The new generation of internal boilers from Huppmann: the Jetstar

NEWSLETTER
Special Jetstar
The new generation of internal boilers from
Huppmann: the Jetstar
Better, gentler, more efficient – and easy to retrofit
Huppmann has developed a new internal boiler that has caught the attention of brewing
experts: the Jetstar. With 2-phase boiling in combination with the innovative subjet system, the
Jetstar is setting new standards in terms of wort quality and efficiency, also in atmospheric
systems. The Jetstar can easily be retrofitted to any wort kettle with internal boiler. Thus,
the innovative technology of 2-phase boiling is also available for conventional atmospheric
systems. In the following we have summarized the most important details about this superior
technology.
Subjet orifice and
two-level wort spreader of the Jetstar
Internal boiler – an established principle
Internal boilers were first used for wort boiling in 1977 and have since established
themselves throughout the world as the dominating boiler principle. 93 % of the wort kettles
manufactured by Huppmann over the past 15 years were equipped with tubular internal boilers;
the remaining systems operate with external boilers. The tubular internal boiler replaced
previous systems such as the cascade boiler or the conical kettle and intensified wort boiling. It
met the demand for high evaporation rates required due to shortened boiling times. Thanks to
the large heating surface, tubular boilers enable an excellent heat exchange at low heating
medium temperatures and achieve high circulation rates. Most systems operate according to the
principle of natural circulation, i.e. they are driven solely by rising steam bubbles in the boiler
tubes.
© Huppmann AG 2006
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NEWSLETTER
Homogeneity of wort treatment
According to Schwill-Miedaner and Miedaner [1], "a basic requirement for constant wort
quality is wort in which the contents are homogeneously distributed during the boiling process".
To meet this requirement, the equipment manufacturers have continually optimised their internal
boiler systems. Particularly the heating phase from lautering temperature to boiling temperature
is critical. Long dwell times connected with increased thermal load in the boiler tubes can occur
when the wort is distributed unevenly in the kettle and is thus heated unevenly.
Relief openings
In 1984 Huppmann largely eliminated this accumulation of wort in the boiler tube through
the introduction of relief openings and thus distinctly reduced the thermal load of wort during
heating-up.
External heating-up
In plants with an energy storage system, wort can be preheated rapidly and gently to boiling
temperature through the use of an external plate heat exchanger with a booster stage, so that the
critical phase of heating-up in the internal boiler is completely eliminated. Very efficient
scrubbing of undesired flavours in the entire content of the kettle can be achieved through
pressure relief combined with dynamic low-pressure boiling. In this manner, homogeneous
wort treatment is guaranteed in this system configuration. This is confirmed by the results [2].
Forced flow
The forced flow of the internal boiler, pump-assisted, was also implemented in various
breweries and by several equipment manufacturers. This led to improvements, primarily during
heating-up. Nevertheless this does not completely solve a decisive problem during wort boiling:
the homogeneity of the kettle content. As Delgado and Baars [3 – 6] have shown, circulation of
wort by means of a deflector can generate short-circuit flows which are an obstacle to uniform
treatment especially in the heating-up phase. To achieve uniform wort treatment, dead zones
and short-circuit flows must be prevented. It is required that the wort circulates vertically downwards
in piston flow and is drawn-in as evenly as possible by the internal boiler.
The Jetstar operation in detail
Short-circuit flows can largely be prevented by discharging the wort below the wort level
with the so-called "subjet", because the wort is distributed evenly. The new boiling system from
Huppmann operates with this principle. The results of the new internal boiler system "Jetstar"
are presented below.
View inside the wort kettle of
Löwenbräu Brewery in Munich:
Jetstar in subjet operation in phase 1.
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NEWSLETTER
The new 2-phase boiling method
Heating-up
In the presented case, transfer from the pre-run tank to the wort kettle is carried out within
20 minutes for all brews using a wort heater with an energy storage system up to 92 °C. At a
kettle volume of 500 hl, heating-up commences with the wort being discharged through the
subjet orifice.
Two-phase boiling
Thanks to the subjet orifice, it is possible for the first time to divide the wort boiling process
into two phases with an internal boiler with natural circulation.
Jetstar during heating-up and in the first
phase, the thermal conversion
Phase 1
Thermal conversion: During this phase, wort flows out of the boiler through the subjet
orifice below the wort level. The known processes such as hop isomerization, protein
coagulation, degradation of flavour precursors (e.g. DMS precursor), sterilization, flavour and
aroma formation take place with the temperature in the work kettle required for these
processes. Homogeneous temperature distribution is achieved throughout the entire content of
the kettle by gentle circulation. The boiler is pressurized only very slightly during this phase
because it is not required to overcome a pumping height for circulation.
High circulation rates combined with the low interfacial temperature conserve the
foam-positive substances. The steam bubbles produced in the boiler tube provide for a high
momentum exchange below the wort surface thanks to the two-phase flow at the boiler outlet.
At the same time, the steam bubbles condense again in the wort, and only very little evaporation
occurs. Due to the homogeneous distribution in the kettle, the duration of this thermal
conversion can be selected irrespective of the required evaporation. Depending on the content
of flavour precursors, thermal conversion generally lasts 50 to 60 minutes. The goal is to reduce
the precursors of undesired flavours as far as possible. The evaporation of flavours takes place
in the following evaporation phase.
Phase 2
For evaporation, the lower outlet is closed and the upper one is opened. Using simple steam
regulation, circulation via the two-level wort spreader commences. The large surface created
thereby enables intensive evaporation of the flavours. Depending on the desired final values and
the target original gravity, this evaporation phase continues for 10 to 20 minutes.
Due to the intensive degradation of the DMS precursor during the thermal conversion
phase, a relatively low evaporation rate suffices to achieve the desired values of free DMS and
other flavours in the finished wort. Thanks to the consistent division of boiling into two phases,
it is possible to reduce total evaporation to values under 4 % without difficulty. An input of
additional evaporation energy during phase 1 would not accelerate the degradation of flavour
precursors at all. Evaporation of the substances is not necessary at this time, because the
degradation reaction is not inhibited by the content of free DMS. Only a temperature increase
of the wort by increasing the pressure in the kettle space can accelerate the decomposition
processes further and thus shorten the cycle time. The combination of dynamic low-pressure
boiling with the Jetstar will open up new possibilities.
In phase 2, discharging via the two-level
wort spreader ensures intensive
evaporation.
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© Huppmann AG 2006

NEWSLETTER
DMS [µg/l], %
120,0
100,0
80,0
60,0
40,0
20,0
0,0
Typical view inside the wort kettle:
The wort is intensively evaporated via the
two-level wort spreader (phase 2).
Series 1: Conv. 70 min, 9.5% Series 2: Conv. 55 min, 6.6 %
Series 3: 2-phase boiling, 55/15 min, 3.1 %
Total red.DMS
in %
Red. DMS-P in
%
Setpoint
DMS-f CW
DMS-f Half-time
of cooling
DMS precursor and free DMS during
2-phase boiling with the Jetstar
Trial results
In the Löwenbräu Brewery in Munich, part of the InBev Germany group, trials were
conducted with light lager in a conventional wort kettle, with a volume of 710 hl cast wort. The
ideal technology was determined in a series of preliminary trials. The two boiling phases were
optimally adjusted to each other. The values determined in this manner were compared with
those of conventional boiling over 70 minutes, with evaporation rates of 8 – 9 %. The same raw
materials were used to ensure comparability of the analyses. As a further trial, the existing
boiling process was simply shortened in order to operate with 6 % evaporation with a boiling
cycle of 55 minutes. This procedure is widely used in practice. The goal was to show that it is
possible to save energy by simply reducing the boiling time, however not without reducing wort
quality. To ensure the comparability of the brews, heating-up was carried out with the same
procedure for all brews. Different procedures were used only after the boiling temperature
was reached. It was possible to double the ramp rate from 0.6 K/min to 1.2 K/min without
impairing the protein ratios. Despite the high heating-up power, the content of the kettle did not
foam at all.
DMS ratios
As representative of the wort flavours, the behaviour of the DMS precursor was examined.
The diagram clearly shows the efficiency of precursor decomposition in the different procedures.
Irrespective of evaporation, it was possible to reduce the total DMS by approximately 77 % and
the DMS precursor by approximately 67 % with the same dwell time of 70 minutes. On the other
hand, the shortened boiling time of 55 min led to a reduction of only 67 % or 57 %. Therefore
the same results were achieved with the reduced energy input of 3.1 % total evaporation as
with 9.5 %. It is astonishing that this also applies to the free DMS during casting. An absolute
value of 12 µg/l on average was achieved in both cases. With a value of 17 µg/l during casting,
reduced boiling did not perform poorly either. However, the known phenomenon of
reproduction of free DMS in the whirlpool occurs here. Midway through wort cooling, the value
of 98 µg/l was just under the threshold value of minor 100 µg/l. In contrast, the other two
procedures were both under 70 µg/l.
TBI-increase
Coag. N. [mg/l]
25
20
15
10
5
0
Series 1: Conv. 70 min, Series 2: Conv. 55 min, Series 3: 2-phase
9.5% 6.6 % boiling, 55/15 min, 3.1 %
25
20
15
10
5
0
Setpoint
Significant: the smaller thermal load
during 2-phase boiling
Series 1: Conv. 70 min, Series 2: Conv. 55 min, Series 3: 2-phase
9.5% 6.6 % boiling, 55/15 min, 3.1 %
The coagulable nitrogen ratios also
indicate a smaller thermal load.
Thermal load: TBI
Parallel to this, the TBI increase is interesting. As expected, conventional boiling showed the
worst performance. Here the increase from kettle-full to end of boiling was 21 units. The lowest
increase of 15 units occurred with the shortest total time of 55 minutes. However, the Jetstar
two-phase boiling showed a much smaller increase of 16 units with a total time of 70 minutes,
than conventional boiling with 70 minutes. This illustrates the extremely gentle, homogeneous
circulation of the wort with the Jetstar.
Coagulable nitrogen
In the preliminary trials it was possible to set the content of coagulable nitrogen at the end
of boiling in ranges of 18 to 43 mg/l. The appropriate optimum value must be determined
based on the head retention and cold stability for the respective plant. It is known that the value
of the still coagulable nitrogen, the parameter for good or bad beer foam until now, can be used
as an indication at best. The possibility to influence this value deliberately is decisive. The
degradation rates from kettle-full to the end of boiling were 55 % for conventional boiling,
54 % for shortened boiling and 51 % for two-phase boiling. The absolute content during
conventional boiling of 18 mg/l was certainly at the lower limit of the desired range of 15 to
25 mg/l. However, beers with perfectly satisfactory foam values also resulted from these worts.
The shortened boiling time of 55 minutes yielded a value of 17 mg/l on average; two-phase
boiling produced 21 mg/l. An improvement is noticeable in combination with the reduced
thermal load.
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© Huppmann AG 2006

NEWSLETTER
Literature
[1] Schwill-Miedaner, A. und Miedaner,
H., Würzekochung – heutiger Stand der
Technologie und Technik, Brauwelt 141
(2001), 18, 670 – 673
[2] Bühler, Th., Michel, R., Kantelberg,
B., Baumgärtner, Y., Die dynamische Niederdruckkochung
– systematisch qualitätsoptimiert,
Brauwelt 143 (2003), 38,
1173 – 1178
[3] Biwanski, T., Baars, A., Kowalczyk,
W., Delgado, A., Schmidt, T. und Bühler, Th.,
The subjet-wort boiling system of low
expenditure and high benefit, EBC-Kongress,
EBC-Proceedings, Prag, 2005
[4] Baars, A., Herbster, T., Schmidt, T.,
Delgado, A., Realisierung einer technologiegerechten
Durchströmung der Würzepfanne
mit Innenkocher durch gezielte Modifikation
der Geometrie, Brauwelt, 144 (2004), 38,
1164 – 166
[5] Delgado, A., Baars, A., Kurz, T.,
Hartmann, C., Schaumentwicklung und
Schaumzerstörung beim Betrieb einer
Würzepfanne mit Innenkocher, Technologisches
Seminar, Weihenstephan, 2003
[6] Baars, A., Werner, F., Delgado, A., Untersuchung
der Strömung in einer Würzepfanne
mit Innenkocher, Technologisches Seminar,
Weihenstephan, 2000
Conclusion
The Jetstar enables two-phase boiling with an internal boiler with natural circulation
for the first time. This means the separation of thermal conversion processes and necessary
vaporization (evaporation) in an atmospheric wort kettle. Thanks to the thermosiphoning
principle, the wort is subjected to a very gentle and homogeneous treatment. Technological
advantages are achieved through the minimized heat load during pulsation-free heating. Greatly
reduced steam temperatures are also used during thermal conversion. The desired analytical
parameters can be set deliberately and separately from one another. The homogeneous
temperature distribution in the kettle guarantees high conversion rates. Evaporation is carried
out effectively via the large surface of the two-level wort spreader.
In view of system design, the Jetstar can be easily retrofitted without much installation
effort and without additional consumption of electric energy. The hygienic design ensures
excellent cleaning properties. Thanks to the small thermal load, daily intermediate cleaning is
not necessary. Thus, the costs for water and cleaning agents can be minimized. The primary
energy savings are not reduced by the use of other energy forms. When an energy storage system
is used, the hot water balance is closed within the brewhouse. Thus complete condensation of
the vapour is possible also during atmospheric boiling.
Installation and retrofitting
The Jetstar can be installed with little downtime. If the design data of the existing
tubular boiler are right, a new optimized outlet cone for improved flow with a two-level wort
spreader is mounted on the existing boiler. The subjet orifice is located in the upper part of
the outlet cone below the wort level during casting. Variations in the cast-out quantity can be
compensated for by a simple mechanism. Depending on the kettle design, the mechanical
equipment for opening and closing the two outlets is installed on the kettle bottom or at the
kettle outlet.
Summary
Huppmann AG has developed a new boiler generation. For the very first time, the Jetstar
enables a division of wort boiling into thermal conversion and evaporation in internal boilers
with natural circulation. This procedure enables wort boiling to be more flexible and allows the
specific setting of all important wort parameters. The Jetstar can be easily retrofitted in all wort
kettles with an internal boiler. The system saves primary energy without reducing wort quality.
Acknowledgments
Huppmann AG would like to thank the Löwenbräu Brewery in Munich, part of the InBev
Germany group, represented by Dr Lehmann, Mr Viehhauser and Mr Kaup, for their excellent
cooperation. The authors would like to thank Mr Sven Milosevic for conducting the trials. They
would also like to thank Prof. Delgado and the staff members of the Chair for Fluid Mechanics
and Process Automation of the Technical University of Munich for the fruitful discussions.
All the best,
Your Huppmann Team
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© Huppmann AG 2006