I made Mozarella yesterday and with the whey - ricotta. Turned out beautiful! Excellent stuff. Today's Mozarella turned out fine but the ricotta didn't. Had 2 gallons of whey and heated it to about 190 and dumped 3/4 cup of white vinegar. No ricotta. :nooo It did not separate... I did something different yesterday than today, I added a 1/2 gallon of older milk to my whey at about 190 and then added the vinegar. I got a good portion of ricotta - excellent ricotta. What could I be doing wrong?