262 Chapter 10
is able to utilize entrapped oxygen, making it
unavailable for mold development. The
reductive power may be elevated at higher
temperatures due to increased culture activ-
ity. Because older cheeses contain lower
microbial populations, they do not have
much capacity to utilize oxygen present in
the cheese package. Mold growth appears to
increase at lower temperatures for relatively
young cheeses. Consequently, cheese should
be held at a temperature higher than refrig-
eration for one or two days immediately after
packaging to utilize entrapped oxygen.Gas Barrier Properties
It is critical to control the amount of oxygen
permeating through the material or seal of the
cheese package. Some literature suggest an
oxygen barrier for cheese of not less than
5 cc/100 in^2 /24 hours at 22.8 ° C (73 ° F) and
50% relative humidity. Cheese variety and
conditions of storage can affect the necessary
barrier requirements, and a barrier of less
than 1 cc/100 in^2 /24 hours may be necessary
in some cases.
As indicated earlier, the extensive gas
evolution of Emmental (Swiss) varieties may
inhibit mold development. Films for use in
these cheeses often have relaxed barrier attri-
butes, which allows diffusion of CO 2 from
the package and prevents package rupture.
The hydrophilic properties should be consid-
ered when selecting a fi lm. Storage at high
relative humidity or direct contact between
a hydrophilic material and cheese portion
can adversely affect the water vapor and
gas barriers. Decreasing temperature gener-
ally improves the barrier characteristics of
fi lms; the extent of change depends on the
material.Seal Leaks
Seal leaks are probably the most common
and important factors leading to mold devel-
opment in fi lm - packaged cheese. They have- Leakage through punctures or chafed
areas of the fi lm - Permeation of oxygen through the fi lm
The oxygen - loss factors are absorption of
oxygen by cheese (bacterial action, reducing
systems) and utilization of oxygen by mold
growth.
Entrapped Oxygen
Shrink fi lms generally provide close fi lm
contact with the cheese body, resulting in
minimal oxygen entrapment. Very soft or
non - uniform cheeses (mozzarella, pizza), in
which entrapped oxygen may be a problem
due to irregularities of the cheese, are com-
monly packaged in shrink fi lms. Process and
artifi cial cheeses can be hot - poured directly
into packaging materials. This also provides
close fi lm contact with the cheese. Sliced
processed cheese may be rolled off cold
drums, sliced, and automatically packaged.
Alternatively, it may be hot - packaged by
extrusion into a tube and then sealed, com-
pressed into a fl at strip, cooled, cut, and over-
wrapped in a polyester fi lm.
The concentration of entrapped oxygen
can decrease within a package due to evolu-
tion of gases during cheese ripening. It has
been observed that oxygen concentration
declines rapidly after the fi rst few days of
storage, whereas CO 2 concentration increases
in certain types of cheeses. In general, no
mold growth is observed when the oxygen
concentration in the gas underneath the
wrapper is less than 2% and that of CO 2 is
greater than 27%. Most cheeses produce a
small amount of CO 2 ; the extent of its evolu-
tion depends on the type of microorganisms
present. However, Swiss - type cheeses prod-
uce extensive CO 2 during ripening and stor-
age, so mold development due to entrapped
oxygen is unlikely.
Entrapped oxygen also may be utilized by
the cheese. Freshly packed cheddar cheese
possesses considerable reducing power and