The document discusses the advantages of twin-screw extrusion processing in aquafeed production, emphasizing its efficiency in managing various raw materials and controlling product characteristics. It outlines the twin-screw extruder's ability to improve mixing, cooking, and pellet quality through precise control of moisture and temperature during processing. Additionally, it highlights the importance of selecting appropriate ingredients to maintain nutritional value and achieve desired pellet properties for aquatic feeding.

1. May | June 2011
Feature title: Aquafeed twin-screw extrusion processing - Versatile and ideal for aquafeed
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The International magazine for the aquaculture feed industry

2. F: Extrusion F: Extrusion
Mr Daniel mainly by screw speed and screw and consequently ensures efficient control
Durand configuration, which can be varied of the expansion of the melt at the die.
extensively to modulate this energy In comparison with single-screw extrud-
- thermal energy input determined by er, twin-screw is more responsive. By vary-
direct steam heating and indirect bar- ing the cooking parameters it is possible to
rel heating maintain more precise limits on product
Twin-screw extruders are able to process characteristics such as density to achieve
a large range of raw materials consistently floating, low sinking and sinking pellets.
with high levels of flexibility and pumping Expansion can be further enhanced by
efficiency. The
intermeshing
screws allow
handling of
viscous, oily,
sticky or very
wet materials
and provide a
very intense
MADE IN HOLLAND
mixing, where
m a c ro m i x i n g
and micromix-
ing double shafts adjusting paddles ing result in a
assembly maintains the feed particles at very homo-
the optimum moisture between 20–23 geneous melt
percent and temperature around 90°C with excellent
during two to three minutes average lipid binding.
retention time. Preconditioning helps to In a co-
maintain starch and nutriment quality rotating twin-
Aquafeed twin -screw extrusion processing and allows increased extrusion capacity,
while reducing extruder screw wear and
screw extruder,
throughput
Versatile and ideal for aquafeed mechanical energy requirements. and screw
speed are not
AL30O
Twin-screw Extruder / Thermo- interdependent;
By Mr Daniel Durand, Senior Extrusion Expert at Clextral mechanical cooking for a given High capacity extruders and expanders.
The preconditioned feed mix is submit- formulated feed
T
ted to the controlled thermo-mechanical mix, the mul-
he aquafeed manufactur- combination of ingredients with the proper Mixing cooking which is the main stage in extrud- tiple operating
ing industry is widely levels of essential nutriments required for Mixing accuracy depends on the proper- ing aquafeeds. points combine
www.extruder.nl
recognised as one of the the animal species. The formulation is also ties of the components, which should be Thermo-mechanical cooking of the feed with a high con-
fastest expanding food based on cost, availability and chemical similar in density and particle size. Additives mix in an extruder requires two energy trol efficiency Almex b.v., Verlengde Ooyerhoekseweg 29, 7207 BJ Zutphen
industries in the world. Fishmeal is composition of the raw materials. Ingredient or micro ingredients are added at this step. inputs: of the barrel The Netherlands, tel. +31 (0)575 572666, fax +31 (0)575 572727
the main protein source in aquafeed, selection has a direct impact on final prod- The required mixing time depends on the - mechanical energy input defined temperature E-mail info@almex.nl, www.almex.nl
but supply is limited, which means uct characteristics. type of mixer technology used, as well as
that alternative sources must be According to their functions, these dry ingredient mixing time before liquids
used. ingredients can be divided in three groups: are added.
- Nutriments: to meet the require-
From a processing point of view, extru- ments of fish Extrusion cooking The twin screw extrusion expert
sion is the most efficient way of turning - Functional product: binders, expan- This step of the aquafeed processing line
plant protein into fish feed. Twin-screw sion, hardness can be divided into three stages: precondi-
extruders offer a definite advantage in this. - Palatants and attractants tioning, thermo-mechanical cooking and die
The goal for production of aquatic feed texturization-shaping
Pre- grinding / grinding
HIGH QUALITY
is to manufacture a nutritionally complete
product that achieves the desired product It is essential to decrease the particle Preconditioning
characteristics. While all aspects of the size to a powder state before mixing the The primary objective of precondi-
process are important, a number of the unit ingredients. Post grinding achieves the best tioning in an extrusion cooking process Aquatic Feed
operations of the manufacturing process final performance. is to initiate the hydration and the
are critical to achieve this goal. In addition, particle size is dependent cooking of the feed mix. The dry feed
These operations are organized along on the final size of the pellets. For die mix and the liquid parts (slurry, oil From 300kg/h to 30 000kg/h
the process as follows: openings up to 3mm, the largest particle …) are separately introduced into the
size should not be larger than 1/3 of the preconditioner where they are continu-
Selecting raw materials die opening. Smaller particles improve pel- ously mixed, heated and moisturised by
The first step of the aquafeed process let durability, water stability and decrease the injection of water and steam. The
line is feed mix preparation–selecting a pellet friability. intense mixing created by the rotat-
30 || InternatIonal AquAFeed || May-June 2011
30 InternatIonal AquAFeed May-June 2011 May-June 2011 || InternatIonal AquAFeed || 31
May-June 2011 InternatIonal AquAFeed 31

3. F: Extrusion F: Extrusion
The drying parameters must be applied must be lowered to approximately • reduction of anti-nutriments
to remove the moisture while maintaining 50°C otherwise, the water in the • flavouring improvement
pellet quality. (that is, limiting fine gen- pellets will start boiling because of • protein/lipid complexes
eration, maintaining palability and pigment the vacuum applied (0.2 bar absolute • increase digestibility
ingredients, minimum energy losses and pressure). • texturization, shaping
moisture variance) The vacuum coating process allows the • expansion, density
Floating and sinking product characteris- oil to be drawn into the pellets by capillary • hygienic, salmonella-free pellets
tics can be influenced by the drying condi- forces ensuring perfect control of the pellet
tions. Elevated temperatures can lower oil absorption and the addition of more Challenges ahead
residual moisture and improve floatability. oil into the product while ensuring a dry The major challenge is to expand sus-
Sinking aquatic feeds are preferably dried surface and limiting the oil discharge in the tainable aquaculture to achieve enhanced
at moderate temperatures until the storage natural environment. food security and economic development
stability of the pellets is obtained. With this technology it is possible to for the global population as a whole. In the
In aquafeed processing lines, extruded achieve more than 40 percent total product context of substitution of fish meal with
pellets are generally dried on one of the fat content. plant-derived feedstuffs, extrusion technol-
following dryer designs:
- Horizontal belt dryer
- Vertical counter flow dryer
- Fluidized bed dryer
And recently, rotary dryer tech-
nology: the Rotante type rotary
dryer was previously designed
to process other cereal based
products. Through gentle stirring
of the product to eliminate build-
up, the “Rotante” design achieves
injection of steam into the extruder bar- aquafeed processing line as it determines moisture level is to make the product excellent heat exchange close to
rel, which increases thermal energy inputs. the physical quality of the final product. shelf stable. Most aquatic products are that obtained in a fluidized bed.
Where higher product densities are required Micro-aquatic feeds often used as start- best processed at moisture levels between Other advantages include a per-
for certain feeds, the extruder barrel can be ers are products smaller than 2.0mm. 20-28 percent. Moisture levels as low as fectly controlled residence time
configured to include a vent stuffer to reduce Specific die design allows direct extru- 20 percent can be required for some light with virtually no dispersion, of
product temperature through evaporative sion of micro-aquatic feeds down to 0.5mm. density aquafeed pellets. Some moisture is type FIFO (First In, First Out) and
cooling.Vacuum regulation can be connected Products are pasteurised and very nicely lost during flash evaporation as the cooked precise product moisture homo-
to the vented stuffer barrel to increase the shaped.Water stability is excellent and floating product exits the die. Then, the products geneity at dryer output. To master
product density even further with higher products are possible. Raw material must be are conveyed to the dryer to reduce the drying barema, temperature &
degrees of evaporative cooling. carefully ground and sifted to achieve proper the moisture content from 18–24 percent moisture are precisely regulated,
particle size before extrusion. down to 8–10 percent, this corresponds which helps to prevent product
Texturisation-shaping Macro-aquatic feeds with sizes up to to a water activity (aW) around 0.5–0.4, in cracks. Clextral’s Research and
of aquafeed pellets 30mm emphasize the physical quality of order to obtain satisfactory water stabil- Test Centre in France is equipped
The end of the last barrel of the extru- the pellet and the related process history. ity. with a ‘Rotante’ and tests have proven this Cooling pellets ogy has a role to play in reducing the level
sion chamber is capped with a final die, A combination of twin-screw mixing and Several factors control the water dryer to be particularly efficient for fish On completion of the fat coating proc- of anti-nutriments. (Kaushik 2006)
which serves two major functions. First, the cooking, special Rotante drying technol- removal from the aquafeed pellets: feed, ensuring complete homogeneity of ess, the pellets are cooled and sieved before Twin-screw extrusion technology has
die restricts product flow thereby causing ogy and dedicated die design will produce - Air related factors: depending on the drying with lower energy consumption. the final conditioning. Cooling is required to contributed and will carry on the tre-
the extruder to develop the required pres- pellets with sufficient resistance to avoid air flow characteristics around the remove excess heat to prevent condensation mendous improvements, both in terms of
sure and shear; and second, the die shapes breakage and dust, yet porous enough to pellets, temperature and humidity of Fat coating from occurring in the storage bins or the final nutritional value and in terms of physical
the extrudate. deliver all the nutrients to the digestive the drying air Fat addition is commonly done after packages. At this stage, the aquafeed pellets’ quality characteristics of the aquafeeds.
A face cutter is used in conjunction with system of the fish. - Pellet related factors: depending dryer, while the dried extrudates are still temperature should be cooled down to a With the continued economic devel-
the die, which consists of cutting knives on the initial moisture content and warm. For that, the oil is sprayed directly temperature range close to the storage or opment of aquaculture, each venture,
revolving in a plane parallel to the face of Pellet drying temperature, porosity and size of the on pellets. During this stage, fats, pigments, transportation temperature. and species will be subject to important
the die. The relative speed of the knives and The primary purpose of reducing pellet pellet attractants and even powdered ingredients research efforts so as to obtain, under
the linear speed of the extru- can be added. Conclusion acceptable economic conditions, efficient
date result in the desired Table 1: Indication of final pellets bulk density /floating or sinking properties: This processing stage can be imple- Clextral systems can easily produce high feeds delivered at the right time, which
product length. Feed characteristics Fast sinking Slow sinking Neutral floatability Floating mented two ways: energy feed, allowing a delicate balance of are non-polluting and which care for
Die design –cutter • under atmospheric pressure: the proteins, oils and carbohydrates, processed the health of the fish as well as the
assembly is one of the most added oil, temperature around 40°C, for total digestibility with no waste. It’s the consumers.
Bulk density gr/l >640 540 - 600 480 - 540 <450
important sub-units of the is diffused from the surface of the right formula for high quality products that
product to the centre and is stored in “turn feed into flesh.” Output range from
Species Salmon Trout Cod Carp Tilapia Cat fish Shrimp cavities in the pellets’ structure. 25 to 30,000kg/h. More inforMation:
• under vacuum pressure: this consists Thanks to twin-screw extrusion, high Clextral
1 Rue du Colonel Riez
of a closed system with a mixing quality aquafeed pellets are achieved:
Final pellet total fat % >35 15 - 35 15 - 25 5 - 15 5 - 10 5 - 10 <5 Firminy, F-42700 France
shaft or screw and spray system in • denaturing of proteins Website: www.clextral.com
Texture bulk density Slow sinking Slow sinking Slow sinking Floating Floating Floating Fast sinking the top. The product temperature • gelatinization of starch
32 || InternatIonal AquAFeed || May-June 2011
32 InternatIonal AquAFeed May-June 2011 May-June 2011 || InternatIonal AquAFeed || 33
May-June 2011 InternatIonal AquAFeed 33

4. LINKS
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