May | June 2014

Evolution in Extrusion of Aquatic Feeds

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 2014 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

Aquatic feed production has under-gone tremendous changes as the industry has advanced towards efficiency and sustainability of the

aquaculture industry.

SustainableBusiness.com, published in 2011, stated that aquaculture is in a rapid industry growth phase, that is “Driving the scientists' research is the recognition that aquaculture is one of the fastest growing food production sectors in the world.

“It has grown at an average annual rate of 8.4% since 1970 and total production reached 65.8 million tons in 2008 according to the Food and Agriculture Organization of the United Nations (FAO).

“Today, aquaculture is a US$100-plus bil-lion industry that provides more than half of all seafood consumed in the world, surpassing wild-caught seafood.”

If it is a food fish it can be fedLet’s review here how the art of

production of feed, for aquatic animals by extrusion, is prepared and advancing for various species; predominately the major species are carp, eel, salmon, trout, shrimp tilapia, catfish and a collection of additional species that are regionally farmed.

Basically, if it swims and is a food fish then feeds can be prepared for their consumption.

The aspects of the feed are defined by researchers for those specific species. Generally, this includes the nutritional requirements and physical characteristics required in the feed for select species. Historically, aquatic feeds were simply other fish caught to feed the more valuable marketable species. The shift occurred when advanced feed produc-

tion methodology was applied which initially centered on the use of pellet mills. This would be the art of compounding feed ingredients into pellets which were sinking in design due to the equipment abilities, compounding or pressing the ingredients by force into a pellet shape.

Today, this method is still used as there are various values applied to the final product, the fish.

Economics apply even in aquaculture as some species do not have the market value for advanced feed production methods, or simply they are not required for that species.

Extrusion does have advantages in formu-lation abilities and in some cases the feeds are actually less costly due to mainly the reduced starch requirement in sinking feeds. Less starch give more room for nutritional

building blocks allowing lower cost protein uses in the feed.

As this industry in whole is advancing technically other methods of feed production emerged, mainly extrusion cooking. Why?

Initially, it was seen that the density of a feed from an extrusion cooker was floating. Researchers found they could monitor the fish and feed consumption easily with the use of a floating feed for many species in effect chang-ing the feed pellet characteristics desired.

This effect was seen in the catfish indus-try and others where additional advantages including formulation cost reduction and feed production methods allowed for feed cost improvements.

Thus, aquaculture became a business, a big business, with entrepreneurs studying all aspects of it.

Any advantage that could improve the bottom line was of interest. Small aquatic farmers with a few ponds turned their operations into large 1000-hectare farms, small feedmills turned into huge bulk feed production plants, usually in specially designed configurations.

The implication of changeLet’s review extrusion and the impli-

cations of changes effecting this indi-vidual method of production.

A definition of extrusion cooking: “Extrusion cooking is the process where expandable biopolymers such as protein and starch are plasticized in a tube by a combination of heat, shear, and pres-sure resulting in the denaturation of the protein, the gelatinization of the starch, and the exothermic expansion of the extrudate.”

Explained on the basis of aquatic feed production expandable biopolymers, starchy ingredients and functional pro-

by Joseph P. Kearns, Wenger Manufacturing, Inc, Sabetha, KS, USA

Various aquatic feeds by extrusion

cooking

Example of a Large Aquatic

Feed Production Plant, Skretting,

Norway

Evolution in Extrusion of Aquatic Feeds

34 | INTERNATIONAL AQUAFEED | March-April 2014

FEATURE

teins, are required to hold the pellets together and to impart the needed ingredients to make the feed float, sink slowly or sink rapidly.

Usually the starch requirement in extrusion is in the 10 percent range for sinking and 20 percent range for floating.

Proteins are added for the nutritional value with good quality functional proteins or ones which have not been overheated before extrusion also allow binding of the pellet. Extrusion is usually a high temperature/short time (HT/ST) process with extreme changes occurring in the extruder barrel.

In about 30 seconds the powdery raw material is melted into a plastic state by heat via friction, shear by design of the barrel com-ponents and pressure by forcing the material through this device. T

he result is the final product. The question is how to control all of these parameters and make an individual feed or many different styles of aquatic feeds with the same machine?

Historically, this process started out very simply, that is what the industry had to offer, simple but an advanced extruder which was designed to expand products.

Honestly, these machines came from the petfood industry and it just happened they were the driver for extrusion in aquatic feed applications. The industries mirrored each other - believe it or not. At that time it was

typically eight to ten tons per hour maximum capacity with restrictions.

Early on the restrictions were how much fat or fresh meat can be placed in the extruder as well as capacity, smaller diameter feed capacity, was greatly reduced when compared to larger feed sizes. Pellet of 15mm or larger were unheard of and when someone asked for sinking feeds, heads were scratched.

Over the years the petfood industry asked for more fat in the extruder, more fresh meat, density control, control of the air cell sizes in the pellets, more durable products to mention a few.

Coincidentally, many of these top-ics matched the questions from the aquatic industry.

Advancements in extrusion equipment

Let’s review these based on the flow through an extruder.

Early on it was seen that the dry feed flow rate to the extruder needed to be even. Same for the liquids. If they varied the pressure in the barrel changed and the expansion then varied or yielded different diameter pellets.

Advancements of using loss-in-weight feed

systems advanced this area greatly, even allowing for compensation while the bin emp-ties at different fill levels. Dry ingredient flow coupled with the liquid flows as a percentage greatly increased the accuracy of complex formulation extrusion.

In other words as oils or fats, water, steam, startup waste streams, ground meats and any

Large Capacity Single Screw Extruder for Salmon and Floating Feed Applications, 17

tons per hour dry rate after extruder

Open Twin Screw Extruder Barrel. Discharge on right where the plasticized mass is about

to exit the extruder. Shows the flow to melted state phase changes

March-April 2014 | INTERNATIONAL AQUAFEED | 35

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Turning ideas into opportunities.PROGRESSIVE AQUAFEED PROCESSING

Imagine the possibilities

wenger.com

BElGIUm TAIwAN BRASIl ChINA TURkEy INDIA

Leave it to Wenger to redefine aquatic feed production via twin screw extrusion. Based on the proven Wenger Magnum twin-screw series, the new TX-3000 features barrel geometries that allow greater capacities than any other extruder in its class.

The combined features allow increased production capacity of up to 30 percent compared to previous and competitive aquatic machines — totally redefining cost/benefit. The TX-3000 can be equipped

with either the High Intensity Preconditioner (HIP) or the High-Shear Conditioner (HSC) to match specific process and capacity requirements, making it ideal for processing a full range of aquatic feed products.

Contact us now. With new concepts and visionary leadership, we’re ready to help you select the right tools for your extrusion and drying needs.

Our business in life is not to get ahead of others, but to get ahead of ourselves. —Stewart B. Johnson, Dutch Artist

TX-3000 RAISES ThE BAR ON AQUATIC FEED PRODUCTION

Wenger14.TX3000.Ad.210x147.indd 1 4/9/14 7:34 AM

other solutions added could be done very accurately. Tremendous improve-ment as the mix became very exact going into the extruder.

A major step forward in predict-ability on the extrudate coming out of the machine. All of this could be done with flow meters and manual operation. Computers are generally the operations control method today for advanced production and profitability.

Preconditioners, a standard device on most extruders as well as pellet mills, was the device that takes the ingredients both dry and wet and prepares them for the actual extruder barrel.

Many designs are available from single cylinders, multiple cylinders and dual shaft conditioners. All work as they were designed for at the time.

Current technology would include dual-shaft conditioners with each shaft having speed and rotational control. Residence time is considered one of the main advancements between cyl-inder designs.

Water and steam could always be added, the question is how do you like cleaning an extruder?

The older cylinder designs mixed everything together but in some cases the result was so sticky that flow from the conditioner to the extruder barrel stopped: The point downtime and cleaning started. Newer designs over the years, improved residence time, eliminated this problem area as the increased time allowed for absorption of the liquids into the dry feed allowing for a non-blocking, free-flowing powder to easily flow into the extruder barrel.

The petfood industry pushed for more meat addition which offered advantages in the aquatic sector also. The development of a High Intensity Preconditioner, HIP, has allowed for unsurpassed inclusion of protein sourc-

es such as terrestrial land animal liquid streams or ground up fish waste up to 50 percent when mak-

ing a finished feed. That is 50

percent meat and 50 percent cereal or dry ingredients extruded into pellets.

Eighty-five percnet has been achieved when extrusion of an ingredi-ent is required. Combination of soy-bean meal and fish waste dried to be stored for future use, other dry ingredients can be used also.

Extruder barrel advancements cent-er on gaining control of the process as well as increased capacities.

In the case where a single product is made the extruder can be set up for that application, such as a plant always making salmon feed. Of course, there can be differences within this sector requiring modifications or various con-trols to achieve the range of products needed.

How about the aquatic feed manu-facturer in an area where there are numerous styles of feeds required? This extruder application would require a higher degree of flexibility to make all the style feeds.

Tools to assist in extrusions success

Buoyance of aquatic feeds still receives attention and this is mainly due to the fact that formulations are in constant flux.

Price variations of ingredients and the nutritional knowledge for the spe-cies is most definitely moving aquatic feeds to least cost formulations. As more is known about the use of indig-enous and wide varieties of ingredients technology will assist the feed makers in achieving the required feed densities.

Traditionally, the method for chang-ing density is to modify the open area of the extrusion die in relation to the energy needed to cook and expand the product. Low density requires less open area and the opposite is true for heavy feeds.

Imagine you make a feed and the formulator modifies the formula slightly for cost advantages and you have a range of let’s say 50 formulas you manufacture in various different diam-eters. Different diameters have differ-ent capacities and different rates of expansion in each die design. Each is

Photo of small cell structure needed for vacuum coated feeds for elevated oil content

0.5 mm Shrimp Feed, example of small diameter extruded feeds

Photo of a large diameter aquatic feed. Center hole in pellet to aid in drying and digestion. Hole

can be left out for semi moist feed production for large marine fish such as tuna

Sample off of a HIP Preconditioner, 50% fresh meat, 11.5% steam added, 3.4 minutes retention time and

a 35% moisture content. The perfect conditioned free flowing powder ready for the extruder

High Intensity Preconditioner with Dual Drive, Speed and Rotational Control

36 | INTERNATIONAL AQUAFEED | March-April 2014

FEATURE

scheduled to be made depending on the requirement by your clients. This is almost an impossible situation to man-age effectively.

Either you restrict the formulation changes so as the extruder setup is well defined for that product or you might elect to use technical devices to assist in the management of the required equipment changes so the formulation can move slightly due to market costs.

There are a number of devices depending on your extruder supplier that can assist in this area allowing elevated flexibility while greatly reduc-ing down time.

Flow restrictors in the extruder bar-rel are designed to change the rate of passage through the barrel.

Anytime you restrict the flow you increase friction or energy input. Increased energy input generally increases expansion. Reduced energy input or opening the barrel up for easier flow makes the feed heavier or less expanded. Where in the barrel to place a device depends on the actual application.

The extruder barrel can be taken apart and the screw configuration changed to achieve flow restriction. Devices have been developed to avoid

costly down time as much as possible with the use of devices that can be changed while running.

Typically they are used at the end of the barrel or midway in the extruder barrel thus Back Pressure Valves and Mid Barrel Valves. Back Pressure Valves are used at the end of the extruder and Mid Barrel towards the center. Devices at the end of the extruder usually assist in mak-ing a difficult to float formula float easier.

Mid barrel valves are typically used when making slow sinking or sinking style feeds. Exceptions do exist as other technology can be combined with the above flow restricting devices.

In the case of requiring more open area than traditional possible, design changes with larger dies and cone head designs has allowed for increased open area greatly improving the capacity on sinking feeds predominately the smaller sizes.

When controlling density the open area is an important factor in the floatability of the feed thus more open area results in higher capacities on sinking feeds. Larger extruders can also do the job but if a smaller extruder is used and achieve a higher rate the investment cost just went down per ton produced.

This photo shows a specialized C²TX, Conical Twin Screw extruder for shrimp feed production, notice the single shaft tapered conditioner, High

Shear Conditioner. Also show it the Oblique Tube Die at the discharge with a Back Pressure Valve

directly behind

Extruder Barrel with an Atmospheric Vent (shown closed) and Manual hand crack operated Mid Barrel Valve. Motorized version also available

March-April 2014 | INTERNATIONAL AQUAFEED | 37

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Extruder OEE for the Production of Fish FeedExtruder OEE for the Production of Fish Feed

AMANDUS KAHL GmbH & Co. KG, Dieselstrasse 5-9, D-21465 Reinbek / Hamburg, Phone: +49 40 727 71 0, Fax: +49 40 727 71 100, info@amandus-kahl-group.de www.akahl.de

The development of the Oblique Tube Die has increased the open area by about three times effectively allowing extruders to achieve as an example four tons per hour of sinking shrimp feeds of 1mm in diameter. Technology is just starting that can perhaps double this to the eight to 10 tons per hour on small diameter feeds using traditional twin-screw extruders.

As mentioned above increased pressure in the extruder barrel yields floating feeds. Thus an early solution was to vent the barrel and allow escape of pressure and some moisture for sinking feeds. The result was an increase in density.

Further developments showed that there could be an advantage for pulling a vacuum out of this vent to enhance the sinking effect. This technology is used for aquatic feeds on a limited basis when special combinations of ingredients are passed through the extruder. Typically this would be a mid-range fat level sinking feed.

Also discussed was the requirement of pet food manufacturers to increase meat inclusion levels. History has shown that cooking high levels of fresh meat type products does not work well in frictional designed extruders. The challenge was met and the design of the ther-mal twin-screw extrusion allowed 10 times the steam inclusion moving the operational conditions from frictional cook to thermal

cook allowing highly elevated meat inclusion rates.

Species-by-species reviewFeeds for farmed aquatic animals

will always need work to elevate improvements and to handle the new technology related to varie-ties of ingredients so the industry continues to move forward.

Recently, reviewing an article by Mike Urch published in World Fishing and Aquaculture (Jan. 13, 2014), he stated in the article on cobia, “Cobia is a beautiful fish with a firm, white flesh,”

Mr Myrseth says, “So we had great hopes for it. But we did have some production problems.

“It seemed to eat a lot, but at a certain size it stopped growing or it grew too slowly. So the feed factor was very high and we had problems making money on it.

“There seems to be a problem with using dry feed for this fish.”

Right now work is progressing on aquatic feeds with the Thermal Twin-Screw design mentioned above.

Possible use for new technology to change the way of making some select marine fish feeding situations

viable. If you can take half the formula or so and use ground waste aquatic material such as head, frames etc and couple this with the semi-moist concept of not drying the feeds, then you can in effect make a soft feed that has a texture that might be more conducive to select species.

Tuna, cobia, grouper and other

marine fish might do well on different feed design then what is traditionally available in dry form.

It must be better than feeding whole fish which is considered not sustainable. It would also allow for furthering the studies of what they require nutritionally to allow reduced feed cost and increase their acceptance as a possibility for increased farming.

Terrestrial land animal waste products should also be considered as protein sources or as amino acid building blocks which in some cases might partially replace the ever decreasing availability of fish meal.

Salmon feed is a good example of improv-ing feed techniques.

These feeds went from single digit oil levels years ago to nearly 40 percent oil in the feeds at this time. This caused a complete reversal in equipment design. The industry went from making sinking pellets off the extruder to floating pellets which were then later infused with oil via atmospheric coaters and later with vacuum coaters for the extreme high oil inclusions.

The oil added externally filled the air sacs in the pellets eliminating the air resulting in sinking pellets.

Communication between researchers and equipment designers allowed for discussion which resulted in the process we have today. It was not that simple and one point that stood out was keeping the oil in the pellets after vacuum coating. Protein sponges need to be made that did not release the oil in the bag. Studies showed that energy input was the key. Higher specific mechanical energy inputs gave a smaller cell structure which hold the oil effectively.

Shrimp feeds is one that stands out as an unusual feed. 100 percent sinking, good

water stability, small diameters and

Twin Screw Extruder complete with a Density Management System, included vent and

vacuum pump system. For those mid-range fat level sinking feeds, formula dependent

Thermal Twin Extruder making a high inclusion level wet fish paste seen in tank to left pumped into the HIP Conditioner at 50% of the capacity

38 | INTERNATIONAL AQUAFEED | March-April 2014

FEATURE

differences in formulations have shown that special feed production equipment might be the answer for this animal.

Single-screw extrusion has been used and is still used in some areas. Everything needs to be exact as any change in the formula can disrupt the production. Twin-screw extrusion is more forgiving in this case. Twin-screw extruders are more positive pumping devices thus less susceptible to screw wear changing the cook-ing effect in the barrel. Not to mention the need for pressure to shove feeds through die holes which are sometimes in the 0.8mm and above ranges. The above mentioned OTD was designed for this sector specifically as well as other micro feed diameters.

Traditional floating feeds is the most stable of the aquatic sectors. Large capacities are desired due to the low margin on catfish, carp and tilapia feeds. In some cases these feeds are easily formulated for the nutri-tional aspects required however the struggle is in filling the formula with inert or high fiber lower cost ingredients. This is where devices to impart more energy come into play as discussed above. Also better grinding of the fibrous ingredients do make extrusion easier.

Post extrusion processesAs one part of the process advances the

rest need to do the same to keep pace. The two main areas here are drying and

coating. Dryers have advanced for better and more even water removal, +/- 0.5 per-cent moisture variance. Sanitary dryer designs improve downtime for cleaning with easier internal access. Floor space requirements are reducing based on equipment designs.

Coating is another topic. High oil levels use vacuum coating. Low oil levels use atmos-pheric coaters.

Ever consider how to apply probiotic or prebiotics as well as the other liquid ingredients which are showing great interest? At what percent are they applied? Real low percentages? New atmospheric coaters with control allow for low Coefficient of Variance application down into the 0.5 percent applica-tion range.

Controls have had tremendous advancements.

Density check, moisture checks, NIR, photo recognition, float or sinking rates and other aspects can now be monitored on line and computer control adjustment based on the data for corrective action to move the process back in the characteristic ranges needed.

In summary, the feed production support industries for the aquaculture industry are in the same exponential growth phase keeping pace with the research and advancements in this industry ensuring the needed improve-ments for advancements.

Better cages, pond designs, water quality systems, novel ingredients, the feeds them-selves and the feed production equipment are all moving forward as communication between disciplines in this industry continue to challenge each other to improve.

Atmospheric Coater for effective external application of liquids from

0.5% to 8% to 10% range

Source Technologies Principal Device to take samples in line while on

line for moisture, density and other product attributes for advanced

equipment computer control

March-April 2014 | INTERNATIONAL AQUAFEED | 39

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www.aquafeed.co.uk

LINKS

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Assessing the potential of polychaete meal in

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INCORPORAT ING F I SH FARM ING TECHNOLOGY

Use of a heat-stable protease in salmonid feeds

– experiences from Canada and Chile

Fish Farming Technology supplement

Nets and cages Recirculating aquaculture

systems

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