Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Distillation Method
The present invention relates to a distillation method.
When producing ethanol by fermentation, alcohols with more than two carbon
atoms.
such as 2-Methyl-1-Propanol. 3-Methyl-l-Butanol and 2-Methyl-l-Butanol are
formed
during the fermentation process. Within the fermentation industry these
alcohols are
generally known as fusel oil.
Fuse] oil imparts an characteristic odour and taste to ethanol and is
therefore
traditionally removed therefrom during the distillation process. The removal
of fusel
oil from distilled ethanol has hitherto taken place by removing a fusel oil-
containing
fraction from the distillation column where the liquid phase has an alcoholic
strength
of 40-50% v/v. At this strength the fusel oil, which is soluble in ethanol but
less
soluble in aqueous mixtures, is kept dissolved in the eyhanol/water mixture.
In order
to remove it, it has been necessary to add 11/,-2 volumes of water to the
fraction in
order to separate the fusel oil from the alcohol by rendering it insoluble in
the
ethanol/water mixture. Having a lower density, the fusel oil rises to the
surface of the
separation vat from where it can be drawn off, while the diluted ethanol/water
mixture
can be recycled to the distillation column.
There are several disadvantages associated with this system. For example, the
continuous addition of water to the distillation process requires the input of
additional
energy in order to maintain a sufficient distillation temperature in the
distillation
column. An increase in the volume of waste water present in the bottom of the
column will also occur, which can lead to capacity restrictions. Moreover,
impurities
in the added water may be deposited on the walls of the distillation column,
which
accordingly requires more frequent cleaning.
International Patent Application W094/21779 (Labatt Brewing Company Limited)
describes a process for brewing fermented malt beverages, typically beer, in
which a
freezing step is used in order to cause ice crystal formation in the beer. The
object of
CA 02228908 1998-02-05
this process is to prevent "chill haze" and other problems normally associated
with
beer. Due to the formation of ice crystals during the chilling process. beers
produced
by such methods are often referred to as "Ice" beers. The process effectively
allows
the removal of water from the brew but is not suitable for removal of fuse]
oil.
The present invention overcomes the problems of the prior art by providing a
method
for preparing a distilled alcohol or a distilled alcoholic beverage which
comprises
the removal of fusel oil contaminants at a reduced temperature.
According to a first aspect of the present invention, there is provided a
process for
removing fusel oil from an aqueous alcoholic medium, comprising the steps of:
(a) cooling the medium to effect separation of fusel oil from the medium; and
(b) removing at least part of the fusel oil from the medium.
A fusel oil. as referred to herein, is an alcohol or mixture of alcohols
having more
than two, typically four or more, carbon atoms, whose presence in alcoholic
solutions
may be undesirable on account of its characteristic effect on taste and/or
aroma. By
reducing the temperature of alcoholic aqueous media containing fusel oil, the
solubility of the fusel oil in the solution may be reduced, to the point where
it no
longer remains in solution. The fusel oil being lighter than aqueous alcohol,
the
medium separates into two phases, and the fusel oil phase may be removed. A
better
separation of fusel oil from the alcoholic aqueous phase is thus obtained than
is
possible through conventional dilution processes.
Agricultural alcohol is produced by distillation of a variety of raw materials
from
agricultural sources, for example potato and grain. This spirit is the basis
of a variety
of alcoholic beverages, such as bitters, aquavit, gin and vodka. The
production of,
for example, aquavit, may require a second distillation step, and have
flavouring
substances added thereto, while others, such as vodka, may be subjected to
only a
single distillation, and possibly also a filtration step.
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As used herein. "Agricultural alcohol-, "ethanol" and "spirit drink". as well
as
"vodka" and the snecific names of other alcoholic beverages, are as defined in
EC
Directive 1576/89 of 29th May 1989, incorporated herein by reference.
"Ethanol" is
synonymous with "ethyl alcohol", and "agricultural alcohol" is synonymous with
"agricultural ethyl alcohol".
The removal of fusel oil according to the present invention is carried out
during the
distillation. An alcoholic aqueous fraction containing fusel oil is removed
from the
distillation apparatus, which is typically a distillation column, and
subjected to fusel
oil removal before being returned to the distillation apparatus. Fraction
removal may
be iteratively repeated but is preferably operated continuously throughout the
distillation process.
The alcoholic aqueous fraction preferably has an alcohol content of 10% v/v or
more.
Advantageously, it is between 10 and 40% v/v. Preferably, the alcohol content
is
between 20 and 30% v/v. The concentration of alcohol is thus lower than in the
dilution methods used in the prior art.
Advantageously, the alcoholic aqueous fraction is removed at a temperature of
between 80 and 98 C, preferably between 85 and 95 C, and most preferably at or
around 90 C, at atmospheric pressure.
The alcoholic concentration and the temperature of the fraction removed from
the
distillation are linked. Thus, an aqueous alcoholic fraction removed from a
grain
distillation with a strength of 10% v/v will have a temperature of about 92 C,
while a
40% fraction will have a temperature of about 82 C, at atmospheric pressure.
Different temperatures may be applicable at other pressures.
The alcoholic aqueous fraction may be cooled in one or more steps. For
example, an
efficient way initially to reduce the temperature is to pass the fraction
issuing from the
distillation apparatus to a first heat exchanger, wherein heat exchange takes
place
against processed aqueous alcoholic fraction material from which fusel oil has
already
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been removed and which is being returned to the distillation apparatus.
Alternatively.
or. preferably. in addition, the fraction may be further cooled by
refrigeration or
further heat exchange steps. The fraction may be cooled by any suitable means.
such
as refrigeration using coolants such as liquid nitrogen, but preferably it is
cooled by
ammonia evaporation.
The fraction is preferably cooled to below about 0 C, more preferably -5 C to -
15 C,
and advantageously around -10 C.
Fusel oil contained in the alcoholic aqueous fraction is preferably rendered
substantially insoluble at the reduced temperature, and may be removed, for
example
by tapping off the fusel oil fraction in a separator vessel. The fusel oil
being less
dense than the alcoholic aqueous fraction, it rises to the top and may be
removed from
the surface of the alcoholic aqueous fraction.
By "substantially insoluble", it is intended that the fusel oil becomes
insoluble in the
alcoholic aqueous mixture to a point where it begins to come out of solution
and form
an independent liquid phase. This can be removed as described, for example in
a
separation vat.
Clearly, by chilling the alcoholic aqueous phase further, the fusel oil may be
more
efficiently removed therefrom, since its solubility therein will be further
reduced.
Since the application of a low temperature step is necessary in the process
according
to the invention, it is referred to as freeze distillation.
In a preferred embodiment, therefore, the invention provides a freeze
distillation
process for preparing a freeze distilled alcohol, the process comprising
partial or
complete removal of fusel oil by the steps of:
(a) removing an alcoholic aqueous fraction comprising alcohol and fusel oil
from the distillations;
(b) cooling the fraction to reduce the solubility of the fusel oil therein,
rendering it substantially insoluble; and
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(c) separating the aqueous fraction from the fusel oil, and returning the thus
separated aqueous fraction to the distillation.
As used herein. "freeze distillation" refers to a distillation process in
which fusel oil is
removed according to the invention as described above.
The distillation process may include further steps, depending on the final
product
which it is intended to produce. Thus, further distillation steps, optionally
with
flavourings, filtrations and the like may be included. Optionally, the
distillation
process may yield a spirit drink directly. In a preferred aspect, the
invention provides
a distillation process for the production of agricultural alcohol which
involves the use
of six distillation columns, namely an analyser, a rectifier, a hydroselection
column, a
concentration column, a finishing column and a feints and heads column. The
alcohol
is obtained at the bottom of the finishing column, and preferably has a
strength of at
least 96% v/v.
Further processing of the agricultural alcohol into a spirit drink, for
example in the
production of vodka, may involve dilution with water. For producing vodka, the
use
of softened mineral water is preferred, although demineralised water may also
be
used.
According to a second aspect of the invention, there is provided a freeze
distilled
alcohol. As used herein, a "freeze distilled" substance is an substance at
least part of
which is an alcohol which has been produced by a method as described in the
first
aspect of the invention. In a most preferred embodiment, the alcohol is
ethanol. It is
preferably used as the basis of alcoholic spirit drinks and other beverages.
The
invention therefore also provides a freeze distilled alcoholic beverage made
with an
alcohol produced according to the invention.
Preferably, the alcoholic beverage has a final ethanol concentration of at
least 15%.
Advantageously, the alcoholic beverage is freeze distilled vodka.
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A third aspect of the invention provides an apparatus for distilling an
alcohol.
comprising a distillation column, a withdrawing system for removing a fraction
from
the distillation apparatus. at least one heat exchanger or cooler. a
separation vat and a
replacing system reintroducing for material from the separation vat to the
distillation
column, wherein, in use. an alcoholic aqueous fraction comprising ethanol and
fusel
oil is taken from the distillation apparatus via the withdrawing system,
cooled in the
heat exchanger or cooler to a point such that the fusel oil becomes
substantially
insoluble in the alcoholic aqueous fraction, the fusel oil is separated from
the alcoholic
aqueous solution in the separation vat and the alcoholic aqueous fraction is
returned to
the distillation column via the replacing system.
The invention is further described, for the purposes of illustration only, in
the
examples below, in which reference is made to the following figures.
Modifications
of the method within the scope of the present invention will be apparent to
those
skilled in the art.
Figure 1 is a diagram of the fusel oil removal apparatus in a freeze
distillation process
according to the invention. An alcoholic fraction is withdrawn from
distillation
column (1) by pump (2), at a temperature of 90 C (100 litres/h). This is
passed
sequentially through heat exchangers (3) and (4). in the latter of which it is
cooled to
-10 C by ammonia (8). The fraction then passes to separation tank (5) wherein
the
fuse] oil is separated and removed (6). Pump (7) removes the residual
alcoholic
fraction, which passes through heat exchanger (3) wherein it is warmed to
approximately 78 C before being returned to the distillation column.
Figure 2 is a diagram of a six-column distillation apparatus used for the
production of
agricultural alcohol. Mash (10) is fed into analyser (B). Slops (11) are
discarded,
whilst the distillate (12) passes to the rectifier (L). A fraction is taken at
(13) for fusel
oil removal, with the distillate passing to hydroselection column (F). Heads
(14) are
removed. Water (15) is added, heads passing in part to the feints and heads
column
(E), and the remaining fluid passes to the concentration column (K). The
distillate is
passed to the finishing column (S), from which agricultural ethanol is
obtained (16).
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Example 1.
Laboratory scale distillation procedure
Wheat grain is ground into flour and mixed with water, heated to 150 C for 3
minutes
and allowed to cool to room temperature. Starch converting enzymes and yeast
are
added according to standard distillation protocols, and the mixture allowed to
ferment
for 3 days.
The fermented mash is then distilled on a distillation column according to
standard
procedures for the production of agricultural alcohol, as defined in EC
Regulation No
1576/89. From this distillation column an alcoholic aqueous fraction is taken
at a
temperature of 90 C. This fraction is an aqueous alcoholic fraction with an
alcohol
content of 19.6% v/v.
The fraction is cooled to -8 C. Fusel oil separates from the alcoholic aqueous
phase
and rises to the top surface, where it has a yellowish oily appearance. The
alcoholic
aqueous phase remains liquid, and no ice crystals are formed.
Analysis of both phases gives the following results:
Substance Oil phase (mg/11 Aqueous phase (mall)
1-propanol 200 100
2-methyl- l -propanol 26000 3000
1-butanol 300 60
3-methyl-l-butanol. 273000 8500
2-methyl- l -butanol 202000 6400
water 12.2 g/100ml
A comparative assay, using the dilution methods of the prior art, yielded the
following
results:
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Substance Oil phase (m(.,/1) Aqueous phase (mg/1)
1-propanol 300 200
2-methyl-l-propanol 31200 6500
1-butanol 600 120
3-methyl-l-butanol 341000 17000
2-methyl- l -butanol 253000 13000
water 10.5 g/100ml
The results demonstrate superior removal of fusel oil from the aqueous phase
by
cooling than by dilution.
Example 2.
Industrial scale distillation
A distillation system comprising 6 distillation columns (obtained from
Vogelbusch,
Vienna, Austria) as shown in figure 2 is set up according to conventional
parameters
for the production of agricultural alcohol. In a continuous process, mash
derived
from whole wheat grain is fermented conventionally and introduced into the
distillation apparatus at a rate of 8 m3 per hour and heated to 90 C.
An aqueous fraction containing 25 % ethanol is taken from the distillation
column.
This fraction, having a temperature of approx. 85 C' is led to heat exchanger
1 and is
cooled as much as possible by means of the heat exchange with the lower phase
from
the separation vat. The liquid is subsequently led to heat exchanger 2 in
which it is
cooled to -10 C by direct evaporation of liquid ammonia.
Having been cooled down to this temperature, the liquid is led to a separation
vat.
Here the fusel oil rises to the surface from where it is drawn off.
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The lower phase is pumped directly to heat exchanger 1 in which the liquid is
heated
to approx. 72"C and then led back to the column.
The distillation is continued through 5 columns, as shown in figure 2, with
residuals
being purified in the sixth column.
By applying this new method an improved separation of fusel oil is obtained,
wherein
an approximate improvement of 3% is achieved in respect of alcohols having
more
than 4 carbon atoms. The composition of the fusel oil removed varies according
to
the raw material used, but in general fusel oil removed by the method of the
invention
comprises slightly more ethanol, since the percentage of ethanol in the
aqueous
mixture will be slightly higher that that in a mixture which has been
separated by a
dilution method.
The distilled ethanol is mixed with water to produce vodka spirit. Freeze
distilled
vodka prepared using freeze distilled ethanol subjectively has a smoother
flavour.
