8 cups milk, preferably whole (but any kind will work)
2 tablespoons yogurt, labeled “contains live cultures” (not just made with)
1/4 to 1/2 cup sweetened condensed milk
1 cup heavy cream
1 teaspoon vanilla
Clean and prep the Instant Pot. Since we’re going to be growing culture in it, it is super important that a 6 or 8-quart Instant Pot's stainless steel, lid, and sealing ring are nice and clean. Hot soapy water and a hot rinse before drying with a clean kitchen towel should do the trick.
Boil the milk in the Instant Pot. Pour the milk into the Instant Pot. Lock the lid in place but leave the pressure valve open (you can also cover it with a glass lid if you have one). Press the yogurt button until it says to boil. For most Instant Pots, you’ll just need to hit the yogurt button once or twice and then press start. The Instant Pot will use the heating element to bring the milk mixture close to a boil. After 25 to 35 minutes (depending on your model), the Instant Pot will beep indicating the boiling cycle has finished. Stay close as your model make take more or less time to come to temperature.
Check the milk’s temperature, and then cool to 110°F. Our goal in boiling isn’t 212°F but rather 180°F or above. Use a thermometer to test the milk’s temperature. If you’ve got 180°F, remove the insert and let it cool at room temperature for about an hour. Alternatively, you can cool the mixture by filling your sink with ice water and gently submerging the bottom of the insert in the ice water — this will take about 10 minutes. Your goal temperature for cooling is 110°F.
Mix 1 cup of warm milk with the starter yogurt and add sweeteners or flavorings. Return the insert to the Instant Pot (make sure the bottom is dry if you used the water cooling method). With a clean ladle, ladle off about a cup of the warm milk into a small bowl or measuring cup with a spout. Add the yogurt and whisk to combine. Return the yogurt mixture to the Instant Pot and whisk gently to combine. If you’re sweetening or flavoring your yogurt, this is also the time to add those optional ingredients.
“Cook” on the yogurt setting for 6 to 10 hours. Lock the lid in place but leave the pressure valve open again. Hit the yogurt button once more until it reads 8:00, then press start. This will begin a count-up the clock on the incubation period. After about 3 hours the yogurt will begin to thicken. Start checking the thickness and flavor at about 6 hours by gently dipping a spoon into the yogurt. Avoid mixing the yogurt while it cooks, or you’ll have very loose yogurt. 8 hours of cooking will yield perfectly thickened and delightfully tangy yogurt — about what you’d expect from typical whole-milk yogurt. You can continue to cook the yogurt for 2 hours more for thicker, tangier yogurt. You can also take the yogurt and strain it through cheese cloth, this will remove the liquid (whey) making it thicker. You can use this whey to add to other foods.
Refrigerate the yogurt in the Instant Pot insert for 4 hours or overnight. Remove the insert and lightly cover with plastic wrap. Refrigerate until chilled through, at least 4 hours or overnight, the yogurt will thicken slightly more when chilled. Transfer to airtight containers for long-term airtight storage. Remember to save some of this yogurt if you plan on making more yogurt in the near future.