Principles of Cheese Technology 249Residual calf rennet and recombinant chy-
mosin hydrolyze casein fractions and produce
precursors of cheese fl avor. In this regard,chymosin specifi cally attacks α (^) s1 - casein,
whereas β - casein is not affected by rennet.
Starter cultures proliferate in the early stages
of ripening, reaching as high as 500 CFU/g in
three to four days. However, their numbers
dwindle soon after, reaching 30 million/g
after four weeks. The dead cells release
enzymes, which continue hydrolyzing caseins
and milk fat. The leuconostocs generate CO 2
from inherent lactose and citrate to create
small eyes and produce diacetyl and other
potent fl avor compounds. In Swiss cheese
varieties, propionibacreia are allowed to
grow by keeping cheese blocks at 20 ° C
(68 ° F) for about three weeks, resulting in
enough CO 2 production for generation of
large eyes in the cheese body.
High humidity (90% to 95%) and air cir-
culation (for oxygen supply) are required in
surface - ripened cheeses such as Camembert
and Brie to encourage the growth of molds
Penicillium camemberti and Penicillium
roqueforti. Similarly, in smear - ripened
cheeses, Brevibacterium linens is encouraged
to grow by maintaining high humidity.
Simultaneously, the growth of mold is
restricted by repeated surface washing. In
addition to starter cultures, non - starter lactic
acid bacteria (especially lactobacilli and
pediococci) also play an important role in
cheese ripening.
Several enzyme preparations are available
for accelerated ripening. They are derived
from dairy or non - dairy sources, most of
them lipases and proteases. Enzyme capsules
also are designed to liberate enzymes at
certain stage of ripening. Heat or freeze -
shocked proteolytic cultures have been used
as well.
The chemistry of cheese fl avor is
reviewed by several authors (Fox, 2000 ,
2003b ; Singh and Cadwallader, 2008 ). The
origin of the cheese fl avor profi le is summa-
rized below.
barrier properties to permit escape of the gas.
The moisture barrier packages are vacuum -
treated to expel air and are often fl ushed with
CO 2 or N 2 gas to prevent mold growth during
ripening. Flushing with CO 2 offers the advan-
tage of solubility characteristics of the gas,
making the package tight enough to cling to
the surface of the cheese. Shrink fi lms also
give skin - tight packaged after dipping them
in hot water or by passing them through a
steam chamber. Packages containing cheese
curd or cheese shreds are fl ushed with nitro-
gen to avoid fusion of curd particles.
Ripening
Pressed cheese blocks are protected from
moisture loss and growth of undesirable bac-
teria and molds by wax coating, rind forma-
tion, enrobing in special emulsions, or
vacuum wrapping in plastic fi lms. Rind for-
mation is characteristic of Italian cheese but
is also practiced in some cheddar cheese pro-
duction. Cheddar and American cheeses are
ripened in fi lm - wrapped blocks. The pack-
ages are then allowed to ripen by placing
them in ripening rooms with controlled tem-
perature. For some cheeses the humidity also
is controlled. The ripening period varies from
zero to two to fi ve years for hard varieties.
During ripening, the major constituents of
cheese (lactose, fat, protein, and metabolic
products of culture) growth are further broken
down to form the typical cheese fl avor and
texture.
Cheese ripening is associated with the
action of several enzymes and cultures.
Plasmin and lipoprotein lipase are the milk
enzymes involved. Plasmin survives pasteur-
ization of milk and cleaves caseins, espe-
cially in Swiss cheese. However, the role of
plasmin is minimal in cheese made from
ultrafi ltered milk that contains β - lactglobulin,
an inhibitor of plasmin. Lipoprotein lipase
hydrolyzes milk fat to generate fl avorful
compounds, but its role is restricted only to
cheese made from raw milk.