We next draw the whey down to the curd--leaving enough to stir it in
easily, and cool the whole mass down to 90 degrees, to avoid too much
packing, and draw off the balance of the whey. The whey should be run
off before the acid develops, because acid, formed from the milk in
the sugar, dissolves the minerals and cuts some of the oils in the
curd, and these run off in the whey. Many curds, by remaining in the
whey too long, become whey-soaked, and make cheese that is soggy and
hard, with a sour flavor. This kind of firmness is not desirable,
notwithstanding it is called for by buyers, who seldom know anything
about cheese making. If the acid develops before the whey is properly
expelled, or the curd is "cooked," it carries off the minerals, which
are in the form of phosphates, and this makes the cheese poor indeed.
These phosphates are of lime, iron, magnesium, etc., but the principal
is phosphate of lime. The affinity of these minerals for lactic acid
is stronger than for phosphoric acid; so they let go of the latter
and unite with the lactic acid, forming lactates and leaving the
phosphoric acid free. But if we get all of the whey out of the curd
that we desire, and then get the curd out of the whey--that is, draw
off the whey--before the acid comes on, we retain the phosphates and
fats in the cheese--all the goodness that belongs in it. The acid will
come on afterward, but we have reduced the sugar to a minimum, and the
amount of acid developed does no serious injury. As the whey is already
expelled, of course it cannot wash out the minerals that are dissolved.
These remain, and in the process of curing recombine with the
phosphoric acid. We have left in the curd about 3-1/2 parts of the 87
parts in 100 parts of milk. The whey left in the curd contains, we will
say, 1-10th of the sugar that was in the milk. The acid formed from
this, though too small to do any known injury, is large enough to do
all the good required, if it does any good at all. We are, therefore,
safe when we get the whey out of the curd and the curd out of the whey
before the development of the lactic acid.