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!
1/4 cup vinegar to 1 gallon milk should have worked, but it didn't so you hug in there way to go! The vinegar won't hurt the cheese so adding more was a good thing. Lemon juice works well also.
In reading posts by owners of milk cows (so they are using raw milk), different times of year and different types of feed (hay vs fresh grass) can affect how quickly or effectively milk coagulates, or cream churns into butter. Store-bought milk should be fairly consistent, unless you used a different brand.
If your vinegar has been around awhile, sometimes that will lower its acidity, too. It doesn't hurt to add a bit more, though, as Debi says.
Oh, the white vinegar had been in my cabinet for a LONG time, so I'll bet that was it. The cider vinegar (which I use more frequently) was fresher and it coagulated everything instantly. Good to know that age affects acidity of vinegar - I'll be sure to buy a fresh bottle!
try adding the acid when the milk is around 80 degrees, it gives it more time to do it's thing.