place slow cooker liner into slow cooker, if using
pour milk into slow cooker, cover and cook on high for 2-3 hours (depending on your slow cooker) or until milk temperature reaches 180°F. It takes me just about exactly 2 hours in my 6qt Crockpot brand slow cooker.
½ gallon fat free milk
turn off slow cooker and allow milk to cool to between 110° and 120°F
while milk is cooling, allow ½ cup plain yogurt with live active cultures to come to room temperature
½ cup yogurt with live and active cultures
when milk is as close to 110°F as possible (but not less), carefully mix room temperature yogurt fully into milk
replace cover and then drape slow cooker with a towel (or two) for up to 8-12 hours. It is important that the yogurt/milk mixture to be in the dark. After about 6 or so hours, you can move your crockpot into the refrigerator if you won't be able to get to it before the total timing exceeds 12 hours. This will allow you to handle the next step when your schedule permits
after sitting, your yogurt will have a layer of liquid on top of it. If you want regular yogurt, just pour off the top layer and serve!
to make Greek yogurt, place cheesecloth into a yogurt straine or a strainer lined with cheesecloth. Place strainer into a bowl that has room for draining.
add yogurt into cheesecloth/strainer and allow extra liquid to drain. This can be done in the refrigerator or on the counter. The longer you allow it to drain, the thicker and more creamy your yogurt will be (but the less volume of yogurt you will have).
enjoy your homemade yogurt!!!