FBA Issue 4: September / October 2005
Extrusion of aquatics feeds
by Joseph P. Kearnes
Production of aquatic feeds fall into one of four production categories: floating feeds, slow sinking feeds, sinking feeds and soft moist feeds. Extruders are also capable of producing ingredients that can be used in aquatic feeds. The production process utilizing an extrusion cooker for all of the above categories is very similar.
The diagram above shows the following processing areas: raw material area, extrusion processing area, post extrusion processing, drying and cooling processing, post-drying and cooling processes.
Raw material area and processes
In this area, formulations are stored and prepared for processing.
There are a number of methods and strategies for preparing raw materials, which can be completely automated or labour extensive. In either case, the raw materials are stored in bags or in bulk. The ingredients are weighed, mixed, passed through a final grinder and sieved prior to entering the extrusion cooker. This ensures the removal of particles that could plug the extruder die.
For products smaller than 4 mm, the raw material must be ground so that a minimum of 99 percent passes through a screen of 840 micron opening (US Standard 20 Mesh). If this specification is met, then the geometric mean diameter of the particles will be approximately 40 microns (about 40 US Standard Mesh).
In producing semi-moist aquatic feeds, liquid ingredients are used to increase the moisture content and control water activity. Liquefied raw materials may be used when producing dry feeds. These are prepared and mixed before being pumped into the extruder system.
Vitamin solutions and marine oil top coating are then applied to the surface of the final product after extrusion and drying.
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