1literor 1 quart/4.25 cups whole fat milk(I used 3.5%)
1tbsp.whole fat powdered milk
1heaping tbsp. whole fat plain unsweetened yogurtmake sure it says live and active cultures
Measure out the yogurt and leave on the counter, so it comes to room temperature. Pour all but 1/2 cup of the milk into a large pot. Mix the 1/2 cup milk with the powdered milk until well combined and there are no lumps in the milk. Pour the powdered milk mixture into the pot with the rest of the milk. Over medium heat bring the milk to a temperature of 180f or 82c. If you do not have a thermometer allow the milk to heat just until it begins to froth/bubble not allowing it to boil. Turn the heat off, remove from stove and set aside to cool.
After 15 minutes check the milk temperature, it should still be warm but not scorching. Test by placing your clean pinky finger into it and if you can comfortably leave it in there for a few seconds then you can proceed, if not continue to cool down. The milk needs to be lukewarm. It is very important for the milk not to be too hot so the yogurt cultures are not killed by the heat.
Mix in the 1 tbsp. of plain white yogurt to the pot, mix well to throughly to distribute the yogurt into the scalded milk. Cover the pot with lid, wrap the whole pot in a thick blanket or towel, and place inside the oven to incubate. The oven should be turned off, but if you can, leave the oven light on to create a bit of heat inside. (Instead of placing the wrapped yogurt inside the oven it can also be left in a warm spot in your kitchen.) Leave for 3 to 6 hours in the turned off oven, or warm kitchen spot. During this time is when the yogurt cultures begin to react/grow and the milk begins to set into yogurt.
Allowing to sit for 3 hours creates a milder yogurt, allowing it to sit longer creates a more acidic yogurt. If after 3 hours the yogurt has not thickened then it needs to sit longer. I leave mine for 6 hours and feel the taste is great, just a little acidic but perfect to my liking, but also the yogurt is always thick after 6 hours. After the 3 or 6 hours of incubation, unwrap the yogurt but leave the lid on. Place the pot in the refrigerator to thicken further for a few hours or overnight. I like to leave mine overnight so it's ready for breakfast the next day.
The next day or after a few hours the yogurt will have thickened. You can test by tasting with a tablespoon. You can further thickened the yogurt to make it Greek style. We can do so by draining some or most of the whey.
To drain of whey and for a thicker Greek Yogurt like consistency:
Line a fine sieve with muslin cloth or a clean kitchen towel, and place over a bowl to collect the whey. Pour the yogurt into the muslin cloth, gather up the cloth, and twist. Place in the refrigerator and allow to drain for 2 hours or until you achieve the consistency or yogurt thickness desired.
Reserve some of the whey incase the yogurt needs to be thinned down. If you feel the strained yogurt is too thick simply pour a bit of the drained whey into it, mix and check thickness again.
Store the yogurt in an airtight container in the refrigerator. Consume within a week, if you don't eat it before then that is.
How To Make Homemade Greek Yogurt https://mexicanmademeatless.com/how-to-make-homemade-greek-yogurt/