Heat the milk in a stainless steel pan on the stove over medium heat until it reaches 180°F.
Pour heated milk into clean canning jars and cool, either by sitting on the counter or in a cool water bath until the temperature drops to 115°F.
Use a clean whisk to mix the yogurt starter into the cooled milk.
Place the jars into the oven with the light on for 12-24 hours. The light should provide a consistent heat of about 110°F.
Put jars into the refrigerator until the yogurt is cold and set.
Once the yogurt is set you can pour off the liquid whey from the top or strain the yogurt using a cheesecloth for a thicker consistency.
Instant Pot Method
To heat the milk in the Instant Pot, press the yogurt button until the display reads boil.
When it beeps, check that the temperature is at least 180°F.
Cool the heated milk by either letting it sit on the counter or in a cool water bath in the sink until the temperature drops to 115°F.
Use a clean whisk to mix the yogurt starter into the cooled milk.
Return the inner pot to the Instant Pot and press the yogurt button until the display reads a number of hours.
Press the "+" or "-" button until the display reads the desired length of time. I like to incubate mine for at least 12 hours. Incubating for 24 hours will yield the tangiest yogurt with the least amount of lactose left. Do not incubate for longer than 24 hours or the probiotics will start to die off from lack of food.
Once the time is up, put the pot of yogurt into the refrigerator until the yogurt is cold and set.
Once the yogurt is set you can pour off the liquid whey from the top or strain the yogurt using a cheesecloth for a thicker consistency.
Enjoy!
Notes
For the yogurt starter, just use any plain yogurt with live active cultures.If you'd like to make a smaller batch just use a ratio of 2 TBSP starter for each quart of milk. If you'd like to make a larger batch (such as using the Instant Pot to make a gallon) just double the ingredients listed.