Originally Posted by MrJames
I used rennet, is that what you mean?
There are 2 ways to make moz. The way I normally use is with citric acid and rennet. There is another way which uses thermophilic culture to raise the acidity instead of the citric acid and rennet.
If you are trying to make ricotta with just reheating your whey it works much better if you are using whey that came from the thermophilic culture and rennet method. Otherwise there is a method for making ricotta using whole milk and an acid (vinegar or citric or whatever)
This link has both methods for ya . . .