Place 1/4C yogurt in a glass bowl or measuring cup. Make sure it is large enough to add some of the pasteurized milk to it later.
Add your milk to the instant pot and set your pot to the high boil setting.
Using a rubber spatula, slowly stir the milk. You want to prevent the milk from scorching while it heats up.
Use your candy thermometer to monitor the milks temperature. You want it to get up to 180 degrees Fahrenheit.
When the thermometer reaches 170-175 degrees, plug your sink up, start filling it with cold water, and add ice to the water. Don't fill the sink too full, maybe 4" deep or so. Move the faucet so it is above the other side of the sink, to prevent water from dripping in your heated milk.
When you reach 180 degrees, use a towel or oven mitts to transfer the yogurt to the ice water.
Using your rubber spatula, continue stirring the yogurt, while watching the temperature of the milk. The milk needs to get down to 118 degrees before we can add our culture.
At 120 degrees, remove the insert from the ice water, placing on a towel. This will catch any water that drips off the insert.
Using a ladle, scoop 2 or 3 ladles full of milk into the glass with the yogurt culture, mixing together slowly and carefully, with a whisk or rubber spatula.
Slowly incorporate the mixed culture into the milk. Don't mix it aggressively.
Place the insert back in the instant pot, lock the lid in place, and OPEN the pressure release valve.
Press the yogurt setting, make sure it is set to low, and time your yogurt for 8-12 hours.
When the timer on the instant pot beeps, remove the lid and place the lid on a towel. There is a lot of moisture on the lid that you don't want in your yogurt, and the towel prevents a watery mess on your countertop.
With a whisk, mix the yogurt together until it is smooth.
Ladle the yogurt into the four mason jars.
Date your jars and place them in the refrigerator.
Enjoy!