding yourself), to half an inch or so below the rims of the containers. Leaving the containers themselves uncovered, put the lid on the cooler and place it where it won't need to be moved or disturbed.
Leave the cooler alone for at least eight to 10 hours. I've accidentally left mine for up to 16 hours with no ill effects, but much more than that could allow the yogurt to start spoiling. Remove the lid and lift the yogurt out of the water bath. There may be a little whey on the top. This is normal. You can pour the whey off, if you like, or stir it in when you scoop it out to serve it. It's best not to stir the yogurt in the container unless it's to be consumed right away. Again, do not use metal implements to serve or stir. That will keep the cultures in good shape for making your next batch. Put lids on your containers and store them in the refrigerator, although I would recommend having a bowlful of warm, fresh yogurt first! There's nothing like warm yogurt sprinkled with a little sugar, drizzled with maple syrup, or mixed with fruit!
My six-pack cooler holds two quart jars or six six-ounce containers. I've experimented with making flavored, single-serving, fruit-on-the bottom yogurt and had some success at that. Just add fruit, sugar, vanilla, etc. to the starter in the bottom of the container before you pour in the warm milk. (Again, don't stir the starter!) Play with the ingredients to get a mix you like. If you add too little flavoring or sugar, you can always add more when you serve it.
Yogurt supplies are available from: