yogurt and milk separating

[Guest guest]

my last two attemps at making yogurt ended when I heated the milk to

180 degrees. Upon cooling the milk separated into something you

could describe as curds and whey. Do you think my thermometer is

inaccurate and i heated it to high? Could it be that the milk

wasn't fresh enough? It tasted ok. I use raw goat milk , it was a

week old in a very cold refrigerator. Also sometimes my yogurt

comes out thick and other times thinner. Any ideas are welcome.

Thanks for your time, Maddie