Process for membrane filtration of mash to produce wort

This invention relates to a process for the preparation of wort starting from mash, comprising the separation of spent grain from the mash to form a clear wort in at least one membrane filtration unit having a pore size of the filter not exceeding 2.0 .mu.m, if desired addition of hops to the wort and boiling of the wort.

BACKGROUND OF THE INVENTION 
This invention relates to a process for the preparation of wort starting 
from mash, comprising the separation of spent grain from the mash. More in 
particular, the invention relates to a continuous process for the 
preparation of wort. 
When making beverages from cereals, more in particular when brewing beer, 
wort is used. A conventional preparation of wort occurs by mixing the 
starting materials, e.g., comprising unmalted grain (for example maize). 
The solid materials are first crushed (pulverized) and then mixed with the 
water. The resulting suspension is kept for some time at a temperature of 
at least 40.degree. C. in the presence of an enzyme source, e.g., malt. 
Gelatinization and liquefaction thereby occur. In a next step the 
enzymatic conversion of the mixture (mash) is continued after 
supplementary addition of malt and/or an external enzyme source. 
It is also possible to prepare wort on the basis of malt and water. Then 
the first step is omitted. 
The product thus obtained consists mainly of water, insoluble components of 
the raw materials, as well as soluble components, such as fermentable and 
unfermentable sugars and proteins. In the conventional method this mixture 
is filtered to remove the insoluble components, the spent grain. The 
filtrate or extract is the wort. For brewing beer, hops are then added to 
the wort, which is boiled. The flakes formed, if any, are removed, and the 
wort is cooled to about 8.degree. C. and fermented. 
European patent application 0 265 152 discloses the filtration of wort 
using a membrane having a pore diameter of from 10.0 to 100.0 .mu.m. As 
appears from the text of this publication, the membrane is intended to 
separate the spent grain from the mash, the advantage residing in that a 
smaller particle size of the starting products can thus be used. This has 
advantages relative to the extraction efficiency of the sugars from the 
raw materials. 
The membrane filtration according to this publication does not result in a 
clear wort which is suitable for further use. In particular, it appears 
from the text of the application that the wort as initially produced is 
not free from suspended particles, so that a supplementary filtration is 
required. This is a drawback of this method. Moreover, the process as 
described in this publication cannot be carried out continuously. 
The object of this invention is to provide a process for the preparation of 
wort starting from mash, the separation of the spent grain from the mash 
to form a clear wort, which process has the advantage that it can be 
carried out continuously, while furthermore the separation takes place at 
a higher yield of extract. 
SUMMARY AND DESCRIPTION OF THE INVENTION 
The invention is characterized in that spent grain is separated from the 
mash in at least one membrane filtration unit having a pore size of the 
membrane not exceeding 2.0 .mu.m, if desired followed by addition of hops 
to the wort and boiling of the wort. 
Surprisingly, it has been found that an improved separation of the spent 
grain from the mash is obtained by using the process according to the 
invention. Not only is the wort clear, which means that it can be mixed 
with hops and boiled without further purification, but the yield of 
extract is also better. Moreover, much less fouling of the membrane occurs 
with the process according to the invention than with the method according 
to European patent application 0 265 152. The latter has the advantage 
that the process can be carried out continuously, since much less cleaning 
of the membranes is required. 
The membrane filtration is carried out by using at least one membrane 
filter, but preferably by using a multi-stage filter, e.g. a multi-stage 
counterflow filtering apparatus, such as a three-stage apparatus or a 
multi-stage cross-flow filtering apparatus. 
The membranes in the membrane filter have a pore size not exceeding 2.0 
.mu.m, preferably ranging from 0.1 to 1.5 .mu.m. Such a pore size results 
in an optimum activity of the filtration unit, because at this pore size a 
good clear wort is obtained with a high efficiency. The membrane filter 
also has a good self-cleaning capacity. The material of the membrane is 
not very critical. Of special importance is the mechanical stability at 
the temperature of the wort to be filtered. In addition, the material must 
be suitable for use in contact with foods. Particularly suitable are 
membranes on the basis of ceramic materials. 
A surprising aspect of the process according to the invention is the fact 
that the particle size of the solid materials only has a slight effect on 
the activity of the membranes, contrary to what is suggested in the cited 
European patent application. 
The wort obtained with the process according to the invention has a clarity 
measured as EBC units at 65.degree. C. of from 0.25 to 5. The clear wort 
is mixed with hops, and the mixture is boiled. Flocculation of material, 
such as proteins and polyphenols, may then occur. If desired, these flakes 
are removed, e.g., with a separator or a `whirlpool`. After cooling the 
wort to a temperature ranging from 2.degree. to 25.degree. C., preferably 
to about 8.degree. C., the wort can be fermented to beer. 
The boiling of the wort preferably takes place continuously, with recovery 
of at least part of the heat. Apparatuses suitable therefore are known 
from the literature. These apparatuses may be based, e.g., on multi-effect 
evaporators with a heat exchange of the spent gases with the wort. 
The mash converted according to the invention to wort can be obtained in 
different ways, e.g., by a conventional treatment in batchwise operating 
mashers. Within the scope of the invention, however, the use of an 
apparatus for continuous mashing is preferred. 
According to a preferred embodiment of the invention a plug flow reactor is 
used therefore, that is to say a reactor showing little back-mixing and 
pre-mixing of the reactants. 
It is possible to carry out the process in one or more plug flow reactors. 
The number of reactors partly depends on the nature of the raw materials 
to be used. 
When using unmalted grain two reaction steps are carried out, in the first 
of which the pulverized material is gelatinized and liquefied under the 
influence of an enzyme system. This enzyme system often originates from 
malt. In a second step malt and/or additional enzyme system is added, and 
further reaction occurs. It is thus necessary to use two reaction steps, 
which may advantageously be carried out in two reactors. When only malt is 
used, without unmalted grain, it is sufficient to carry out only the 
second reaction step, which can be done in one reactor. 
The solid components, such as malt and unmalted grain, are first 
pulverized, e.g., in a hammer mill, to a particle size that can pass 
through screens with a mesh size of from 5 .mu.m to 5 mm. 
The pulverized solid materials are mixed with the water and fed to the 
reactor or reactors. When unmalted grain is used, a temperature ranging 
from 40.degree. to 100.degree. C. is maintained in a first reaction step. 
Gelatinization and liquefaction under the influence of the enzyme system 
present thereby occur. In the second reaction step malt and/or the enzyme 
source and water are added, together with the product obtained in the 
first reaction step. In this reaction step enzymatic conversion occurs. 
The temperature in this reaction step generally ranges from 30.degree. to 
80.degree. C. When no unmalted grain is used, this is the only reaction 
step, and a mixture of malt and water is fed to this reaction step. 
As plug flow reactor, various types of reactors may be used, in which 
connection it is 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 
suitable type of reactor is formed by the so-called rotating disc 
contactor, which is a known type of column reactor as described in, e.g., 
Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition, Vol. 9, 
page 702. 
Such a reactor generally consists of a 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%. By rotating the shaft and the 
discs in the column a proper dispersion of the solid matter in the liquid 
occurs. 
In connection with the desired possibility to clean the column a system is 
preferably used in which the shaft can be easily removed, e.g., due to the 
absence of baffles in the column. 
The use of a rotating disc contactor has the surprising advantage that the 
particle size of the raw materials can be adjusted almost independently of 
the apparatus used, without the occurrence of problems with settling or 
accumulation of solid matter. In combination with the use of membrane 
filtration this means that the particle size of the starting materials can 
be chosen almost freely, so that this particle size can be adjusted 
optimally, independently of the nature of the process apparatus. As 
compared with the situation in the conventional batch filtration this is a 
great advantage. For in batch filtration there are hardly any 
possibilities of varying the particle size, because this will immediately 
lead to problems in the wort filtration. 
The cooled wort can be fermented, optionally after residence in a buffer 
vessel. The invention therefore also relates to a process for brewing beer 
using the wort prepared as described above. 
The invention will now be illustrated with reference to the accompanying 
drawings showing an example of a process scheme according to a preferred 
embodiment of the invention, as well as an embodiment of two membrane 
filtration systems.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The process scheme of FIG. 1 shows a mixer 1, to which water having a 
temperature of about 55.degree. C., pulverized unmalted grain and 
pulverized malt are passed through lines 2, 3 and 4, respectively. After 
mixing, the mixture is passed through a line 5 to the first rotating disc 
contactor 6, which comprises an agitator shaft 7 provided with discs 8. 
The reactor 6 is provided with heating elements, not shown, with which the 
reactor contents can be adjusted to and maintained at the desired 
temperature. 
The product from the reactor 6 is passed through a line 9 to the rotating 
disc contactor 10. Water or about 55.degree. C. and pulverized malt are 
passed through lines 12 and 13 to a mixer 11. The resulting mixture is 
passed through a line 14 to the bottom of the column 10 where it is mixed 
after some residence time with the product from the reactor 6. Through a 
line 15 the resulting mash being free from prior filtering is passed to a 
membrane filtration 16 to which, in addition, water is passed through a 
line 17. Through a line 18 the clear wort obtained is discharged from the 
membrane filtration unit. The spent grain is discharged through a line 19. 
The clear wort is mixed with hops supplied through a line 20. The mixture 
of wort and hops is fed to a heat exchanger 21, in which it is preheated 
with heat from the boiling step. The preheated wort is fed to the wort 
boiler 22, in which it is boiled for some time. The boiled product is 
passed through a line 23 to the separator 24, in which floculated 
materials, such as proteins and polyphenols, are separated. The clear 
boiled wort then passes through a line 25 into a cooler 26, in which it is 
cooled. Through a line 27 the wort can be discharged, e.g., to a 
fermentation unit. 
FIG. 2 shows a possible arrangement of a three-stage counterflow membrane 
filtration unit. 
In this Figure the mash is passed through a line 51 to the first membrane 
filter 52, from which the clear wort is discharged through a line 53. Part 
of the retentate of the filter 52 is returned through a line 54 to the 
feed end of the filter, together with the permeate of the second membrane 
filter 55. The rest of the retentate is passed through a line 56 to the 
second membrane filter 55. The permeate of this membrane is returned 
through a line 57 to the first membrane filter. The retentate of the 
second filter 55 is partly returned to the feed end of the second membrane 
filter 55, through a line 58, while the rest is passed through a line 59 
to the third membrane filter 60. The permeate of this third membrane 
filter 60 is returned through a line 61 to the feed end of the second 
membrane filter 55. Part of the retentate of the third filter 60 is 
returned through a line 62 to the feed end of the third filter 60, 
together with water supplied through a line 63. The rest of the retentate, 
the spent grain, is discharged through a line 64. 
The description of this system is based on a three-stage filtration unit, 
but it is of course possible to adapt the number of stages as required, 
using the same principle. 
FIG. 3 shows an embodiment of a cross-flow filtration unit, on the basis of 
a three-stage apparatus, but the number of stages can be adapted as 
required, using the same principle. 
In FIG. 3 the mash is passed through a line 100 to the first membrane 
filter 101, from which the clear wort is discharged through a line 102. 
The retentate of the filter 101 is partly passed through a line 103 to the 
second membrane filter 104 and partly returned through a line 112 to the 
feed end of the filter 101. Through a line 105 water is passed to the feed 
end of the filter 104. The permeate of the membrane filter 104 is 
discharged through a line 106 and combined with the permeate of the first 
membrane filter 101. The retentate of the second filter 104 is partly 
passed through a line 107 to the third membrane filter 108, together with 
water supplied through a line 109, and partly returned through a line 113 
to the feed end of filter 104. The permeate of this third membrane filter 
108 is combined through a line 110 with the permeate of the first two 
filters. The rest of the retentate, the spent grain, is partly discharged 
through a line 111 and partly returned through a line 114 to the feed end 
of the filter 108. 
The invention will be further illustrated with reference to an Example, but 
is not limited thereto. 
EXAMPLE 
To the mixer 1 of an apparatus as shown in FIG. 1 are added per hour 5 kg 
maize, 2.5 kg malt and 22.5 l water having a temperature of 55.degree. C. 
The maize and the malt were pulverized in a hammer mill to a particle size 
that can pass through a 1.5 mm screen. The mixture had a temperature of 
50.degree. C. The mixture was passed to a rotating disc contactor, in 
which the temperature was increased to 95.degree. C. The total residence 
time of the mixture at 50.degree. C. was 5 min., while the residence time 
at 95.degree. C. was 10 to 15 min. 
To mixture 11 were added per hour 15 kg malt of the same particle size and 
45 l water having a temperature of 55.degree. C. The mixture obtained 
therein had a temperature of 50.degree. C. and was passed to the bottom of 
the second rotating disc contactor. 
The product from the first rotating disc contactor was passed to the second 
rotating disc contactor at such a level that the residence time of the 
malt/water mixture was about 15 min. at 50.degree. C. By admixing the hot 
product the temperature increased to 65.degree. C. This temperature was 
maintained for 30 min., after which it was raised to 76.degree. C., which 
temperature was maintained for another 5 min. 
After this treatment a mash was obtained having an extract content of about 
21.5%, which was passed to the membrane filtration unit 16. This unit was 
as shown in FIG. 2. The membrane filtration using membranes having a pore 
size of 0.4 .mu.m gave a wort having a clarity of 0.3 EBC units (at 
65.degree. C.). After mixing with hops, boiling, separating flakes formed 
and cooling, a cold wort having a temperature of 8.degree. C. was 
obtained, which could be fermented to beer.