The aquafeed manufacturing industry is widely recognised as one of the fastest expanding food industries in the world. Fish meal is the main protein source in aquafeed, but supply is limited, which means that alternative sources must be used. From a processing point of view, extrusion is the most efficient way of turning plant protein into fish feed. Twin-screw extruders offer a definite advantage in this.

1. Digital Re-print - March | April 2011
Aquafeed twin-screw extrusion processing
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2. FEATURE FEATURE
Twin-screw Extruder/Thermo- ing the cooking
mechanical cooking parameters it is
The preconditioned feed mix is submit- possible to main-
ted to the controlled thermo-mechanical tain more precise
cooking which is the main stage in extruding limits on product
aquafeeds. characteristics
Thermo-mechanical cooking of the feed such as density to
mix in an extruder requires two energy achieve floating,
TECHNOLOGY
inputs: low sinking and
- Mechanical energy input defined mainly sinking pellets. ENGINEERING
by screw speed and screw configuration, Expansion
which can be varied extensively to
modulate this energy
can be further
enhanced by SERVICE
- Thermal energy input determined by injection of steam
direct steam heating and indirect barrel into the extruder Visit us on
heating barrel, which VICTAM
Twin-screw extruders are able to process increases thermal 2011
a large range of raw materials consistently energy inputs. Booth D 063
with high levels of flexibility and pumping Where higher
efficiency. The intermeshing screws allow product densities
handling of viscous, oily, sticky or very wet are required for
materials and provide a very intense mixing, certain feeds, the
where macromixing and micromixing result extruder barrel
in a very homogeneous melt with excellent can be configured
lipid binding. to include a vent
aquafeed twin-screw extrusion
In a co-rotating twin-screw extruder, stuffer to reduce
throughput and screw speed are not inter- product tem-
dependent; for a given formulated feed mix, perature through
the multiple operating points combine with a evaporative
processing high control efficiency of the barrel tempera- cooling. Vacuum
ture and consequently ensures efficient con- regulation
trol of the expansion of the melt at the die. be connected to
can
In comparison with single screw extruder, the vented stuffer Benefit through Technology www.petkus.de
twin-screw is more responsive. By vary- barrel to28.02.2011
increase
Versatile twin-screw extruder ideal for aquafeed 511314Grain_Feed_190x58gb_4c:Dammann Services 13:25 Uhr Seite 1
T
he aquafeed manufacturing industry dients can be divided in three groups: Extrusion cooking
is widely recognised as one of the - Nutriments: to meet the requirements This step of the aquafeed processing line
fastest expanding food industries of fish can be divided into three stages: precondi-
in the world. Fish meal is the main - Functional product: binders, expansion, tioning, thermo-mechanical cooking and die ... Follow the leader in bulk goods handling, dust-extraction and ventilation plants
he
est t
protein source in aquafeed, but supply hardness texturization-shaping The QUICK CONNECT pull-ring makes the acclaimed Original Quality to a Modular Design
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Requ talogue!
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is limited, which means that alternative - Palatants and attractants Jacob modular pipe system even more economical • Straight welded, lipped-end pipes and components. NEW Hotline 80 or at
u
1 955systems.e
sources must be used. From a process- Preconditioning for installation. In new plants for animal feed, • ø 60 mm to ø 800 mm in a standard range. (0)57
+49 acob-pipe
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www
ing point of view, extrusion is the most Pre- grinding / grinding The primary objective of precondition- pharmaceuticals, chemicals, food, glass, semi- • Larger diameters / special requirements upon request.
efficient way of turning plant protein It is essential to decrease the particle ing in an extrusion cooking process is to conductors or environmental technology as • Larger than ø 350 mm also available with flange connection. Fr. Jacob Söhne GmbH & Co. KG
Germany
into fish feed. Twin-screw extruders size to a powder state before mixing the initiate the hydration and the cooking of well as for upgrading existing layouts user- • Powder coated steel or hot-dipped galvanised steel as well as stainless steel. Phone +49 (0)571 95580
www.jacob-pipesystems.eu
offer a definite advantage in this. ingredients. Post grinding achieves the best the feed mix. The dry feed mix and the friendly system installation becomes precise • 1 - 3 mm wall thicknesses.
final performance. liquid parts (slurry, oil…) are separately and easy due to the great versatility of • Shock-explosion certified pipes and components available.
The goal for production of aquatic feed In addi- mass-produced pipe components. • Up to ø 400 mm normally dispatched immediately from stock.
is to manufacture a nutritionally complete tion, parti- Table 1: Indication of final pellets bulk density /floating or sinking properties:
EUROPE’S NO. 1 IN MODULAR PIPEWORK SYSTEMS – Used in all industrial sectors
product that achieves the desired product cle size is Feed characteristics Fast sinking Slow sinking Neutral floatability Floating
characteristics. While all aspects of the proc- dependent
ess are important, a number of the unit on the final Bulk density gr/l >640 540 - 600 480 - 540 <450
operations of the manufacturing process are size of the
critical to achieve this goal. pellets. For die openings up to 3mm, the introduced into the preconditioner where
These operations are organized along the largest particle size should not be larger they are continuously mixed, heated and
process as follows: than 1/3 of the die opening. Smaller particles moisturized by the injection of water and
improve pellet durability, water stability and steam. The intense mixing created by the
Selecting Raw materials decrease pellet friability. rotating double shafts adjusting paddles
The first step of the aquafeed process line assembly maintains the feed particles at
is feed mix preparation–selecting a combina- Mixing the optimum moisture between 20–23
tion of ingredients with the proper levels of Mixing accuracy depends on the proper- percent and temperature around 90°C
essential nutriments required for the animal ties of the components, which should be during 2 to 3 minutes average retention
species. The formulation is also based on similar in density and particle size. Additives or time. Preconditioning helps to maintain
cost, availability and chemical composition of micro ingredients are added at this step. The starch and nutriment quality and allows
the raw materials. Ingredient selection has a required mixing time depends on the type of increased extrusion capacity, while reduc-
direct impact on final product characteristics. mixer technology used, as well as dry ingredi- ing extruder screw wear and mechanical
According to their functions, these ingre- ent mixing time before liquids are added. energy requirements.
34 | march - april 2011 Grain &feed millinG technoloGy Grain &feed millinG technoloGy march - april 2011 | 35

3. FEATURE
Table 2: Species / product characteristics example: temperature must be lowered to
Species Salmon Trout Cod Carp Tilapia Cat fish Shrimp
approximately 50°C otherwise, the
water in the pellets will start boiling
Final pellet total fat % >35 15 - 35 15 - 25 5 - 15 5 - 10 5 - 10 <5 because of the vacuum applied (0,2
bar absolute pressure)
Texture bulk density Slow sinking Slow sinking Slow sinking Floating Floating Floating Fast sinking
The vacuum coating process
allows the oil to be drawn into the
the product density even further with higher temperature and humidity of the drying pellets by capillary forces ensuring perfect
degrees of evaporative cooling. air control of the pellet oil absorption and the
- Pellet related factors: depending addition of more oil into the product while
Texturisation-shaping of aquafeed on the initial moisture content and ensuring a dry surface and limiting the oil
pellets temperature, porosity and size of the discharge in the natural environment.With
The end of the last barrel of the extrusion pellet this technology it is possible to achieve
chamber is capped with a final die, which The drying parameters must be applied more than 40 percent total product fat
serves two major functions. First, the die to remove the moisture while maintaining content.
restricts product flow thereby causing the pellet quality. (that is, limiting fine generation,
extruder to develop the required pressure maintaining palability and pigment ingredi- Cooling of pellets
and shear; and second, the die shapes the ents, minimum energy losses and moisture On completion of the fat coating process,
extrudate. variance) the pellets are cooled and sieved before
A face cutter is used in conjunction with Floating and sinking product character- the final conditioning. Cooling is required to
the die, which consists of cutting knives istics can be influenced by the drying con- remove excess heat to prevent condensa-
revolving in a plane parallel to the face of the ditions. Elevated temperatures can lower tion from occurring in the storage bins or
die. The relative speed of the knives and the residual moisture and improve floatability. the final packages. At this stage, the aquafeed
linear speed of the extrudate result in the Sinking aquatic feeds are preferably dried pellets’ temperature should be cooled down
desired product length. at moderate temperatures until the storage to a temperature range close to the storage
Die design –cutter assembly is one of the stability of the pellets is obtained. or transportation temperature.
most important sub-units of the aquafeed In aquafeed processing lines, extruded pellets
processing line as it determines the physical are generally dried on one of the following Conclusion
quality of the final product. dryer designs: Clextral systems can easily produce high
Micro-aquatic feeds often used as starters - Horizontal belt dryer energy feed, allowing a delicate balance of
are products smaller than 2.0mm. - Vertical counter flow dryer proteins, oils and carbohydrates, processed
Specific die design allows direct extrusion - Fluidized bed dryer for total digestibility with no waste. It’s the
of micro-aquatic feeds down to 0.5 mm. and recently, rotary dryer technology: right formula for high quality products that
Products are pasteurized and very nicely the Rotante type rotary dryer was previ- “turn feed into flesh”. Output range from
shaped. Water stability is excellent and float- ously designed to process other cereal 25 to 30,000kg/h.
ing products are possible. Raw material must based products. Through gentle stirring Thanks to twin-screw extrusion, high
be carefully ground and sifted to achieve of the product to eliminate build-up, the quality aquafeed pellets are achieved:
proper particle size before extrusion. “Rotante” design achieves excellent heat • denaturing of proteins
Macro-aquatic feeds with sizes up to exchange close to that obtained in a flu- • gelatinization of starch
30 mm emphasize the physical quality of idized bed. Other advantages include a • reduction of anti-nutriments
the pellet and the related process history. perfectly controlled residence time with • flavouring improvement
A combination of twin-screw mixing and virtually no dispersion, of type FIFO (First • protein/lipid complexes
cooking, special Rotante drying technol- In, First Out) and precise product moisture • increase digestibility
ogy and dedicated die design will produce homogeneity at dryer output. To master • texturization, shaping
pellets with sufficient resistance to avoid the drying barema, temperature & moisture • expansion, density
breakage and dust, yet porous enough to are precisely regulated, which helps to • hygienic, salmonella-free pellets
deliver all the nutrients to the digestive prevent product cracks. Clextral’s Research
system of the fish. & Test Center in France is equipped with a Challenges ahead
“Rotante” and tests have proven this dryer The major challenge is to expand sustain-
Pellet drying to be particularly efficient for fish feed, able aquaculture to achieve enhanced food
The primary purpose of reducing pel- ensuring complete homogeneity of drying security and economic development for the
let moisture level is to make the product with lower energy consumption. global population as a whole. In the context
shelf stable. Most aquatic products are best of substitution of fishmeal with plant-derived
processed at moisture levels between 20-28 Fat coating feedstuffs, extrusion technology has a role to
percent. Moisture levels as low as 20 percent Fat addition is commonly done after play in reducing the level of anti-nutriments.
can be required for some light density aqua- dryer, while the dried extrudates are still (Kaushik 2006)
feed pellets. Some moisture is lost during warm. For that, the oil is sprayed directly Twin-screw extrusion technology has
flash evaporation as the cooked product on pellets. During this stage, fats, pigments, contributed and will carry on the tremen-
exits the die. Then, the products are con- attractants and even powdered ingredients dous improvements, both in terms of nutri-
veyed to the dryer to reduce the moisture can be added. tional value and in terms of physical quality
content from 18 – 24 percent down to This processing stage can be implement- characteristics of the aquafeeds.
8 – 10 percent, this corresponds to a water ed two ways: With the continued economic develop-
activity (aW) around 0,5 – 0,4, in order to *Under atmospheric pressure: the added oil, ment of aquaculture, each venture, and
obtain satisfactory water stability. temperature around 40°C, is diffused from species will be subject to important research
the surface of the product to the centre and is efforts so as to obtain, under acceptable eco-
Several factors control the water stored in cavities in the pellets’ structure nomic conditions, efficient feeds delivered at
removal from the aquafeed pellets: *
Under vacuum pressure: this consists of a the right time, which are non-polluting and
- Air related factors: depending on the air closed system with a mixing shaft or screw which care for the health of the fish as well
flow characteristics around the pellets, and spray system in the top. The product as the consumers.
36 | march - april 2011 Grain &feed millinG technoloGy

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5. LINKS
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