I made ricotta yesterday for the second time, and instead of following Ricki Carroll's recipe (in which diluted citric acid is added to the milk before heating), I decided to try it the "easy" way by heating the milk to 200 degrees, then adding vinegar. I added 1/4 cup of white vinegar and the milk coagulated, but not fully. I scooped out about 1/2 lb of curds, but the "whey" didn't look like whey at all - it still looked like milk! I reheated it to 200 and added a couple of tablespoons of cider vinegar, at which point I got a nice clean break and an additional 3/4lb of curds, approximately.
Anyway, just wondering if you had any thoughts. According to my vinegar bottle, I was using white vinegar with 5% acidity - did I just not use enough to curdle the full gallon? I didn't realize it worked like that - I figured it would either coagulate or not, instead of something inbetween. Anyway, the ricotta tastes great so I don't think I did any damage by doing it in two stages. Cheesemaking is quite the adventure!