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Product Transfer Many different conveying devices are employed in the pet food manufacturing facility. Variations in conveying principles include the following:

1. Eliminate where possible (the principle of gravity can be an asset) 2. Consider hygienic design for minimal material buildup and ease of cleaning

3. Explore emerging technologies such as closed loop systems 4. Evaluate heated air intakes and heated transfer points

The most popular systems for conveying pet food products from the extruder to the next unit operation (usually a dryer) are pneumatic transport systems (see Figure 3). Although these are efficient conveying systems, the air for transport is a large volume (over 8,000 cubic meters per hour for a standard pet food line) and it is drawn off the floor of the plant just underneath the die/knife assembly of the extruder. The extrusion process is often the critical control point as product temperatures are usually well above to kill point for salmonella. Pasteurized product discharged off the extruder can be recontaminated by plant air draw off the floor into the pneumatic transport system.

Figure 3: Typical Pneumatic Transport System for Pet Foods

Equipment Design and Construction Equipment for the manufacture of pet foods is designed to minimize dust, product buildup and accumulation, exhaust streams and emissions, and easy access for inspection and cleaning. Transitions between preconditioning devices and extruder inlets are available in dust-tight designs to reduce fugitive dust and to minimize leakage and spillage. Extruders are mounted on hygienic, stainless steel frames (Figure 5) which minimize horizontal surfaces and eliminate corners which could be difficult to clean and where product could accumulate. Dryers and coolers are designed to reduce emissions, minimize product accumulation, control product cross-contamination, and for easy access for cleaning and inspection.

The product transport systems shown in Figure 3 are being replaced by hygienic transport systems (Figure 4) which have the following features:

1. HEPA filter air intake 2. Burn-out sanitizing mode

3. Strategically located temperature sensors 4. Positive pressure in die/knife area 5. Positive pressure at sampling port

The hygienic transport systems draw the air for transport from a location away from the floor of the plant and through a HEPA filter to remove bacteria-laden dust.


Recycling of Under-Processed Product Closed loop systems (WRS or Waste Recycling Systems) are available which capture, contain, and recycle fugitive and under-processed material. Wet or dry product that has not been exposed to the required temperatures for critical control points can be collected and recycled into the extrusion system.

Control Systems and On-line Testing Devices The digital age has brought control technology to the pet food process where operating parameters can be stored, applied, and tracked as required for certain product specifications. Product monitors and on-line testing devices decouple personnel from direct product contact and can measure a host of product properties:

1. Bulk density 2. Moisture

3. Temperature 4. Photographic recognition

Figure 4: Hygienic Pneumatic Conveying Systems

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