ORIGINAL PAPER

Ronnie G. Willaert Æ Gino V. Baron

Applying sustainable technology for saving primaryenergy in the brewhouse during beer brewing

Received: 30 September 2003 / Accepted: 2 March 2004 / Published online: 1 May 2004� Springer-Verlag 2004

Abstract Wort boiling is the most energy intensive stagein the brewing process. For this reason considerableattention has been given to improve the efficiency ofwort boiling systems. Alternative wort boiling technol-ogies, such as low pressure boiling and high temperaturewort boiling, have been studied in detail during the lastdecades, with a focus on the reduction of primary energyconsumption. Recently, new boiling systems have beendeveloped and commercialised. The new systems re-duced the energy consumption still further and are allcharacterised by exerting a low thermal stress on thewort during boiling.

In this review, an overview of wort boiling objectives,possibilities to reduce the thermal stress on wort andenvironmental aspects of wort boiling are discussed.Furthermore, recent wort boiling systems—i.e. dynamiclow pressure boiling and boiling systems which are basedon low thermal stress boiling in combination with vol-atile stripping (steam, film and vacuum stripping)—aregiven special attention.

Introduction

In the brewhouse of a beer brewery, wort is produced bythe mashing process where the soluble content of groundbarley is extracted with brewing water. The wort pro-duced is filtered and is pumped to the boiling kettle.Wort boiling is a complex process during which a widerange of chemical, physico-chemical, physical and

biochemical reactions occur. Brewhouses which areequipped with old technology require a lot of energy toheat up the wort and are characterised by a long lastingboiling process. Nowadays, considerable primary energycan be saved using boiling systems which are designed toreduce the thermal stress during wort boiling and energyrecuperation systems.

Wort boiling objectives

The wort has to be boiled just before it is aerated andused as the nutrient broth for the alcoholic fermentationby the yeast cells. The wort boiling process has severalobjectives (see Table 1).

Extraction and isomerisation of hop components

Bitter hops—hop cones, pellets type 90 or 45—are addedat the start of the boiling process. It is necessary tosustain a high temperature for a certain time to obtain ahigh isomerisation yield of the a-acids. The isomerisa-tion yield depends on: the nature of the isohumulone(cohumulone gives the best yield), the duration of theboiling, the pH (a higher pH gives a higher yield, but thebitterness obtained at lower pH is more balanced andfiner), the humulone concentration (decreasing yieldupon increasing concentration), precipitation of iso-humulone with the hot break, the use of more efficientextraction procedures (e.g. use of higher temperatures),size of the hop fragments (extraction rate is higher formilled hop cones or pellets). Recently, the brewer canchoose between different hop products. Some hopproducts—i.e. isomerised pellets, isomerised kettle orhop extracts, and reduced isomerised a-acids—arealready isomerised before they are used and need not beadded at the wort copper, but can be applied at the endof the brewing process. By using these new hop prod-ucts, it is no longer necessary to keep the wort for a‘‘long’’ time at a high temperature.

R. G. WillaertDepartment of Ultrastructure, Flanders Interuniversity Institutefor Biotechnology, Vrije Universiteit Brussel, Pleinlaan 2,1050 Brussel, Belgium

G. V. Baron (&)Department of Chemical Engineering, Vrije Universiteit Brussel,Pleinlaan 2, 1050 Brussel, BelgiumE-mail: gvbaron@vub.ac.beTel.: +32 2 629 32 46Fax: +32 2 6293248

Clean Techn Environ Policy (2005) 7: 15–32DOI 10.1007/s10098-004-0249-8

Hot break formation

During boiling, two types of compounds are formed: (a)compounds consisting of proteins and polyphenols, andcompounds consisting of proteins and oxidised po-lyphenols which are insoluble in hot wort and precipitateas hot break; (b) compounds formed from protein deg-radation products and polyphenols which remain insolution during boiling, and only precipitate as coldbreak when the wort is cooled (Kunze 1999). Polyphe-nols are not directly involved in protein coagulationsince protein–polyphenol complexes are based onhydrogen bondings which have only a very weak bindingenergy at boiling temperatures and are unstable underthese conditions (Miedaner 1986; Narziss 1992). Hotbreak formation is encouraged by longer boiling times,vigorous movement of the boiling wort (which improvesthe reaction between proteins and polyphenols), and alow pH since the coagulation is best accomplished at theisoelectric point of the proteins. To obtain a sufficientcoagulation, a pH of 5.2 is recommended (Narziss 1992;Kunze 1999). The very low isoelectric pH of some pro-teins—such as b-glubulins, d- and �-hordein—is very low(4.9) and cannot always be realised during wort boiling.The removal of high molecular weight, coagulable pro-teins is very important for the composition and thequality of the finished beer. Insufficient coagulation andremoval result in a poor fermentation since the transportof substrates to and products from the yeast cells ishindered by the hot break adsorbed on the yeast cellwalls. This leads to an insufficient pH drop during theprimary fermentation and thereby to an incompleteelimination of proteins during the main fermentation,followed by a poor clarification during storage. This canresult in a beer with a harsh bitterness (‘‘protein bitter-ness’’) and a poor colloidal stability. The level of coag-ulable nitrogen in the finished wort is an importantfigure for the characterisation of the efficiency of wortboiling processes, and the evaluation and comparison ofdifferent boiling systems. The level of coagulable nitro-gen in unboiled wort is in the range of 35–70 ppm and is

reduced during boiling to 15–25 ppm with a recom-mended optimal value of 15–18 ppm. A low coagulablenitrogen concentration is beneficial for a good colloidalstability in the finished beer, but too low a concentrationcan result in head retention problems (Miedaner 1986).Protein coagulation is affected by physical and techno-logical factors (Narziss 1992), see Table 1.

Wort sterilisation and enzyme inactivation

Only a short boiling time is necessary to obtain a sterilesolution. The microflora of the malt, hop and otheradjuncts are readily destroyed. The inactivation ofresidual enzymes, which survived the mashing process, isalso necessary to fix the wort composition. There is onlya residual activity of polyphenoloxidase and a-amylases.Also, a short boiling time is needed to denature theresidual active enzymes.

The Maillard reaction

During wort boiling, the Maillard or nonenzymaticbrowning reaction is rather intensive, resulting in theproduction of various volatile and non-volatile aromacompounds and coloured melanoidins (brown nitroge-nous polymers and copolymers). The reaction starts withan interaction of low molecular weight proteins—i.e.amino acids—and reducing sugars, and the Amadorirearrangement (Danehy 1986). From there, a rathercomplex reaction network is described, including theStrecker degradation. The progress of the Maillardreaction can be observed by an increase in wort colour,by measuring the concentration of intermediate prod-ucts (such as 5-hydroxymethylfurfural (HMF), furfural,furfuryl alcohol, 2-acetylfuran, 2-acetylpyrrol and het-erocyclic nitrogen compounds (Narziss et al. 1983)), ormeasuring the increase of the concentration of reduc-tones using the ‘‘Indicator Time Test’’. A too intensive,uncontrolled reaction can lead to unattractive flavoursin beers. The melanoidins formed are reducing

Table 1 Objectives of the wort boiling process (Narziss 1978; Hough et al. 1982; Narziss et al. 1982a; Miedaner 1986; Enari 1991; Narziss1992; Kunze 1999)

Objective Influencing parameters

Æ Extraction of a-acids Temperature, fragments sizeÆ Isomerisation of a-acids Temperature, boiling time, pH, humulone concentrationÆ Coagulation of proteins (hot break formation) Boiling time, nature and manner of boiling, heating system,

copper shape and wort flow configuration, temperature of heatingmedium, wort composition (malt modification, kilning temperature,mashing temperature, pH)

Æ Wort sterilisation and inactivation of enzymes to fixthe wort composition

Boiling time, temperature

Æ Formation of reducing and aromatic compounds(Maillard reaction)

Water content, pH, oxygen concentration, temperature,reaction (boiling) time

Æ Formation of colouring substances pH, parameters influencing the Maillard reactionÆ Removal of undesired volatile aroma compounds Temperature, boiling time, pH, evaporation rateÆ Acidification of the wort Hop addition, intensity of the Maillard reaction, alkaline

phosphates and Ca++ and Mg++ content, malt typeÆ Evaporation of water Temperature, boiling time

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compounds, but are also involved in the oxidation ofhigher alcohols in fresh beer resulting in volatile alde-hydes (Hashimoto 1972). Melanoidins can exert pro-and antioxidant effects (Ames 2001a). Although thestructures of melanoidins isolated from foods are un-known (Ames and Nursten 1989; Ames 2001b), consid-erable progress has been made in recent yearsconcerning the structures of melanoidin-like materials.

Formation of colouring substances

Wort boiling results in an increase in wort colour: typ-ically 4 EBC units for a light coloured beer. This in-crease is due to the formation of melanoidins, thecaramelisation of sugars and the oxidation of polyphe-nols. Since the extent of the Maillard reaction is higherat a higher pH, the colour increases with increasing pHof the wort. Thermal stress during wort boiling can alsobe monitored by the thiobarbituric acid coefficient(TBC), number (TBN) or index (TBI). The TBC valuescan also give (in combination with the coagulablenitrogen concentration) information about the expectedfoam stability of the beer produced (Wasmuht andStippler 2000).

Removal of unwanted volatiles

During malting S-methylmethionine (SMM) is formed.This compound is the precursor of dimethylsulphide(DMS) which gives a unpleasant smell and taste whenpresent in the finished beer. At high temperatures—i.e.during kilning, mashing (decoction method) and boil-ing—SMM is decomposed to DMS (Anness and Bam-forth 1982). DMS is very volatile and can be readilyremoved with the vapour during boiling. The transfor-mation of SMM to DMS fits a first order reaction with ahalf lifetime of 30 to 70 min at 100 �C (Narziss 1992).The formation of DMS is considerably lower at pH 5.0compared to a pH of 5.5–5.8. This fact determines thelower pH limit value of the wort at the start of boiling.An optimal combination of boiling time and tempera-ture has to be used since when the boiling time is toolow, the DMS concentration will be too high (butcoagulable nitrogen can be OK); when the boiling time istoo short DMS concentration will also be too high (thecoagulable nitrogen content can be correct) (Schwill-Miedaner and Miedaner 2001). On the contrary, a toohigh boiling temperature and too long boiling time willresult in a too low coagulable nitrogen content.

The removal of other unwanted volatile compoundsduring boiling is also necessary. These volatiles can beclassified into three groups: malt-derived volatiles, hopoils and volatiles which are formed during wort boiling.Several unwanted volatiles have been detected in thevapour condensate during boiling; e.g. a five-foldquantity of 2-acetylthiazole has to be evaporated (Wa-ckerbauer 1983). Myrcene is a very volatile hop oil,which gives a harsh and unpleasant aroma. In contrast,

b-caryophylene, b-farnesene and humulene give a wan-ted hop oil aroma.

Acidification of the wort

Upon boiling, the wort becomes slightly acidic (typically0.1–0.3 pH units for a classical boiling process) due tothe formation of melanoidins, the addition of hop acids,the precipitation of alkaline phosphates and the acidifi-cation action of Ca++ and Mg++ ions with phosphates.The use of dark malts (intense Maillard reaction duringkilning) will also give a larger pH decrease compared topale malts.

Evaporation of water

Wort boiling results in the evaporation of water (andvolatile organic components) and the concentration ofthe wort. During classical (conventional) atmosphericboiling 8–12% of the initial wort volume was evaporated(some breweries even boiled for 2 h with an evaporationrate of up to 18%). It has been shown that reduction ofevaporation to as little as 2% can be achieved withouthazard to flavour or other beer qualities such as bitter-ness, head retention, total nitrogen haze life and colour(Buckee and Barrett 1982).

Reduction of thermal stress

Recently, new boiling systems have been developedwhich exert a low thermal load on the wort. A lowthermal load has a positive influence on the sensorialand foam characteristics of the beer produced. Thethermal stress can be quantitatively assessed by mea-suring the colour, TBN or the concentration of hightemperature indicators (Manger 2000). Possibilities ofreducing the thermal load are:

– Application of the infusion mashing technique (in-stead of decoction mashing)

– Reduction of the heating time of the wort beforeboiling

– Reduction of the boiling time– Reduction of the temperature during boiling and high

temperature holding periods– Reduction of the filling and rest time of the whirlpool– Reduction of the wort cooling time

Energy saving during wort boiling

The brewhouse is the biggest energy consumer in thebrewery (Fig. 1). Since the oil crisis in 1972 and morerecently since the introduction of stringent ecology lawsand taxes, the reduction of the use of primary energyduring wort boiling is of primordial concern to thebrewer. Today, various possibilities of energy recuper-ation are available.

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In the brewhouse, thermal energy is required to heatthe mash and the wort, and to boil the wort. Nowadays,the energy required for the mash and wort heating isalready recuperated during the wort cooling process.There is still some potential energy recuperation possibleduring wort cooling. Cooling of the wort after boilingcan be accomplished in two steps: before and after thewhirlpool, since it has been shown in large-scale teststhat cooling of the wort by casting out at a temperatureof 89 �C significantly reduced the TBC (lower thermalstress) and improved the flavour stability of the beerproduced (Coors et al. 2000; Krottenthaler and Back2001).

The recuperated energy can be used for pre-heatingand boiling of the wort, and for hot water production(Vollhalls 1994; Thüsing 2000). Energy recuperation canbe accomplished by (see Fig. 2)

– Reducing the boiling time– The use of a vapour condenser for the production of

hot service water with or without wort heating– Mechanical vapour compression– Thermal vapour compression with or without wort

heating

Thermal and mechanical vapour compression ismainly used in the atmospheric boiling method since thevapour compression demands calandria for largeramounts of wort. An outlet temperature of 107–108 �C

is required if a calandria in combination with lowpressure boiling is used. The choice of an energy recu-peration system will depend on the total evaporationrate, the hot water demand and the costs for thermal andelectrical energy (Thüsing 2000, 2001).

Energy saving with vapour condenser

The evaporated water mass during boiling contains ahigh energy content. The condensation of 1 kg of steaminto 1 kg of water at 100 �C gives an energy of 2,260 kJ.Considerable heat can be saved using a vapour con-denser and an energy storage system (see Fig. 3). Insteadof a one-tank storage tank, a two-tank—one tank con-taining the hot water (±99 �C), the other the used hotwater (±80 �C)—energy storage system can also be used(Lösch and Körber 1984; Lenz 1994). Nowadays, asingle-layer plate heat exchanger is used as vapourcondenser. The energy recuperated by the condenser isstored in the energy saver and used to heat the lauteredwort before boiling. The energy saver is a hot waterdisplacement storage. The vapour condensate can befurther cooled to approximately 30 �C using cold waterwhich is normally a prerequisite for its discharge into awaste water system. The vapour condensate cooler canproduce hot water of a temperature of approximately85 �C. Only 4–5% of the total evaporation is sufficientfor the production of hot water exclusively for the wortheating. The same system can be used for low pressureboiling. Low pressure boiling works with a reduced

Fig. 1 Energy consumption in the brewhouse (N.N. 2001a):A percentage of total heat energy requirements; B percentage oftotal electrical power requirements

Fig. 2 Possibilities of energy recuperation with atmospheric orpressure boiling (Thüsing 2000)

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evaporation rate compared to atmospheric boilingwhich results in a lower production of hot service water.If the vapour condenser is included in the pressure sec-tor, energy storage water of about 100 �C can be pro-duced.

Energy saving with vapour compression

During atmospheric boiling, the vapour produced has atemperature of about 100 �C. If this vapour is com-pressed to a few tenths of a bar overpressure, the tem-perature is raised to 102–108 �C and it can be reused forheating. Vapour compression can be achieved by using amechanical compressor or a steam jet compressor(thermocompression). The condensate, which is devel-oped at the heater by the condensation of the vapour,leaves the cyclic process through a condensate cooler,which produces hot driving water (see Fig. 4).

Using a mechanical compressor, the vapour is com-pressed to an overpressure of 0.3–0.4 bar. The wort isheated to boiling temperature using fresh steam. Theboiling process is maintained in operation using heatfrom the compressed vapour. The additional use of avapour condenser is not possible because all the vapoursare directly led back to the boiling process. Conse-quently, the lautered wort is not preheated whenmechanical vapour compression is employed (Fig. 4A).Additional disadvantages are the complicated plantengineering, noise production, high maintenance costsand peak electricity demands.

In thermal vapour compression, live steam from aboiler with an overpressure of at least 8 bar and up to18 bar is fed to the steam jet pump. The vapour issucked in and compressed to 0.1–0.4 bar overpressure.About 30–35% of the vapour is condensed in the kettlevapour condenser to produce hot water that can be usedfor preheating the wort (Fig. 4B). The advantages anddisadvantages of using thermal vapour compressor aresummarised in Table 2.

Environmental aspects

Vapour is produced during wort boiling. The vapourcontains 99% water and organic constituents from hopsand malt; it is free of salts (Hackensellner and Pensel1993). More than 160 constituents have been identifiedand grouped into aldehydes, alkanes, alcohols, esters,furans, ketones and terpenes (Buckee et al. 1982;Drawert and Wächter 1984). Using a vapour condenser,hydrophilic vapour components are completely con-densed. Hydrophobic vapour constituents (includingsome hop aroma components) are not completely con-densed (Wächter et al. 1985). The non-condensable ele-ments are discharged to the atmosphere as residual gasor can be decomposed in a biofilter.

If the vapour is allowed to escape from the chimney,odour pollution is caused. By using a vapour con-denser, polluting volatiles can be received and treatedin the brewery’s waste water plant. However, a hightotal evaporation (larger than 4–5%) requires an escapeof the share which is not necessary for the hot waterproduction through the chimney. In this case, odouremissions can be reduced using a biofilter. The exhaustvapour is therefore first cooled using an air-to-air heatexchanger with ambient air (Reischmann and War-

Fig. 3 Pressure wort copper with vapour condenser (pressureless);energy storage system and wort heating (Vollhals 1994): 1, wortcollecting vessel; 2, wort kettle; 3, wort heater; 4, vapour condenser;5, energy storage tank

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necke 1997). Subsequently, the exhaust air flows into acountercurrent scrubber and next to a high capacitybiofilter where the odour substances are biologicallydecomposed.

In the context of lowering specific waste water levelsarising in a brewery and in order to push down the costs,possibilities have been proposed for the utilisation of

treated or non-treated vapour condensate. Reverseosmosis and activated carbon filtration have beeninvestigated (Back et al. 1996; Lenz 1996; Chmiel et al.1997; Back et al. 1998). The treated condensate has beensuccessfully used as brewwater for the production of apale beer. Non-treated vapour condensate can also beused in the brewery in all processes which require water

Fig. 4 Wort boiling with Amechanical and B thermalvapour compression (Thüsing2000): 1, wort collecting vessel;2, wort kettle; 3, external boiler;4, condensate cooler; 5, vapourcondenser; 6, wort heater;7, balance tank; 8, energystorage tank; 9, steam jet pump

Table 2 The advantages and disadvantages of thermal vapour compression (N.N. 1993; N.N. 1995; Lambeck and Hintzen 1996; Fohr andMeyer-Pittroff 1998; Kunze 1999; Thüsing 2000)

Advantages Disadvantages

Æ A trouble free, cheap, safe and low maintenance compressor,Æ Low noise and vibration,Æ Especially profitable for small and medium-sized breweries,Æ Lower investment costs compared to mechanical vapour compression,Æ One steam jet compressor is sufficient for any size of plant,Æ Driven by live steam,Æ Stepless control by injector needle valves.

Æ Requires a high steam pressure (new pipework needed),Æ A relative high quantity of hot process water arising,Æ Large specific heat transfer surface with a high circulationrate (external heater needed or internal heater withrecirculation pump),

Æ A higher quantity of vapour condensate, waste and hotwater arising and more boiler feed water required comparedto mechanical vapour compression.

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and where the organic constituents in the vapour con-densate are not detrimental; e.g. for general cleaningpurposes, sparging for lauter tuns and mash filters,flushing of false bottoms of lauter tuns, cooling waterfor condensers, cooling towers and motors (Fohr et al.1999).

Wort boiling systems

Today, different boiling systems are being used. Table 3shows an overview with some characteristics of thepresent-day systems. In this review, dynamic low

pressure boiling and the recent boiling systems whichare characterised by a low thermal stress phase with asubsequent volatile stripping phase will be discussed indetail.

High temperature boiling (HTWB) is an alternativeboiling system. It is a continuous system and the idea isquite old (Dummet 1958; Daris et al. 1962; Evers 2002).At high temperatures of 130 �C or 140 �C very satisfyingwort analysis data can be obtained although very shortboiling times of ca. 5 min are used (Narziss et al. 1982b;Narziss et al. 1983). Narziss et al. (1991a, 1991b) pro-duced the best beers with a boiling temperature of130 �C and a high temperature holding period of 180 s.

Table 3 Overview of thepresent-day boiling systems

aBoiler outletbTemperature of the low ther-mal stress phase

Boiling system Temperature(�C)

Boilingtime (min)

Totalevaporationrate (%)

Classical atmospheric boiling 100 60–80 ca. 8Low pressure boiling (LPB):Classical 103–104a 55–65 6–7Dynamic 103–104a 45–50 ca. 5High temperature wort boiling (HTWB) 130–140 2.5–3 6–8Low thermal load phase+stripping phase:Steam stripping: Meura system 100b 40–45 2.5–4Film stripping: Merlin system 100b 35 5–6Vacuum stripping:Ziemann system 100b 40–50 6Nerb system 103a/99b 50–60 4.7–5.4Schulz system 97.5b 60 8

Fig. 5 Temperature profileduring dynamic low pressureboiling (after Kantelberg andHackensellner 2001)

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The wort is heated in three steps. In the first two steps,vapour from the flash-off chambers is reused. Consid-erable energy savings can be obtained due to the shortboiling time and energy recuperation. Alternative con-tinuous systems have been developed, e.g. continuouspressure boiling in a multistage column comparable to atray distillation tower (Krüger and Ehrlinger 1984) orthe use of multiple-effect evaporators (Korek 1981).

A new boiling system using microwaves has beentested by the company Huppmann (Herrmann 1999;Isenberg 1999). Microwaves are produced in a separategenerator. These microwaves are guided to the wortkettle via a copper waveguide and brought into the wortthrough the ‘‘applicator’’. The total wort volume is he-ated uniformly and no burn-on danger exists. Wortboiling trials (5 hl scale) with microwaves (4%, 6% and8% evaporation) have been compared to conventionalboiling (90 min and 8% evaporation). The analysis ofthe beers obtained showed that the aroma was compa-rable to that of the beer obtained from the conventionalboiling although the boiling time could be reduced to45 min (5% evaporation). The taste stability was ratherpoor for the ‘‘microwave beers’’ produced (Meilgaard2001).

Wort boiling at low pressure

Conventional boiling at low pressure has been intro-duced in breweries since 1979 to decrease the energycosts (Lenz 1982). The pressure is kept constant duringboiling at a value of 1.08–1.21 bar (boiling temperaturefrom 102 �C to 105 �C). This technology has been fur-ther developed and the state of the art today is dynamic

low pressure boiling with several subsequent shortphases of pressure building up and pressure release withcorresponding multiple wort stripping (N.N. 2001b;Hackensellner 2001; Kantelberg and Hackensellner2001; Schwill-Miedaner and Miedaner 2001). Thistechnology has been commercialised by the companyHuppmann (Kitzingen, Germany).

After an atmospheric pre-boiling phase of 3 min at100 �C, the pressure is periodically built up (1.17 bar,104 �C) and released (1.05 bar, 101 �C) (see Fig. 5). Theboiling is ended with a post-boiling phase of 5 min at100 �C. The pressure reduction phases ensure an inten-sive boiling phase with stripping of wort volatiles. Atotal evaporation rate of 4.4–4.5% is obtained. Thevapour produced is used to produce hot water and therecuperated energy can be stored in a hot water storagetank (see Fig. 6). Part of this stored energy can be usedto heat up the wort before boiling. Recent results haveshown that—due to the reduced thermal stress on thewort—the head retention of the beers produced wasincreased (N.N. 2001c). Results of an industrial trial(265 hl) are shown in Table 4.

Heating and boiling of the wort are performed usingan internal boiler. The recent internal boiling systemsare designed to minimise the thermal load during heat-

Fig. 6 Dynamic low pressureboiling with energyrecuperation systems(Hackensellner 2001): 1, wortcollecting vessel; 2, wort kettle;3, heat exchanger; 4, vapourcondenser; 5, energy storagetank

Table 4 Results obtained with dynamic low pressure boiling(Schwill-Miedaner and Miedaner 2001)

Parameter Before boiling After boiling

Coagulable nitrogen (mg/l) 54 23TBN 28 41Free DMS (lg/l) 289

ing and boiling, and are characterised by (Hackensellner1999; N.N. 2001d; Kantelberg and Hackensellner 2001):

– Lowest heating medium temperatures possible– Maximal surface temperature of 107 �C– Boiler geometry perfectly adjusted to wort kettle size– Adequate heating tube geometry– Much larger boiler outlet nozzle (for high circulation

capacity)– The smallest temperature difference possible between

vessel content and heated wort in the boiler– The wort spreader to extend the evaporation surface

A force-type circulation can also be used during wortheating and boiling. A connection pipe, which is bran-ched off from the casting pipe downstream of the castingpump and terminates again in the wort vessel under-neath the inner boiler (Stippler and Wasmuht 1999a) ora recirculation pipe and pump can be used in the sameway (Hoefig 1994).

A further reduction of the thermal load and the sta-bilisation of the DMS concentration can be achieved bypre-cooling the wort before it enters the whirlpool(Krottenthaler and Back 2001; N.N. 2001c). A decreaseof the temperature from 98 �C to 89 �C resulted in areduction of the DMS concentration to 40 lg/l; and theTBN (and the colour) decreased by 7–10 units. The beersproduced scored better after a forced ageing experiment.

Wort boiling in combination with steam stripping

In wort boiling, most of the reactions are only time/temperature dependent (Reed and Jordan 1991; Schwill-Miedaner 2002): the inactivation of enzymes, the steril-isation of the wort, extraction of hop compounds,isomerisation of a-acids, coagulation of the proteinfraction, lowering the pH and formation of reducing andaromatic compounds. For all these reactions, no evap-oration is needed. A simple hot wort stand at boilingtemperature is enough to guarantee that these reactionsoccur. Additionally, this methodology ensures a low

thermal load, which guarantees a balanced beer withgood foam stability.

In contrast, for a few specific goals evaporation isrequired: initially to achieve the desired gravity of thewort at the end of boiling and secondly the high evap-oration rates generally applied are meant to eliminateunwanted volatile compounds. In classical wort boiling,evaporation ratios of 7 to 10% are common. Unfortu-nately, in conventional wort boiling, large energy lossesmay occur since a wort kettle is not necessarily designedfor efficient stripping by evaporation. The effectiveevaporation surface per unit volume is very low whichrenders the elimination of volatile compounds moredifficult (Reed and Jordan 1991). For this reason a vig-orous wort boil is generally required. Different tech-nologies of wort boiling are in use and all these systemshave one thing in common: they all try to increase theeffective surface to facilitate the removal of the volatilecompounds.

This problem has been approached by developing anovel two-stage wort boiling system (Baron et al. 1997;Seldeslachts et al. 1997; Baron 2000). In the first step, thewort is kept at wort boiling temperature and no signif-icant evaporation occurs. The volatile compoundsformed through chemical reactions and extracted fromthe added hops are accumulated in the wort. In thesecond stage, after wort clarification, the volatile com-pounds are eliminated, very efficiently, in a ‘‘wortstripping column’’.

The motivation for developing this system was basedon a number of potential benefits. Firstly, it is a tech-nology which could generate significant energy savings.Secondly, it could form a means of efficient processcontrol. The amount of volatile compounds present inthe final wort and the colour of the wort can be bettercontrolled. With regard to the output of CO2, linked tothe use of primary energy, legislation in the individualcountries is becoming more and more stringent. Anotherimportant advantage, which is related to the previousone, is that wort stripping could reduce the output of thevolatile organic compounds (VOCs). In this matter, new

Fig. 7 Process layout includingwort stripping (Baron et al.1997): 1, wort kettle;2, sedimentation tank (wortclarification); 3, wort stripper;4, wort cooler

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regulatory initiatives are also to be expected to reducethe output of the amount of VOCs in the atmosphere.

Process layout

The process layout (Fig. 7) shows that the wort strippingprocess occurs best between wort clarification and wortcooling. The reason for this is simple. In the classicalprocess the additional amount of volatile compoundsformed after the end of boiling can no longer be elimi-nated and therefore pass to the fermenter, whilst duringwort stripping, the amount of volatile compoundsformed from their precursors during the hot wort stand,can be eliminated.

A detailed view of the wort stripping column is shownin Fig. 8. The wort first passes through a heat exchangerto heat the wort to its boiling temperature at the columnpressure. With the wort distribution plate, the wort isspread uniformly over the entire cross section of thecolumn, avoiding foaming as much as possible. Thepacking used was Cascade Rings (Glitsch) for their openstructure with a low risk of fouling. At the bottom of thecolumn the wort is gently guided via the column wall tothe wort buffer, again avoiding foaming. The wort thengoes to the wort cooling heat exchanger. At the top ofthe column, the steam saturated with volatile compo-nents is condensed and eliminated.

Processing sequence

A wort boiling system with wort stripping has beenoptimised and used on an industrial scale at the Leuven(Belgium) plant of Interbrew. The characteristics anduse of this system will be discussed.

In the wort kettle, the total residence time is keptidentical as for a conventional wort boil, but threesubphases can be distinguished. In the first subphase, atthe start of boiling, a short period of heavy boiling(100 �C) is introduced (e.g. 5 min). This short period is

mainly aimed at initialising the trub formation and athomogenising the hops just added to the wort kettle(Reed and Jordan 1991). After this first period, there is along period (±30 min) at 100 �C during which thesteam supply to the kettle is shut off. During this stageany evaporation and cooling down of the wort is avoi-ded by closing the doors and if possible the valve in thechimney. The third subphase in the wort kettle involvesa short period of heavy boiling (100 �C). During thisperiod of 5–10 min the accumulated volatile compoundsare partially eliminated. The boiling time determines thedownstream load for the stripping. For this reason, thissecond heavy boiling period can be used to regulate thefinal volatile content after stripping. Thanks to thestrong mixing the hot break formation is activated.Naturally, it must be verified that the desired gravity ofthe wort at the end of boiling has been reached. Thetotal evaporation in the kettle can be easily kept below2.0% of the total wort volume.

The wort clarification consists of a cylindro-conicaldecanter combined with a centrifuge. During the trialsno changes were applied to this part of the process.

The wort stripping is carried out just before wortcooling. The clarified wort is pumped at 400–450 hl/h.Before entering the 1-m diameter, 2-m packing heightcolumn, the wort is heated again to its boiling point, inequilibrium with the chosen pressure. If the wort enteredthe stripper at a suboptimal temperature, the steam in-jected would be used partially to warm the wort to itsboiling point, instead of stripping out the volatile com-pounds. In such a case, the stripping efficiency woulddrop enormously! The flow rate of the steam injection isregulated at 0.5 to 2.0% of the wort flow rate. In case thewort enters the column at boiling point, the amount ofsteam injected equals the amount of condensate.

DMS formation and elimination during the hot wortperiod

During the optimisation of the industrial pilot strippingcolumn, DMS has always been used as a marker to

Fig. 9 Evolution of SMM and DMS during wort boiling for aclassical wort boiling and a reduced wort boiling with threesubphases (wort stripping) (Seldeslachts et al. 1997)

Fig. 8 Vertical section view of the wort stripping column(Seldeslachts et al. 1997)

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measure the efficiency of the stripping. In Fig. 9, it canbe seen that during the wort boiling the SMM is de-graded continuously and transformed into DMS. In caseof a conventional wort boil, the DMS present as well asthe freshly formed DMS are continuously eliminated,albeit through strong boiling with evaporation andresulting energy loss. In the case of the wort boilingstrategy with three subphases in the wort kettle, an in-crease of the DMS in the second subphase was recordeddue to the further degradation of SMM along with avery low or lack of evaporation. In the last subphase inthe wort kettle, the DMS is reduced to a set level, tomatch the column efficiency in order to reach a suffi-ciently low level of DMS.

During the subsequent hot wort period, from worttransfer to the settling tank, until the hot stand beforewort cooling, the remaining amount of SMM is furtherdegraded into DMS. The DMS formed cannot beeliminated due to a lack of evaporation in this phase. Inboth cases (conventional wort boiling and reduced wortboiling) the levels of DMS increase proportionally to theamount of SMM left after wort boiling and further de-graded during this hot wort period. For a conventionalprocess, this amount of DMS passes directly to thefermenter. For the ‘‘wort stripping’’, this DMS is par-tially eliminated.

During wort stripping, a high amount of DMS (inthis case between 170 and 190 ppb) enters the column.At the bottom of the column, the stripped wort leaveswith a DMS level of about 20 ppb. The average strip-ping efficiency (for DMS) amounts to 85 to 90% withthe actual industrial pilot stripping column. Other vol-atile compounds, such as wort aldehydes, are eliminatedas well. The elimination efficiency of individual com-pounds depends on their boiling point, or better on theirrelative volatility. Because the process of wort cooling isdirectly following the stripping column, this low amountof 20 ppb DMS passes directly to the fermenter. In thecase of a classic wort boil, the amount of DMS goinginto fermentation is determined by the amount of DMS

present at the end of boiling plus the fraction formedduring the rather long hot wort stand, and may evendouble again in that time.

Industrial trials

A number of 420-hl brews at the end of boiling wereprocessed using the two alternative wort boiling systems:firstly the control beer was boiled conventionally andsecondly the trial beers were boiled following the three-step boiling process combined with wort stripping.Figure 10 confirms the previously discussed results.During the two short periods of heavy boiling in the‘‘wort stripping’’ process, a decrease in DMS contentwas recorded. After stripping, the DMS level fell belowthe values obtained for the control beer. Typically DMSin the wort drops from 190 ppb to values between 20and 30 ppb. The DMS eliminated can be measured inthe condensate. Amounts of 10,000 ppb DMS and morewere measured in this stripping condensate.

The DMS values from both the trial and the controlbeers were further followed in the downstream process.In the bottled beers, about the same values for bothbeers (38 and 39 ppb respectively) were measured. Thefinal level of DMS in the finished beers is a function ofthe amount in the wort, and of the combined effect ofDMS stripping and DMS formation (out of DMSO)during fermentation (Nakajima and Narziss 1978; Lee-mans et al. 1993).

Most physico-chemical parameters of the finishedbeers were similar. It can be concluded that both beershave the same profile. In a triangular tasting session, asignificant difference at the 5% level between the beers,with more preferences for the trial beer, was found. Inthe descriptive panel, however, no significant differencesbetween the beers could be found for individual de-scriptors. Recently, data were gathered supporting theview that the beers that passed over the stripping columnhave an improved flavour stability.

Benefits of applying wort stripping

The energy savings come largely from the enormousreduction in evaporation energy needed. Because thewort volume in the kettle at the start of boiling is alsosmaller, it is not necessary to warm this supplementarywater from 78 �C to 100 �C. The injection of a smallamount of live steam is of course a cost in the eco-nomical evaluation. However, there is the possibility topartially recover the residual heat in the condensate. Inthe case where an external boiler is used, there is abenefit from the potential gain of the reduced electricityconsumption as well.

In terms of applying wort stripping in a new brewery,the wort kettle could benefit from a simpler design. Also,the steam boilers could have a lower capacity. This couldbe important when the brewing capacity needs to beexpanded. Installing a wort stripping column in such a

Fig. 10 Evolution of DMS during wort boiling, wort clarificationand wort cooling during an industrial trial on a 12 �Pl lager beer(classic wort boiling+wort stripping) (Seldeslachts et al. 1997)

25

case, could eventually postpone or avoid the investmentfor a new steam boiler. The condensation of the un-wanted volatile compounds prepares the brewery forfulfilling current and future environmental constraints.

Energy savings

The energy consumption calculation for this new boilingsystem is shown in Table 5 (Braekeleirs 2001). As can benoticed, a considerable amount of energy can be saved(order of 60%). The data were obtained on a retrofittedprototype equipment and further reduction is possiblewith better integration. Nowadays, this technologyis commercialised by the company Meura (Tournai,Belgium) (N.N. 2001b; Braekeleirs 2001).

Recently, the concept of steam stripping has alsobeen introduced in a continuous wort boiling system(Visscher and Versteegh 2000). Here, the wort is heatedto boiling temperature and flows through a plug flowreactor. Subsequently, a continuous steam strippingcolumn is used to remove the unwanted volatiles.

Wort boiling in combination with film stripping

Recently, the company Anton Steinecker Maschinen-fabrik (Freising, Germany) introduced a new boilingsystem, named ‘‘Merlin’’. The Merlin is a vessel con-taining a conical heating surface which serves for boilingand evaporation (stripping) of the wort (see Fig. 11)(Schu and Stolz 1999; Stippler and Wasmuht 1999b;Jacob et al. 2001). A whirlpool positioned under theMerlin serves as a wort holding vessel. A circulationpump is also necessary. For hop addition, the usual hopdosing system is used. This system can be coupled to anenergy storage tank (Manger 2000; Weinzierl et al. 2000;Schwill-Miedaner and Miedaner 2001).

Processing sequence

The wort is initially lautered into a pre-run vessel and isthere heated by means of a lautered wort heater from72 �C to 90 �C. Next, the wort is pumped over theconical heating surface of the Merlin to heat it nearly toboiling temperature and subsequently enters the whirl-pool. The heating up of the wort in the lautered wortheater is provided by hot water (96 �C) that is drawn offfrom the top of the energy storage tank. The cooledwater (76 �C) is returned to the tank at the bottom. Thewort is heated to boiling temperature by pumping it in acirculation loop across the conical heating surface of theMerlin. When the boiling temperature is reached in thewhirlpool, the boiling cycle of 35 min starts. The firsthop dosage takes place at the beginning of the boilingcycle in the whirlpool. At the end of the boiling cycle,there is a whirlpool pause of 20–30 min, followed by the‘‘stripping’’ with wort cooling. The stripping is accom-plished by pumping the wort from the whirlpool onceagain across the heated surface of the Merlin on its wayfrom whirlpool to plate cooler. In this way, unpleasantaroma volatiles are removed from the wort.

The energy contained in the vapours is recoveredduring the course of the whole process by means of avapour condenser. This recuperated energy is stored—inthe form of hot water at 96 �C—in the energy storagetank. For an overall evaporation of slightly more than4%, the energy storage system is balanced, which meansthat the recuperated condensation energy matches theenergy required to heat the lautered wort.

A Merlin can also be installed to act solely as astripper. In this case, it is set up between the whirlpooland the wort cooler. In this arrangement, the wort isfirst boiled in a conventional wort kettle. In order to

Table 5 Energy savings of the wort boiling system with steamstripping compared to conventional boiling; currency=Euro(Braekeleirs 2001)

Working cost Conventionala Steam stripping Savings/yearb

Brew per brew per brew 2600 brews

Steam 104.7 43.9 158,080Electricity 2.2 0.9 3,380Process water 33.0 30.6 6,240Demin. water 1.0 �2,600Extract losses 0.4 �1,040CIP/waste water 3.7 �9,620Total 154,440

a9% evaporationbGas price= 3.6/GJ

Fig. 11 Schematic of a brewhouse featuring Merlin and whirlpoolwith energy storage (Schwill-Miedaner and Miedaner 2001): 1, hopdosage; 2, Merlin; 3, whirlpool as collecting vessel; 4, vapourcondenser; 5, steam control valve; 6, heat exchanger

26

minimise evaporation, the boiling time is reduced to40 min. The aim of this type of arrangement is to greatlyreduce the boiling time in order to assure gentle handlingof the foam-positive substances and still achieving asufficient DMS reduction (Weinzierl et al. 2000).

Industrial trials

Results of trials on a 100-hl scale demonstrate the lowthermal stress on the wort, which is reflected by themuch less increase of the TBN, and colour (Table 6). Asmall total evaporation rate of less than 4% can beobtained (Table 7). The degree of evaporation is deter-mined by adjusting the steam pressure during the strip-ping process. SMS and free DMS values after strippingwere higher compared to conventional boiling.

During tasting experiments of the beers produced, allMerlin beers were preferred. They were found to bepurer and smoother. Their aroma was cleaner and thecharacteristic hop aroma was not removed by thestripping process. It was found that the foam stabilitywas considerably increased. The results concerning thetaste stability were also better, which could be correlatedto the low thermal stress.

Energy savings

A comparison between the Merlin boiling system andconventional boiling (atmospheric boiling with 12%evaporation) without using any heat recovery system is

given in Table 7. It is calculated that savings for specificenergy requirements are respectively 67% or 72% whena wort cooler or a vapour condensate cooler is also used.This figure will be somewhat lower if the conventionalboiling system is also equipped with a vapour condenserand an energy storage tank, and if the evaporation rateis reduced to a lower value, e.g. 7–8%.

Table 6 Wort characterisationduring film boiling andstripping (Wienzierl et al 2000)

aConventional boiling

Coagulablenitrogen (mg/l)

Colour (EBC) TBN (–) Free DMS(lg/l)

SMM(lg/l)

Merlin Conv.a Merlin Conv.a Merlin Conv.a Merlin Conv.a Merlin Conv.a

Kettle full 43.0 50.0 6.0 6.4 18.6 25.8 357 620 505 620Cast wort 32.0 – 7.0 – 31.3 – 49 – 203 –Before stripping 28.7 – 7.7 – 37.0 – 146 – 76 –After stripping 28.0 20.0 7.7 12.2 38.3 51.1 49 40 84 40

Table 7 Comparison of Merlinboiling to a conventionalmethod (Wienzierl et al 2000)

Merlin Conventionalwithout heatrecovery

Kettle full amount (hl) 163 163Temperature before heating (�C) 90.0 72.0Measured energy requirement heating up (MJ) 1,374 2,216Evaporation related to kettle full (%) 3.55 12Total evaporation (mean of 3 brews) (hl) 5.78 19.6Measured energy requirement boiling (MJ) 1,251 4,986Measured energy requirement boiling, gross total (MJ) 2,625 7,202Specific requirement (MJ/(hl cast wort)) 16.70 50.21Savings specific energy requirement related to same cast out amount (%) 66.7With wort cooling and vapour condensate coolerTotal energy requirement, gross (MJ) 2,185 7,202Specific requirement (MJ/(hl cast wort)) 13.90 50.21Savings specific energy requirement (%) 72.3CO2 emission (t/a) 325 1,175

Fig. 12 Process diagram of the Ziemann vacuum evaporation plant(N.N. 2001e): 1, vacuum vessel; 2, vapour condenser; 3, vacuumpump

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Wort boiling in combination with vacuum stripping

Ziemann system

Recently, the company Ziemann (Ludwigsburg, Ger-many) introduced a vacuum evaporation plant whichcan be installed in the brewhouse as an additionalmodule (N.N. 2001b; N.N. 2001e) (see Fig. 12). Thismodule is placed after the whirlpool. The combinationof a relatively short boiling phase with a low evapora-tion rate and the vacuum evaporation gives a boilingsystem with a low energy cost, a reduced thermal loadand sufficient stripping of unwanted volatiles.

Process description

Firstly, the wort is boiled for 40–50 min with theexisting boiling system. An evaporation of approxi-mately 4% is achieved. Next, the whirlpool is employedas usual. After the rest period in the whirlpool, thewort is led tangentially as a thin film through theby-pass of the existing wort pipe into the vacuumvessel. The necessary vacuum of approximately 0.4 barunderpressure for an evaporation of 2% is produced bymeans of a liquid ring vacuum pump. After the startand during the flash evaporation process, the vacuum ismaintained by vapour condensation. Undesired fla-vouring agents (e.g. free DMS, degradation product offat, Strecker aldehydes, ...) are driven off with the va-pour produced. The vapour that is formed during thisprocess is condensed in the vapour condenser with theproduction of hot water at 80 �C. In the condensatecooler, the resulting condensate is also used for heatingbrewing water before it goes to the gully. During thewort flow, the vacuum in the flask tank is controlledthrough the temperature of the wort after the flashevaporation. The wort volume in the flash tank is keptconstant by means of a speed-controlled wort pump,which is positioned underneath the tank outlet. Thiswort pump is designed to ensure that the wort reachesthe existing wort cooler with more or less the samepressure and volume flow as before.

Energy and hot water balance A comparison betweenwort boiling with subsequent vacuum evaporation andconventional wort boiling with 8% evaporation isshown in Table 8. The reduced generation of hot waterduring the wort cooling process with vacuum evapora-tion is compensated by warm water generation duringthe vapour/condensate cooling process. A comparisonof the primary energy demand showed that wort boilingwith subsequent vacuum evaporation enables savings ofapproximately 50% of thermal primary energy which isrequired only for wort boiling compared to conventionalboiling.

Nerb system

The company Nerb (Freising Attaching, Germany) re-cently introduced on the market the boiling system‘‘VarioBoil’’ (Krottenthaler et al. 2001; N.N. 2001b).This system combines atmospheric and vacuum boiling.A schematic process layout of this boiling system is

Table 8 Comparison of boilingwith subsequent vacuumevaporation to conventionalmethod (8% evaporation)(N.N. 2001e)

Boiling with 4%evaporation and 2%vacuum evaporation

Conventional boilingwith 8% evaporation

Wort coolingVolume of wort to be cooled (hl) 1000 1000Wort inlet temperature (�C) 87 98Wort outlet temperature (�C) 8 8Ice water inlet temperature (�C) 3 3Ice water outlet temperature (�C) 82 82Volume of hot (82�C) water (hl) 990 1120Vapour condenser for vacuum evaporation incl.vapour condensate coolingVapour temperature (�C) 87 –Vapour volume (hl) 20 –Water inlet temperature (�C) 15 –Water outlet temperature (�C) 82 –Generation of hot (82 �C) water (hl) 170 –Total generation of warm water/brew (hl) 1160 1120

Fig. 13 Process diagram of the Nerd boiling system with vacuumevaporation (Krottenthaler et al. 2001): 1, wort kettle; 2, expansionvessel; 3, vapour condenser; 4, external boiler

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shown in Fig. 13. This boiling system is composed of awort vessel, an external boiler, an expansion evaporatorwith a vacuum pump and a vapour condenser coupled toa hot water storage tank. Additionally, vapour com-pression can also be used during boiling. Instead of thewort boiling vessel, a buffer tank or the whirlpool can beused.

Process description

The wort is pumped through the external boiler into theexpansion vessel. The wort flows tangentially into thisvessel and as a thin film at the inner surface. Duringboiling, the pressure is atmospheric in the expansionvessel. The vapour produced upon expansion is con-densed in the vapour condenser. An outlet pump is usedto pump the wort back to the wort kettle and to controlthe level in the expansion vessel. After the boiling pro-cess, the expansion vessel is evacuated. The wort is thenpumped via the expansion vessel to the whirlpool. Thevacuum evaporation results in a wort temperature of88 �C. The advantages of wort pre-cooling are in thisway achieved.

Industrial trials

The Nerb boiling system has been evaluated on anindustrial scale. Normal (60 min, 5.4% evaporation),short (50 min, 4.7% evaporation), and long (70 min,4.4% evaporation) boiling schemes have been tested out.Interesting results were found for the normal and shortboiling schemes. Table 9 shows some results concerningthe evolution of the wort quality during boiling andvacuum evaporation. These results confirm the lowthermal stress exerted on the wort and a sufficient re-moval of unwanted volatile components. The aromaprofile of the short and normal boiling schemes werecomparable and positively evaluated. On the contrary,the long boiling scheme resulted in an unwanted taste.

Kaspar Schulz system

The company Kaspar Schulz (Bamberg, Germany) re-cently presented a new boiling system (N.N. 2001f;Binkert and Haertl 2001). Wort boiling is divided intotwo phases: in the first phase, the wort is kept at atemperature just below the boiling point (approx.97.5 �C); the second phase is a vacuum evaporation

Table 9 Quality of the wort obtained using the Nerb boiling system with subsequent vacuum evaporation: comparison of a normal (5.4%evaporation) and short (4.7% evaporation) boiling scheme (Krottenthaler et al. 2001)

TBN (–) SMM (lg/l) Free DMS(lg/l)

2-Furfural(lg/l)

Steckeraldehy-desa (lg/l)

Fat degrad.prod.b (%)e

Shortc Normd Shortc Normd Shortc Normd Shortc Normd Shortc Normd Shortc Normd

Before boiling 12 16 825 821 283 285 82 87 911 916 100 100After 30 min 22 22 352 360 97 126 121 87 431 374 32 39End of boiling 25 26 251 214 103 68 160 160 404 362 25 17After vacuumcooling

28 30 208 191 35 26 193 187 380 351 18 19

Fig. 14 Process diagram of theboiling system of Schulz using avacuum expansion evaporator(Binkert and Haertl 2001):1, wort kettle; 2, whirlpool;3, vacuum evaporator;4, vapour condenser; 5, plateheat exchanger

aSum of the Steckeraldehydes (2-methylbutanal, methylbutanal,methional, 2-phenylethanal)bSum of the fat degradation products (hexanal, heptanal, pentanal,2-pentanon, benzaldehyde, c-nonalacton, 2-cis-6-nonadienal,1-hexanol, 1-pentanol, 1-octanol, 1-octen-3-ol)cShort boiling: boiling time=50 min, evaporation during boil-ing=2.9% and vacuum evaporation=1.8%; temperature in theexternal boiler=103 �C and in the wort kettle=99 �C

dNormal boiling: boiling time=60 min, evaporation during boil-ing=3.5% and vacuum evaporation=1.9%; temperature in theexternal boiler=103 �C and in the wort kettle=99 �CeCompared to the value found before boiling

29

phase. A total evaporation rate of 8% is obtained.Considerable energy is saved by keeping the wort justbelow the boiling point during the hot holding phase(since there is no evaporation energy cost). This patentedboiling method has been tested on a pilot (50 l) and anindustrial (240 hl) scale.

Process description

The process diagram is schematically shown in Fig. 14.The wort is heated in the wort kettle to 97.5 �C andkept at this temperature for 60 min. The wort is stirredconstantly with an impeller. The length of this hotholding period is dependent on the isomerisation yieldof the a-acids and the value of coagulable nitrogenobtained, and can be adjusted. During this period, theevaporation rate is approximately 1%. The next step isthe removal of hot trub and hops debris. After awhirlpool rest period, the clarified wort is pumped tothe vacuum evaporator. The pressure in this expansionvessel is approximately 300 mbar. Due to the tangentialinflow of the wort in this vessel, the wort flows down ina thin liquid film along the inner surface of the vesselwall. An evaporation rate of 7% is obtained. A vapourcondenser is used to produce hot water. In the evap-orator, the wort is cooled to ca. 63 �C. Next, a plateheat exchanger is used to further cool the wort tofermentation temperature.

Industrial trials

The wort quality obtained using this boiling system isshown in Table 10 and compared with that for a con-ventional boiling system. After 40 min, a coagulablenitrogen content of 25–28 mg/l was reached. The com-parison of the beer analysis between the beers obtainedusing the new system and using the conventional systemrevealed that no significant difference could be found (nodata were given).

Energy balance

Table 11 shows the energy balance of this new system,which is compared to a conventional boiling system with8% evaporation. Due to the use of an impeller, a wortpump and a vacuum pump, an additional current con-sumption has to be introduced into the energy balance(estimated as 15 kWh for boiling 225 hl of wort). Thevacuum evaporation cools the wort to ca. 63 �C whichresults in the subsequent wort cooling with the plate heatexchanger in hot water with a temperature of only60 �C. Compared to a conventional system, the tem-perature difference is 18 K and the total saving com-pared to a conventional system becomes 56% (seeTable 11). This figure can be increased when the evap-oration heat is also recuperated.

Table 10 Quality of the wort obtained using the Schulz boiling system with subsequent vacuum evaporation (Binkert and Haertl 2001)

Coagulable Nitrogen(mg/l)

Real extract(%)

Free DMS(lg/l)

SMM(lg/l)

Schulza Conv.b Schulza Conv.b Schulza Conv.b Schulza Conv.b

After hot holding period 2.16 2.10 11.65 12.4 348 17 43 97After cooling 2.00 1.90 12.15 12.3 58 68 46 44

aThe exact length of the hot holding period is not mentionedbConventional boiling: 8% evaporation

Table 11 Energy balance of the Schulz boiling system compared to a conventional boiling system (Binkert and Haertl 2001)

Energy costs for conventional boilingWort volume(hl)

Evaporation(hl)

Fuel consumption(L/hl evaporation)

Fuel consumption(L/hl wort)

Fuel price(DM/L)

Evaporation costs(DM/hl wort)

225 18 11.3 0.91 0.65 0.59Energy costs for the hot holding periodWort volume(hl)

Evaporation(hl)

Fuel consumption(L/hl wort)

Costs hot holding(DM/hl wort)

Additional currentrequirement (kWh)

Current costs(DM/kWh)

Total costs(DM/hl)

225 0.5 0.26 0.17 15 0.12 0.18Savings (DM/hl) Savings (%)0.41 70Costs for heating hot waterHot water requirement for wort heating(hl)

Temperaturedifference (K)

Fuel consumption(L/hl wort)

Costs(DM/hl wort)

Total savings(DM/L)

Total savings(%)

100 18 0.12 0.08 0.33 56Savings with heat recoveryHot water productionTotal(hl/hl wort)

Requirement brewhouse(hl/hl wort)

Service hot water(hl/hl wort)

Fuel savings(L/hl wort)

Savings(DM/hl wort)

Total savings(DM/hl wort)

Total savings(%)

1.7 1.35 0.35 0.2 0.13 0.46 77

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Conclusion

During the last 10 years, several new wort boiling sys-tems have been introduced into breweries. In contrast toearlier systems, wort boiling and removal of unwantedvolatiles are two separate processes in the new designs.In this way, the thermal stress on the wort and heatingcosts are reduced considerably. A wort clarification stepbefore the stripping phase gives a better wort qualitythan the conventional reversed strategy where a veryhigh thermal load was necessary during the boilingphase to avoid DMS formation during wort clarifica-tion. The removal of the unwanted volatiles can beperformed at a much higher efficiency. Additionally,modern wort boiling systems are equipped with efficientenergy recovery systems. Environmental aspects includethe prevention of odour pollution using vapour con-densers, biofilter treatment of recuperated vapours, re-use or membrane filtration of vapour condensate.

All new systems are characterised by a considerablereduced overall energy cost compared to classical sys-tems. Investment costs depend on the system’s com-plexity and ease of integration into the existing process.In Table 12, the various boiling systems discussed arecompared (classical atmospheric boiling with atmo-spheric venting is taken as the reference situation) withrespect to thermal stress reduction, integration possi-bility in existing systems, obtained reduction in VOCemission, achieved reduction of operation costs andadditional extra investment costs.

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Table 12 Comparison of thedifferent boiling systems

aBased on the total evaporationratebClassical atmospheric boilingwith atmospheric venting istaken as the reference situationcClassical boiling vessels do notallow boiling under pressure;low pressure boiling necessitatesexpensive pressure-resistantvessels

Boiling system Thermalstressreduction

Integrationin existingsystems

Reduction ofVOC emissiona

Reduction ofoperation costs

Extrainvestmentcosts

Classical atmospheric boiling:Atmospheric venting –b – – – –Vapour condensor – +++ +++ + +Vapour compression – – +++ + +++Low pressure boiling:Classical + –c ++/+++ ++ +++c

Dynamic ++ –c ++ ++ +++c

High temperature wort boiling ++ – ++/+++ +++ +++Low thermal load phase+stripping phase:Steam stripping +++ +++ + +++ ++Film stripping +++ + ++ +++ ++Vacuum strippingZiemann system +++ +++ ++ +++ +++Nerb system +++ ++ +/++ +++ +++Kaspar Schultz +++ +++ +++ +++ +++

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