May | June 2013

Pelleting and extrusion in aquafeed technology

The International magazine for the aquaculture feed industry

International Aquafeed is published six times a year by Perendale Publishers Ltd of the United Kingdom.All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2013 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058

INCORPORAT ING f I sh fARm ING TeChNOlOGy

64 | InternatIonal AquAFeed | May-June 2013

Pelleting and extrusion in aquafeed technologyby Doris Du, sales representative, Allance Machinery, China

Aquacultureisadevelopingactivityaroundtheworld.Astheindustrygrows, so does the aquafeedmarket.Aquafeedsarecomprised

of a number of ingredients that are mixedin various proportions to complementoneanother to form a nutritionally completecompound diet. According to the physicalcharacteristics, they can be divided intopowder, particle, pelleted and extrusionaquafeed. They can also be divided intosinking, slow sinking and floating aquafeedaccording to their buoyancy. On the basisofaquafeedenergy,theycanbedividedintolowenergy,mediumenergyandhigh-energyaquafeeds.

Raw materials for aquafeed production

Common basic raw materials to themanufactureofmostaquafeedsaresimilartothoseemployedinthemanufactureofothertypes of animalfeeds.However,itshould be notedthat aquafeedsshould avoid theuse of high levelsof plant or veg-etable fibres andcarbohydrateswhich are poorlydigested and

transformedbyfish.Rawmaterialsforaqua-feeds include cereals (maize, wheat, barley,rice, oat etc.), cereal by-products (wheatflour,cornbran,wheatbranetc.),meatmeal,fishmeal, shrimp meal, squid meal, bloodmeal, poultry by-product meal, (full fat)soybeanmeal,othervegetableproteinmeals,fatsandoils,vitaminandmineralpremix,salt,stabilizersandbindersetc.

The major components of aquafeeds areprotein (plant protein, animal protein andsingle cell protein), starch (sinking aquafeedconsistsmorethan10%andfloatingaquafeedconsistsmorethan20%),crudefat,rawfibre,crudeashandmicronutrients.Starchhasgreatgelatinization under high temperature andhigh humidity conditions. It can improve thestabilityofaquafeedsandextrusiondensityofextrudedaquafeeds.

Aquafeed processing technologyThemanufacture of aquafeeds ismore

complex than common feed manufacture.

Hardness, size, buoyancy, durability andwater stability must all be taken intoaccount. Aquafeed processing technologyisnotunique.Itreliesonthedevelopmentmadeinconventionalanimalfeedprocess-ing technology, but with some specificapplications. The main processing tech-nology for aquafeeds is pelleting (mainlyproduce sinking aquafeeds) and extrusion(can produce sinking or floating extrudedaquafeeds).

Aquafeed pelleting technology is stricterthancommonanimalpelletedfeed.Typically,sinkingaquafeedsaremostlymadewithfeedpellet mills. Pelleting is still the predominatemethod for sinking feed production. Theaquafeed pelleting processes is describedbelow:

GrindingIt isaparticlesizereductionprocess forrawmaterialsbyhammermills.Grindingisbenefi-cialforthemixingoperationandcanimprove

thenutritional utilizationof raw materials. Foraquafeed processing, anultra fine feed hammermillisnecessary.

MixingThe ground materialsmust be mixed withthe proportioned rawmaterials to obtain a

Table 1: Classification of aquafeeds based upon the energy levels and processing technology

low energy Medium energy High energy

Protein (%) 30-40 43-52 40-48

Fat (%) 6-13 12-25 22-35

Processing machine aquafeed pellet mill extruder/aquafeed pellet mill extruder

target species salmon, trout seabass, turbot carp, tilapia

34 | InternatIonal AquAFeed | May-June 2013

FEATURE

May-June 2013 | InternatIonal AquAFeed | 35

homogeneous mixture. During the mixingprocess,feedribbonblenderordoublepad-dle feedmixer is themost commonlyusedequipment.

PelletingPelletingcanbedefinedastheagglomerationofsmallparticlesintoalargersolidwithagivenshapeandtexture,bymeansofamechanicalprocess in combination with moisture, heatand pressure. The main factors which affectpelletingare ingredientscharacteristics,mois-turizingorsteamingbeforepelleting,diethick-nessandbindersetc.Theringdieaquaticfeedpelletmillistheprofessionalpelletingmachineforaquafeedprocessing.

CoolingThe temperature of the aquafeed pelletssqueezed out the pellet mill is high. They

shouldbecooledbeforeotheroperations.Acounterflow pellet cooler is a high-efficiencycoolingmachine.

Coating Coating can improve upgrade the aquafeedquality. The physical property of the feed isimproved. The fat sprayed on the aquafeedpelletshascertainpermeability;itcanperme-ate into the pellets in subsequent crafts andtransportprocess.Thatcanreducethescatterof feed particles and dust. The fat sprayingmachine isalsoknownas feedpelletcoatingmachine.

CrumblingIt is a necessary process in aquafeed pelletprocessingas some fishneed smallerpellets.The roll type crumbler can break the aqua-feedpelletsintosmallerparticles.

Screening In order to improve aquafeed quality, finesfrom cooled aquafeed pellets should beremoved and the pellet size should be uni-form. Rotary feed pellet grading sieve is justthemachine.

Aquafeed extrusion technologyA significant application of the extrusion

process is in the production of aquafeeds.Extrusion has won some popularity and iswidely accepted. Compared to the pellet-ing method, extrusion can be defined as atechnological process, namely, forcing feedrawmaterialinoneormoreofthefollowingprocess conditions (such as mixing, heating,cuttingetc.)flowthroughthedie,makemate-rialformingoreruptiongasification.Extrusionallows buoyancy control to make floating,sinking or slow sinking feed by changing the

34 | InternatIonal AquAFeed | May-June 2013 May-June 2013 | InternatIonal AquAFeed | 35

FEATURE

Table 2: Starch contents of common energy feed raw materials

raw material Starch content (dry matter) raw material Starch content

(dry matter)

Whole maize 70-75% Sorghum 71.6%

Flour 75-80% Whole rice 81%

Wheat bran 5-8% Whole barley 60%

Winter wheat 65.5-82% Whole oat 45%

Wheat middling 21.5% Soybean meal (44%) 0.5%

EXTRUDER

EXPANDER

Almex b.v., Verlengde Ooyerhoekseweg 29, 7207 BJ Zutphen, The Netherlands, tel. +31 (0)575 572666, e-mail info@almex.nl, www.almex.nl

High capacity extruders and expanders.

EXTRUDER

EXPANDER

AD System

extrusion condition including temperature,pressure, die aperture diameter and shearrateetc.

Dry or wet extrusionDifferent shapes and sizes of aquatic

feed can be produced using extrusiontechnology.Extrusionwithsteamprecon-ditioning is known as wet extrusion andextrusion without steam preconditioningis called dry extrusion. Dry extruderswere used in processing low moisture,highly expanded starch products and inprocessing whole soybeans to full-fat

soy flour for both the food and feedindustries.

Preconditioningisaveryimportantpartofthewetextrusionprocessforsteamorwaterinjection into either the conditioner and/ortheextruderbarrel.

Themostimportantaspectoftheprecon-ditioningsystemisthepotentialforadditionalmixingandtheretentiontime,whichisneces-saryforchemicalorphysicalreactionstotakeplace. The Allance aquafeed extruder forexample,canproducedryandwetaquafeeds.Dry feedpelletsarestable forrelatively longperiods, for convenient storage anddistribu-

tion.Thewet typeprocess-ing needs a boiler to makesteamtotheconditionerandripen the raw material inadvance.

Twin-screw extrusion is ideal for aquafeed

According to the opera-tion methods, extrusionequipmentgenerallyfallsintotwo categories: single-screwextruders and twin-screwextruders. Producing smallpellet aquafeed by single-

screwextrudersdirectlyhasmanyadvantages,suchaslowingredientcost,lessfinegenerat-ed,goodwaterstabilityandpleasantappear-ance.Twin-screwextruderswerefirstusedinthe 1950s for manufacturing thermoplastics.Theyweredevelopedonthebasisofsingle-screwextrusionmachine,withadoublescrewinstalled side by side in the barrel. A fullymeshed co-rotating (both screws turn samedirection)extrudergreatlyimprovedmaterialconveying,pumpingandmixingcharacteristics.Comparedtoasingle-screwextruder,aTSEhas a much wider operating range in termsof use of moisture, internal fat, mechanicalenergyinputandproductsize.

The domestic high quality twin-screwextruder has reached an advanced level intechnicalperformanceandmanufacturinglevelwithhighpropertyprice ratioand is thebestchoiceoftheaquaticfeedprocessingindustry.

The main advantages of twin extruderdescribedasfollows:• Twin-screwprocessmandatorydelivery

and self-cleaning feature, making thematerial stay in the barrel for a shorttimeanduniformity

• Astwoscrewskneadandrubeachother,extruder enables material mixed and rip-enedmorefullyinlowerenergyconsump-tion.Thewholeripeningdegreecanreachmore than 95percent,water stability lastfor24hours

• Thebiggestcharacteristics is that itcanmixallkindsofrawmaterialsregardlessofitsformation.Thiswillalsoenablefishfarmersuseawiderrangeofingredients

ConclusionThe production of aquafeed is the fast-

est growing sector in the global feed industry.Although a large amount of aquatic feed isstillproducedbyconventionalpelleting technol-ogy,extrusionisbeingutilizedtoalargerextentbecause ithasseveraladvantagesoverpelleting.So,pelletingorextrusion?It’saccordingtovariousfactorsthatdiscussedabove.

Table 3: extruded aquafeeds versus pelleted aquafeeds

extruded feed Pelleted feed

Bonding degree strong strong

Floating and sinking beneficial just sinking

Stability in water better good

Fines in aquafeeds fewer few

nutriment digestibility higher lower

Funding bigger smaller

Processing cost higher lower

equipment wear slower quicker

36 | InternatIonal AquAFeed | May-June 2013

FEATURE

More InforMatIon:Website: www.pellet-machine.net

36 | InternatIonal AquAFeed | May-June 2013

www.oj-hojtryk.dk

Die and roll re-working machines

O&J Højtryk A/SØrnevej 1, DK-6705 Esbjerg ØCVR.: 73 66 86 11

Phone: +45 75 14 22 55Fax: +45 82 28 91 41

mail: info@oj-hojtryk.dk

O&J HØJTRYK A/S endeavours to be a powerful, vigorous and energeti c company. With our customers needs and the

immediate environment as our point of departure, we want to be a trendsett er in our core area of business - Mechanical

Engineering - Re-working of Dies and Rollers for the manufacture of Feedstuff s and Biopellets, as well as the sale

and delivery of wearing parts in connecti on with Roller Re-working - as well as to

remain open to new initi ati ves and business opportuniti es.

O&J HØJTRYK A/S has drawn up a strategy plan setti ng out guidelines for

how we as an organisati on must conduct and develop ourselves in order to make

our mark, not just in the present, but also in the future.

O&J HØJTRYK A/S must achieve success by adapti ng to the conditi ons of the market more quickly

and effi ciently than our competi tors. As a service organisati on we must, in relati on to our customers,

att ach great importance to our own vitality and effi ciency by constantly living up to the ever-growing demands made on

the services we provide.

www.aquafeed.co.uk

LINKS

• Seethefullissue• VisittheInternationalAquafeedwebsite

• ContacttheInternationalAquafeedTeam

• SubscribetoInternationalAquafeed

They are what they eat Enhancing the nutritional value of live feeds

with microalgae

Controlling mycotoxins with binders

Ultraviolet water disinfection for fish

farms and hatcheries

Niacin – one of the key B vitamins for sustaining

healthy fish growth and production

Volume 16 I s sue 3 2 013 - mAY | J uNe

INCORPORAT ING f I sh fARm ING TeChNOlOGy

Thisdigitalre-printispartoftheMay|June2013editionofInternationalAquafeedmagazine.Contentfromthemagazineisavailabletoviewfree-of-charge,bothasafullonlinemagazineonourwebsite,andasanarchiveofindividualfeaturesonthedocstocwebsite.Pleaseclickheretoviewourotherpublicationsonwww.docstoc.com.

Topurchaseapapercopyofthemagazine,ortosubscribetothepapereditionpleasecontactourCirculationandSubscriptionsManageronthelinkabove.

INFORMATIONFORADVERTISERS-CLICKHERE