PROCESSING FISH FEEDS
Pelleting and Extruding
Steam pelleting, through compression, produces a dense pellet that sinks rapidly in water. Extrusion is a process through which the feed material is moistened, precooked, expanded, extruded, and dried, producting low density feed particles that float in water. Steam pelleting is significantly less expensive than extrusion; however, extruded feeds are very popular with catfish farmers in the United States because they allow the feeder to observe the fish feed (see Figure 5.1).
Steam pelleting involves the use of moisture, heat, and pressure to agglomerate ingredients into larger homogeneous particles. Steam added to the ground feed mixture (mash) during pelleting partially gelatinizes starch, which aids in binding the ingredients. Generally, an amount of steam is added to the feed mixture to increase moisture content to approximately 15% to 18% and temperature to 70°C to 85°C before it is pressed through the pellet die. The moisture in the pellets is reduced by forcing nonheated air over the surface of the hot pellets immediately after they leave the pelleting apparatus (see Figure 5.2).
PROCESSING FISH FEEDSPelleting and ExtrudingSteam pelleting, through compression, produces a dense pellet that sinks rapidly in water. Extrusion is a process through which the feed material is moistened, precooked, expanded, extruded, and dried, producting low density feed particles that float in water. Steam pelleting is significantly less expensive than extrusion; however, extruded feeds are very popular with catfish farmers in the United States because they allow the feeder to observe the fish feed (see Figure 5.1). Steam pelleting involves the use of moisture, heat, and pressure to agglomerate ingredients into larger homogeneous particles. Steam added to the ground feed mixture (mash) during pelleting partially gelatinizes starch, which aids in binding the ingredients. Generally, an amount of steam is added to the feed mixture to increase moisture content to approximately 15% to 18% and temperature to 70°C to 85°C before it is pressed through the pellet die. The moisture in the pellets is reduced by forcing nonheated air over the surface of the hot pellets immediately after they leave the pelleting apparatus (see Figure 5.2).
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