CA2441729A1 - Thin film process for wort production - Google Patents

Abstract

In a brewing process, the removal of off flavour volatiles from the wort is accomplished by treating the wort in an agitated thin film evaporator. Preferably the wort is prior boiled prior to its being introduced to the evaporator and at its boiling point. A vacuum can be applied to the evaporator.

Description

THIN FILM PROCESS FOR WORT PRODUCTION
FIELD OF THE INVENTION
The present invention relates to the production of wort, and in particular to the removal of wort volatiles having undesirable flavour impact on the resulting beer.
BACKGROUND OF THE INVENTION
In the production~of beer, wort production traditionally begins with the mashing in of the malt with foundation water in a mash tun. Extraction of mash carbohydrates etc. from mash bill ingredients, including adjuncts, proceeds in known manner. Clnce the extraction has been completed, the resulting wort is separated from the spent grains in a Tauter tun, or in a mash filter.
The wort is then boiled, typically in conventional batch systems, in a brew or hop kettle in conventional batch systems, but in any case with the intention of achieving a variety of purposes, including: inactivation of enzymes; wont sterilization and concentration; and removal of undesirable volatiles; formation of Maillard reaction compounds; formation of reducing compounds; isomerization of alpha-acids to iso-alpha-acids; protein coagulation and a slight pH
reduction. It may be noted that according to Moll in Beers and C~olers, 1991, a traditional hop kettle is equivalent to a one-plate distillation column in the removal of volatiles.
In continuous wort boiling systems, wort heaters or heat exchangers may be used and are preferably of the plate or shell-and-tube heat exchanger type. I:n this heater the incoming wont is heated with steam from the filtration temperature (typically 75'° C.) to the boiling temperature.
Also utilizable in continuous wort boiling systems could be an evaporator (for example of the falling-film type), which could be used for heating the wont as well as producing the steam for the generally later stripping section. In any case, in such continuous systems, the wont is then transferred into a holding column, operating at a temperature of from 75° - 125° C. and a pressure of 1 to 2 bar, to obtain the required residence time for the several reactions as described above to take place at temperatures close to the boiling temperature of the medium. The rotating disc column (or rotating disc contactor) is equipped with a rotating axis fitted with a large number of discs. The discs serve two purposes:
( 1 ) to apply a gentle stirring to aid the coagulation and agglomeration of trub particles and keep them in suspension, thus preventing excessive fo~xling of the column internals, and (2) to obtain a controllable residence time distribution so that all the wort is treated for the same duration at the higher temperature.
As a plug flow reactor, various types of reactor may be; used, it being of special importance that no unacceptable back-mixing and/or pre-mixing of the components occur.
Examples thereof are tubular reactors and cascades of more or less ideally agitated tank reactors.
A preferred type of reactor is the so-called rotating disc contactor, which is a known type of vertical column reactor as described in detail in, e.g. Kirk-Othmer, Ehcyclopedia ~f ~'hemical Technology, Third Edition, Vol. 9, Page 702. Such a reactor generally consists of a vertical column provided with a central agitator shaft having attached 'thereto 10 or more discs or plates.
These discs or plates cover at least 80% of the cross section of the column.
In general, this surface does not exceed 95%. The shaft and discs in the column are rotated in an attempt to obtain a proper dispersion of the solid matter in the liquid. The use of a contactor instead of an arrangement of holding tubes has the advantage that, due to the stirring action, when wort passes the holding tubes at low speed (necessary to obtain an acceptable residence time) the agglomerated denatured proteins and enzymes bonded with hop resins or polyphenols from the malt or hops will not settle. This precipitation can cause residvues in the tubes, which form an impenetrable deposit requiring down time to carry out a thorough cleaning action using alternating hot and cold water cleaning cycles to '°crack" the deposits from the tube surface. The rotating discs contactor aims to prevent the formation of deposits by the agitation and the absence of baffles to ensure a minimum of dead-spots inside the column. The volume of the plug flow reactor and more in particular the rotating disc contavetor is chosen to provide a holding time of 45-75 minutes, it being considered that, during this time all the desired reactions will have proceeded sufficiently.
Once the wort has been boiled, whether in the case of either the batch or continuous processes mentioned above it, in some prior processes, it is fed t~ a distillation type stripping column, operating for example as described above at temperatures of from 75° - 125° C. and a pressure of 1 to 2 bar. The column is fitted with trays on which the wort is stripped, preferably counter-currently, with fresh saturated steam. Because of the large number of trays (at least five trays) and subsequent equilibrium stages the volatile components are removed in a very short time at fairly high efficiency. The residence tine in the column is typically up to ten minutes, but preferably the apparatus is scaled to the volumetric throughput so that the stripping takes place in the range of about 30 seconds to 2 minutes. Because of the high efficiency the use of stripping steam is smaller than the net evaporation during traditional wort boiling and the gain in energy consumption can therefore be significant. In continuous operations, the stripping steam can be used to heat the incoming wort. Optionally the wort is heated and partially evaporated in an evaporation unit, the generated vapors serving as the stripping medium in the stripping column. In the stripping section, various types of stripping and/or distillation equipped can be used, such as a tray or packed column, for example using the ;>o-called Sulzer TM packing, or a baffled column. A stripping column will preferably have five or snore trays or a packed height of at least 2 meters. The tray-type column with down flow assures a good mixing of steam and wort and has a broad operating range. As the volume is very :>mall this type of column can be cleaned by successive filling and draining of the column in either normal flow or reverse flow.
Care has to be taken during mash filtration prior to the boiling of the wort as particles resulting from inadequate mash separation may block the upper trays. ;saturated steam is fed through a bottom inlet below the bottom tray or packing. Because of the highly efficient mass transfer the steam flow can be set as low as 4-6 wt. % of the mass flow of wort. A good insulated column is necessary to maintain equilibrium between wort and steam temperature to prevent steam condensing in the wort resulting in undesired dilution of the wort and inefficient steam usage.
The use of a holding column in combination with a stripping column is purported to offer a number of benefits from a process-technological view. As one of the most important off flavour components, dimethylsulphide (DMS), is formed from a non-volatile precursor, the holding stage is intended to assure that a maximum amount of the precursor is transformed into DMS entering the stripping section. It is therefore very important that DMS
and other undesirable volatiles are rapidly and efficiently removed from the wort prior to the fermentation stage. As indicated previously, (refer Technology Brewing an~~' Malting, Wolfgang Kunze;
Translation by Dr. Trevor Wainwright), all wort production processes involve compromises.
With respect to the removal of undesirable volatiles, and especially dimelthysulphide (DMS) production and elimination, the longer and more intensive the boiling, the more efficiently DMS
can be eliminated. However, extended boiling is not a real option for, inter alia, costs reasons.
Attempts have therefore been made to subject the wont to a boiling stage which has a separate volatile eliminate step, sometimes called "stripping". Refer for example to WO
95/26395 and WO 97115654. However, these proposals leave something to be desired.
SUMMARY OF THE IN'VEN7.'ION
It has been realized that such removal or stripping of volatiles is a mass transfer -controlled process; efficiency is not controlled primarily through heat transfer. A volatile component has to be transported to the medium interface and only then be vapourized. Transport of such components within that wont is usually accomplished by molecular diffusion or by eddy diffusion. The former found, for example, in lamina flow, is extremely slow and decreases with increasing viscosity of the liquid.
In accordance with the present invention therefore the removal of off flavour volatiles from wont is effected using an agitated thin elm evaporator, sometime referred to as a "wiped film evaporator". These inherently simple devices generally consist of two major components, namely, a cylindrical housing, the inner or treatment surface of this being heated and an internal rotor assembly which has blades whose radially outermost edges are generally parallel to the axis of the rotor and either are spaced from, but adjacent to, with a fanal clearance from the interior surface of the housing or actually contact and scrape that interior surface.
In both instances, the blades create a "bow wave" in the wort at their leading edge as they pass through the device which waves provide a highly turbulent flow resulting in optimum heat flux and mass transfer.
This action provides an efficient evaporation of the undesirable volatiles and allows their removal from the wort.
In one embodiment therefore, the present invention provides a process for removing undesirable volatiles from wort, which process comprises feeding wort through a thin film evaporator device which has at least one mechanically wiped cylindrical evaporator surface, providing a film of said wart on said surface, which wont is maintained preferably at an elevated temperature preferably of about its boiling point whereby said volatiles are evaporated and separated from said wort.
It is preferred that the wort prior to entering the evaporator has been boiled to allow the bitter substances to go into solution and coaguable protein to precipitate and, subsequently, filtered. Usually the wort would already be at an elevated temperature of from say 70° - 80° C.
Although this wort could be introduced to the evaporator device, it is preferred to raise its temperature even up to about its boiling point, say 100° - 105°
C prior to introducing same to the evaporator. This allows for the rapid removal of the volatiles at relatively low temperatures thereby with less possibility of the wort being adversely affected by the heating regimen.

DESCRIPTION. OF TIIE DItAVVIloTGS
The present invention will be further described, but not limited by reference to the accompanying drawings in which:
FIG.1 is a simple diagrammatic representation of the process of wort production in a conventional brewing process.
FIG. 2 is a cross-section through an agitated thin-film evaporator or "wiped film evaporator", used in accordance with the present invention;
FIG. 3 is an upper angled perspective along the line X-~X of FIG. 2.
FIG. 4 is a view of a blade of the device of FIGS. 2 and 3 showing the clearance between its radially outermost part and the rotor blade device treatment surface.
FIG. 5 is a similar view to that of FIG. 4 but wherein there is no clearance between the radially outermost part of the rotor blade and the treatment surface.
FIG. 6 is a cross-seetion through an alternative agitated thin film evaporator for use in the present invention.
Turning to FIG.1, this illustrates in diagrammatic form, part of a typical brewing process. Briefly, malt from hopper 50 and associated grist mill. 52 is transferred to mashing vessel 54. Following completion of the mashing, the mash is transferred to the tauter tun 56 wherein the liquid is separated from the mash solids and passed to the wort kettle 58. In the wort kettle 58, all the usual processes required to bring about desired fermentable wort are affected.
The wont is then cooled, fermented to form green beer, aged and packaged in the usual manner.
As a general comment, there have been many suggestions to increase the efficiency of wort production.

Turning to FIG. 2, this is a cross-section through an agitated thin -film device, generally designated 10, which has a cylindrical body or housing 12 having an inner wort treatment surface 14. Surrounding the housing 12 is a jacket 16 which is provided with a heating on cooling medium inlet and outlet ports 18 and 20. Enclosed within housing 12 is a rotor assembly generally designated 22 which comprises a number, in this case four, rotor blades 24 carried and rotated by shaft 26, the assembly 22 having an internal bearing; 28 at its base. A heated wort inlet port is shown at 30 and, depending on the selected configuration, vapourized impurities exit via port 32, i.e. countercurrent to the flows of incoming wort a:nd exiting vapourized volatiles, or in a less preferred embodiment, 34 wherein both treated wort a.nd vapourized impurities exit at the base section of the device - but obviously via different ports - the wont via port 34. This device is obtainable from LCI Corporation, P.O. Box 16348, Charlotte, North Carolina 28297.
Turning to FIG. 3 this shows in more details the heating zone 16, a rotor blade 24 travelling in the direction of the arrow and the bow-wave 35 formed in front of blade 24.
In the present embodiment, the rotors can be of fixed clearance type - refer to FIG. 4, or of the wiped film type - refer to FIG. S - which actually contacts the interior surface 14 of the housing. In either case, vigorous agitation is provided in the wort film being heated at the housing wall 14.
The device operates as follows. The wort enters at port. 30 above the heating zone and is evenly distributed over the device's inner heating surface by the rotor 24. As the wont spirals down the wall as indicated by helix 2, bow waves 35 developesi by the rotor blades 24 - refer to FIG. 3 - create a highly turbulent flow resulting in very efficient heat and mass transfer. The undesirable volatile components are rapidly evaporated. Preferably, the vapours containing the volatiles flow counter-currently and exit via port 32. Alternatively, they can flow concurrent and exit via port 34. Obviously, the vapours can then be condensed and further processed or simply discarded as desired. The stripped wort is discharged through port 6. It should be noted that continuous washing of the housing wall by the bow wave minimizes possible wall fouling by the wort components and allows for long term continuous operation without shutdown for cleaning.

Turning to FIG. 6,. this shows an alternative form of the film evaporator system which may be used in accordance with the present invention This device is obtainable from VIC Inc., Joliet, Illinois. In this device, the wort is introduced at 11 to tree evaporator depicted generally as 12. The wont feed contacts product distributor plate 13 rotated. by shaft 14 connected to gear motor 15. The feed is flung by centrifugal force against the interior wall of heater jacket 16 and flows downwardly along the interior wall. The interior wall of heater jacket 16 is continuously wiped with roller wipers depicted at 17 and l 8. Three sets of rollers are used, each set mounted on a shaft driven in an annular path by product distribution plate 13. The rollers serve to insure that a thin wont film of the desired thickness is maintained on the interior wall of heather jacket 16. Heater cycle fluid is fed at 20 to the interior of heater jacket 16 and removed at 21 to maintain the desired temperature on the interior wall of heater jacket 16. An exhaust vacuum, if desired, may be drawn at 22 by known means not shown, to maintain the desired pressure inside the evaporator 12. Internal condenser 23, if required, is fed with cooling water at 24 and the cooling water is discharged at 25 to maintain internal condenser 23 at the desired temperature.
The distillate which condenses on internal condenser 23 is removed at 26. The wort with volatiles removed flows down the interior wall of heater jacket 16 is collected and discharged at 27.
In more detail, a pilot device of this type has an evaporator surface of 0.1 meters. The hot wort at about its boiling point is pumped from a wort heater (not shown) into the device via port 11 where it is distributed into a thin film by means of the r~ighly efficient self cleaning roller wiper system. This system consists of a wipe basket with an upper holding plate and stabilized rings, which are interconnected by the holders of the guide rods for the PTFE
rollers. The wort is flung by centrifugal forces from the distribution plate 13 against the upper part of the evaporator surface where the wort is immediately spread onto the surface in the from of a film having generally uniform thickness. The rollers supported on the guide rods are pressed into the product film by centrifugal forces. No wont remains in the basket - it all gets incorporated into the film. Consequently, substantially none of the wort is subjected to excessive or uneven heat treatment. The internal condenser is not generally needed in the treatment of wort. Volatiles are rapidly and readily removed from the wort through exit port 22 for collection.
The wont exits via port 27 and is passed to the next stage in the overall brewing process as described above. The open construction of the wiper basket with its large distance between the individual rollers assures a direct discharge of the vapours at very little pressure loss. The roller wiper system provides a uniform turbulent mixing of the film on the entire evaporator surface. So called "dead zones" are avoided due to overlapping of the rollers as well as wiping on unheated areas. At the same time, the liquid film on the rollers themselves is continuously renewed, resulting in a very low residence time of the evaporating volatiles on the evaporat;~r surface.
There is little build-up of material on the evaporator surface or on the rollers and this allows for continuous operation with little or no down time.
In the operation of both of the above described thin film evaporator devices, a vacuum may be applied to further assist removal of the undesirable volatiles as they are formed. This added feature also allows for a reduction in the amount of and time of heating of the wort required to effect the desired evaporation, not only producing a saving in energy but reducing any adverse efforts of heating wort to the higher temperatures.
In summary, this device provides:
1. Very short residence/processing time at relatively low temperatures thereby having minimal adverse effects on the wort.
2. High turbulence resulting in efficient volatization of undesirable components;

3. Rapid surface renewal which is important in preventing heating damage to the wort and maintain the quality thereof.

4. Minimal pressure drop resulting in the use of lower boiling temperatures;

5. No stripping gases are required as in prior processes when steam is used in that capacity.
The net result is high quality wort with good flavour ch;~racteristics.

Claims

CLAIMS:

(1) A process for treating wort to remove undesirable volatiles therefrom comprising treating said wort by passing it into and through a heated agitated thin film evaporator and extracting a gaseous stream containing said volatiles and a liquid stream containing treated wort.

(2) A process according to Claim 1 wherein said wont is heated in the evaporator at a temperature at about its boiling point.

(3) A process according to Claim 2 wherein said wont is at a temperature of from 75° -105° C, prior to being introduced into the evaporator.

(4) A process according to Claim 1 wherein said wont has been boiled and filtered prior to being introduced to the evaporator.

(5) A process according to Claim 1 wherein a vacuum is applied to said evaporator.