1 Quart canning jar with lid. I prefer wide mouth just to make it easier to get yogurt out but I've used regular mouth with the same results.
Direct read thermometer
Large measuring cup/bowl that the milk can be heated in.
Insulated container. I made mine, quite easily, I'll describe it later.
4 cups of milk. I generally use skim because that's what we have around and it works well. Higher fat content milk yields higher fat content and thus richer tasting yogurt.
Yogurt culture, store bought plain yogurt with live and active cultures, or the last little bit from the last batch (which is what I normally use). I can get yogurt culture from a local beer and wine making supplier or it can be ordered online from a number of sources.
Step 1: Heat the Milk
You need to heat the milk to about 180 degrees F. The milk comes pasteurized from the store but could pick up some wild bacteria that could impart an off taste. This is relatively low temperature pasteurization so should preserve the integrity of the milk. I use the microwave, it takes me 8 1/2 minutes on high in the glass bowl. Your results will vary depending on your bowl and microwave. I recommend starting at 5 minutes and take a temp and sneak up on it the first time. You DON'T want to boil the milk over. Trust me, big mess. If you don't have a microwave, heat the milk on the stove but watch carefully, you really don't want to boil this over.
Step 2: Cool the Milk
I cool the milk to between 115F and 120F in the sink with ice water. It takes about 10-12 minutes this way. I've also had great results just leaving it on the counter and checking periodically. Make sure you get below 120F, higher temps could kill off the good bacteria.
Step 3: Add Milk to Culture
When the milk gets to the right temp, 115F-120F, pour it into the wide mouth canning jar with the culture or last bit of yogurt from the last batch. Make sure the jar is clean, a run through the dishwasher or good hot handwashing is a good idea. Clean work ensures consistent results.
Step 4: Insulate and Wait
Loosely cap the canning jar and place it in an insulated container. I made mine in about 15 minutes from some scrap 2" thick insulation foam from a home center. I cut the pieces to fit my quart jar and hot glued them together. I've heard of other people wrapping the jar with towels, putting in a cooler with hot water, using a heating pad etc. The idea is to keep the bacteria at a happy temperature so they do their job. I usually do this before bed and by the time I get up it's beautiful yogurt.
Step 5: Done
After 8-12 hours you have yogurt through the wonder of fermentation. If you like greek style yogurt all you have to do is strain through a cheesecloth. A real cheesecloth from a cheesemaking supplier, it's a finer weave and makes a huge difference. My favorite way to have it is over homemade granola with a spoonful of homemade jam.