Pour the milk into a large soup pot.

Heat over medium heat until it simmers. Be sure to stir so it does not burn.

Pour the yogurt into a heat-safe bowl to let it cool to room temperature.

Stir in the yogurt. (I usually pull out 2 cups of milk then stir the yogurt into this so it is easier to mix in. Then pour back into the milk.)

Whisk until the yogurt is mixed in.

Place the bowl of milk with the yogurt added into a dehydrator at 105 degrees Fahrenheit for 24-32 hours. You may have to set your dehydrator twice to get a long enough time.

Alternately, place the milk and yogurt mixture into a yogurt maker and set to ferment for at least 24 hours. Again, you may have to set it multiple times to get the full 24 hours.

Alternately, place the milk and yogurt mixture in your oven with a lightbulb that generates a little bit of heat. (Remove the oven light bulb and use a 60 watt bulb. This method is harder with light bulb regulations in the USA.) Turn on the light and the heat generated by the light will reach 100 degrees Fahrenheit. If the oven gets too hot, prop the door open with a wooden spoon. Be sure to monitor the temperature every few hours.

Once the yogurt is fermented, refridgerate until use. It should last a week, if stored properly.