Pour 1/2 gallon of milk in the crock and turn the heat on low for 2.5 hours
After, turn off the crock pot and leave the lid on for another 2.5 - 3 hours.
Take out 1 -2 cups of milk and place in a small bowl
Add yogurt in the bowl and milk well
Add the yogurt mix into the crock pot, cover with the lid and cover with thick towels for 8 - 12 hours.
Yogurt in the Instant Pot
Add Milk to a 6 quart Instant Pot, close and lock lid. Select Yogurt setting and adjust the pressure to boil. This process can take up to an hour.
After, carefully coll the Instant Pot insert in a bowl of ice water. Make sure to stir occasionally, until the milk reaches 100-110 degrees F. This should take 15-20 minutes. Set aside 1 cup of milk
In a medium bowl, whisk together the yogurt and the reserved cup of milk. Stir the mixture into the the milk.
Return the insert into the Instant Pot. Select the yogurt setting again and it will automatically set the time for 8 hours.
Transfer to storage containers, cover and chill the yogurt until its cold which can take 6 -8 hours or up to 10 days.
Notes
Feel free to use whole milk for a thicker and tastier yogurt, but stay away from UHT milk because it is processed at such a high heat that none of the good bacteria remains.
If you want more flavor add honey, fruit, granola, or jam.
Remember that you need to allow your yogurt to culture, meaning it needs to have good bacteria to protect against the bad.
To make a thicker consistency get a bowl, strainer, and coffee filters (or cheese cloth).
Strain yogurt with a coffee filter to filter out some of the whey. Be careful not to leave it to long because it can become the consistency of cottage cheese.
Or add a little bit of gelatin.
If you are using the Instant Pot, use a new silicon ring or totally omit it. The silicon can harbor smells and possibly make the yogurt taste like however your ring smells.
You can use homemade yogurt as a starter for the next batch of yogurt. I would suggest getting a new starter after a few batches to make sure the culture stays prolific.