There's a recipe in Karlin's book that starts by adding EXACTLY 7 teaspoons of distilled vinegar to get the milk to the correct pH. Why isn't this the norm? I would assume that most milk is about the same pH, most vinegar is similarly comparable, so that suggested ratio should always get you the right pH. I guess you could say the same regarding citric acid.
I'm going to try it that way next time and see how it works out.