Thanks, coffee joe. Yeah, we don't get to boiling at 200F degrees here, probably closer to 203F or so. That is 95C and one of the temperatures that a recipe for whole milk Ricotta recommended I heat too. Now, that Ricotta was a dismal failure. "Tougher than a junk yard dog" as the Jim Croce song goes. The milk was from a local dairy and had been pasteurized. Exactly how it was pasteurized is a "secret" since they don't talk about that. Just say it is pasteurized, like the process is a secret. Well, their process is, I suppose. I am guessing it is a higher temp, shorter time method, but not UHT pasteurization. But to be on the safe side, I will get their raw milk next time.
The failure, rather than milk, was likely either the temperature (we went to 95C degrees which is right at the bare edge of boiling here) or it was the amount of vinegar we used. The recipe called for 1/2 cup vinegar for 10 liters of milk. Since we were making with 1 liter of milk, we scaled the vinegar back by 1/10th. 118 milliliters of vinegar in a half cup. I think we may have gone sour there, making the vinegar 18 or 20 milliliters, not 11 or 12 like we should have. (Dim old oven light going off in head as I type this!)
We moved away from "whole milk Ricotta" toward Queso Blanco. Better luck there. We switched to lemon juice for that. It was much closer to what I expected. Not creamy and really didn't need to be drained at all once we spooned it out of the whey. That may be due to to much agitation while heating. Or maybe too much lemon juice though I was quite the conservative sort pourer, following advice that only enough to get the curd to separate out. So I added it by the tablespoon. Two tablespoons and the curd came out, the whey turned greenish and I stopped. Still not perfect, but better. Much better. Wife brought home some "Pata Tim", a braised pork dish and made soup from the remaining bones. I enjoyed sopping up the soup with soft bread and then putting a layer of Queso Blanco on. Made a great petite meal.
So I won't modify lower temperature points in a recipe, but I will err on the side of caution when it gets around 203F or 95C. I hope to make Queso Blanco, Panir (Paneer?) and Ricotta (whey or whole milk) as additions to pizza and other dishes that benefit from a white cheese.
Now the remaining Question about acidic substitutions remains. Lemon Juice in place of Vinegar or Citric Acid Powder. It would really be great if there was some sort of formula or table to consult when these are substituted in cheese making. Interestingly, in cooking, vinegar is sometimes substituted at 1/2 the amount of lemon juice. But for canning, where acidity is key issue and not taste, vinegar is substituted at twice the amount of lemon juice. One website, not specific to cheese, suggested 6 tablespoons of lemon juice to 1 tablespoon of citric acid powder.
So until I can find better information it seems like:
1 tablespoon of Lemon Juice = 2 tablespoons of Vinegar
6 tablespoons of Lemon Juice = 1 tablespoon of Citric Acid Powder
Anyone out there with a PH tester and access to these three ingredients, maybe you could post PH readings?