Principles of Cheese Technology 243teins in curd leads to higher cheese yield.
Because whey proteins have a higher biologi-
cal value than casein, whey protein retention
in cheese curd improves the nutritional
quality of cheese curd. Furthermore, the curd
obtained by acidifi cation at elevated tempera-
tures retains more moisture, giving a harder
texture and imparting a unique non - melting
attribute. Such directly acidifi ed cheeses are
suitable for frying because they do not soften
at frying temperatures and they retain their
shape.Cutting the Curd
After the coagulum is set in a horizontal
(rectangular) cheese vat, a simple test is con-
ducted to determine whether the coagulum
strength is appropriate for cutting. A fl at knife
is inserted at a 45 ° angle to the surface of the
coagulum and slowly pulled out. If the cut is
clean and no curd sticks to the knife, the
coagulum is ready for cutting. The setting
temperature in Swiss cheese is higher than
that in cheddar. Consequently, the Swiss
cheese curd assumes a fi rm form quickly,
necessitating cutting before it becomes too
fi rm.
The size of cutting knife is chosen accord-
ing to the particular variety of cheese. The
curd size is related to retention of moisture
in cheese. High - moisture cheeses such as
soft, ripened varieties are cut with large 2 - cm
knives. Large curds are relatively fragile and
produce more fi nes, leading to less retention
of fat and nonfat milk solids in cheese. In
some cases, the curd may be duly broken for
dipping into forms/molds. Cheddar and
washed - curd cheeses such as colby are cut by
medium size (1 - cm) knives. Small - curd size
(resembling rice grains) leads to low mois-
ture, as in Italian hard cheeses. Recovery of
milk solids is higher in small - curd cheeses.
High - setting temperature also assists in lower
moisture retention.
Manual cutting of curd is done with a
harp - shaped knife in which a series of stain-
less steel wires (resembling piano wires) areChhana, paneer and some Latin American
cheeses (Chandan, 2003 ). In cottage cheese
and cream cheese production, large aggre-
gates of casein form clots in situ as a result
of lactic acid production by the starter culture.
The original pH of milk is around 6.6. As the
acidifi cation proceeds to pH 5.3, coagulation
of casein commences. The coagulation is
completed at pH 4.5 to 4.6, the isoelectric
point of casein. The acid coagulation does
not signifi cantly depend on salt concentration
of milk because it is triggered by the accu-
mulation of free hydrogen ions in the system.
At this stage, milk sets to a gel - like coagulum
which can be processed further into curd and
whey.
In comparison with enzymatic coagula-
tion, acid coagulation results in considerably
lower calcium and phosphorus in cheese
curd. This observation is of important nutri-
tional signifi cance. On a dry matter basis,
cottage cheese curd contains signifi cantly
lower calcium and phosphorus in comparison
with enzymatic coagulated cheese curd, such
as cheddar cheese. The reduced retention of
these minerals in cottage cheese is attributed
to progressive dissociation of calcium phos-
phate from the casein micelles as the pH of
milk drops to pH 4.6, the isoelectric point of
casein. Thus, a signifi cant amount of milk
calcium and phosphorus is leached out in
cottage cheese whey (Clarke and Potter,
2007 ).
The recovery of major whey proteins
(normally lost in whey) in cheese curd
obtained by acid coagulation at ambient tem-
peratures may be engineered by heating milk
to elevated temperatures prior to acidifi cation
by direct addition of food - grade acid. In the
manufacture of Indian cheese, Chhana and
Paneer, heat treatment of milk at 90 ° C to
95 ° C (194 ° F to 203 ° F) for 5 minutes results
in complex formation of κ - casein with β -
lactoglobulin, along with heat - denaturation
of whey proteins, making them insoluble
(Chandan, 2007b , Aneja et al., 2002 ). They
are then trapped in cheese curd along with
casein clots. The incorporation of whey pro-