Retort Control in the Food Industry using the C1960
AG/RCP–006_2
5
▲
The Cook Period
This period is essential in order to properly cook the product, thereby destroying
any organisms that could later spoil it. These organisms, called spores, are able to
withstand several hours of atmospheric boiling water temperature, but are destroyed
in a short time at a temperature of 116 to 121
°
C (240 to 250
°
F).
The correct temperature and the duration of the cook period are equally important in
achieving the desired objectives. Overcooking not only increases costs, it also causes
loss of taste or appearance of the finished product.
▲
Pressure Relief Period
The retort pressure, attained as a result of cooking at high temperature in a closed
vessel, must be relieved before the product can be safely removed. If the retort has
been filled with small cans, the pressure can be reduced to atmospheric immediately
in a process known as
blowdown
.
However, if the retort contains large cans, it is necessary to lower their internal
pressure before blowdown takes place to prevent them from exploding or distorting.
The reduction of internal can pressure is obtained by circulating cooling water through
the retort whilst maintaining retort pressure at the value attained during cooking by
introducing pressurizing air. When can internal pressure has dropped to a safe
value, indicated by the temperature of the cooling water leaving the retort dropping
to a desired value, blowdown can take place without the threat of can damage.
▲
Water Cooling Period
In order to increase retort production, small cans are removed from the retort
immediately after blowdown and immersed in a cooling canal prior to labeling. Larger
cans, after cooling in the retort, may require further cooling in the same manner. The
determining factor is the temperature of the product at the time it is packed in cases.
This temperature is critical because cans that are too cool may rust externally, while
those that are too warm prior to being cased and closely stacked in storage will
cool too slowly and will be damaged by “stack burn”, or spoiled by creating
conditions that encourage the growth of thermophile bacteria.
The cooling canal is a rectangular-shaped, cold-water filled channel near the retort
through which the can-filled baskets are pulled after they are unloaded from the
retort. The length of the canal, the temperature of the water, and the speed of the
conveyor determines the final can temperature. When a cooling canal is used instead
of the retort for final cooling, the reduced retort-time cycle increases production.
Fig. 4 Sparge Tubes