250 Part II: Water, Enzymology, Biotechnology, and Protein Cross-linking
lactose, whey proteins, and soluble salts, streams
from the cut pores, accelerated by gentle agitation,
slowly increasing temperature, and a rising rate of
lactic acid production. These factors are manipu-
lated to the degree desired by the cheese maker.
Eventually the free whey is separated from curd.
Optimum acid development is essential for form-
ing rennet curd and creating the desired cheese mass.
This requires viable, active microbial starters to be
added to milk before the addition of rennet. These
bacteria should survive the cheese making process.
Beta-D-galactosidase (lactase) and phosphorylat-
ing enzymes of the starter bacteria hydrolyze lactose
and initiate the glucose-phosphate energy cycles for
the ultimate production of lactic acid through vari-
ous intermediary compounds. Lactose is hydrolyzed
to glucose and galactose. Simultaneously, the galac-
tose is converted in the milk to glucose, from which
point lactic acid is produced by a rather involved
glycolytic pathway. In most cheese milks, the con-
version of glucose to lactic acid is conducted homo-
fermentatively by lactic acid bacteria, and the con-
versions provide energy for the bacteria. For each
major cheese type, lactic acid must develop at the
correct time, usually not too rapidly, nor too slowly,
and in a specific concentration.
The cheese mass, which evolves as the whey
drains and the curds coalesce, contains the insoluble
salts, CaHPO 4 and MgHPO 4 , which serve as buffers
in the pressed cheese mass, and should the acid in-
crease too rapidly during cooking, they will dissolve
in the whey. In the drained curds or pressed cheese
mass under these circumstances, since no significant
pool of insoluble divalent salt remains for conver-
sion into buffering salts, the pH will lower to 4.7—
4.8 from an optimum 5.2, leading to a sour acid–
ripened cheese. Thus, conservation of a reserve pool
of insoluble salts is necessary until the cheese mass
is pressed. Thereafter, the insoluble salts are changed
into captive soluble salts by the lactic acid and pro-
vide the necessary buffering power to maintain opti-
mum pH at a level that keeps the cheese sweet. Such
retention also is aided or controlled by the skills of
the cheese maker. For Cheddar, excess wetness of
the curd before pressing or too rapid an acid devel-
opment in the whey causes sour cheese. For a Swiss
or Emmental, the time period for acid development
differs; most of it takes place in the press, but the
principles remain the same (Kosikowski and Mistry
1997).
The development of proper acid in a curd mass
controls the microbial flora. Sufficient lactic acid
produced at optimum rates favors lactic acid bacte-
ria and discriminates against spoilage or food poi-
soning bacteria such as coliforms, clostridia, and
coagulase-positive staphylococci. But its presence
does more than that, for it transforms the chemistry
of the curd to provide the strong bonding that is nec-
essary for a smooth, integrated cheese mass.
As discussed earlier, chymosin action on milk
results in curd mass involving dicalcium paracasein.
Dicalcium paracasein is not readily soluble, stretch-
able, or possessive of a distinguished appearance.
However, if sufficient lactic acid is generated, this
compound changes. The developing lactic acid solu-
bilizes considerable calcium, creating a new com-
pound, monocalcium paracasein. The change occurs
relatively quickly, but there is still a time require-
ment. For example, a Cheddar cheese curd mass,
salted prior to pressing, may show an 8:2 ratio of
dicalcium paracasein to monocalcium paracasein;
after 24 hours in the press, it is reversed, 2:8. Mono-
calcium paracasein has interesting properties. It is
soluble in warm 5% salt solution, it can be stretched
and pulled when warmed, and it has a live, glisten-
ing appearance. The buildup of monocalcium para-
casein makes a ripened cheese pliable and elastic.
Then, as more lactic acid continues to strip off calci-
um, some of the monocalcium paracasein changes to
free paracasein as follows:
Dicalcium paracasein lactic acid →monocalcium
paracasein calcium lactate
Monocalcium paracasein lactic acid →free para-
casein calcium lactate
Free paracasein is readily attacked by many
enzymes, contributing to a well-ripened cheese. The
curd mass becomes fully integrated upon the uni-
form addition of sodium chloride, the amount of
which varies widely for different cheese types. Salt
directly influences flavor and arrests sharply the acid
production by lactic acid starter bacteria. Also, salt
helps remove excess water from the curd during
pressing and lessens the chances for a weak-bodied
cheese. Besides controlling the lactic acid fermenta-
tion, salt partially solubilizes monocalcium paraca-
sein. Thus, to a natural ripened cheese or to one that
is heat processed, salt helps give a smoothness and
plasticity of body that is not fully attainable in its
absence.