26 Dairy Products 605Salting The salting step reduces the moisture con-
tent of the curd, inhibits the growth of starter bacte-
ria, and affects the flavor, preservation, texture, and
rate of ripening of the cheese. The final salt content
of cheese ranges from 0.7% to 4% (2–10% salt in
moisture content). The amount of salt, the method of
application of the salt, and the timing of the salting
is dependent on the specific type of cheese. The salt
may be incorporated through (1) mixing with dry-
milled curd pieces, (2) rubbing onto the surface of
the molded cheese, or (3) immersing the cheese in a
salt brine. Following the salting step, the salt diffus-
es into the interior of the cheese, with the subse-
quent displacement of whey. Depending on the size
of the cheese block and the composition of the
cheese, it may take from 7 days to over 4 months for
the salt to equilibrate within the cheese.
Ripening Fresh, green cheese has a bland flavor
and a smooth, rubbery texture. During the ripening
process, the characteristic texture and flavor of the
cheese develop through a complex series of bio-
chemical reactions. Ripening starter cultures are se-
lected to develop the texture and flavor characteris-
tics of the specific cheese type. Enzymes released
following lysis of the microorganisms catalyze the
degradation of proteins, lipids, and lactose in the
cheese. As the ripening time increases, the moisture
content of the cheese decreases, and the intensity of
the flavor increases. The resulting quality attributes
of the finished cheese depend not only on the initial
composition of the milk and the starter cultures
used, but also on the water activity of the cheeses
and the temperature, time, and humidity during the
ripening period. Depending on the type of cheese,
the ripening period can range from 3 weeks to more
than 2 years.
The ripening temperature influences the rate of
the microbial growth and enzyme activity during the
process and the equilibrium between the biochemi-
cal reactions that occurs during ripening. Ripening
temperatures generally range from 5 to 20°C, which
is well below the optimum temperatures for micro-
bial growth and enzyme activity. Soft cheeses are
often ripened at 4°C to slow the biochemical pro-
cesses. An increase in ripening temperature for hard
cheeses reduces the ripening time necessary for flavor
development, with a 5°C increase in ripening tem-
perature reducing the ripening time 2 to 3 months.
However, caution must be exercised in altering
ripening temperatures since not all microorganisms
and enzymes respond to temperature changes in the
same manner, resulting in an imbalance in flavor
characteristics (Choisy et al. 2000).
The growth of most of the starter bacteria added
to the milk in the initial stages of cheese making is
slowed as the pH of the cheese approaches 5.7 and
following the addition of salt, but fermentation and
the decrease in pH continue. The fermentation of
lactose to lactic acid by the starter cultures provides
an environment that prevents the growth of undesir-
able microorganisms through reduced pH and the
formation of an anaerobic environment. The optimal
activity for proteases is between pH 5.5 and 6.5 and
that for lipases is between pH 6.5 and 7.5.
Protease and lipase activity during the ripening is
probably most important to the development of the
flavor and texture of the cheese. Enzymes of the
starter bacteria, nonstarter lactic acid bacteria, and
secondary cultures added during cheese making are
most important in the development of the flavor and
texture of the cheese during ripening. These
enzymes are released by the lysis of the cell wall of
the bacteria. Rennet enzymes and endogenous milk
enzymes, such as plasmin, also contribute to these
hydrolytic reactions during ripening. The extent of
these enzymatic reactions depends on the activity
and specificity of the enzymes, the concentration of
the substrates, pH, water activity, salt concentration,
and ripening temperature and duration. The degra-
dation of the amino acids and fatty acids, through
enzymatic and nonenzymatic reactions, result in
the formation of several important volatile flavor
compounds, including sulfur-containing compounds,
amines, aldehydes, alcohols, esters, and lactones.
Rennet and plasmin are associated with the pri-
mary phase of proteolysis and hydrolyze the caseins
to large polypeptides. This proteolysis alters the
three-dimensional protein network of the cheese to
form a less firm and less elastic cheese. Although
these polypeptides do not have a direct impact on
flavor, they do function as a substrate for the pro-
teases associated with the starter and nonstarter bac-
teria. However, if the primary proteolysis is exten-
sive, bitter peptides, with a high percentage of
hydrophobic amino acids, predominate. Free amino
acids and short-chain peptides contribute sweet, bit-
ter, and brothy-like taste characteristics to the cheese.
Further degradation and chemical reactions of these
peptides and amino acids through the action of