Aquatic feed processing with twin screw extrusion

27 September 20186 min reading

Fish is known as a high value food for humans, with health benefits that include long chain unsaturated fatty acids, vitamins & minerals and a well-balanced protein supply. In 2013, 3.1 billion people received 20% of their animal protein from fish origin. Therefore, fish feed processing technology plays a particularly important role to this industry.


Alain Brisset Feed Extrusion Expert   THE CHALLENGES OF AN ESSENTIAL EXPANDING MARKET The most recent study from the Food and Agriculture Organization of the United Nations [FAO- 2016 (1)] confirms that 50% of the consumed aquatic animals in the world (including finfish, mollusks & crustaceans) come from aquaculture.

With a world population of 7.3 billion people, the average fish consumption (including mollusks and crustaceans) was estimated in 2014 to be 20,1 kg/capita. Obviously, the process of feed manufacturing for finfish and shrimp represents a key issue for insuring the delivery of consistently high quality granulates for these intensive breeding processes; for example, it is estimated that over 60% of the production expenses for farmed salmon comes from the feed cost.

Additionally, we have to face challenges such as limited resources of fish flour and fish oils worldwide and a temperature increase of the earth’s environment creating irregular conditions for fish capture, uncertain cereal and pulse harvests on earth (used more & more to partially replace fish meal in recipes), and the risks to delicate offshore aquaculture breeding facilities (waves, winds, storms, currents, pollution..).

THE POTENTIAL OF TWIN SCREW EXTRUSION Fish is known as a high value food for humans, with health benefits that include long chain unsaturated fatty acids, vitamins & minerals and a well-balanced protein supply. In 2013, 3.1 billion people received 20% of their animal protein from fish origin.

Therefore, fish feed processing technology plays a particularly important role to this industry. It requires: - Easy adaptation to any change in raw-material composition: moisture content, lipid content, particle size distribution, de-mixing of powdered materials. These are due to various sources of raw materials (for example, soy flour can be purchased in many parts of the world), transport and storage conditions, grinding process, … - Flexibility to adjust the sinking/floating properties of the granulates to follow as closely as possible the food habits of each animal family, - Processing a wide range of recipes to respond to industry demand for foods with low or high amounts of lipids, vegetable proteins, or various sources of protein to meet the specific nutritional fish requests and adapt to rapid environmental fluctuations, - Flexibility to adjust the shear, cooking and shaping conditions in the extruder and apply precise drying and coating parameters during the entire production process, - Insuring a high hygienic standard, to avoid any contamination during the feed manufacturing process.

Taking these considerations into account, combined with good manufacturing/breeding practices, scientific education and adapted legislation, we can nurture high quality aquatic animals that offer health benefits to people around the world–using local production to ensure low carbon footprints and maintain reasonable sales prices.

TECHNOLOGY OF CO-ROTATING TWIN SCREW EXTRUDER Single screw extrusion technology has offered a simplified method of continuous cooking of doughs under controlled processing conditions for many decades. 60 years ago, some pioneers developed an alternative process: co-rotating twin-screw technology applied to the food industry (2), which offered much greater flexibility than single screw machines due to its intensive mixing ability with precise shear and temperature control. [“Extrusion Processing Technology”(3)]

With the evolution of electronic PLC’s, mechanical features, gauges, drives, metallurgy, together with heavy R&D investment, these pioneers offered the fish feed industry more sophisticated systems, allowing the industry to move quickly into new areas–such as recipes with high amounts of fat and vegetable protein (4, 5)

To illustrate this trend, S. KAUSHIK, world expert in aquaculture, recently presented the Opportunities and Challenges of the Global Aquaculture (6)

CLEXTRAL (7), a major player in Twin Screw Technology for Food & Feed applications has launched innovations which offer even greater possibilities to the fish farming industry to process original recipes and use raw materials such as new pulses, proteins, insects, krill meals and possibly processed animal proteins, seaweeds, ..Etc.

One of these innovations relates to Intelligence of the machine and the ability of the auto-adaptive extruder to adjust to potential raw material variations. For example, the Advanced Thermal Control (ATC) is a self-learning, proprietary software solution that ensures absolute precision in temperature control of the barrel assembly of the Evolum+ extruder.

ATC continuously monitors production parameters to ensure process and product consistency. ATC is proven to enhance process stability up to 70%, with energy savings averaging 20% by eliminating repeated heating/cooling cycles to maintain process temperature set-points in all circumstances. Combined with automatic start up and shut down procedures, this system represents a powerful tool to enhance the productivity of the extrusion line.

PRECONDITIONING: higher efficiency and improved product texture Another innovation refers to the preconditioning process, a key operation in fish is feed manufacturing. Preconditioning allows moistening of the powdered mix and pre-gelatinization of the starch molecules through the addition of water and steam; thereby increasing the pellets’ water stability, enhancing production capacity and reducing wear on the extruder.

This patented, innovative Preconditioner+ improves heat and mass transfer to the product due to the Advanced Filling Control device (AFC); it interacts directly with the material inside the mixing chamber and enables the filling ratio to be adjusted. The AFC system uses an exclusive conveying screw inside the tank and adjusts the flow by a partial and controlled recycling of the material being processed from the outlet to the entry point, thus intensifying the specific preconditioning functions.

Laboratory tests have proven that the final hardness of fish feed pellets increased between 7 % and 29% using the same recipe and modifying the preconditioning and extrusion parameters versus adjusting the bottom-screw speed.

During the cleaning procedure, the bottom-screw rotation is reversed to facilitate the cleaning procedure of the preconditioning chamber.

HYGIENE Finally, today much attention is focused on hygienic extruder design as food security is a key parameter for the fish feed and food industries.

Fish feed manufacturers want to be able to clean their extruder from the outside using hot water and sometimes with cleaning agents. The stainless steel, hygienic Evolum+ frame structure is designed to avoid water stagnation and all the extruder areas are easily accessible. The internal processing assembly of the twin-screw extruder must be cleaned easily as well: the complete quick barrel extraction device is today a paradigm to the industry. It offers access to the screws and barrels in only few minutes and is a state-of-the-art solution that simplifies preventive maintenance, wear monitoring and cleaning processes.

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