Extrusion has been used to prepare animal feeds for many years and has proved to be an effective means to cook and shape raw ingredients into very specialized products, especially in the highly competitive aquatic feed and pet food market where size, shape, mouth feel and degree of cook are important factors in the success of the product. As a new technology to produce feed, extrusion processing means that in the environment of high temperature(110-200°C), high pressure(25-100kg/cm2) and high water content(10%-20%, even 30%), fish feed stuffs mixture, through heating tempering, deep mixing and particles formation, would puff and afterwards shape into extruded feed when out of fish feed extruder machine.
On the basis of density variation and puffing degree, extruded fish feed can be segmented into floating fish feed and sinking fish feed. Currently, the floating feed is the most widely used extruded feed in fish farming, and it has relatively mature technology. That is, floating extruded feed pellets are both produced through modulator for heating and modulation, via continuous mixing process to fish feed raw materials after entering extruder machine, heating up, pressurizing, ripening, extruding and then puffing and granulating. Compared with floating fish feed, sinking pellets has different requirement on fish feed manufacturing technique because of the diverse request for specific gravity, even if when they use the same fish feed machine. Briefly, fish feed extrusion process requires a hammer mill to grind raw materials, mixer to blend raw materials including vitamin-mineral premix, the wet type fish feed extruder with steam preconditioner (yes, steam is equired for quality pellets) and cutter head to shape the pellets, and finally a dryer-cooler to ensure pellet shelf-life and stability.
Fish feed extruder
Compared with traditional powdery compound feed and pelleted feed, extruded fish feed can well overcome some conventional disadvantages, such as bad water stability, feed disappearing and waste, water quality pollution and so forth. In especial, floating extruded feed makes feeding management convenient because aqua feed can float on water for a long time and there is no need to set feeding station, just at fixed point to feed. Moreover, fish farmers can observe the food intake situation of their fish, adjust feeding quantity timely and master fish growth and health status in time. In a word, extruded fish feed can contribute to scientific feeding and management, saving much time and boost labor productivity. So as the ideal fodder of modern aquaculture, extruded aqua feed has quite good market prospect and wide application fields.
Generally, different aquatic culture animals have various ingestion features, and that is the principle should be followed when choosing diverse extruded fish feed types. For instance, river crab is accustomed to looking for food in water bottom and its eating speed is relatively slower, then aqua feed should not be too hard or too firm, and also need to reduce the loss in the nibble process. By this token, extruded sinking feed is more suitable for river crab because it is easy to soften in water and fit for nibble with longer water resistance time and less crumb loss, decreasing feed waste and water contamination.
In addition to those benthonic animals, most aquaculture species can ingest floating extruded fish feed very well, not only for the famous-special fish species (like aquarium fish), but also for conventional cultivation (like grass crap, crucian, catfish, tilapia and so on). What’s more, in the aspect of breeding method, floating fish feed has more extensive applicability, that is to say, for pond fish farming, culturing fish in rice field, running water fish culture, cage culture, and especially for fish farm with lower breeding density, extruded floating feed has much more superiority than other fish feed.
German equipment manufacturer, Brabender, has been working with research institutions and aqua feed producers on novel feed formulations for a range of farmed fish and crustacean species in its application lab. Whether floating, suspended, or slowly sinking, laboratory extruders make it possible to test aqua feed produced from various raw materials on a reduced scale, added the company.
With new raw materials like insect protein or microalgae, cost is a huge issue though. “Undertaking product development with such raw materials, if you use a large extruder, you will need a lot of raw material, and [chances are] you will waste a lot of it, so it much better to carry out trials with expensive feed ingredients on a small-scale extruder, producing samples that way,” said Landers.
“For floating feed, including suspended or slowly sinking feed, we operate with hot extrusion at temperatures over 100°C. This results in good pellet expansion. For sinking feed, i.e. production of quickly sinking pellets with minimum expansion, cold extrusion is the preferable method,”
Feed formulators and academic researchers want to determine which sources of protein are compatible with extrusion, along with the percentage of protein and carbohydrate within those protein sources. Whether or not a product expands depends on, among other things, the moisture content and the percentage of protein, carbohydrates, and fat in the initial mixture, they said.
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