Page 185 - Small Animal Clinical Nutrition 5th Edition

Commercial Pet Foods 187

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Figure 8-22. A diagram of the continuous process flow of the
hydrostatic retort. Cans enter the feed leg and are brought up to
temperature in the bring-up leg, then enter the sterilization leg
(steam chamber) where the product is sterilized and finally enter
the bring-down leg and cooling leg where the cooling process is
completed.

These temperatures are not hot enough to continue cooking
the cans’ contents.

RETORTS
Retorts have been designed to process all types of packages
Figure 8-23. In a batch retort sterilizer, cans are loaded, processed
from baby food jars to cans that hold more than 3 kg of fruit or and cooled in baskets (batch-type manner) rather than in a continu-
vegetables. Several types of retorts are used by the pet food ous process as occurs in hydrostatic retorts.
industry, but hydrostatic and batch retorts are most common.
The hydrostatic retort is a continuous process machine that processed and cooled in a batch-type manner. These sterilizers
conveys the cans on carriers that are connected to a chain drive can be configured vertically or horizontally; the vertical config-
in a tower layout. The cans advance through the various legs of uration is used most commonly in the pet food industry
the process in a continuous loop transitioning from water to (Figure 8-23). Some batch retorts have three to four baskets
steam and back to water again (Figure 8-22).This type of ster- that are filled and lowered into the retort for processing. The
ilization method is called hydrostatic because the steam pres- baskets must then be lifted out of the retort, the cans cooled
sure, and therefore temperature, is controlled by water pressure and sent for labeling. The benefit to this system is that the
in the water legs. Because the cans slowly rotate on their sides headspace is kept constant because the cans are oriented verti-
throughout the process, the gas bubble is evenly distributed on cally without agitation, resulting in a uniform appearance. The
the outside surface as the cans’ contents. This is evident by the disadvantages are that the system is labor intensive and has a
uniform appearance of pâté and loaf-type products produced in low production capacity.This system works well for test batch-
this manner. es and pilot work.
Batch retort sterilizers, as the name implies, are loaded, The automated crateless system is a newer batch retort. In