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In this article, I will keep awayfrom repackaging informationreadily available inmanufacturer’s brochures andlook at the practical choices anddecisions that brewers arefaced with when consideringbeer processing and filtration.

Imake no apologies for reminding readers ofthe basic physics behind filtration.Whatever decisions are made andtechnologies used, Darcy’s Law from 1856will always apply – the secret is to find waysof improving processes and look at innovativeways to approach the equation. Developinghis law and applying it to beer filtration:

Flow rate =

Permeability factor × Pressure drop × Area of filtration surfaceFilter bed thickness × Liquid viscosity

Pressure Drop across a filter bed =

Flow rate × Filter bed thickness × Liquid viscosityPermeability factor × Area of filtration surface

Applying this equation, it is easy to see howfilter design effects beer filtration.

Maximum pressure drop allowed across afilterModern filters using filter aids are designed towork up to 9 bar inlet pressure, therebyincreasing a filter run because they canoperate at a high differential pressure.Crossflow filters which do not use filter aidshave large surface areas and a very thin filmwhich makes up the filter bed on a membranesurface.

Filter areaIncreasing a filter’s surface area is key to awell performing filter no matter whattechnology is used. Experience has pointed tospecified flow rates for different types of filterwith plate and frame filters running typicallyat 3.5 hl/m2/h, vessel filters at 5-7hl/m2/h, andkieselguhr free crossflow filters are slower at0.5 – 1.0 hl/m2/h

Filter cake thicknessThis is dependent on the solids content of thebeer and dosing rate of bodyfeed powder.Breweries which install centrifuges reduce thesolids presented to the filter, are able to makelarge increases in filtration performance and

capacity. Crossflow filtration works becausethe filter bed thickness is very thin whencompared to a traditional kieselguhr filter.

Beer viscosityBetter brewhouse procedures and maltspecification to reduce beta glucans in thewort, sometimes with the aid of added betaglucanase, have reduced filtration problemsdue to high viscosity beer – howeverproblems are not unknown, if they are, theyare not widely distributed.

PermeabilityThe pressure differential across a filter bed isdetermined by the permeability of the filter

bed, which is dictated by the size and porosityof the filter powder. The amount of solids inan unfiltered beer will affect the bed thicknessand permeability of the filter bed on all typesof filter.

Ways of improving filtrationTraditional cold conditioning involved manydays storage at reducing temperatures downto below 0°C. In the process, beer flavourdevelops, yeast drops out and complexes ofproteins and tannins form and sediment toimprove a beer’s shelf life and haze stability.Modern large breweries have reduced coldstorage times to single numbers of days at-1°C or lower with high gravity brewing and

by Paul ButtrickBeer Dimensions

Choices, choicesBeer processing and filtration

Conical vessels and pipe fences at Früh in Cologne.

use aids such as PVPP and silica gels to givelong shelf-life, thereby saving valuable timeand capital for installing tanks.With order of magnitude estimates for cold

storage in a 500,000 hl/annum brewery for 1week costing £5–7 million, but rising to£30–40 million with eight weeks, it is easy tosee why traditional methods of long, slowcold storage periods have disappeared fromall but the most traditional breweries or thosethat have tanks and cellars to spare.So unless you have large amounts of cash,

or are wedded to tradition as a USP, or maybetruly believe long conditioning gives a better,more harmonious drinking beer, installingcentrifuges is a viable option. On the topic of‘does traditionally conditioned beer tastebetter?’ I’ll sit on the fence, and even after 30plus years I don’t know the answer, exceptthere are some lovely beers out there fromboth sides of the argument. If I had a brewerywith excess tankage, I’d at least have a gowith brewing a premium traditionallyconditioned beer and taste and judge theresults for myself.

Where should a centrifuge bepositioned?With beer solids being fundamental to theefficiency of filtration, it is easy to see howcentrifuges have become popular. So we’reshort on tank and filtration capacity and thedecision has been made to reduce process

times byinstallingcentrifuges ratherthan increasetankage. Does it go between FermentationVessel (FV) and Cold Storage Tank (CST) - socalled ‘green beer’ centrifuges, or betweenCold Storage Tank (CST) and filter?I did not think there was much debate on

where to put a centrifuge until I faced thequestion in a previous employment with aglobal brewing company. The standard wasfor installing centrifuges after CST, beforefiltration. My knowledge in the UK suggested

positioning the centrifuge between FV andCST. Discussing the issue with the centrifugesuppliers was very helpful – we can do eitherand the choice is yours!It seemed to me that positioning a

centrifuge between FV and CST would givethe following advantages:1) Reduced solids in CST, hence much longerfilter runs, reduced down-time, less filter aidusage and reduced losses.

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Above: Two 400 hl/hr rated GEA Westfalia ‘green beer’ centrifugesat a large brewery in Germany.

Right: The new Alfa Laval Brew2001 direct drive centrifuge on testin a European brewery

Valves, valvesand morevalves

Far left: The ubiquitousvalve array at Carlsbergin Denmark

Left: Tuchenhagenvalves at Quinn’sbottling facility inCheshire.

Above: Sudmo valves atCUB, Yatala.

2) Consistently reduced solid loads going tothe filter and longer runs would allow betterplanning for filtration and packaging with lesspackaging down-time. It ticked all the ‘supplythe customer on time’ boxes3) Any issues with oxygen pick up fromcentrifuges was much reduced since there wastime to rectify any centrifuge issuesThen I heard other arguments as to why the

centrifuges should be positioned after CSTjust before filtration.1) There would be the advantages of longerfilter runs, less downtime, as with thealternative option.2) Because yeast was still present inreasonable quantity in the Cold Storage tank,the maturation process and diacetyl reductionwould continue throughout the cold storageperiod, possibly leading to consistently lowerdiacetyl levels in the finished beer.3) Modern centrifuges are more reliable thanearly versions, so worries about breakdownsand oxygen pick up are much reduced.4) Some breweries have had filtrationproblems with prematurely blocked filters dueto high pressure differentials on relatively

clean beer with low yeast counts.So what did we do?Well, as all brewers do,

we carried out some trials which showed thatfiltration benefits were exceptional in bothsituations and there was no issue with earlyblocking of filters due to premature highpressure rises, so the decision was made toinstall centrifuges between FV and CST.Incidentally, having to install only twocentrifuges instead of three was anothersignificant factor in this decision. Everythingwas going well until six months afterinstallation, when horrendously short filterruns were experienced – oh dear. After muchhead scratching, sampling and analysis etc,focus swung on to two areas: timely tankbottoms removal and brewhouse practice inrelation to wort clarity. Going back to basicsand reintroducing ‘best practice’ in both areassolved the problem and no more short filterruns were experienced. So what would Iadvise if asked?Well, I think I would sit onthe fence with the centrifuge manufacturersand do a reasoned analysis of both options inrelation to the particular brewery, brands andcompany philosophy, overall project cost and

work out a decision from there. I am told thatBass in the late 1970s, obviously with plentyof money, used both a green beer centrifugeex FV and a larger diameter, tighter plate packand faster machine after the CST.Isinglass finings are still sometimes used to

aid sedimentation of tank bottoms beforefiltration. It is a simple, low cost (that is littlecapital outlay) option but thought must begiven to losses and handling tank bottomssedimented with finings, which can bedifficult to recover beer from.The main suppliers of modern centrifuges

areAlfa Laval, which manufactured the firstcentrifuge over 125 years ago and GEA-Westfalia who celebrated 100 years of beercentrifugation in 2009.About 50% ofmachines installed are green beer centrifugeswith this figure increasing over the last 5–8years. Both companies have continuallyincreased the size and sophistication of theirmachines, with an emphasis placed onoperational efficiency and reliability backedup by a drive to reduce energy and watercosts. For exampleWestfalia have introducedthe GSE 550 centrifuge to the market with a

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Beer processing

Membrane filtrationThe GEA Pall ProFi system in operation at Carlsberg in Denmark... ...and at MillerCoors, Shenandoah USA.

A Puresep installation for cider filtration at UBL in Ledbury, UK. The Alfa Laval membrane filters at Tucher in Nuremberg, Germany.

one-metre diameter bowl and is in the processof introducing a direct drive machine withoptimised pumping and frequency inverters.Alfa Laval presented their new Brew 2001eDrive centrifuge platform incorporating anew direct drive mechanism at Drinktec 2009,which will reduce energy and maintenancecosts considerably as well as give a modulardesign flexibility.

Alternatives to cold storageAn alternative is to look at other stabilisationoptions. I am an advocate of alwaysprocessing beer at a lower temperature than itis served at, so for me cold storage and properstabilisation with long periods of time, and/orsilica gel and PVPP treatment is currently thebest way of ensuring a good haze stability.However, science moves things on and the useof a proline-specific endo-protease enzymemarketed as ‘Brewers Clarex’by the Dutchcompany DSM has the potential torevolutionise brewer’s views on stabilisation.DSM say that by adding Brewers Clarex towort at the beginning of fermentation thatsubsequent cold storage times can be reducedor even eliminated and temperatures increasedcompared to current practice. Brewers are veryconservative when making changes that effectfinal beer quality, it will be interesting to seehow things have developed if I write a similarreview article in a couple of years’ time.

What are the options forfiltration ?Again its down to choices, and since my lastreview in 2007, more informed choices areavailable, but they are not necessarily anyeasier to make!Kieselguhr-free cross-flow filtrationThe major players Norit (BMF – BeerMembrane Filter, currently in 25 breweries)and Pall (Profi) are still very much promotingthe ‘green’ and quality benefits of kieselguhr-free crossflow filtration and have an increasingnumber of installations around the worldmainly in collaboration with large brewingcompanies.Alfa Laval with Sartoriusequipment are still involved, but to a lesserdegree and have three plants in China, Swedenand Germany. Swiss company Filtrox on theother hand are not yet promoting crossflow forbeer filtration, although they do use ceramicmembranes on their Cerinox filters to recoverbeer from tank bottoms.Listening to various sources, I get the

feeling that the financial justification forinstalling a cross-flow filter are not yet fullyproven and justifications produced to showtotal lifetime costs rely on figures that tend toprove or disprove whatever system thepresenter is championing.Norit introduced their new BMF-18 filter at

Drinktec in 2009. This filter works on thesame principle as their original filter, but withless hardware and components, allowing theCapex to be significantly reduced. Lesscomplexity also results in lower beer losses,and less water usage.

There have also been significantimprovements to CIP, resulting in a reducedneed for chemical cleaning which is replacedby less demanding water back-flushes. TheBMF-18 is so called because is is made up ofskid mounted units of up to 18 modules,giving 150 hl/hr filtration flowrate. This offersa very flexible approach which can be easilyuprated by adding modules and/or skids.Whatever the financial situation, there is no

doubting that kieselguhr-free filtration usingcrossflow will feature more in beer filtration inthe future. To do this, the costs mustdemonstrably reduce to win the argument. Thecost and reliability of membranes is still underscrutiny and there is a view that a ceramic ormore robust membrane needs to be used toincrease reliability, with a guaranteedmembrane life of ten years compared to thecurrent two. Norit’s approach to this issue is tohave a fixed financial guarantee for membranecost, as opposed to a fixed time guarantee.Another way to reduce costs on cross-flowfilters is to reduce the number of modulesused, thus making them smaller and cheaper tomake and renew. Back to Darcy again,increasing the filtration area of a module byreducing the diameter of the capillaries willachieve this.Norit has reported improvements in flavour

stability on beer filtered on their BMF (EBCVenice); this is attributed to lower iron (due tothe absence of kieselguhr) and dissolvedoxygen levels in the beer.The debate over the need for a centrifuge

before a crossflow membrane filter continuesas before with Norit continuing to workwithout a centrifuge, relying on a retentatetank to recover beer solids and Pall usingGEA-Wesfalia centrifuges to remove as muchsolid material as possible before final filtrationand polishing on the membrane filter. Thedebate is highly technical, on the one hand,installing a centrifuge must incur significant

extra cost, but the beer presented to the filterwill always be much cleaner and should meanthat a small filter can be used. Norit say thatcompanies already using ‘green beer’centrifuges do not need an extra centrifugebefore the membrane filter. Both companiesare constantly improving their equipmentwith an emphasis on lower water and beerlosses.

Traditional bed filtrationThe advent of crossflow was thought to signalthe end for installing traditional filters usingpowder regimes. This is not happening and highinvestment costs plus the other currentuncertainties of crossflowmeans that manybrewers still opt for more conventionalsystems. Plate and frame filters are still beinginstalled in remote situations where simplicityrather than technical sophistication is stillprudent. Candle filters, once thought to beoutdated are the predominant filter type usedfor both primary beer and PVPP stabilisation.Screen filters are still popular inAsia, but thesimplicity of candle filters with no movingparts and improvements to the candle designhas been very popular. The leading candlemanufacturers are Filtrox with their Synoxfilter and Krones with their TFS (Twin FlowSystem). Filtrox had their best sales ever in2007/8 whilst Krones have sold nearly 100TFS filters since 2002. The candle diameter ofthe Filtrox Synox is about one third less thanprevious designs. This has enabled morecandles to be installed within the filter vessel,thus significantly reducing the earlierdisadvantage of a high filter volume comparedto filtration area.Krones reports an improvement in beer

filterability of beer brewed from plant whichincludes internal dimple heating elements ontheir ShakesBeer conversion vessel. Theimprovement is thought to be due to differencesin particle size distribution in the mash.

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A large Norit crossflow filter showing modules each of 10m2 and 8 hl/hr flowrate.

The future for KieselguhrThe future for kieselguhr is not as grim as hadbeen predicted by some, mainly among thosewho promote kieselguhr free processes.Speaking to Matt Jordan ofWorld Minerals(Celite brands) there is still plenty of goodquality kieselguhr in deposits around theworld. His main defence was that kieselguhrstill gives the best most consistent beer clarityresults. Due to the production processes used,it is can be made in any number of differentgrades which makes it very flexible and ableto be used in response to brewing problemssuch changes in malt quality. The emphasis isnow on customer service where supplierswork with brewers to optimise their use offilter powder to bring down overall filtrationcosts. This involves selecting the right gradefor the job as well as reducing usage, bymatching dosing rates to beer solids. Spentkieselguhr disposal is still a potential issue,with soil injection still the main option,although using it in composting andincorporation into building materials is beinglooked into.

Kieselguhr-free filter powdersThere appears to be two approaches to thekieselguhr-free world in the brewery, onebeing crossflow filtration, the other beingdevelopment of kieselguhr-free filter aids. Itseems to have gone quiet on this latter ideaand I’m sure we would have seen more in thebrewing press if major breakthroughs hadbeen achieved. HoweverA-BInbev has beenworking on a kieselguhr-free filter aid forsome time and many of their breweries eitheruse it, are doing trials or are set up for its use.

Although it is an ‘in-house’ development atthe moment, it remains to be seen whether itwill be used solely for internal commercialadvantage or will eventually be sold to others.BASF, the German chemical conglomerate,have developed a filter aid called ‘Crosspure’for filtration of beer and other beverages.Apaper on Crosspure was presented at the IBDAfrica Symposium in March 2009 by FiltroxAG. It is a safe, easy to handle andregenerable material, produced bycompounding polystyrene (70%) with PVPP(30%) to form a filter aid with high chemicaland mechanical stability. Polystyrene isextensively used in food packaging whilstPVPP is well known for its beer stabilisationproperties, so at first sight looks to be a‘brewer’s utopia’material. At present it comesin two grades, mid range finer Crosspure F(permeability >170 mDarcy) and CrosspureXF (permeability >100 mDarcy) Crosspurecan be used in a similar way to kieselguhrwith similar dosing rates, but because it hasdifferent flow properties, adjustments have tobe made to filters to handle the material. Thechanges are in relation to particle distributionin order to get an even filter bed. Both theFiltrox Synox and Krones TFS filters can beadapted to change from kieselguhr toCrosspure use. The flow characteristics of theTFS – using external circulation and Synoxusing internal circulation can be optimised foruse with Crosspure.Other equipment required is plant for filter

aid regeneration. The filter aid regenerationprocess involves a number of steps including:rinsing with 85°C hot water; cleaning with2% caustic solution; rinsing with water

followed by an enzyme treatment (40–50°C atpH 4–5); a further treatment and pHadjustment process. It is a lengthy processtaking 4–5 hours and is similar to PVPPregeneration, with the 2% caustic and postrinse taking place on the filter elements priorto the enzyme treatment in a separate vessel.As in all production processes, down time iswasted production time, so I am surereductions in regeneration time will beforthcoming. Losses during regeneration aresaid to be similar to PVPP regeneration atabout 2%.In 2007 I reported on a new development

by KHS called Kometronic, incorporating aregenerable precoat filter replacing kieselguhrwith cellulose fibres. Despite enquiries, itseems things have gone quiet on this methodas well, so I assume that developmentscontinue but at a slower pace.

What about smaller/microbrewers?With more microbrewers investing in bottlinglines, there is a proliferation of bottled beerson supermarket shelves – those of you in thenorth of England will be amazed at the rangeavailable at Booths supermarkets. The microbrewer has a number of choices; go to arecognised processing and packagingcompany (like Robinsons, Camerons orDaniel Thwaites in the UK); go to one of thenew smaller bottling lines or some simply filltheir own beer directly into bottle and sell it asbottle conditioned. The larger contractbreweries are tending to set minimumpackaging lengths – say 75 hl, which is morethan many microbrewers wish to deal in.Bottling beer yourself as a bottled conditionedbeer is very artisan, but many beers becomeinfected and turn sour and it becomes verylabour intensive when sales go well. So whatoptions does the small brewer have? The keyfor them is to have a process that is straight-

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A Krones TFS kieselguhr filter running at 400hl per hour in the Vietnam Brewery , Ho Chi Minhcity, China.

A view above a 400hl/hr Pall CFS sterilisingfilter at Cölner Früh in Cologne, Germany.

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forward to apply, is cost effective and, mostimportantly, gives the right quality results. Amajor problem is that beer may be bright andclear at room temperature, but as soon as itgets near a fridge, a chill haze emerges whichbecomes permanent after a few weeks. Theartisans might say ‘so what’ but in my (andmost of the beer drinking public’s) mind, onlybeer which is supposed to be cloudy such as aHefeweizen should be cloudy, other beershould be bright. So rule number one forsmall breweries is to chill stabilise beercorrectly, which means ensuring the beer isheld at or below zero for a number of days,and don’t forget that beer is densest at 3°C, socooling jackets and temperature probes at thetop of a tank may show a -1°C, but the beerwill still be warm at the bottom.Anotheropportunity may be to use Brewers Clarex.Filtration options are difficult becauseequipment used in larger breweries isexpensive and oversized. The attention andtechnical input to filtering beer commerciallyon a small scale can be too easilyunderestimated.As with large filter plants thelaws of physics still apply and must be

considered when selecting a process andequipment. There are two main options forprimary filtration, whilst cartridge filtration ismost commonly used for final polishing and‘sterilisation’/biological stability.As with all filtration the amount of solids

being presented to the filter will define filterrun length.As a general rule if the solids arenot to be reduced before filtration, atraditional powder/filter aid process should beused. This could involve a simple plate andframe filter using a number of smaller frameswhere flow rates are about 3.5 hl/m2/hr. Apolishing/’sterilising grade’ sheet filter can beincorporated in the same frame with flowrates of 1.5hl/m2.An alternative to open style plate and frame

filters are vessel filters, which could includescreen filters, cartridge filters and perhapsconsideration of ‘Nellie’ filters, which wereused to clarify beer recovered from tankbottoms when I worked withWhitbread.

These from BritishFilters Ltd, PlymouthDevon are prepackedfilters rated at 100 hl/hr,smaller Nellie minors are30 hl/hr, andconsideration is beinggiven to producing a‘Micro Nellie’ for use inmicrobreweries rated at7–10 hl/hr. These wouldseem ideal for smallbreweries, with no messykieselguhr handling, withregeneration/back-washing taking placeafter 250 hl andrepacking at the factory

at longer intervals. Filters can be suppliedfrom normal rough beer clarification to beer‘sterilisation’ duties.Vessel filters offer an alternative to plate

and frames withVelo from Italymanufacturing a full range of horizontal andvertical screen filters ranging from 2–100m2.Smaller filters, ideally sized for smallbreweries up to 5m2 (25 hl/h), are horizontalscreen design, whilst the bigger units up to100m2 (500hl/h) are vertical screen filters.Pall filtration is offering fully enclosed

systems for use by smaller breweries.Filtration takes place on a fully housedmodular lenticular depth filter system calledSUPRAdisk II. The SUPRAdisk elementscome in a variety of grades suitable fordealing with differing quality beers. Housingscan be adapted to suit a variety of throughputsand the number elements can be altered togive increased flexibility.The option of using finings to clear beer

before filtration is an attractive one for smallbrewers. The clarified beer is then filteredusing a standard sheet or membrane cartridgefilter. This method is quite successful if wellmanaged, but finings and filters are not happybedfellows if settling time is not enough or ifany sediment is allowed near the filter,because not enough tank bottoms have beenremoved; losses can also be high.�

� AcknowledgementsI would like to thank those companies who havesupplied information for this article; always adifficult ask when the deadline comes at Christmas.

You can contact the author at:Paul.Buttrick@Beerdimensions.com

Diagram of the new unfiltered beerdistribution in Filtrox’s latest SYNOX candlefilter.

A new kieselguhr and PVPP Filtrox SYNOX filters rated at 400 hl/hr installed in a modern Chinesebrewery.

A roughing filter rated at 30 hl/hr suitable for use in a microbrewery.