My yogurt maker and candy thermometer, you want a thermometer that will clip to your pot. This also goes for making ricotta cheese, mozzarella, etc...a good thermometer is great to have.
The milk makes a huge difference in taste. I go with Kalona SuperNatural whole milk.
So here's the deal, my yogurt maker came with 7, 6oz glass jars, those jars are now spice jars. If you want to make different flavors of yogurts, those individual jars are perfect. If you plan on straining your yogurt to make greek yogurt then those 7 jars are going to be a pain in the butt and extra work to clean. So I use my 7 cup pyrex glass bowl and use that amount of milk. But if you are using a different method or found a larger bowl that fits than just pour your desired amount of milk into a pot and slowly heat it to 110-180 degrees or when it just starts to boil. If you are lucky enough to have raw milk on hand thanks to a family cow or live where you can legally buy raw milk, only heat the milk to 110 degrees. The milk just needs to be at room temp. The same goes for nonraw milk too. I keep meaning to play around with different temps but usually I forget to check the milk until it is around 180.
Cool the milk to 110 degrees and stir in your 4-6oz of plain yogurt. The yogurt needs to be plain, best if organic and whole milk, it has to contain active cultures. I try to keep a 1/2 cup from a previous batch to use in the next batch. Place in your yogurt maker, crockpot or oven and leave it alone for at least 8 hours.
When the yogurt has set (may take up to 10 hours for nonfat yogurt...another reason to always use whole milk!) then remove, cover and cool for at least 3 hours. You are done at this step for regular creamy yogurt. If you want greek yogurt you just have one more step!
NOTE: FOR LACTOSE FREE YOGURT AND IN MY OPINION THE HEALTHIEST YOGURT- FERMENT FOR 24 HOURS AND CHILL FOR 5 HOURS.
Place the yogurt in a cheese cloth, or nonfuzzy kitchen towel lined strainer and place over a bowl to let the whey run out.
Whenever your yogurt is at your desired consistency then simply transfer it to a container and enjoy. If you leave it overnight and it has turned into cream cheese then just stir back in some of the whey.
I use my leftover whey to ferment vegetables and make things just as sauerkraut, pickled ginger, breads...the list goes on.