Another important agent in cheese-making is acid. This you are pretty sure to have, at some stage of the process, and the chief question seems to be as to _when_ you will have it. It is said that milk fresh from the cow manifests the presence of lactic acid. The quantity is very slight, however, and under favorable circumstances the development is slow. Where milk is properly cooled immediately after being taken from the cow, and the factoryman has good facilities for keeping it cool, it will be found, when the time comes to begin the process of working up, what is called "sweet." It will not taste as fresh and clean as when first cooled after milking; but no acid will be perceptible to either taste or smell--not even enough to make it what is termed "old."
Some think age makes the milk all the better for cheese-making, and we believe it is generally understood that milk fresh from the cow does not work quite satisfactorily. However, we place no great stress on this opinion. Old milk will work quicker than new milk; the acid will develop sooner to the point desired by the cheese-maker, and this saving of time doubtless has something to do with the decision in favor of age in milk for the purpose of cheese-making.
Our impression is, that milk cannot be too sweet when the rennet is added, and that if sufficient time is taken to develop the acid in the whey before dipping, the fresh milk will be found to turn out the finest-flavored and best-keeping cheese. The acid is not wanted in the _curd_, but in the _whey_. If the milk is sour, to begin with, or quite advanced toward sourness, the lactic acid must pervade every particle of the whole mass. Now, it strikes us that the correct idea is to expel the whey from the curd, as far as possible, before the acid makes its appearance, and let the acid develop in the whey afterward, so as to furnish a sort of pickle. The acid will develop sharply at some stage in the process; and, as we have before said, the question to be decided seems to be as to what point it is best to have it develop at.
We say, with the light we at present have before us, we think the acid should never be allowed to develop much before the curd is cooked and the whey is properly expelled; then let the whey take on acid to quite a perceptible degree before dipping the curd. We doubt if it makes much difference whether the acidulation takes place while the curd is floating in the whey, or after the whey is drawn off and while the curd stands and drains. There is rather more convenience in handling to leave the whey on and stir the curd sufficiently to keep it from packing; but the "cheddar" cheese, which is generally considered the best of any, is made by stacking the curd, after cooking, and allowing the whey that clings to it to take on acid. But where the milk is all right, to begin with, and the curd is properly managed and cooked, we doubt if it makes any material difference which process is adopted for allowing the acid to develop. With such a curd, there is little danger of its being injured by the acid, as any one can demonstrate by allowing curd to stand unpressed over night, as is often done with small remnants, when the pieces will be found covered with an almost vinegar-sour acid. Grind this curd and put it to press, and there will be no signs of sour cheese.