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Wort Boiling Today – Boiling Systems with Low Thermal Stress
in Combination with Volatile Stripping
Ronnie G. Willaert1 and Gino V. Baron2
1 Laboratory of Brewing and Fermentation Technology, Hogeschool Gent, B-9000 Gent, Belgium;
2 Dept. of Chemical Engineering, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium;
Wort boiling is the most energy intensive stage in the
brewing process. For this reason considerable attention
has been given to improve the efficiency of wort boiling
systems. Alternative wort boiling technologies, such as
low pressure boiling and high temperature wort boiling,
have been studied in detail during the last decades, with a
focus on the reduction of primary energy consumption.
Recently, new boiling systems have been developed and
commercialised. The new systems reduced the energy
consumption still further and are all characterised by
exerting a low thermal stress on the wort during boiling.
In this review, an overview of wort boiling objectives,
possibilities to reduce the thermal stress on wort and
environmental aspects of wort boiling are discussed.
Furthermore, recent wort boiling systems i.e. dynamic
low pressure boiling and boiling systems which are based
on low thermal stress boiling in combination with volatile
stripping (steam, film and vacuum stripping) are
copiously treated.
Cerevisia 26 (4), 2001
Before the wort is aerated and used as the nutrient broth
for the alcoholic fermentation by the yeast cells, the wort
has to be boiled. Wort boiling is a complex process during
which a wide range of chemical, physico-chemical,
physical and biochemical reactions occur.
Wort Boiling Objectives
The wort boiling process suits to obtain the following
objectives (Narziss, 1978; Hough et al., 1982; Narziss et
al., 1982a; Miedaner, 1986; Enari, 1991; Narziss, 1992;
Kunze, 1999):
- extraction and isomerisation of hop components,
- coagulation of proteins (hot break formation),
- wort sterilisation,
- inactivation of enzymes to fix the wort
- formation of reducing and aromatic compounds
(Maillard reaction),
- formation of colouring substances,
- removal of undesired volatile aroma compounds,
- acidification of the wort,
- evaporation of water.
Extraction and isomerisation of hop components
Bitter hops hop cones, pellets type 90 or 45 – are added
at the start of the boiling process. It is necessary to sustain
a high temperature during a certain time to obtain a high
isomerisation yield of the a-acids. The isomerisation yield
depends on: the nature of the isohumulone (cohumulone
gives the best yield), the duration of the boiling, the pH (a
higher pH gives a higher yield, but the obtained bitterness
at lower pH is more balanced and finer), the humulone
concentration (decreasing yield upon increasing
concentration), precipitation of isohumulone with the hot
break, the use of more efficient extraction procedures (e.g.
use of higher temperatures), size of the hop fragments
(extraction rate is higher for milled hop cones or pellets).
Recently, the brewer can choose between different hop
products. Some hop product i.e. isomerised pellets,
isomerised kettle or hop extracts, and reduced isomerised
a-acids are already isomerised before they are used and
need not be added at the wort copper, but can be applied at
the end of the brewing process. By using these new hop
products, the necessity to keep the wort during a “long”
time at a high temperature falls off.
Hot break formation
During boiling, two types of compounds are formed: (a)
compounds consisting of proteins and polyphenols, and
compounds consisting of proteins and oxidised
polyphenols which are insoluble in hot wort and
precipitate as hot break; (b) compounds formed from
protein degradation products and polyphenols which
remain in solution during boiling, and only precipitate as
cold break when the wort is cooled (Kunze, 1999).
Polyphenols are not directly involved in protein
coagulation since protein-polyphenol-complexes are based
on hydrogen bondings which have only a very weak
binding energy at boiling temperatures and are under these
conditions unstable (Ledward, 1979; Miedaner, 1986;
Narziss, 1992). Hot break formation is encouraged by
longer boiling times, vigorous movement of the boiling
wort (which improves the reaction between proteins and
polyphenols), and a low pH since the coagulation is best
accomplished at the isoelectric point of the proteins. To
obtain a sufficient coagulation, a pH of 5.2 is
recommended (Narziss, 1992; Kunze, 1999). The very low
isoelectric pH of some proteins such as b-glubulins, d-
and e-hordein is very low (4.9) and cannot always be
realised during wort boiling (Sandegren, 1947; Biserte and
Scriban, 1953; Waldschmidt-Leitz and Kloos, 1959). The
removal of high molecular weight, coagulable proteins is
very important for the composition and the quality of the
finished beer. Insufficient coagulation and removal result
in a poor fermentation since the transport of substrates to
and products from the yeast cells is hindered by the
adsorpted hot break on the yeast cell walls. This leads to
an insufficient pH-drop during the primary fermentation
and thereby to an incomplete elimination of proteins
during the main fermentation, followed by a poor
clarification during storage. This can result in a beer with
a harsh bitterness (“protein bitterness”) and a poor
colloidal stability. The level of coagulable nitrogen in the
finished wort is an important figure for the
characterisation of the efficiency of wort boiling
processes, and the evaluation and comparison of different
boiling systems. The level of coagulable nitrogen in
unboiled wort is in the range of 35-70 ppm and is reduced
during boiling to 15-25 ppm with a recommended optimal
value of 15-18 ppm. A low coagulable nitrogen
concentration is beneficial for a good colloidal stability in
the finished beer, but a too low concentration can result in
head retention problems (Miedaner, 1986). Protein
coagulation is affected by physical and technological
factors (Narziss, 1992): boiling time, the nature and
manner of boiling (intensity of wort circulation in the
copper), heating system (heating jacket, external and
internal heater), temperature of heating medium, copper
shape and flow configuration of wort, wort boiling
temperature, and wort composition (malt modification,
kilning temperature, mashing method, pH conditions).
Wort sterilisation and enzyme inactivation
Only a short boiling time is necessary to obtain a sterile
solution. The microflora of the malt, hop and other
adjuncts are readily destroyed. The inactivation of residual
enzymes, which survived the mashing process, is also
necessary to fix the wort composition. There is only a
residual activity of polyphenoloxidase and a-amylases.
Also a short boiling time is needed to denature the residual
active enzymes.
The Maillard reaction
During wort boiling, the Maillard or nonenzymatic
browning reaction is rather intensive, resulting in the
production of various volatile and non-volatile aroma
compounds and coloured melanoidins (brown nitrogenous
polymers and copolymers). The reaction starts with an
interaction of low molecular weight proteins i.e. amino
acids and reducing sugars, and the Amadori
rearrangement (Danehy, 1986). From there, a rather
complex reaction network is described, including the
Strecker degration. The progress of the Maillard reaction
can be observed by an increase in wort colour, by
measuring the concentration of intermediate products (like
5-hydroxymethylfurfural (HMF), furfural, furfurylalcohol,
2-acetylfuran, 2-acetylpyrrol and heterocyclic nitrogen
compounds (Narziss et al., 1988)), or measuring the
increase of the concentration of reductones using the
“Indicator Time Test”. A too intensive, uncontrolled
reaction can lead to unattractive flavours in beers. The
formed melanoidins are reducing compounds, but are also
involved in the oxidation of higher alcohols in fresh beer
resulting in volatile aldehydes (Hashimoto, 1972).
Melanoidins can exert pro- and antioxidant effects (Ames,
2001a). Although the structures of melanoidins isolated
from foods are unknown (Ames & Nursten, 1989; Ames,
2001b), considerable progress has been made in recent
years concerning the structures of melanoidin-like
materials (Tressl et al., 1998). The physical parameters,
which have a significant influence on the Maillard
reaction, are the water content, the pH, the oxygen
concentration, the temperature and reaction time.
Formation of colouring substances
Wort boiling results in an increase in wort colour:
typically 4 EBC units for a light coloured beer. This
increase is due to the formation of melanoidins, the
caramelisation of sugars and the oxidation of polyphenols.
Since the extent of the Maillard reaction is higher at a
higher pH, the colour increases with increasing pH of the
wort. Thermal stress during wort boiling can also be
monitored by the thiobarbituric acid coefficient (TBC),
number (TBN) or index (TBI). The TBC values can also
give (in combination with the coagulable nitrogen
concentration) information about the expected foam
stability of the produced beer (Wasmuht & Stippler,
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 when
present in the finished beer. At high temperatures i.e.
during kilning, mashing (decoction method) and boiling
SMM is decomposed to DMS (Anness & Bamforth,
1982). DMS is very volatile and can be readily removed
with the vapor during boiling. The transformation of SMM
to DMS fits a first order reaction with a half lifetime of 30
to 70 minutes at 100°C (Hermann et al., 1985; Narziss,
1992). The formation of DMS is considerably lower at pH
5.0 compared to a pH of 5.5-5.8. This fact determines the
lower pH limit value of the wort at the start of boiling. An
optimal combination of boiling time and temperature has
to be used since when the boiling time is too low, the
DMS concentration will be too high (but coagulable
nitrogen can be OK); when the boiling time is too short
DMS concentration will also be too high (the coagulable
nitrogen content can be correct) (Schwill-Miedaner &
Miedaner, 2001). On the contrary, a too high boiling
temperature and too long boiling time will result in a too
low coagulable nitrogen content.
The removal of other unwanted volatile compounds
during boiling is also necessary. These volatiles can be
classified into three groups: malt-derived volatiles, hop
oils and volatiles which are formed during wort boiling.
Several unwanted volatiles have been detected in the
vapour condensate during boiling; e.g. a five-fold quantity
of 2-acetylthiazole has to be evaporated (Tressl, 1974;
Wackerbauer, 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 wanted
hop oil aroma.
Acidification of the wort
Upon boiling, the wort becomes slightly acidic (typically
0.1-0.3 pH units for a classical boiling process) due to the
formation of melanoidins, the addition of hop acids, the
precipitation of alkaline phosphates and the acidification
action of Ca and Mg ions with phosphates. The use of
dark malts (intense Maillard reaction during kilning) will
also give a larger pH decrease compared to pale malts.
Evaporation of water
Wort boiling results in the evaporation of water (and
volatile organic components) and the concentration of the
wort. During classical (conventional) atmospheric boiling
8 – 12% of the initial wort volume was evaporated (some
breweries even boiled during 2 hours with an evaporation
rate of up to 18%). It has been shown that reduction of
evaporation to as little as 2% can be achieved without
hazard to flavour or other beer qualities such as bitterness,
head retention, total nitrogen haze life and colour (Buckee
& Barrett, 1982).
Reduction of Thermal Stress
Recently, new boiling systems have been developed which
exert a low thermal load on the wort. A low thermal load
has a positive influence on the sensorial and foam
characteristics of the produced beer. The thermal stress
can be quantitatively assessed by measuring the colour,
TBN or the concentration of high temperature indicators
(Manger, 2000). Possibilities of reducing the thermal load
- application of the infusion mashing technique
(in stead of decoction mashing),
- reduction of the heating time of the wort before
- 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
- reduction of the wort cooling time.
A. B.
Figure 1: Energy consumption in the brewhouse (N.N., 2001a): A. percentage of total heat energy requirements, B. percentage
of total electrical power requirements.
Energy Saving during Wort Boiling
The brewhouse is the biggest energy consumer in the
brewery (Figure 1). Since the oil crisis in 1972 and more
recently since the introduction of rigid ecology laws and
taxes, the reduction of the use of primary energy during
wort boiling is of primordial concern to the brewer.
Today, various possibilities of energy recuperation are
In the brewhouse, thermal energy is required to heat
the mash and the wort, and to boil the wort. Nowadays,
the energy required for the mash and wort heating is
already recuperated during the wort cooling process. There
is still some potential energy recuperation possible during
wort cooling. Cooling of the wort after boiling can be
accomplished in two steps: before and after the whirlpool,
since it has been shown in large-scale tests that cooling of
the wort by casting out at a temperature of 89°C
significantly reduced the TBC (lower thermal stress) and
improved the flavour stability of the produced beer (Coors
et al., 2000; Krottenthaler & Back, 2001).
The recuperated energy can be used for pre-heating
and boiling of the wort, and for hot water production
(Vollhalls, 1994; Thüsing, 2000). Energy recuperation can
be accomplished by (see Figure 2)
- reducing the boiling time,
- the use of a vapour condensor for the production of
hot service water with or without wort heating,
- machanical vapour compression,
- thermal vapour compression with or without wort
Figure 2: Possibilities of energy recuperation with
atmospheric or pressure boiling (Thüsing, 2000).
Vat/KEG filling
Process water
air, water
Thermal and mechanical vapour compression is mainly
used in the atmospheric boiling method since the vapour
compression demands calandria for larger amounts of
wort. An outlet temperature of 107-108°C is required if a
calandria in combination with low pressure boiling is
used. The choice of an energy recuperation system will
depend on the total evaporation rate, the hot water demand
and the costs for thermal and electrical energy (Thüsing,
2000, 2001).
Energy saving with vapour condenser
The evaporated water mass during boiling contains a high
energy content. The condensation of 1 kg of steam into 1
kg of water at 100°C gives an energy of 2260 kJ.
Considerable heat can be saved using a vapour condenser
and an energy storage system (see Figure 3). Instead of a
1-tank storage tank, a 2-tank one tank containing the hot
water (± 99°C), the other the used hot water (± 80°C)
energy storage system can also be used (Lösch & Körber,
1984; Lenz, 1994). Nowadays, a single-layer plate heat
exchanger is used as vapour condensor. The recuperated
energy by the condensor is stored in the energy saver and
used to heat the lautered wort before boiling. The energy
saver is a hot water displacement storage. The vapour
condensate can be further cooled down to approximately
30°C using cold water which is normally a prerequisite for
its discharge into a waste water system. The vapour
condensate cooler can produce hot water of a temperature
of approximately 85°C. Only 4 à 5% of the total
evaporation is sufficient for the production of hot water
exclusively for the wort heating. The same system can be
used for low pressure boiling. Low pressure boiling works
with a reduced evaporation rate compared to atmospheric
boiling which results in a lower production of hot service
water. If the vapour condensor is included in the pressure
sector, energy storage water of about 100°C can be
Energy saving with vapour compression
During atmospheric boiling, the produced vapour has a
temperature of about 100°C. If this vapour is compressed
to a few tenths of a bar overpressure, the temperature is
raised to 102 à 108°C and it can be reused for heating.
Vapour compression can be achieved by using a
mechanical compressor or a steam jet compressor
(thermocompression). The condensate, which is developed
at the heater by the condensation of the vapour, leaves the
cyclic process through a condensate cooler, which
produces hot driving water (see Figure 4).
Figure 3: Pressure wort copper with vapour condensor
(pressureless); energy storage system and wort heating
(Vollhals, 1994).
Using a mechanical compressor, the vapour is
compressed to an overpressure of 0.3 à 0.4 bar. The wort
is heated to boiling temperature using fresh steam. The
boiling process is maintained in operation using heat from
the compressed vapour. The additional use of a vapour
condensor is not possible because all the vapours are
directly led back to the boiling process. Consequently, the
lautered wort is not preheated when mechanical vapour
compression is employed (Figure 4.A). Additional
disadvantages are the complicated plant engineering, noise
production, high maintenance costs and peak electricity
At thermal vapour compression, live steam from a
boiler with an overpressure of at least 8 bar and up to 18
bar is fed to the steam jet pump. The vapour is sucked in
and compressed to 0.1 to 0.4 bar overpressure. About 30-
35% of the vapour is condensed in the kettle vapour
condensor to produce hot water that can be used for
preheating the wort (Figure 4.B). The advantages and
disadvantages of using thermal vapour compressor are
summarised in Table 1.
A. B.
Figure 4: Wort boiling with A. mechanical and B. thermal vapour compression (Thüsing, 2000).
Table 1: The advantages and disadvantages of thermal vapour compression (N.N., 1993; N.N., 1995; Lambeck & Hintzen,
1996; Fohr & Meyer-Pittroff, 1998; Kunze, 1999; Thüsing, 2000).
Advantages Disadvantages
a trouble free, cheap, safe and low maintenance compressor, requires a high steam pressure (new pipework
low noise and vibration, needed),
especially profitable for small and medium-sized breweries, a relative high quantity of hot process water arising,
lower investment costs compared to mechanical vapour large specific heat transfer surface with a high
compression, circulation rate (external heater needed or internal
one steam jet compressor is sufficient for any size of plant, heater with recirculation pump),
driven by live steam, a higher quantity of vapour condensate, waste and
stepless control by injector needle valves. hot water arising and more boiler feed water
required compared to mechanical vapour
Environmental Aspects
Vapour is produced during wort boiling. The vapour
contains 99% water and organic constituents from hops
and malt; it is free of salts (Hackensellner & Pensel,
1993). More than 160 constituents have been identified
and grouped into aldehydes, alkanes, alcohols, esters,
furans, ketones and terpenes (Buckee et al., 1982; Drawert
& Wächter, 1984). Using a vapour condensor, hydrophilic
vapour components are completely condensed.
Hydrophobic vapour constituents (including some hop
aroma components) are not completely condensed
(Wächter et al., 1985). The non-condensable elements are
discharged to the atmosphere as residual gas or can be
decomposed in a biofilter.
If the vapour is allowed to escape from the chimney,
odour pollution is caused. By using a vapour condensor,
polluting volatiles can be received and treated in the
brewery’s waste water plant. However, a high total
evaporation (larger than 4-5%) requires an escape of the
share which is not necessary for the hot water production
through the chimney. In this case, odour emissions can be
reduced using a biofilter. The exhaust vapour is therefore
first cooled using an air-to-air heat exchanger with
ambient air (Reischmann & Warnecke, 1997).
Subsequently, the exhaust air flows into a countercurrent
scrubber and next to a high capacity biofilter where the
odour substances are biologically decomposed.
In the context of lowering specific waste water levels
arising 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. Reverse osmosis
and activated carbon filtration have been investigated
(Back et al., 1996; Lenz, 1996; Chmiel et al., 1997; Back
et al., 1998). The treated condensate has been successfully
used as brewwater for the production of a pale beer. Non-
treated vapour condensate can also be used in the brewery
in all processes which require water and where the organic
constituents in the vapour condensate are not detrimental;
e.g. for general cleaning purposes, sparging for lauter tuns
and mash filters, flushing of false bottoms of lauter tuns,
cooling water for condensors, cooling towers and motors
(Fohr et al., 1999).
Today, different boiling systems are being used. Table 2
shows an overview with some characteristics of the
present-day systems. In this review, dynamic low pressure
boiling and the recent boiling systems which are
characterised by a low thermal stress phase with a
subsequent volatile stripping phase will be discussed in
High temperature boiling (HTWB) is an alternative
boiling system. It is a continuous system and the idea is
quite old (Dummet, 1958; Daris et al., 1962). At high
temperatures of 130°C or 140°C very satisfying wort
analysis data can be obtained although very short boiling
times of ca. 5 min are used (Narziss et al., 1982b; Narziss
et al., 1983). The wort is heated up in three steps. In the
first two steps, vapour from the flash-off chambers is
reused. Considerable energy savings can be obtained due
to the short boiling time and energy recuperation.
Alternative continuous systems have been developed, e.g.
continuous pressure boiling in a multistage column
comparable to a tray distillation tower (Krüger &
Ehrlinger, 1984) or the use of multiple-effect evaporators
(Korek, 1981).
Table 2: Overview of the present-day boiling systems.
Boiling system Temperature (°C) Boiling time (min) Total evaporation rate (%)
Classical atmospheric boiling 100 60-80 ca. 8
Low pressure boiling (LPB):
Classical 103-104a55-65 6-7
Dynamic 103-104a45-50 ca. 5
High temperature wort boiling (HTWB) 130-140 2.5-3 6-8
Low thermal load phase + stripping phase:
Steam stripping: Meura system 100b40-45 2.5-4
Film stripping: Merlin system 100b35 5-6
Vacuum stripping:
Ziemann system 100b40-50 6
Nerb system 103a/99b50-60 4.7-5.4
Schulz system 97.5b60 8
aBoiler outlet.
bTemperature of the low thermal stress phase.
A new boiling system using microwaves is tested by
the company Huppmann (Herrmann, 1999; Isenberg,
1999). Microwaves are produced in a separate generator.
These microwaves are guided to the wort kettle via a
copper waveguide and brought into the wort through the
“applicator”. The total wort volume is heated uniformly
and no burn-on danger exists. Wort boiling trials (5 hl
scale) with microwaves (4%, 6% and 8% evaporation)
have been compared to conventional boiling (90 min and
8% evaporation). The analysis of the obtained beers
showed that the aroma was comparable to the beer
obtained from the conventional boiling although the
boiling time could be reduced to 45 min (5% evaporation).
The taste stability was rather poor for the produced
“microwave beers” (Meilgaard, 2001).
Wort Boiling At Low Pressure
Conventional boiling at low pressure has been introduced
in breweries since 1979 to decrease the energy costs
(Lenz, 1982). The pressure is kept constant during boiling
at a value of 1.08-1.21 bar (boiling temperature from
102°C to 105°C). This technology has been further
developed and the state of the art today is dynamic low
pressure boiling with several subsequent short phases of
pressure building up and pressure release with
corresponding multiple wort stripping (N.N., 2001b;
Hackensellner, 2001; Kantelberg & Hackensellner, 2001;
Schwill-Miedaner & Miedaner, 2001). This technology is
commercialised by the company Huppmann (Kitzingen,
Figure 5: Temperature profile during dynamic low pressure
boiling (Kantelberg & Hackensellner, 2001).
After an atmospheric pre-boiling phase of 3 min at
100°C, the pressure is periodically build up (1.17 bar,
104°C) and released (1.05 bar, 101°C) (see Figure 5). The
boiling is ended with a post-boiling phase of 5 min at
100°C. The pressure reduction phases ensure an intensive
boiling phase with stripping of wort volatiles. A total
evaporation rate of 4.4-4.5% is obtained. The produced
vapour is used to produce hot water and the recuperated
energy can be stored in a hot water storage tank (see
Figure 6). Part of this stored energy can be used to heat up
the wort before boiling. Recent results have shown that
due to the reduced thermal stress on the wort the head
retention of the produced beers was increased (N.N.,
2001c). Results of an industrial trial (265 hl) are shown in
Table 3.
Table 3: Results obtained with dynamic low pressure boiling
(Schwill-Miedaner & Miedaner, 2001).
Parameter Before boiling After boiling
Coagulable nitrogen (mg/l) 54 23
TBN 28 41
Free DMS (mg/l) 289 < 10
SMM (mg/l) 185 59
Heating up and boiling of the wort is performed using
an internal boiler (Figure 7). The recent internal boiling
systems are designed to minimalise the thermal load
during heating and boiling, and are characterised by
(Hackensellner, 1999; N.N., 2001d; Kantelberg &
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
- 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 wort
heating and boiling. A connection pipe, which is branched
off from the casting pipe downstream of the casting pump
and terminates again in the wort vessel underneath the
inner boiler (Stippler & Wasmuht, 1999a) or a
recirculation pipe and pump can be used in the same way
(Hoefig, 1994).
A further reduction of the thermal load and the
stabilisation of the DMS concentration can be achieved by
pre-cooling the wort before it enters the whirlpool
(Krottenthaler & Back, 2001; N.N., 2001c). A decrease of
the temperature from 98°C to 89°C resulted in a reduction
of the DMS concentration to 40 mg/l; and the TBN (and
the colour) decreased with 7-10 units. The produced beers
scored better after a forced ageing experiment.
Wort Boiling in Combination with Steam Stripping
In wort boiling, the most reactions are only
time/temperature dependent (Reed & Jordan, 1991): the
inactivation of enzymes, the sterilisation of the wort,
extraction of hop compounds, isomerisation of a-acids,
coagulation of the protein-fraction, lowering the pH and
formation of reducing and aromatic compounds. For all
these reactions, no evaporation is needed. A simple hot
wort stand at boiling temperature is enough to guarantee
that these reactions occur. Additionally, this methodology
ensures a low thermal load, which guarantees a balanced
beer with good foam stability.
On the contrary, for a few specific goals evaporation is
required: initially to achieve the desired gravity of the
wort at the end of boiling and secondly the high
evaporation rates generally applied are meant to eliminate
unwanted volatile compounds. In classical wort boiling,
evaporation ratios of 7 to 10% are common.
Unfortunately, in conventional wort boiling, large energy
losses may occur since a wort kettle is not necessarily
designed for efficient stripping by evaporation. The
effective evaporation surface per unit volume is very low
Figure 6: Dynamic low pressure boiling with energy recuperation Figure 7: Schematic representation of a recent internal
systems (Hackensellner, 2001). boiler (Hackensellner, 2001).
which renders the elimination of volatile compounds more
difficult (Reed & Jordan, 1991). For this reason a vigorous
wort boil is generally required. Different technologies of
wort boiling are in use and all these systems have one
thing in common: they all try to increase the effective
surface to facilitate the removal of the volatile compounds.
This problem has been approached by developing a
novel two-stage wort boiling system (Baron, 1997, 2000;
Seldeslachts et al., 1997). In the first step, the wort is kept
at wort boiling temperature and no significant evaporation
occurs. The volatile compounds formed through chemical
reactions and extracted from the added hops are
accumulated in the wort. In the second stage, after wort
clarification, the volatile compounds are eliminated, very
efficiently, in a “wort stripping column”.
The motivation for developing this system was based
on a number of potential benefits. Firstly, it is a
technology, which could generate significant energy
savings. Secondly, it could form a means of efficient
process control. The amount of volatile compounds
present in the final wort and the colour of the wort can be
better controlled. With regard to the output of CO2, linked
to the use of primary energy, legislation in the individual
countries is becoming more and more stringent. Another
important advantage, which is related to the previous one,
is that wort stripping could reduce the output of the
volatile organic compounds (VOC’s). In this matter, new
regulatory initiatives are also to be expected to reduce the
output of the amount of VOC’s in the atmosphere.
Process layout
The process layout (Figure 8) shows that the wort
stripping process occurs best between wort clarification
and wort cooling. The reason for this is simple. In the
classical process the additional amount of volatile
compounds formed after the end of boiling can no longer
be eliminated and therefore pass to the fermentor, whilst
during wort stripping, the amount of volatile compounds
formed from their precursors during the hot wort stand,
can be eliminated.
A detailed view of the wort stripping column is shown
in Figure 9. The wort first passes through a heat exchanger
to heat the wort to its boiling temperature at the column
pressure. With the wort distribution plate, the wort is
spread uniformly over the entire cross section of the
column, avoiding foaming as much as possible. The
packing used were Cascade Rings (Glitsch) for their open
structure with low risk of fouling. At the bottom of the
column the wort is gently guided via the column wall to
the wort buffer, again avoiding foaming. The wort then
goes to the wort cooling heat exchanger. At the top of the
column, the steam saturated with volatile components is
condensed and eliminated.
Figure 8: Process layout including wort stripping (Seldeslachts et al., 1997).
Figure 9: Vertical section view of the wort stripping column
(Seldeslachts et al., 1997).
Processing sequence
A wort boiling system with wort stripping has been
optimised and used on industrial scale at the Leuven
(Belgium) plant of Interbrew. The characteristics and use
of this system will be discussed.
In the wort kettle, the total residence time is kept
identical as for a conventional wort boil, but three
subphases can be distinguished. In the first subphase, at
the start of boiling, a short period of heavy boiling
(100°C) is introduced (e.g. 5 minutes). This short period is
mainly aimed at initializing the trub formation and at
homogenising the hops just added to the wort kettle (Reed
& Jordan, 1991). After this first period, there is a long
period (± 30 min) at 100°C during which the steam supply
to the kettle is shut off. During this stage any evaporation
and cooling down of the wort is avoided by closing the
doors and if possible the valve in the chimney. The third
subphase in the wort kettle involves a short period of
heavy boiling (100°C). During this period of 5 to 10
minutes the accumulated volatile compounds are partially
eliminated. The boiling time determines the downstream
load for the stripping. For this reason, this second heavy
boiling period can be used to regulate the final volatile
content after stripping. Thanks to the strong mixing the
hot break formation is activated. Naturally, it must be
verified that the desired gravity of the wort at the end of
boiling has been reached. The total evaporation in the
kettle can be easily kept below 2.0% of the total wort
The wort clarification consists of a cylindro-conical
decantor combined with a centrifuge. During the trials no
changes were applied to this part of the process.
The wort stripping is carried out just before wort
cooling. The clarified wort is pumped at 400 - 450 hl/h.
Before entering the 1 m diameter, 2 m packing height
column, the wort is heated again to its boiling point, in
equilibrium with the chosen pressure. If the wort entered
the stripper at a suboptimal temperature, the steam
injected would be used partially to warm up the wort to its
boiling point, instead of stripping out the volatile
compounds. In such a case, the stripping efficiency would
drop enormously! The flow rate of the steam injection is
regulated at 0.5 to 2.0% of the wort flow rate. In case the
wort enters the column at boiling point, the amount of
steam injected equals the amount of condensate.
DMS formation and elimination during the hot wort
During the optimisation of the industrial pilot stripping
column, DMS has always been used as a marker to
measure the efficiency of the stripping. In Figure 10, it can
be seen that during the wort boiling the SMM is degraded
continuously and transformed into DMS. In case of a
conventional wort boil, the DMS present as well as the
freshly formed DMS are continuously eliminated, albeit
through strong boiling with evaporation and resulting
energy loss. In the case of the wort boiling strategy with 3
subphases in the wort kettle, an increase of the DMS in the
second subphase was recorded due to the further
degradation of SMM along with a very low or lack of
evaporation. In the last subphase in the wort kettle, the
DMS is reduced to a set level, to match the column
efficiency in order to reach a sufficiently low level of
During the subsequent hot wort period, from wort
transfer to the settling tank, until the hot stand before wort
cooling, the remaining amount of SMM is further
degraded into DMS. The formed DMS cannot be
eliminated due to a lack of evaporation in this phase. In
both cases (conventional wort boiling and reduced wort
boiling) the levels of DMS increase proportionally to the
amount of SMM left after wort boiling and further
degraded during this hot wort period. For a conventional
process, this amount of DMS passes directly to the
fermentor. For the “wort stripping”, this DMS is partially
0 10 20 30 40 50 60
ppb DMS / SMM
DMS Classic
Wort Boiling
DMS Stripping
Wort Boiling 3 Phases
Classic + Stripping
TIME ( minutes )
0 30 60 90 120 150 180
ppb DMS
Column in
Column out
TIME ( minutes )
Figure 10: Evolution of SMM and DMS during wort boi- Figure 11: Evolution of DMS during wort boiling, wort clari-
ling for a classical wort boiling and a reduced wort boiling fication and wort cooling during an industrial trial on a 12°Pl
with 3 subphases (wort stripping) (Seldeslachts et al., 1997). lager beer (classic wort boiling + wort stripping) (Seldeslachts
et al., 1997).
During wort stripping, a high amount of DMS (in this
case between 170 and 190 ppb) enters the column. At the
bottom of the column, the stripped wort leaves with a
DMS level of about 20 ppb. The average stripping
efficiency (for DMS) amounts to 85 to 90% with the
actual industrial pilot stripping column. Other volatile
compounds, such as wort aldehydes, are eliminated as
well. The elimination efficiency of individual compounds
depends on their boiling point, or better on their relative
volatility. Because the process of wort cooling is directly
following the stripping column, this low amount of 20 ppb
DMS passes directly to the fermentor. In the case of a
classic wort boil, the amount of DMS going into
fermentation is determined by the amount of DMS present
at the end of boiling plus the fraction formed during the
rather long hot wort stand, and may even double again in
that time.
Industrial trials
A number of 420 hl brews at the end of boiling were
processed using the 2 alternative wort boiling systems:
firstly the control beer was boiled conventionally and
secondly the trial beers were boiled following the 3 step
boiling process combined with wort stripping. Figure 11
confirms the previously discussed results. During the 2
short periods of heavy boiling in the “wort stripping”
process, a decrease in DMS content was recorded. After
stripping, the DMS level fell below the values obtained for
the control beer. Typically DMS in the wort drops from
190 ppb to values between 20 and 30 ppb. The DMS
eliminated can be measured in the condensate. Amounts of
10,000 ppb DMS and more were measured in this
stripping condensate.
The DMS values from both the trial and the control
beers were further followed in the downstream process. In
the bottled beers, about the same values for both beers (38
and 39 ppb respectively) were measured. The final level of
DMS in the finished beers is a function of the amount in
the wort, and of the combined effect of DMS stripping and
DMS formation (out of DMSO) during fermentation
(Nakajima & Narziss, 1978; Leemans et al., 1993).
Most physico-chemical parameters of the finished
beers were similar. It can be concluded that both beers
have the same profile. In a triangular tasting session, a
significant difference at the 5% level between the beers,
with more preferences for the trial beer, was found. In the
descriptive panel however no significant differences
between the beers could be found for individual
descriptors. Recently, data were gathered supporting the
view that the beers that passed over the stripping column
have an improved flavour stability.
Benefits of applying wort stripping
The energy savings come largely from the enormous
reduction in evaporation energy needed. Because the wort
volume in the kettle at the start of boiling is also smaller, it
is not necessary to warm up this supplementary water
from 78°C to 100°C. The injection of a small amount of
live steam is of course a cost in the economical evaluation.
However, there is the possibility to partially recover the
residual heat in the condensate. In the case where an
external boiler is used, there is a benefit from the potential
gain of the reduced electricity consumption 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 could
be important when the brewing capacity needs to be
expanded. Installing a wort stripping column in such a
case, could eventually postpone or avoid the investment
for a new steam boiler. The condensation of the unwanted
volatile compounds prepares the brewery for fulfilling
current and future environmental constraints.
Energy savings
The energy consumption calculation for this new boiling
system is shown in Table 3 (Braeckeleirs, 2001). As can
be noticed, a considerable amount of energy can be saved.
Nowadays, this technology is commercialised by the
company Meura (Tournai, Belgium) (N.N., 2001b;
Braekeleirs, 2001).
Recently, the concept of steam stripping has also been
introduced in a continuous wort boiling system (Visscher
& Versteegh, 2000). Here, the wort is heated to boiling
temperature and flows through a plug flow reactor.
Subsequently, a continuous steam stripping column is
used to remove the unwanted volatiles.
Wort Boiling in Combination with Film Stripping
Recently, the company Anton Steinecker Maschinenfabrik
(Freising, Germany) introduced a new boiling system,
named “Merlin”. The Merlin is a vessel containing a
conical heating surface which serves for boiling and
evaporation (stripping) of the wort (see Figure 12)
(Stippler & Wasmuht, 1999b). A whirlpool positioned
under the Merlin serves as a wort holding vessel. A
circulation pump is also necessary. For hop addition, the
usual hop dosing system is used. This system can be
coupled to an energy storage tank (Manger, 2000;
Weinzierl et al., 2000; Schwill-Miedaner & Miedaner,
Table 3: Energy savings of the wort boiling system with steam stripping compared to conventional boiling (Braeckeleirs,
Working cost Currency Conv.a Brew Steam stripping Savings/yearb
per brew per brew 2600 brews
Steam EUR 104.7 43.9 158080
Electricity EUR 2.2 0.9 3380
Process water EUR 33.0 30.6 6240
Demin. water EUR 1.0 -2600
Extract losses EUR 0.4 -1040
CIP/waste water EUR 3.7 -9620
Total EUR 154440
a9% evaporation
bgaz price = 3.6 EUR/GJ
Processing sequence
The wort is initially lautered into a pre-run vessel and is
there heated up by means of a lautered wort heater from
72°C tot 90°C. Next, the wort is pumped over the conical
heating surface of the Merlin to heat it up nearly to boiling
temperature and enters subsequently to the whirlpool. The
heating up of the wort in the lautered wort heater is
provided by hot water (96°C) that is drawn off from the
top of the energy storage tank. The cooled water (76°C) is
returned to the tank at the bottom. The wort is heated till
boiling temperature by pumping it in a circulation loop
across the conical heating surface of the Merlin. When
boiling temperature is reached in the whirlpool, the boiling
cycle of 35 min starts. The first hop dosage takes place at
the beginning of the boiling cycle 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 accomplished by pumping the wort from
the whirlpool once again across the heated surface of the
Merlin on its way from whirlpool to plate cooler. In this
way, unpleasant aroma volatiles are removed from the
Figure 12: Schematic of a brewhouse featuring Merlin and
whirlpool with energy storage (Schwill-Miedaner &
Miedaner, 2001).
The energy contained in the vapours is recovered
during the course of the whole process by means of a
vapour condenser. This recuperated energy is stored
under the form of hot water of 96°C in the energy
storage tank. For an overall evaporation of slightly more
than 4%, the energy storage system is balanced, which
means that recuperated condensation energy match the
required energy to heat up the lautered wort.
A Merlin can also be installed to act solely as stripper.
In this case, it is set up between the whirlpool and the wort
cooler. In this arrangement, the wort is first boiled in a
conventional wort kettle. In order to minimise
evaporation, the boiling time is reduced to 40 min. The
aim of this type of arrangement is to greatly reduce the
boiling time in order to assure gentle handling of the
foam-positive substances and still achieving a sufficient
DMS reduction (Weinzierl et al., 2000).
Industrial trials
Results of trials on a 100-hl scale demonstrate the low
thermal stress on the wort, which is reflected by the much
less increase of the TBN, and colour (Table 5). A small
total evaporation rate of less than 4% can be obtained
(Table 6). The degree of evaporation is determined by
adjusting the steam pressure during the stripping process.
SMS and free DMS values after stripping were higher
compared to conventional boiling.
During tasting experiments of the produced beers, all
Merlin beers were preferred. They were found to be purer
and smoother. Their aroma was cleaner and the
characteristic hop aroma was not removed by the stripping
process. It was found that the foam stability was
considerably increased. The results concerning the taste
stability were also better which could be correlated to the
low thermal stress.
Energy savings
A comparison between the Merlin boiling system and
conventional boiling (atmospheric boiling with 12%
evaporation) without using any heat recovery system is
given in Table 6. It is calculated that savings for specific
energy requirements are 67% and 72 when a wort cooler
and vapour condensate cooler is also used. This figure will
be somewhat lower if the conventional boiling system is
also equipped with a vapour condensor and an energy
storage tank; and if the evaporation rate is reduced to a
lower value, e.g. 7 à 8%.
Wort Boiling in Combination with Vacuum Stripping
Ziemann system
Recently, the company Ziemann (Ludwigsburg, Germany)
introduced a vacuum evaporation plant which can be
installed in the brewhouse as an additional module (N.N.,
2001b; N.N., 2001e) (see Figure 13). This module is
placed after the whirlpool. The combination of a relative
short boiling phase with a low evaporation rate and the
vacuum evaporation gives a boiling system with a low
energy cost, a reduced thermal load and sufficient
unwanted volatile stripping.
Table 5: Wort characterisation during film boiling and stripping (Wienzierl et al, 2000).
Coagulable Colour TBN Free DMS SMM
nitrogen (mg/l) (EBC) (-) (mg/l) (mg/l)
Merlin ConvaMerlin ConvaMerlin ConvaMerlin ConvaMerlin Conva
Kettle full 43.0 50.0 6.0 6.4 18.6 25.8 357 620 505 620
Cast 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
aConventional boiling
Table 6: Comparison of Merlin boiling to a conventional method (Wienzierl et al, 2000).
Merlin Conventional
without heat recovery
Kettle full amount (hl) 163 163
Temperature before heating (°C) 90.0 72.0
Measured energy requirement heating up (MJ) 1,374 2,216
Evaporation related to kettle full (%) 3.55 12
Total evaporation (mean of 3 brews) (hl) 5.78 19.6
Measured energy requirement boiling (MJ) 1,251 4,986
Measured energy requirement boiling, gross total (MJ) 2,625 7,202
Specific requirement (MJ/(hl cast wort)) 16.70 50.21
Savings specific energy requirement related (%) 66.7
to same cast out amount
With wort cooling and vapour condensate cooler
Total energy requirement, gross (MJ) 2,185 7,202
Specific requirement (MJ/(hl cast wort)) 13.90 50.21
Savings specific energy requirement (%) 72.3
CO2 emission (t/a) 325 1,175
Process description
Firstly, the wort is boiled during 40 50 min with the
existing boiling system. An evaporation of approximately
4% is achieved. Next, the whirlpool is employed as usual.
After the rest period in the whirlpool, the wort is led
tangentially as a thin film through the by-pass of the
existing wort pipe into the vacuum vessel.
Figure 13: Process diagram of the Ziemann vacuum
evaporation plant (N.N., 2001e).
The necessary vacuum of approximately 0.4 bar
underpressure for an evaporation of 2% is produced by
means of a liquid ring vacuum pump. After the start and
during the flash evaporation process, the vacuum is
maintained by vapor condensation. Undesired flavouring
agents (e.g. free DMS, degradation product of fat, Strecker
aldehydes, …) are driven off with the produced vapour.
The vapour which is formed during this process, is
condensed in the vapour condensor with the production of
hot water of 80°C. In the condensate cooler, the resulting
condensate is also used for heating up brewing water
before it goes to the gully. During the wort flow, the
vacuum in the flask tank is controlled through the
temperature of the wort after the flash evaporation. The
wort volume in the flash tank is kept constant by means of
a speed-controlled wort pump, which is positioned
underneath the tank outlet. This wort pump is designed in
a way to ensure that the wort reaches the existing wort
cooler with more or less the same pressure and volume
flow as before.
Energy and hot water balance
A comparison between wort boiling with subsequent
vacuum evaporation and conventional wort boiling with
8% evaporation is shown in Table 7. The reduced
generation of hot water during the wort cooling process
with vacuum evaporation is compensated by warm water
generation during the vapour/condensate cooling process.
A comparison of the primary energy demand showed that
wort boiling with subsequent vacuum evaporation enables
savings of approximately 50% of thermal primary energy
which is required only for wort boiling compared to
conventional boiling.
Nerb system
The company Nerb (Freising Attaching, Germany)
introduced recently 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 shown
in Figure 14. This boiling system is composed of a wort
vessel, an external boiler, an expansion evaporator with a
vacuum pump and a vapour condensor coupled to a hot
water storage tank. Additionally, vapour compression can
also be used during boiling. Instead of the wort boiling
vessel, a buffer tank or the whirlpool can be used.
Process description
The wort is pumped through the external boiler into the
expansion vessel. The wort flows tangentially into this
vessel and as a thin film at the inner surface. During
boiling, the pressure is atmospheric in the expansion
vessel. The produced vapour upon expansion is condensed
in the vapour condensor. An outlet pump is used to pump
the wort back to the wort kettle and to control the level in
the expansion vessel. After the boiling process, the
expansion vessel is evacuated. The wort is then pumped
via the expansion vessel to the whirlpool. The vacuum
evaporation results in a wort temperature of 88°C. The
advantages of wort pre-cooling are in this way achieved.
Table 7: Comparison of boiling with subsequent vacuum evaporation to conventional (8% evaporation) (N.N., 2001e).
Boiling with 4% evaporation Conventional boiling
and 2% vacuum evaporation with 8% evaporation
Wort cooling
Volume of wort to be cooled (hl) 1000 1000
Wort inlet temperature (°C) 87 98
Wort outlet temperature (°C) 8 8
Ice water inlet temperature (°C) 3 3
Ice water outlet temperature (°C) 82 82
Volume of hot (82°C) water (hl) 990 1120
Vapour condenser for vacuum evaporation incl. vapour condensate cooling
Vapour 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
Figure 14: Process diagram of the Nerd boiling system with
vacuum evaporation (Krottenthaler et al., 2001).
Industrial trials
The Nerb boiling system has been evaluated on an
industrial 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 short
boiling schemes. Table 8 shows some results concerning
the evolution of the wort quality during boiling and
vacuum evaporation. These results confirm the low
thermal stress exerted on the wort and a sufficient removal
of unwanted volatile components. The aroma profile of the
short and normal boiling schemes were comparable and
positively evaluated. On the contrary, the long boiling
scheme resulted in an unwanted taste.
Kaspar Schulz system
The company Kaspar Schulz (Bamberg, Germany)
presented recently a new boiling system (N.N., 2001f;
Binkert & Haertl, 2001). Wort boiling is divided into two
phases: in the first phase, the wort is kept at a temperature
just below the boiling point (approx. 97.5°C); the second
phase is a vacuum evaporation phase. A total evaporation
rate of 8% is obtained. Considerable energy is saved by
keeping the wort just below the boiling point during the
hot holding phase (since there is no evaporation energy
cost). This patented boiling method has been tested on
pilot (50 l) and industrial (240 hl) scale.
Process description
The process diagram is schematically shown in Figure 15.
The wort is heated in the wort kettle to 97.5°C and kept at
this temperature during 60 min. The wort is stirred
constantly with an impeller. The length of this hot holding
period is dependent on the isomerisation yield of the a-
acids and the obtained value of coagulable nitrogen and
can be adjusted.
Table 8: Quality of the obtained wort 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 free DMS 2-Furfural SteckeraldehydesaFat degradation
(-) (mg/l) (mg/l) (mg/l) (mg/l) productsb (%)e
Before boiling 12 16 825 821 283 285 82 87 911 916 100 100
After 30 min 22 22 352 360 97 126 121 87 431 374 32 39
End of boiling 25 26 251 214 103 68 160 160 404 362 25 17
After vacuum 28 30 208 191 35 26 193 187 380 351 18 19
aSum of the Steckeraldehydes (2-methylbutanal, methylbutanal, methional, 2-phenylethanal).
bSum of the fat degradation products (hexanal, heptanal, pentanal, 2-pentanon, benzaldehyde, g-nonalacton, 2-cis-6-nonadienal, 1-
hexanol, 1-pentanol, 1-octanol, 1-octen-3-ol).
cShort boiling: boiling time = 50 min, evaporation during boiling = 2.9% and vacuum evaporation = 1.8%; temperature in the external
boiler = 103°C and in the wort kettle = 99°C.
dNormal boiling: boiling time = 60 min, evaporation during boiling = 3.5% and vacuum evaporation = 1.9%; temperature in the external
boiler = 103°C and in the wort kettle = 99°C.
eCompared to the value found before boiling.
Figure 15: Process diagram of the boiling system of Schulz using a vacuum expansion evaporator (Binkert & Haertl, 2001).
During this period, the evaporation rate is approximately
1%. The next step is the removal of hot trub and hops
debris. After a whirlpool rest period, the clarified wort is
pumped to the vacuum evaporator. The pressure in this
expansion vessel is approximately 300 mbar. Due to the
tangential inflow of the wort in this vessel, the wort flows
down in a thin liquid film along the inner surface of the
vessel wall. An evaporation rate of 7% is obtained. A
vapour condensor is used to produce hot water. In the
evaporator, the wort is cooled to ca. 63°C. Next, a plate
heat exchanger is used to further cool down the wort to
fermentation temperature.
Industrial trials
The obtained wort quality using this boiling system is
shown in Table 9 and compared with a conventional
boiling system. After 40 min, a coagulable nitrogen
content of 25-28 mg/l was reached. The comparison of the
beer analysis between the obtained beer using the new
system with the conventional system revealed that no
significant difference could be found (no data were given).
Energy balance
Table 10 shows the energy balance of this new system,
which is compared, to a conventional boiling system with
8% evaporation. Due to the use of an impeller, a wort
pump and a vacuum pump, an additional current
consumption has to be introduced in the energy balance
(estimated as 15 kWh for boiling 225 hl wort). The
vacuum evaporation cools the wort to ca. 63°C which
results in the subsequent wort cooling with the plate heat
exchanger in hot water with a temperature of only 60°C.
Compared to a conventional system, the temperature
difference is 18 K and the total savings compared to a
conventional system becomes 56% (see Table 10). This
figure can be increased when the evaporation heat is also
Table 9: Quality of the obtained wort using the Schulz boiling system with subsequent vacuum evaporation (Binkert & Haertl,
Coagulable nitrogen Real extract Free DMS SMM
(mg/l) (%) (µg/l) (µg/l)
After hot holding period 2.16 2.10 11.65 12.4 348 17 43 97
After cooling 2.00 1.90 12.15 12.3 58 68 46 44
aThe exact length of the hot holding period is not mentioned.
b8% evaporation.
Table 10: Energy balance of the Schulz boiling system compared to a conventional boiling system (Binkert & Haertl, 2001).
Energy costs for conventional boiling
Wort volume Evaporation Fuel consumption Fuel consumption Fuel price Evaporation costs
(hl) (hl) (L/hl evaporation) (L/hl wort) (DM/L) (DM/hl wort)
225 18 11.3 0.91 0.65 0.59
Energy costs for the hot holding period
Wort volume Evaporation Fuel consumption Costs hot holding Additional current Current costs Total costs
(hl) (hl) (L/hl wort) (DM/hl wort) requirement (kWh) (DM/kWh) (DM/hl)
225 0,5 0.26 0.17 15 0.12 0.18
Savings (DM/hl) Savings (%)
0.41 70
Costs for heating hot water
Hot water requirement Temperature difference Fuel consumption Costs Total savings Total savings
for wort heating (hl) (K) (L/hl wort) (DM/hl wort) (DM/L) (%)
100 18 0.12 0.08 0.33 56
Savings with heat recovery
Hot water production
Total Requirement Service hot water Fuel savings Savings Total savings Total savings
(hl/hl wort) brewhouse (hl/hl wort) (hl/hl wort) (L/hl wort) (DM/hl wort) (DM/hl wort) (%)
1.7 1.35 0.35 0.2 0.13 0.46 77
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As a sequel to the early collaborative work which was initiated in 1956 and culminated in the publication of three papers in 1965, the future of the Haze Group of the E.B.C. is envisaged as one of liaison between individual scientific workers who are engaged in fundamental enquiries and brewing technologists who are concerned with problems at the production level. The Group will continue to make arrangements, where appropriate, for collaborative work. In view of the many common factors involved in haze and in foam formation, it is suggested that the name of the group be amended to include the topic of beer foam within its sphere of interests.
Nature is the international weekly journal of science: a magazine style journal that publishes full-length research papers in all disciplines of science, as well as News and Views, reviews, news, features, commentaries, web focuses and more, covering all branches of science and how science impacts upon all aspects of society and life.
For an individual, especially a civilized person, the selection of foods is determined largely by flavor. Concern for physical well-being and the nutritional values involved come far behind flavor as a factor determining human dietary choice. The gradual recognition that complex, presumably nonenzymatic transformations, which take place in certain foods, responsible for deterioration in some cases and for the development of traditionally valued flavors in others, have a common chemical basis leading to the carrying out of experiments in relatively simple model systems. The reaction initiating the sequence between a carbonyl group and a trivalent nitrogen atom is the most thoroughly investigated and best understood of all the reactions. Many bland or even downright unpleasant-tasting substances are transformed into some of the most desirable flavors and popular foods by roasting. The enormous variety in flavor is due almost entirely to the large number of permutations from the interactions of a relatively few primary reactants and to the importance of balance among the components finally present. Since humans began to cook meat and bake bread, they have been familiar with the aromas and flavors produced by Maillard browning reactions. The presence and the consumption of products of browning reactions in foodstuffs present two possible problems for human health, one nutritional and the other mutagenic. Investigations in the field of Maillard chemistry are now directed to the solution of an ever-widening circle of problems, which differ more and more from each other, though each is still attached to the core.
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