344 Chapter 19
the headspace (Mathlouthi 1986 ). Exhaustion
is also carried out by heating, mechanical air
removal, or by steam injection; if the last is
applied, cans are immediately sealed. During
can cooling, a vacuum is generated due to
steam condensation, but if the headspace is
excessive, a vacuum is not formed. Also, if
air is not completely removed from the can,
bacteria such as Bacillus subtilis and B.
mycoides can grow.Thermal Treatment
This includes three cycles: heating, tempera-
ture holding, and cooling. Time - temperature
relationships during the heating phase are
calculated according to microbial destruction
and enzyme inactivation criteria, as described
earlier, whereas cooling is applied for practi-
cal reasons, such as handling.
Commercial sterilization can be carried
out by several methods, all based on the
theoretical principles already discussed.
The main methods are batch still retorts or
continuous operations.
The batch method is still used in large
industrial operations handling cans and glass
jars, and all types of containers in small oper-
ations. However, Crang and others (2006)
describe a process for bottling and canning
sausage meat with domestic equipment. The
authors concluded that some of the products
in jars of thicker glass require a longer pro-
cessing time to give the same level of safety.
The method basically consists of loading the
retort, closing it, and fi lling it with steam.
The second cycle, temperature holding,
depends on the time - temperature relationship
to satisfy the processing parameters (D, z, F).
Cooling is carried out by closing the steam
valves and injecting cold water into the
retorts. Care must be taken to gradually
reduce the retort pressure in order to avoid
deformation or breaking of containers.
Continuous retorts are generally used in
large operations. The retort pressure differ-
ence is controlled to avoid deformation ofaccording to certain formulations (curing,
cooking, smoking, etc.). In the case of lun-
cheon meat, an emulsion is prepared and the
can fi lled with the raw meat batter.
Can Filling
Heat penetration depends on the solid - liquid
ratio and the food distribution inside the can.
In canned sausage distributed along the verti-
cal axis, a convection - conduction mechanism
takes place; if the solid material is loosely
packed, the heating rate will be faster. In
general, 30% of the can volume should be
fi lled with a liquid, such as brine, to provide
a high heat - transference rate. The brine is
always added after the solids; in the case of
pastes, the fi lling operations are generally
carried out with automatic fi lling equip-
ments; care must be taken not to incorporate
bubbles. The headspace must be 0.5% of
total can volume; effi ciency during the
exhausting phase depends on the headspace.
Exhausting
Oxygen is a very reactive substance that acts
on food components. It modifi es color, fl avor,
and overall quality. Air removal from the
headspace is necessary to prevent these
changes, as well as to improve the heat pen-
etration rate and reduce the growth of aerobes.
Vacuum formation in the can also prevents
the risks of an increase in the pressure inside
the can during heating, and possible can
blowing or deformation.
Exhausting is carried out at normal atmo-
sphere or under vacuum. If large meat pieces
are put into the can, exhausting during fi lling
and sealing is enough to evacuate the air;
however, if pastes are canned, air can be
incorporated if this operation is not carried
out under vacuum. Cans are heated at 75 ° to
95 ° C immediately before fi lling and sealing;
alternatively, the cans are placed in a con-
veyor where they are heated at 85 ° to 95 ° C,
removing approximately 90% or more from