Page 176 - Small Animal Clinical Nutrition 5th Edition

178 Small Animal Clinical Nutrition

manufacturer receives ingredients depends on the physical
VetBooks.ir makeup of the manufacturing plant and how much and what
kind of storage units are available. Most ingredient suppliers
offer multiple shipment options to best suit the needs of the
manufacturer.

Grinding
Ingredients supplied as large particles may need to be ground
before mixing (pregrinding) to enhance their nutritional and
process characteristics. Generally, the larger the particle size,
the more likely that pregrinding is necessary. A good example
of this type of ingredient is whole yellow corn. A milling
device known as a hammer mill is most often used to grind
raw materials and the final dry mix. The hammer mill is a
large capacity-milling machine that contains multiple free-
Figure 8-12. Process flow diagram for dry commercial pet food swinging steel hammers and a sieve or screen that can be
production. changed to create the desired particle size. Centrifugal force
spins the hammers against the screen, pulverizing whole
Raw Materials grains to 1,000 microns or less (Rokey, 1995).
Ingredients used to manufacture pet foods often are received in The entire dry mix is usually ground to achieve the desired
bulk (90,000 kg by train cars; 25,000 kg by truckload) as in the uniform particle size (e.g., usually the consistency of coarse
case of grains or meat meals, which are the primary ingredients flour). A uniform size is critical for proper water absorption,
of any dry product, or in 25- to 50-kg bags for ingredients used optimal passage through the extruder and thorough cooking by
in small proportions (e.g., trace minerals, crystalline amino the extruder (Rokey, 1995). Large uncooked particles may clog
acids and vitamins). Ingredients received in bulk are usually the extruder die and may reduce palatability, product appear-
stored in silos until needed. Generally, the form in which a ance and digestibility.

Figure 8-13. The same steps are used in bread baking and extrusion cooking: 1) mixing (preconditioner), 2) kneading (extruder barrel), 3)
proofing (extruder barrel), 4) shaping (die plate), 5) rising (die plate) and cutting (rotating knives).