1 gallon 2 percent milk
1/2 c plain yogurt
Remove the starter from the refrigerator a couple of hours ahead of time to warm to room temperature. Divide it into 1/2 portions for use as future starters. These instructions (118 degrees, 18 hrs) are based on using Parmalat brand “Cremoso: Creamy Whole Milk Yogurt” plain yogurt from El Super, which has “S. thermophilus, L. bulgaricus, L. lactis, L. casei, L. acidophilus, and Bifidobacterium.”
Pour milk into Instant Pot. Push Yogurt button until it says “boil.” Cover with the glass lid. When it beeps several times (temp at 180), take the liner out and cool it quickly in an ice bath, stiring constantly, and remove it as soon as it drops to exactly 120 (on a TempPro digital meat thermometer*, 110 on small instant read meat thermometer, 120 on small black instant read, 117 on blue lab thermometer). It will continue to cool a couple of degrees, hitting the 118 target. Immediately stir in starter, return the liner to the instant pot, and push the Yogurt button until says 24:00. Let it go for 18 hours. Strain through a cheese cloth.
* https://www.amazon.com/ThermoPro-Thermometer-Accurate-Grilling-Backlight/dp/B07MF18JHT