Successful moisture control in aquatic feeds


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Successful moisture control of aquafeed can be seen through the safety of the product and in its profitability. Feed products must be dried sufficiently in order to prevent growth of microorganisms after the packaging process. However, over-drying the products will result in poor production yields and energy losses. The two challenges for feed manufacturers are 1) to find the highest moisture content for a given product that will still prevent growth of moulds and other microorganisms, and 2) to find a drying control method that will help achieve and maximise that moisture content.

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Successful moisture control in aquatic feeds

  1. 1. I N C O R P O R AT I N G f i s h far m ing t e c h no l og y January | February 2014 Successful moisture control in aquatic feeds 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 The International magazine for the aquaculture feed industry
  2. 2. Fatten up your bottom line. Bühler high-performance animal and aqua feed production systems are used by leading companies around the world. These producers know they can rely not just on the technology itself, but also on the support that accompanies it. A service combining local presence with global expertise both lowers feed mill operating costs and increases capacity utilization. To find out more, visit Bühler AG, Feed & Biomass, CH-9240 Uzwil, Switzerland, T +41 71 955 11 11, F +41 71 955 28 96, Innovations for a better world.
  3. 3. FEATURE Successful moisture control in aquatic feeds by Roger E. Douglas, director of engineering, Drying Technology, Inc., Texas, United States S uccessful moisture control of aquafeed can be seen through the safety of the product and in its profitability. Feed products must be dried sufficiently in order to prevent growth of microorganisms after the packaging process. However, over-drying the products will result in poor production yields and energy losses. The two challenges for feed manufacturers are 1) to find the highest moisture content for a given product that will still prevent growth of moulds and other microorganisms, and 2) to find a drying control method that will help achieve and maximise that moisture content. The first challenge requires the feed manufacturer to determine the highest possible target and upper moisture limits for each individual product. One of the main reasons to keep moisture content as high as possible is profitability. The incremental amount of water left in the product can be considered a production increase, and energy is saved by not having to remove it. However, for reasons of product stability and safety it is important to set an upper limit on the feed’s moisture content. The water activity and moisture content of a specific product are related values, but are calculated in different ways. Both centre on the ‘free’ water or free moisture, in other words the water that is readily available for biological use. Moisture content is a measurement of the total free and bound water in the product, whereas water activity only takes into account the free water. Bacteria, mould and yeast all require moisture for growth and each microorganism has a minimum water activity, below which it would not grow. Therefore, for a safe product that will not develop mould during storage, the water activity level should be below the minimum value for some or all types of microorganism. Table 1 lists some major microorganisms and the minimum water activity level that makes their growth viable. Constructing an isotherm Figure 1: Typical water isotherm for a product Water activity values are a more accurate reflection of the stability and safety of feed products than the total moisture content. Many food 12 | InternatIonal AquAFeed | January-February 2014 table 1: Typical minimum water activity levels for common microorganisms (Source: Fontana, 2000) Water activity Microorganisms generally inhibited 0.950 Pseudomonas, escherichia, Bacillus, Clostridium perfringens, some yeast Salmonella, C. botulinum, 0.910 lactobacillus, Pediococcus, some moulds 0.870 Many yeasts Most moulds (mycotoxigenic 0.800 penicillia), Staphylococcus aureus, most Saccharomyces 0.750 Most halophilic bacteria, mycotoxigenic aspergilla 0.650 Xerophilic moulds 0.600 osmopholic yeasts, few moulds and feed industries use 0.65 as a minimum water activity value in manufacturing their products, each of which will have its own relationship between moisture content and minimum water activity value. By analysing product samples at various moisture content levels, a water isotherm can be constructed, plotting moisture content against the water activity value (see Figure 1). The moisture content for any given water activity value can then be determined with accuracy. The moisture content corresponding to the industry standard 0.65 water activity can be different for each product. Relative differences in the raw materials used can affect the amounts of free and bound water it contains, producing unique isotherms for each formulation. In fact, the formulation used can be a
  4. 4. FEATURE helpful tool in increasing the moisture content allowed by the minimum water activity. Moreover, the water isotherm and moisture sample data can be used to calculate the moisture target and the upper control limit. For most dried products, the portion of the isotherm at and well below the critical water activity value of 0.65 is linear, giving a proportional relationship between water activity and moisture content. A simple linear equation can therefore be used to determine the water activity value from the moisture content, or vice versa. The isotherm in Figure 1 shows that a moisture content of 8.92 percent will give a water activity of 0.65. For this product, then, 8.9 percent would be the upper control limit. Sample variance The target moisture value must also take into account variance between samples. Here, the moisture sample history can be used to calculate a standard deviation: ±3 standard deviations from the average will account for nearly 100 percent of samples. The moisture target can then be calculated using the upper control limit and the number of standard deviations required. Target moisture = UCL – N(s.d.) UCL: Upper control limit N: No. of standard deviations s.d.: Standard deviation of the product samples To give an example, using a standard deviation of 0.6 and the above upper control limit of 8.9 percent, and three standard deviations, you would receive a target moisture level of 7.12 percent. With current dryer control methods, only 0.14 percent of moisture samples would have a chance of exceeding the upper control limit. Many users of statistical process control methods will use 2 or 2.5 standard deviations in the target moisture calculation, giving targets of 7.42 percent and 7.72 percent respectively (see Table 2). The key values here are the percentage of samples that may be statistically above the upper limit. table 2: Results of altering the number of standard deviations on target moisture calculation target moisture UCl number of Standard standard deviation deviations As seen in the equation above, a reduction in the standard deviation will result in an increase in the target moisture. The results of this are increased production and energy savings. Assume, for example, that through improved dryer control the standard deviation was reduced by 30 percent, to 0.42 (see Table 3). The new target moisture would be 7.66 percent, 0.54 percent higher than the previous figure of 7.12. As this shows, improved dryer control – obtained by drying with cooler temperatures and being careful not to over-dry the product – can allow a safe increase in average moisture levels, resulting in a 0.5 percent production increase. Cooler drying temperatures would also result in energy savings. % above UCl 7.12 8.92 3 0.6 0.14 7.42 8.92 2.5 0.6 8.92 2 0.6 target moisture, with improved standard deviation values number of Standard % above standard deviation UCl deviations target moisture UCl 7.66 8.92 3 0.42 0.14 7.87 8.92 2.5 0.42 0.62 8.08 8.92 2 0.42 2.28 0.62 7.72 table 3: Number of standard deviations vs 2.28 With a method of calculating target moistures and upper control limits in place, we can give attention to optimising dryer control to reduce the moisture variance. A/S January-February 2014 | InternatIonal AquAFeed | 13
  5. 5. FEATURE Figure 2: Locations and dead times of moisture sensing package based on a model derived from first principles. The Delta T model, Moisture = K1(ΔT)p – K2/Sq relates the product moisture exiting a dryer to the temperature drop (ΔT) of the hot air after contact with the wet product, and the production rate or evaporative load (S). The model solves the two main problems with sensing and control by producing a rugged, reliable, ‘inside-the-dryer’ moisture sensor, and a control algorithm that precisely adjusts the dryer temperatures for evaporative load changes. Figure 2 illustrates an example of the soft sensor location, compared with the present standard moisture sample methods of online moisture meters and hand-sampling. As previously discussed, the reduction of standard deviation is in part tied to the reduction of dead time in the process, and therefore to the location of the sensor. Consumer benefit Figure 3: Actual results of improved moisture control Lowering dead time, improving control Even when the dryer is well maintained and running well, a main reason for poor moisture control is the timeliness and accuracy of the moisture sensing and the resulting control changes. The usual practice for most manufacturers is to periodically take moisture samples, using these for feedback to adjust the dryer temperatures. A few have had success with online moisture sensors, however, these are always after the dryer exit or after-the-fact. In either case, the ‘dead time’ – the time it takes for a load change entering the dryer to be detected – is long, and detection of moisture changes only take place after the product has left the dryer. By lowering the dead time, or by sensing the load changes earlier in the drying process, control changes could be made in a timelier manner, lowering the standard deviation. The standard deviation of the moisture samples is proportional to the dead time and, as previously stated, lowering the standard deviation allows the target moisture to be increased. Sensing moisture changes earlier in the dryer and making immediate control changes would reduce the dead time and improve moisture variance. In recent years, advances in process control and modelling have improved the drying process: for example, a soft sensor now exists that can measure and detect changes inside the dryer. Soft sensors use measurable process inputs and a mathematical model to produce a measurement of a process variable that cannot be measured directly with a hardware sensor. In this particular case, the soft sensor uses dryer temperatures to derive a measurement of product moisture while the product is still in the dryer. By detecting the moisture changes in this way, control adjustments can be made immediately, and moisture correction can begin before the product leaves the dryer. The Delta T Moisture/Dryer Control System is one such soft sensor and control 14 | InternatIonal AquAFeed | January-February 2014 With the combined approach of finding the highest moisture content that product safety allows and using a moisture sensing/ control method, the average product moisture can be optimised. The opportunity to ‘sell more water’ is too financially beneficial to ignore. For example, a 0.5 percent increase in average moisture content for a feed plant producing 25,000 tons per year at $800/ton would realise $100,000 extra sales revenue. The increase in moisture would also bring with it significant energy savings. Figure 3 shows actual moisture sample data before and after the advanced moisture control system was implemented in the feed dryer. The new regime achieved a 35.5 percent reduction in the moisture variance’s standard deviation, and a 0.5 percent increase in the actual moisture level of the product. Regardless of the formulation of feed products, the water activity value can be used to find the highest possible moisture content while protecting against mould growth, and do this in a relatively short period of time. The method of storing products at different moisture contents for months at a time, and continually checking for microbial growth throughout the period, is long and tedious for determining each individual upper moisture limit. Advances in sensors and process control provide the ability to control dryers and related equipment to produce the highest quality and safest product for your customers. More inforMation: Roger Douglas Website: www.
  6. 6. Subscribe today Get 6 editions of International Aquafeed magazine, and a copy of the International Aquafeed Directory I N C O R P O R AT I N G F I S H FA R M I N G T E C H N O L O G Y I N C O R P O R AT I N G F I S H FA R M I N G T E C H N O L O G Y I N C O R P O R AT I N G F I S H FA R M I N G T E C H N O L O G Y Animal co-product hydrolysates: Pellet distribution modelling: New functional fish feeds to reduce cardiovascular disease VO L U M E 1 6 I S S U E 6 2 0 1 3 - VO L U M E 1 6 I S S U E 5 2 0 1 3 - IAF13.05.indd 1 S E P T E M B E R | O C TO B E R VO L U M E 1 6 I S S U E 4 2 0 1 3 - 13/09/2013 09:24 J U LY | A U G U S T IAF13.04.indd 1 VO L U M E 1 6 I S S U E 3 2 0 1 3 - 24/07/2013 14:33 Profitable aquafeed moisture control Bioenergetics VO L U M E 1 6 I S S U E 2 2 0 1 3 - 13/05/2013 16:03 IAF13.02.indd 1 – from porcine blood in diets for Atlantic salmon parrs Towards aquafeeds with increased food security M AY | J U N E IAF13.03.indd 1 Spray-dried plasma – application in aquaculture nutrition Ultraviolet water disinfection for fish farms and hatcheries – channel catfish N OV E M B E R | D E C E M B E R 22/11/2013 14:38 Niacin – one of the key B vitamins for sustaining healthy fish growth and production EXPERT TOPIC – Salmon Chicken viscera for fish feed formulation Nutritional benefits of processed animal proteins – in European aquafeeds – as growth promoter for adult Nile tilapia EXPERT TOPIC I N C O R P O R AT I N G F I S H FA R M I N G T E C H N O L O G Y Transforming aquaculture production using oxygenation systems Controlling mycotoxins with binders Effect of probiotic, Hydroyeast Aquaculture AquaNor event review – a tool for improved feed delivery in sea cages They are what they eat Fine particle filtration in aquaculture – in compound feeds for aquaculture Understanding ammonia in aquaculture ponds – an update I N C O R P O R AT I N G F I S H FA R M I N G T E C H N O L O G Y Enhancing the nutritional value of live feeds with microalgae The potential of microalgae meals – a source of key molecules in aquaculture feeds Prevalence of mycotoxins in aquafeed ingredients: IAF13.06.indd 1 I N C O R P O R AT I N G F I S H FA R M I N G T E C H N O L O G Y Maintaining ingredient quality in extruded feeds The shrimp feed industry in China MARCH | APRIL VO L U M E 1 6 I S S U E 1 2 0 1 3 - 04/04/2013 16:17 + – an overview IAF13.01.indd 1 JA N UA RY | F E B R UA RY 23/01/2013 10:51 One year subscription only £69 / €84 / US$114 Your FREE copy of the Directory - woth £85 Choose your language English language Edited by the esteemed Professor Simon Davies, International Aquafeed is now in its 28th year of leading the way in aquaculture communication. - find out more at Special Chinese langauge editions 中文专刊 It is with great honour that the worldrenowned Dr Yu Yu and Dr Kangsen Mai edit our Chinese edition. With China leading the way in global aquaculture production it is important that we have the very best on hand to bring you the latest news. Subscribe at: Or contact our circulation manager, Tuti Tan on: +44 1242 267700 • Edición Española Iván Marquetti and Pablo Porcel head up our team in South America and are working tirelessly to ensure that our Spanish language edition reflects the needs and interest of both our clients and readers throughout the Spanish-speaking world. - find out more at
  7. 7. LINKS This digital re-print is part of the January | February 2014 edition of International Aquafeed magazine. Content from the magazine is available to view free-of-charge, both as a full online magazine on our website, and as an archive of individual features on the docstoc website. Please click here to view our other publications on I N C O R P O R AT I N G f I s h fA R m I N G T e C h N O l O G y Successful moisture control in aquatic feeds Current challenges and opportunities in amino acid nutrition of salmonids • See the full issue • Visit the International Aquafeed website • Contact the International Aquafeed Team • Subscribe to International Aquafeed Whisky by-products: – a sustainable protein source for aquaculture Closing the food waste loop: – a new angle for insect-based feeds Vo l u m e 1 7 I s s u e 1 2 0 1 4 - JA N uA RY | F e B R uA RY To purchase a paper copy of the magazine, or to subscribe to the paper edition please contact our Circulation and Subscriptions Manager on the link above. INFORMATION FOR ADVERTISERS - CLICK HERE