Pour your milk into your pot. If using an instant pot with a yogurt button, press the yogurt button until the display reads "boil"
Important Note- if using an Instant Pot Lid, you must set the pressure release valve to "Venting" I prefer to use a regular sauce pot lid instead of the Instant Pot lid and it works fine.
You want to bring your milk up to about 180℉. The Instant Pot will beep when it has finished but you should check the temperature to make sure it reached 180℉. If you are making this in a sauce pot on the stove, make sure to stay close to the pot as you do NOT want it to boil over on the stove - Trust me this is a mess you don't want to clean!
Remove pot carefully and allow to cool until your food thermometer reaches 110℉. If left to cool on it's own this can take a few hours but the process can be sped up by carefully placing the pot in cold water in the sink, just keep an eye on the temperature.
Remove a cup or two of your cooled milk, stir in your 1/4 cup of yogurt (this can also be taken from your previous batch of yogurt once you do this regularly) stir thoroughly.
Stir mix into your cooled milk without scraping the bottom of the pot incase any milk solids have stuck to the bottom of the pot.
At this point, if using the Instant Pot, you can return the pot to the base, cover (make sure lid vent is on venting if needed)and press yogurt button until time counter is displayed, Set timer for anywhere between 10 and 19 hours, I have found 19 hours works great for me but know friends who set it to 10 and have great results. Pot will auto shut off after allotted time.
**If using a sauce pot, cover and wrap warm pot in a blanket or towels and let sit for 10-12 hours in a warm place to allow the mixture to incubate. You can also just place the pot into your oven with just the oven light on as you would to raise bread and let sit for 10-12 hours.
To see if your yogurt is ready, stand a long handled spool up in the pot. If it stays standing it's ready!
For a thin yogurt, place pot in the refrigerator for at least 6 house to chill and finish setting.
For a thicker, Greek style yogurt, put a cheese cloth lined strainer (I usually use two layers of cheese cloth) in a large bowl and pour in yogurt to allow whey to strain off until desired thickness. I usually leave this in the fridge over-night.