1. Heat milk to 185 °F.
2. Cool milk to 77 °F and add yogurt culture. (Culture usage: 1/8 tsp per 1/2 gallon - 4 gallons of milk.)
3. Stir in gently until dissolved.
4. Hold temperature at 75-77°F for approximately 16 to 18 hours.
5. Refrigerate 

I have made buttermilk by heating the milk anywhere from 75°F up to 185F   and it works fine at any temperature.