604 Part VI: Fermented Foods
skim milk in conjunction with heat treatment. Ri-
cotta cheese is the most common cheese prepared in
this manner.
Lactic acid bacteria (LAB) cultures are added to
the milk in conjunction with the rennet. Although
the LAB cultures do not have a significant role in the
coagulation of casein, they contribute to the changes
that occur during the ripening process. The different
strains of starter cultures differ in such characteris-
tics as growth rate, metabolic rate, phage interac-
tions, proteolytic activity, and flavor promotion (Stan-
ley 1998). Frequently, mixed-strain cultures, which
contain unknown numbers of strains of the same
species, are used. Mesophilic L cultures containLeu-
conostocspecies, includingLn. mesenteroidesssp.
cremorisandLn. lactis,while the main species in
mesophilic D cultures areLactococcus lactisssp.
cremoriswith lesser amounts ofLc. lactisssp.lactis.
Mesophilic DL cultures would consist of both lacto-
cocci and leuconostocs. The thermophilic cultures
consist ofStreptococcus thermophilusand one of the
following:Lactobacillus helveticus, Lb. delbrueckii
ssp.lactisorLb. delbrueckiissp.bulgaricus.
Cutting the Coagulum Cutting the coagulum
increases the drainage of the whey from the curds
and contributes to a sharp decrease in the moisture
content of the curds. Acid-coagulated and rennet-
coagulated cheeses differ in the pH at which curd
formation occurs and, subsequently, the pH at which
the coagulum is cut. For acid-coagulated cheeses,
curd formation occurs at pH 4.6, the isoelectric
point of casein. Curd formation of rennet-coagulated
cheeses occurs at higher pH, ranging from pH 6.3 to
6.6. Following the cutting of the coagulum, the curd
and whey mixture is heated and agitated in a process
called “scalding.” The agitation is necessary to keep
the curds suspended in the whey and to promote
drainage of whey from the curds. The temperature
during the scalding process is dependent on the type
of the cheese and ranges from 20 to 55°C. The tem-
perature affects gel formation and gel viscoelasticity
and regulates the growth of the lactic acid bacteria.
A high temperature results in greater drainage from
the cheese and a firmer cheese.
The conversion of lactose to lactic acid by starter
cultures decreases the pH of the curd, which con-
tributes to the loss of whey from the curd and a
decrease in moisture content. While the curds are in
the whey, diffusion of lactic acid into the whey and
lactose into the curds occurs. The rate of acid pro-
duction is affected by the amount and type of the
starter culture, the composition of the milk, and the
temperature during acid production.
When the required acidity of the cheese curds is
reached, the whey is drained to recover the curds.
Following the separation of the curds from the whey,
acid production continues at an increased rate, be-
cause of the lack of diffusion of the lactic acid from
the curd. To minimize excess acid development fol-
lowing the drainage of the whey, some types of
cheese include a washing step to reduce the lactose
content. The moisture content of the curd is affected
by the extent the coagulum is cut, the temperature of
the curd after cutting, and agitation of the curd in the
whey.
The handling of the curd following the cutting of
the coagulum greatly affects the characteristics of
the cheese. The cheddaring process, used in the man-
ufacture of Cheddar, Colby, Monterey, and moz-
zarella cheeses, involves piling blocks of curd on top
of each other, with regular turning to allow the curds
to fuse together. In Colby and Monterey cheeses,
vigorous stirring during the drainage of the whey
inhibits the development of a curd structure and
results in a softer cheese with a higher moisture con-
tent. Frequently, the whey may be partially drained
off and replaced with water or salt brine to remove
lactose and reduce the development of acidity, as is
done in the processing of Gouda and Limburger
cheeses.Shaping and Pressing The resulting curds are
shaped to form a coherent mass that is easy to handle.
The curds are placed in a mold and are often pressed
with an external force to cause the curds to deform
and fuse. The pressure and time of pressing ranges
from a few grams per square centimeter for a few
minutes for moist cheeses to 200–500 g/cm^2 for up to
16–48 hours for cooked and hard cheeses. The tem-
perature (20–27°C) and humidity (95% relative
humidity) of the pressing room is controlled to opti-
mize the growth of the lactic acid bacteria and facili-
tate the deformation and shaping of the curd. Acid
production by LAB and additional drainage of whey
from the curd continues during the shaping and
pressing stage. Deformability is affected by the com-
position of the cheese, and it increases until the curds
reach a pH of 5.2–5.3. Deformability also increases
with an increase in moisture content and temperature.