244 Chapter 10
to facilitate syneresis and extend product
stability.
After the cooking temperature is attained,
the cheese vat agitation is set to high speed
and the curd - whey mixture is stirred vigor-
ously for another 45 to 60 minutes to promote
more syneresis of whey. During the cooking
and afterward, the acid production by the
starter culture continues and the titratable
acidity of whey increases (pH decreases),
further promoting syneresis of the curd. The
status of colloidal calcium phosphate associ-
ated with casein begins to change by becom-
ing soluble as acidity builds up in whey. In
fresh cheeses, the pH drops to 4.6 to 4.7 and
all of the colloidal calcium ends up in whey.
However, in renneted curd varieties, the pH
of curd is higher (greater than 5.3) and some
colloidal calcium is retained in the cheese
curd. Depending on the pH developed after
cooking, the cheese curd retains varying
levels of calcium, which affects the cheese
texture accordingly. In general, fast acid
development results in low - pH curd, thereby
causing low calcium retention in cheese curd
and leading to a crumbly texture, as in
Cheshire cheese. On the other hand, as in
Swiss cheese, slow acid development (higher
pH) results in a higher calcium content in the
curd and a more elastic and rubbery texture.
Lactose of milk is partitioned between
whey and the cheese curd. Its content in curd
is proportional to moisture content of the
curd. Equilibrium is established between
curd lactose and whey lactose. Because
lactose is metabolized to lactic acid, its
content in curd provides potential fermenta-
tion ability and acid development. After
the curd and whey are separated, the lactose
in curd is metabolized quickly. However, if
the curd and whey stay together longer, more
acid is generated, causing changes in the
physical properties of the curd. The buffering
capacity of the curd is reduced due to acidity -
induced loss of calcium and phosphate to
whey. Under such conditions, the lactose in
curd stays intact longer, which in turn fer-stretched across a stainless frame in a vertical
or horizontal fashion. The horizontal - wired
stainless steel knife is pulled through the
curd, followed by a vertical knife to complete
the three - dimensional cut to form cubes of
the curd. The cutting time is important to
control the curd character and should be
completed within fi ve to 10 minutes. The
cutting process is designed to increase the
surface area of cheese cubes for enhancing
syneresis or whey expulsion and effi ciency
of heat transfer during the cooking step.
After cutting, the curd is allowed to “ heal ”
by leaving it undisturbed for 10 to 15 minutes.
During this period, the curd cubes form new
intramolecular linkages and they expel more
whey and develop fi rmness. If a low - moisture,
fi rmer cheese is needed, the curd is agitated
for 30 minutes before the cooking phase.
This step helps to avoid surface toughness of
the curd cube. The cutting quality can be
determined by how much fat is lost in whey
(normally 0.2% to 0.3% fat).
Cooking the Curd
Cooking refers to application of controlled
heat to the curd cubes. Hot water is circulated
in the cheese vat jacket to transfer heat to the
curd - whey mixture while the curd is stirred
at a slow speed. The fi nal temperature is
37 ° C to 41 ° C (98.6 ° F to 106 ° F) for many
cheeses; it is as high as 53 ° C (127 ° F) for
Swiss and parmesan cheese. The fi nal tem-
perature is consistent with the thermal sensi-
tivity of the starter cultures used in a cheese
variety. The rate of heating the curd also
depends on the cheese variety. In general,
heating the whey - curd mixture starts slowly;
stirring is likewise slow to preserve the integ-
rity of the fragile curd at this stage. As time
passes, and the curd assumes a fi rmer texture,
the rate of heating picks up until the desired
cooking temperature is achieved in 30 to
40 minutes. It is customary to cook some
fresh cheeses such as cottage, cream, and
Neufchatel to 52 ° C to 60 ° C (126 ° F to 140 ° F)