Note: Descriptions are shown in the official language in which they were submitted.
~his ln~ention relates to the mar.u~acture of iso-u-
acids 9 suitable for use in beer maki~ from o-acids extrac-
ted from hops.
It is co~mon practice to extract various constituents-
from hops and to use these extracted constituents in place
of ho~s themselves in makin~ beer. ~he principal coDstitue~ts
which haYe been ~o extracted previously are the resins and in
particular the ~-acid. fraction of the soft resins which on
chemical rearrangement give iso-~-acids which are the main
bitteri~g components of beerO ~he main advan-tage of extrac-
ting o-acids is that the ~_acids can be used much ~ore effi-
cientl~ than is possible in traditional beer m~ing. In
traditional beer making typically only 25% to 35% of the ~-
acids in the original hops are utilized. By extracting the
o~acids, iso~erizing them separately from the beer and addi~g
the iso~acids produced to beer a~ter fermentation o_acid
utilization caQ be much higher, typically from 6~/o to 85~'.
further substantial ad~a~tage i~ using extracts~is that
they can be ~tored for longer periods without the; presumably
oxidative, degradation especially of the bitter pri~ciples
includi~g the ~-acids that occurs in hsps under extended
storageO
! ~ Conventional hop extractio~ procedures i~volve the use
o~ organic sol~ents such as methylene chloride 7 trichloro-
ethylen~, hex~e and~or meth~nol~ ~hese solvents will readily
dissol-~re nvl, o~y the d~sired a~acids but relativel~ l&rge
propor~ivns vf ~ acids~ tanni~,s, chloroph-gll and ~ariOllS othe
.
~r~ 6
,,. ~k
"
., . ~, ~ - .
.
:
, . '
.,
'.,' .
hop constituents.
A primary extract made by extracting hops with an
organic ~olvent would typically ha~e the follo~Jin~ composi-
tion:
wt. %
~-acids 8-45
~-acids 8-~0
uncharacterized soft xesins 3-8
hard resins 2-10
hop oil 1-5
: fats and waxes 1-2
total~ resins 15-60
t~nnins 0.5-5
chlorophyll up to 1
fines (cellular debris) 2-5
inoxganic salts 0.5-1
residual solvent (usuall~
: C~2C12 or C~3o~) 1.5-2.2
water 1-15
~o obtain high quality o_acids suitable for isomeri- -
~ation the cxude extract has to be extensively puxi~ied ofte~
: involvin~ other organic solvents and invariably i~olving
man~ and o~ten complex steps. ~urther, it is difficult to
e~tirely remove the organic ~olvent from the extract,
typical cs~mercial extracts can contain oYer 1% b~ weight
solvent~ Whilst i~ is believed that residual. solvents par~i-
cularly of methylene chLorid~ srd methQnol are lost entirely
~3
' ' ' ,' ~':
,,
: ,
- ,
~7~
duxing b~er making3 it i.s not a wholly satisfactory
position to rely on such 'accidental' elimina~ion of
possibly noxious ~aterials during production of a foodstuff.
.Further5 although there is at present no great technical
difficulty in meeting the public health requirements for
levels of residual solvents there may well be considerable
difficulties in the future,.
~n organic solve~t extract, purified to be suitable
for isomerization to give an iso-~-acid preparatio~ suitable
for use in bittering beer, would typicall~ have the ~ollowing
composition: -
wt . %
a~acids 60-80
~-acids o.3 o,5
uncharacterized soft resins 1-2
hard resins 1-5
hop oil up to 1
fats and waxes caO 0~1
total resins 70_90
tannins ca. 0~1
chlorophyll ca. 0.1
fines nil
inorganic salts æubsta~tially nil
xasidual solvent~ 0.5-1
water up to 10
~ I~ addition ~o CE?C12 and C~30H which are com~only used
both i~ extract-io~ and purlfication, ~hese solvent residues
.. .
,,
. . .
.
: ," ' " '~' . '
,':' '
,,
~97~
may include solvents such as ethyl acetate, butanol and
tric~oroe-thylene.
Fluid carbon dioxide either in tne form of the liquid
or the supercritical gas has been suggested as an extraction
medium for hops. ~hus, ~ritish Patent Specification
~o. 1,~88,581 describes a method of making a hop extract b~
extracting hops with a variety of gases in the supercri'cical
state with respect to temperature and pressure~ Carbon
dioxide is stated to be the most preferred gas, ~xtraction
under such supercritical conditions with C02 typically yields
~ an olive-green pasty product which contains o-acids, ~-acids,
uncharacterized soft resins, hard resins and small quantities
of t~nnins. The extraction conditions can be varied to give
yields of o_acids proportionately higher than the concen-
trations in the starting hops, the best extracts described~
however, containing onl~ about one_third a-acids. ~he optimum
extraction conditiRns are stated to involve extraction under
a pressure substa~tiall~ in excess oX the critical pressure9
which for C02 is about 72.8 atmospheres, preferably in excess
of 100 atmospheres ~gauge) and temperatures of from 40 to
50C. It is stated that by appropria$e selection of the
extraction conditions 3 it is possible to extract substantially
all the ~oft resins and the essential oil of hops whilst mini-
mizing th~ extraction of hard resins or that ~he proportion-
~te extraction of ~acids can be reduced but at the expense
of increasing the proportion of hard resin,s extracted~
~brther, it is ebated tc be pos,sible to ertract hop~ with
8i~
liquid C02 but this does not form part of the invention
of this prior patent because 'its dissolving power is less
than that of supercritical C02'.
The extract as described in Specification No.
1,388,581 compares favourably with t~pical primary extracts
obtained using organic solvents and would appear -to be
suitable for use in brewing beer, eOg. by addition to the
copper~ However, the extract described would not be
suitable for isomerization without considerable purification
to remove components which would produce ad~erse flavours
under typical isomerization conditions and also result in the
formation of substantial quantities of haze when added to
beer~ (It is not practical to effect purification aftPr
isomerization because the mixture is even more complex than
the impure extract). In the present state of extract
technology, this would require the use of organic solvents,
thus giving up one of the main advantages of using super-
critical C02 in extracting hops.
Li~uid C02 is described as an e~traction medium for
hops in USSR Author's Certificate ~o. 167,798 i~ the name of
Pekhov~ Ponamarenko and Prokopchuk and by Pekhov in
Masloboino-Zhirova~a~a Promyshlemnost VolO 34~ part 10 (1968),
pages 26 to ~9. The product obtained by extraction of hops
with liquid C02 at 20 to 25C is stated in the Author's
Certificate to be a light brown viscous mass~ ~hafto~ and
Naboka in ISU Sev-Kauk ~auchn ~sentra Ugssh S~, Ser ~ekh
- ~auk 1975$ 3(3), 29-31 [Chem ~bs Vol 84 (1976) 120046a~
.
,
.
7~
describe C02 extracts of hops as comp]e~ mixtures of ~-,
~ and ~-acids, o~ a~d ~-soft resins and hard resins
which are subject to substantial deterioration, especiall~
b~ fairly rapid autoxidation on storage. The purity and
stability of such C0 extracts i9 not altogether certain
but, although it ma~ be possible to use them in beer making
by addition to the copper it is clear that they could not be
isomerized to give an iso-o_acid preparation without sub-
sta~tial purification and, in any event 9 are considerabl~
less stable under storage than conventional hop extracts
made using organic solvents~ ~eretofore it has not been
recognized that a primary extract of hops could be obtained
which would be satisfactory for direct isomerization to give
an iso-o-acid prepara-tion suitable ~or bittering beer. ~he
present in~ention is based on the discovery that extracting
hops with liquid C02 (i.e. under sub-critical conditions) can
be carried out to ~ield a primar~ extract which can be
satisfactorily isom0rized without needing prior purification.
; It is an object of the present invention to provide
an improved process for the ma~u~acture of iso-o-acids pre-
parations suitable ~or addition to beer and in particular to
~igh quality preparations suitable for additlon to bright
beer after filtratio~.
~he present invention accordingly provides a method of
making aQ iso-o_acid preparation which method comprises con-
tacti~g hops with liquid carbon dioxide at a temperature of
i not less than -5C thereby extracting at least a portion of
' ~ .
7--
,
the ~-acids contained in the hops into the liquid carbon
dioxide 9 isolating a primary hop extract of high purity
from the li~uid carbo~ dioxide and isomerizing the ~-acids
present in the hop extract to iso-o-acids.
In the practise of the present invention the high
purity primary hop extract isolated as an intermediate produot
generally contains ~-acids, ~ acids,hop oil, usually small
~uantities of water and usually no more than trace quantities
of the main impurities seen in primar~ organic solvent
extracts vi~: uncharacterized soft resi~s, hard resins~
tannins and chlorophyllO
~able 1 sets out the purity of the primary extract as
measured by the quantities of the impurities which interfere
with the subsequent isomerization. Column A gives the maximu~
permissible proportion of the impurities abo~e which we have
found that the impurities i~terfere substantially with subse-
quent isomerization, Column B gives the expected maximum
proportion o~ the impurities extracted b~ liquid C02 under the
general conditions set out herein ~nd Column C gives figures
typical of what we expeot to obtain.
,
,
768~
~ I-D~ L vt. % on extract
uncharacterized , (2)
soft resins 3 001 < 001
hard resins 0.5 0.1 none
Tannins 0.5 0.1 none
Chlorophyll 0.2 0.1 none
fats and waxes 0.2 0~1 < 0.1
fines 005 none none
inorganic salts O.5 O.1 ~ O.1 (2)
_ l
otal ! 4% 0.3 0.1
(1) See below for a sllmmary o~ the ~nalytical techniques
used.
(2) These figures indicate that with some primary extracts
the impurities were qualitatively just detected with
the Analytical techniques used but that the amounts
were too small to be estimated with an~ degree of
accuracy,
The figures given as maximum values represent the limit
of the analysis; the actual quantities of the
impurities present may be even smaller.
The main components of the primary extract are as
indicated above, ~-acids~ ~-acids and hop oil extract has the
following composition in respeot of these components.
:- _9_. .
,
'
7 ~ ~
wt~ o~ (1)
~_acids 40 to 75 (~)
~-acids 20 to 40
total resins 70 to 98
hop oil up to 10 (3)
water up to 5
~1) These figures are based on analyses for the resins
performed by the method described in Analytica ~BC,
published by Schweiæer ~rauerei Rundschau, ~rd Edition,
1975, page E49 and analyses for the non-resin components
especially the tannins and chlorophyll by the method
described by JO Jerumanis in ~ulletin Association
Anciens ~tudiants ~rasserie ~ouvain, 1969~ volume 65
page 113.
(33 The maximum analytical figures for o-acids and hop oil
will only generally be attained with hops containing
unusually high proportions of these materials. Most
usually the upper limits will be about 65% for ~-acid.s
a~d about ~% for hop oil.
By referring to the primary extract as being of high
purity we mean that the undesired impurities as set out i~
Table 1 are present in qua~tities less than those given i~
~ column A of ~able 1. Under the conditio~s, as ,set out herein
; under which we have extracted hops with liquid C02 we ha~e
obtained results which are much better than the maximum
~igures given in column ~. -
For practical purposes the composition of the eYtract
,. . . .
-10-
:
.. . . ... .
".
, -: - .
::. - . ,.
~,~ , . .. . .
~; - . - : .
', - , . . .
;' ' -
7~
ca~ be summarised as
wt. %
a-acids 40 to 75 more usually 40 to 65
~-acids 20 to 40 more usually 25 to 35
total resins70 to 95 more usually 80 to 95
hop oil up to 10 more usually up to 3
water typicall~ 2 to 5
and substantially no organic impurities originating from the
hops.
~he amount of water present in the extract is not, in
itself, critiGal, but, as is discussed below, if substantial
amounts of water are present in the carbon dioxide at the
point of extraction then tannins ma7 be extracted from the
hops~ It seems that, using suitably dry li~uid C02, the
amount of water in the extract depends on the amount present
in the hops and thus, whilst the figures given above are
typical, amounts outside the range indicated ma~ be obtained
n svme circumstances.
~he high ~uality primary extract has the golden yellow
colour of ~-acids and, at ambient temperature is usually a
solid or semi-solid cr~stalline material, the exact form
depending on the particular conditions of extraction and the
type of hop extracted. A further indication of the puxity
is that typical primary extracts separate identifiable
c~ystals of ~- and ~-aGids on cooling to caO 4C~ Gonven-
tional primary solvent eY.tracts show no signs of such
crystallizatio~.
It ~ill be noted that this primary extract is a ver~y
much cleaner material than typical organic solvent primar~
extracts and especially with regard to the hard resin and
uncharacterized soft resin components, is substantially
purer than conventional organic solvent extracts even after
purification. ~ principal difference is that the extract
obtained using liquid carbon dioxide contains substantially
more ~-acids than typical conventional purified extracts.
It seems that the ~-acids can be tolerated at these much
higher levels because of the otherwise outstanding cle~nness
and purity of the extract. ~hus, the high level of ~-acids
does not prevent the satisfactory isomerization of the ~-acids
in the production of an iso-~-acid preparation and the ~-acids
can be removed from such an iso-~-acid preparation b~
filtration at a suitable pH.
As far as we are aware, this has not previously been
reported, indeed the tenor of prior art discussions on the
amounts of ~-acids tolerable in extracts to be isomerized
indicate, on the contrary~ that the maximum tolera~le amoun-ts
of ~acids were very small, typically less than 1%. In the
present invention we believe that it is possible to isomerize
the ~_acids because the levels of other materials which
might interfere with isomerization are so low.
~he general physical conditions of temperature and
pres~ure used in the extraction step are to some extent
critical to the invention. If the extraction is performed
at temperatures below -5~C undesired org~nic compounds te~d
,:
.. . .
,. . . . .
- :
.,
.: . . ,
., .
. .
~ ~7 ~ ~ ~
to be extracted~ These compounds seem to be mainly fats
and waxes but at lower tempera-tures increasing quan-tities
of hard resin and probably tannins are extractedO At sub-
critical temperatures above -5C, we have been able to
obtain high purity extracts. The extraction temperature is
sub-critical because, as i5 clear from British Patent
Specification ~o. 1~388~581, the use of supercritical temper-
atures results in the extraction of substantial quantities of
hard resins 7 chlorophyll, tannins, etc.
W1thin this temperature ra~ge good results can be
obtained but generally we prefer not to use temperatures
close to the critical temperature in order to avoid the
possibility of the C02 beco~ing supercritical accidentallyO
T~e generally preferred temperature range is from -5 to 20C.
~he pressure at which the extraction is performed
must clearly, be sufficient to keep the C02 liquid and not
~o high that the C02 behaves like the supercritical fluid as
described in British Specification ~o~ 1,388,581. Generally
it is both convenient and preferred to operate under the
vapo~ pressure of liquid C02 at the extraction temperature.
In orde~ to allow ~or minor temperature differences between
different parts of the extraction apparatus, particularly
when ~ub-ambient tempera~ures are used for extractionl ~nd
also to ~llow for hydrostatic pressure differences within
the apparatus, the pressure will normall~ ~8 slightly, e.g~
up to 1~/o~ i.n excess of the vapour pressure. The variation
of the vapour pressure of liquid ~2 ~iith temperature is
-13-
shown in ~able 2~
__ ~able 2
~emperature Vapour Pressure
o~ Atmospheres
_ (absolute)
31 (crit. temp.) 72.8
71.2
56.5
44.~
O 34.4
_ _ 30.1
~rom an engineer~ ng standpoint it is desirable to h~ve the
pressure as low as possible and to have the temperature as
near ambient as possible~ ~hese requirements are not
strictly compatible and i~ practice a compromise taking
these considerations into account as well as the rate of
extraction, selectivity and purity of the extract will
usually determine the optimum opelating temperature i~ any
particular caseO
~he form in which the hops are extracted is not
especially critical in that efficient extractions can be
achieved from green or dried hops~ hop cones, milled,
powdered, pelleted powdered hops or crushed hop pelletsO
However~ the bulk density o~ hop cones is very low
2~ and as a practical matter it is preferred to use powdered or
pelletted hops in the extraction. Powdered hops seem to be
s~tisfactory for extraction in the inventio~ a~d the further
processing required to pellet hops see~s to provide no
~14~
,, ,~, , , . -
., . . ~ . ~ .
'' - ~ -'
' ' : : . '
.
particular advantage in extra~tionO ~he optimu~
extraction conditions may vary depending on the particular
form used but determination of precise optima seems to be
a matter of straigh-tforward chemical engineering.
Of course, the hops should themselves be of suitably
high qualityO Inferior or deteriorated hops may not produce
satisfactory extracts. ~he particuiar ~ype (cultivar) of hop
used does not seem to be critical to the extraction itself and
both seeded and seedless hops can be satisfactorily extracted.
~he particular composition of the extract and ~ield obtained
is a function of the hop cultivar extracted and whether it
is seeded or seedless. We have produced satisfactory
extracts from the following cultivars: Wye ~orthdown,
W~e Saxon~ Northern ~rewer, Wye Challenger, ~ullion, Comet,
Pride of Ringwood and Styrian Golding.
~he amount of liquid C02 needed to extract the hops
appears to be a fu~ction of the solubility of a-acids in the
C02, the t-gpe of extraction system and of the precise
conditions employedO We have not yet determined the li~its
of sol~bilit~ of a_acids in fluid C02 but have experienced
no difficulties in achie~ing concentrations of 3O7 grams per
litre and higher concentration~ could well be possibleO
Extraction efficiency both in terms of the proportion of
acids extracted and the amount of C02 nbecessary to extract
them i5 i~creased by increasing the effective contact time
between the C02 and the hops. This can be done for example
by ~imple recycling of ~he C02 through a~ extraction bedO
15-
,. .
,
,.,
,. . .
~'
Alternatively, this can be done b~ using a semi-continvous
or continuous extraction procedure, e.gr employing counter-
current techniques. Although it is desirable to increase
the effective contact time between the liquid C02 and the
hops we have found that substantially complete extraction
can be obtained in the laboratory in times comparable to the
contact times used in conventional comr~ercial solvent extrac-
tions. ~le believe that, i~ fact, liquid C0z will extract
hops substantiall~ more rapidly than conventional organic
solvents and that this does not specifically appear in the
relatively small scale experiments we have performed to date
because of the relative and absolute flow rate limitations
imposed by the small scale of the apparatus used for
extraction.
~he degree of extraction of o-acids is a function of
the precise method adopted. We have successfully extracted
more than 9~/o of ~vailable o_acids without difficulty and
believe that even higher rates of extraction are possible
without great difficulty.
~he e~tracted o_acids can xeadily be recovered from
the liquid C02 extract by 'boiling off' the C02 as gas.
~his can conveniently be done by heating the solutio~ under
constant pressure so that the liquid C02 boils. ~his
approximates to isothermal conditions~ ~lternatively, the
evaporation of the ~aseous C02 can be perfo~med by reducing
or releasing the pressure, iae. approximately adiabaticallyo
Both of ~hese metho~s are satisfactory on a small scale, the
-16
, . .. . ~ . . . . .. .. ... ... .
. .
7~
quality of the product not being afiected4 It is
preferable 9 particularly in commercial operation, to recover
the C02 and recondense and reuse it as the extractin~
liquid. It is easier and thermodynamically more efficient
and thus more economic to perform this recycling under
approximately constant pressure thus taking advantage of the
low specific heat and laten-t heat of vaporization of C02 to
accomplish the necessar~ changes of state The large
pressure and temperature changes on adiabatic evaporation
make it rather less preferred in this respect.
When the extract is isolated by warming the liquid C02
to evaporate it, it i~ desirable to use a heat source at a
moderately high temperature, e.g. 30 to 40C, in order to
ensure adequate heat transfer. ~urther~ because the extract
tends to bacome fairly viscous and may even start -to
c~ystallise out at low tempeIatures, e.g. below about 5C,
it is thus desirable to isolate the extract at near or
slightly abo~e ambient temperature to avoid these potential
problems.
~he primary hop extract thus obtained is a virtually
pure mixtl~e o~ o-acids and ~acids toge~her with part of
the es~e~tial oil ~'hop oil7) present in the hops1 ~ut not
u~ually any hard resins, chloroph~ll or ta~nins. We ha~e
had no difficulty in isolating crude extracts which are
~ubstantially free from hard resins, chlorophyll, tannins~
e~c~ ~is purity of the product is a mar~ed ad~ance over
the products obtained by previously reported hop extraction
17-
techniques~ A quantitative exslmination of the crude
product indicates that there is a rather higher proportion
of ~acids as compared with ~ acids in the product than
would be expected solely on the basis of the relative
proportions of a- and ~-acids in the hops. ~he degree of
this selectivity is significantly higher thSan that reported
in Specification ~o. 1,388,581 and we cannot explain why the
conditions we use for extraction are particularly adva~tage-
ous in this way as well as in other aspects of purity.
As has been set out abovez the primary extract produced
i~ the method of the present invention is usually a mixture
; - of o_acids, ~-acids and at least a substantial part of the
essential oil of hops. ~he mixture will usually contain
moisture but this is not regarded as san impurity for further
processing S~lthough it ms~y be convenient and/or desirable to
dry the extract if it is to be stored over long periods. ~he
high purity extract is yellow in colour9 i.e. the colour of
the o-acids, and not green, brown or other~ise dark in colour
as is usual with conven~ional primary hop extracts including
those described in Specification No. 1,388,581. ~ypically
the extract is solid or viscous paste or liquid, the precise
~orm depending lslrgely on the temperatureO
The extract includes some hop oil and since this can
be a ~alua~le product in its own right it can be removed from
~5 the primary extract by stes~m distillation under vacuum, e.g,
u~der the general conditions of temperat~e and pressure set
` out in the specification of United Sta~es Patent
:, ,
~ --18
;~,3
~.- , , ' ,, ~ ' . ' . ,
~ - . ,
ij: '-' ' . ' ' ' '
,,; ' ' , ' ' .
h
;, ~ ' , ' , : , '
~o. ~,979~527 to ~aws and PickettO Thus, convenientl~ the
separation can be effected by mixing the extract with water
and distilling the mixture under vacuum at a te~perature of
less than 50C, typically from 20 to 25C~ ~he distillate,
an emulsion of hop oil in water, can be collected as a
dispersion in ice by cooling the vapour to below 0C, more
usually to -20C or below. Xop oil distilled from the extract
in this wa~ can be used to impart hop aroma and flavour to
beer. However, we have found that using liquid C02 substan-
tiall~ all of the hop oil is removed ~rom the hops so, as
described in the above specification, care must be taken to
select only the desired fraetion on steam distillation as
described. ~urther, it seems that some of the more volatile
components of the hop oil are extracted very rapidly by the
C02 and unless care is taken these components may be lost,
even during the time when residual air is being flushed out
of the extraction apparatus. ~or these reasons it seems
; preferable, if hop oil is desired as a separato product, to
extract the hop oil from the hops prior to the extraction
with liquid C02. In any event, it is probable that the
liquid C02 e~tract will co~tain at least some hop oil
components.- Since, during isomerization some components of
the hop oil may be degraded and contribute to o~f flavours
and aromas t it will usually be desirable to remove the hop
oil from the extract.
hs discussed in United States Patent ~o. 3,979,527,
the qu~rltities of hop oil which will normally be desired in
beer to give hop aroma a~d fla~our such as is obtained by
19-
dry hopping, are in the range of 0.5 to 2 ppmO The amou~t
of hop oil ln the primary C02 extract is usually such that,
if all the hop oil were re-tained, the ~nount of tbe oil added
to beer by using the final product iso-a-acid preparation
would be considerably in excess of what is desirable to give
the beer hop aroma and flavour. This will be particularl~
true when the type o~ hop extracted is one having a high
proportion of available hop oilO It is thus desirable to
remove at least sufficient hop oil to prevent this becoming
a serious problem.
O~e further practical point favouring separation o~ the
hop oil before use of the iso-o_acid preparation is that a
brewer will generally prefer to use e3sentially pure materials.
~hus, where he wishes to use the iso-~-acid preparation
~5 produced by the invention and also hop oil isolated ~rom the
primary extract, he will prefer to have these materials
supplied separatel~ for use rather than to be supplied with a
pre prepare~ ~nseparated mixture.
When the preferred isomerization technique, described
; 20 in more detail below, is used it is not necessary to, and
i~ indeed it i~ preferred not to~ speci~ically remove the hop
oil from the extract before i~omeriæation~ ~owever, if it
i~ desired to so purif~ the extract then this can be do~e by
; ste~h distilli~g all the hop oil off. HoweYer, care should
be taken to avoid excessive heating as this can damage or
destro~ the bittering potential of the extract. Such
damage can be avoided by perforning the steam distillat~o~
"
-20-
.,
'. , , .:: -
. . . . .
,. . . .
-
'. . ' ' ' '
.. . . . . .
: . . -, - . ' ....... . . ' : :
'. : - ., . : , : :
at suitably reduced pressure, e.g. such that the temper-
ature is not more than 50C.
In connection with the purity of the extract we have
noted that the extract will readily form complexes ~lith a
number of me-tals such as iron and copper. ~hus, passing
extract containing liquid C02 through mild steel or copper
tubing particularly in the presence of moisture results in
iron or copper respectively being leached from the walls of
the tubing, ~his is undesirable because it can give rise to
corrosion problems in the extraction apparatus~ salt
crystallization in the extraction apparatus~ especially with
copper which form blue crystalline slats with the soft resin
acids and conta~inates the product with heavy metals.
Although iron is not toxic, as is copper, it is undesired
becaus~ other heavy metals which may be toxic may be carried
with the iron and the presence of iron in the extract seems
to reduce the stability of the product particularly with
regard to oxidative degradationO ~2tracts contaminated with
iron are typically bro~ rather than yellow in colour~ ~he
problem of contamination by metals c~n be ovexcome by using
a suitably inert material for, or to line the extraction
equipme~t. We have found tha~ making the extraction equip-
ment principall~ of stainle~s steel, glass (for ~iewing parts)
and suitably i~ert plastics materials overcomes this problem.
Other materials are no doubt suitable a~d selection of suitable
inert materials is within normal chemical engineering skill.
~s is mentioned briefly above, the quality of the
extract may be spoiled if excess water is present in the
C2 used as extraction fluid~ particularly insofar as tannins,
being relatively soluble in water, may be extracted in the
water carried with the liquid C02. Commercial quality liguid
C2 in the United Kingdom~ such as is available from
Distillers Company (Carbon Dioxide) Iimited, is a hi~h quality
product whose water content i~ measured in parts per million
(typically about 20 ppm)~ Such C02 is adequately dry for use
in the present invention. r~he purity of such liquid C02 is
well within the relevant British Standard (BS No~ 4105/1967~.
We believe that liquid C02 complying with this ~ritish StandaId
is of sufficient purity for use in the present invention. ~he
use of less pure liquid C02 may give rise to problems in the
quality of the extract.
~he possibility of heavy metal contamination and the
pre~sure of water and/or other impurities ln the liquid C02
may, we believe 9 be at least in part responsible for the
failure of the prior art proposals on extracting hops with
liquid C02 to produce a product approaching the purity of
that of the primary extract in the present inventionO
~he isomerization step in the method of the invention
- can be performed by an~ suitable method. However, some
techniques such as photoisomerization methods may re~uire
that the extract be purified before isomerization a~d even
though with the high purity extracts obtained in the present
method such purification is relati~ely straightforward it
constitutes a further step which is not necessar~ when the
-22-
, .
'
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. . , .. :, , .: . .
: . . . . .
. .
.: . : ~ ~ .. .
. . ~, ~ .
,
. . .
,.
&~3
pxeferred method of isomeriza-tion is employed" Other
techniques frequently include the use of organic solvents
and are thus not preferred. Organic solvents are not
necessary in the preferred method of isomerizationO
~he preferred method is to isomerize the ~_acids by
heating and preferably boilin~ an aqueous solution of the
extract which has been renclered alkaline. ~ypically the
extract is dissolved in alkali, e.g. sodium and/or potassium
hydro~ide or preferably carbonate preferably to give a
solution having a pH of f'rom 8 to 11. For solutions not
requiring subsequent dilution (see below) the concentration
of ~acids is typically from 0.5 to 5 gl 1 and the concen-
tration of sodium and/or potassium carbonate is from 0.01 to
0.5~. ~he solution is then boiled, e.g~ for from 5 minutes to
2 hours to isomerize the ~-acids to iso-o_acids. During
boiling hop oil is driven o~f with the steam. It is known
that the alkali isomerization of ~-acids can be carried out
in relatively concentrated solution, e.g. up to about 35% by
weight ~-acids. Such high concentrations can be used i~ the
isomerization stage of the present invention if desiredO ~he
U8e of high concentrations can be advantageous in reducing
the heating re~uirement during isomerization and the subse~
quent cooling requirement and in that the total amount of
i alkali needed to maintain the desired pH of 8 to 11 is some-
t 25 what less than is necess~ry with more dilute solutions. ~his
latter point may be relevant7 as a xeduction in the level of
inorg~nic matter reduces the likelihood of inorganic s~lts~
.: .
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e.gO KCl or NaCl crystallizing out if the eventual iso-a-
acid preparation is concentrated substantially, eOg. to
between 30 and 4~/o by wei~ht. ~hus, the concentration of
~-acids during isomerization is not limiting on the present
invention, and concentrations up to e.g. 400 gl 1 are
contemplated. The particular concentration chosen is a matter
for selection depending on the particular circumstances and
we do not expect the skilled man to have any serious difficult~ -
in this regard. ~ypically the concentration will be in the
xange of 0.5 to 300 gl 1, more usually ~ to 100 gl 1~
~he solution is then cooled preferably at least to
ambient temperature and optimally to between O and 10C. ~h~
pH of the solution is then made acid, e.gO from 20 5 to 5~
preferably 3.5 to 4.5, aQd optimally about 4Ø This can
convenientl~ be done by adding a ~uitable quantity of acid
such as hydrochloric acidO ~t this acid pH the ~ acids are
much less soluble than the iso-~_acids and are precipitated
and can be removed, e~g. by filtration sr centri~ugation.
~ere the isomerization has baen carried out with a relatively
concentrated solution of o-acids then, because the solubility
of iso-~-acids at the acid pHs used to precipitate the ~aGids-
i~ fairly low5 the isomerized alkaline extract solution may
have to be diluted before acidification in order to avoid
undesir~d loss of iso~ acids. ~hus, at the optimum acidi-
fication pH of about 4s iso-~-acids are soluble to about 0~5%
weight (ca. 5 gl 1) 7 and alkaline isomerization solutions more
concentrated than this should be diluted before acidi~ication
:
24-
,
.
'.. , ''', ' ~: ' ' '
: . - . ' .: ,:
:. -, . : .
. .
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6B~3
to avoid precipitation and thus possible loss of iso-u-
acids. ~he preferred concentration of iso-u-acids at this
stage is pH dependent but is generally i~ the range 0~5 to
5 gl 1 and optimally between 3 and 5 gl 1.
Con~eniently the solution is filtered with a filter
aid such as kieselLuhr. After filtration the iso-extract can
be added directly to beer, as is described in detail below,
to bitter it. However, the iso-extract is not very stable on
storage at acid pHs and 9 especially if the extract is not to
be added to beer immediately, it is thus preferable to make
the p~ moderately alkaline, e.g. to pX 8 to 10, preferably
about 9.0 by adding a suitable alkali, eOg~ sodium a~d/or
potassium hydroxide a~d/or carbonate, and the solutio~
concentrated to a desired extent (usually 10 to 4~/0 iso o_
acids).
We have found that if the isomerization is completed
rapidly then a small proportion of the hop oil may not be
boiled of~ with the steam~ If complete removal of the hop
oil is desired then this can be done by continuing boiling
the alkaline mixture~ ~owever, when the iso-extract is
co~centrated before use as described below we have fou~d that
any remaining hop oil ca~ co~veniently be remo~ed ~ith the
water evaporated from the iso-extract~
ConcentraJGion can be carried out to obtain solid
crystalline iso-a-acids as the appropriate alkali metal salts
if desired. Since iso-a~acid can be lost by decompositio~
by overheating especially during concentratio~ by evaporatio~
~25--
:
.
. . . .
~ ~7~
it is preferred that in the evaporation the solution is not
,heated to more than 50C and more preferably not more than
40C. We have experienced no difficulty in performing the
evaporation at 35C~ Conveniently rapid evaporation can be
performed under a partial vacuum~ ~'he concentration of the
iso-extract need not, of course, be carried out to give solid
iso-~-acids~ ~or storage and transportation concentration to
form 10 to 4~/o w/~ is generally satisfactory. ~urther,
provided that there is no undue delay the step of making the
iso-extract solution alkaline may be per~ormed after, or even
during concentration i~ desired.
~he use o~ the preferred isomerization technique is
especially advantageous because it enables the method of the
invention to be carried out in a particularly elegant manner.
~hus, in an especially highly preferred aspect the invention
provides a method of making an isomerized hop extract which
method comprises the steps of :-
~i) extracting hops, preferably in crushed pellet
~orm, with liquid C0~ at a te~perature of from
_5C to 30C, preferably from -5C to 20C and
under a pressure slightly greater tha~ that of
the corresponding vapour pressure of liquid
C2 at the extraction temperature;
, (ii) recovering a primary hop extract of high purit~
by evaporating the liquid C02;
(iii) without further puri~ication, preparing an
alkaline aqueous solution containing the
. .
-26;
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.
.
extract preferably in an ar~ount co.rre~ponding
to from 1 to 1Q0 gl 1 of ~-acids, containing
sodium and/or po-tassium carbonate, preferably
in a concentration of from 0.01~ to 0.5N and
preferably havin~ a pH of from 8 to 11;
(i~) boiling this solution to convert substantially
all the cx-acids present therein to iso-o-acids
and to remove hop oil components, preferably
for a period of from 5 minutes to 2 hours;
(v) cooling the solution preferably to a temperatuxe
of from 0 to 10C;
(vi) if necessary dilutin~ the alkaline solutio~ to
a concentration of not mo.re than about 5 gl 1 iso-
~-acids and adjusting the p~ of the solution to
from abou-t 2 to about 5, preferably about 4.07
by adding acid;
(vii) filtering this acidified solution to remove ~-
acids precipitated therefrom whilst retai~ing the
iso-o-acids in solution; a~d optionally
(viii) concentrating the solutio~ of iso-~-a~ids thus
obtai~ed to R predetermined extent by evaporation,
preferably at a temperature of not more tha~
40C, and
: (ix) either before, during or after concentration,
adjusting the p~ of the filtered solutio~ to from
8 to 101 preferably about 9.0, by adding alkali.
-27~-
: -
. .. . .
- - , : , , ,
~he isomeriæed extract ~roduced by the method of the
invention is of excellent quality and can be obtained in high
yield. We have been able to extract 85 to 95% of the ~-acid
of hops without any substantial difficulty and we expect that
higher levels of extraction are possible. Typically up to
about 7~0 of the ~-acids are also extracted. Although the
soft resin acids content of different varieties of hops
varies 7 we have not experienced difficulties in extracting a
number of different hop cultivars as set out above.
The conversion o~ the ~-acid content of the extract to
iso-o-acid can be performed substantially quantitatively by
the preferred isomerization method used in the invention,
losses in the filtration to remove the ~-acids being slight.
~osses during evaporation are not normally significant
provided the temperature is kept below about ~0C. ~hus the
effective yield of the method of this invention can be
typicall~r as high as 9~/o and higher yields are probably
obtaina~le without very great difficulty~ -
It is an outstanding advantage of the iso~-acid pre-
paration obtained by the method of the invention that it does
~ot cause measurable haze on addition to beer~ This co~pares
highly ~svourably with isomerized extracts available com-
mercially~ ~he isomerized product of the i~ve~tion is of a
sufficiently high quality that it can be added to bright beer
~5 after filtration without significant hazingO ~his has not
- heretofor~ been practically possible; even the best com~nercial
isomerizates ha~ing to be adde~ before fi~al ~iltration a~ ~he
.
-2~
.
latest because of their tendency to cause haze~ The effective
utilization of the bittering potential of the hops is tnus
reducedO With commercial isomerized extracts the utilizatio~
obtainable under normal conditions is between 70 and 75% and
the maximum under carefully controlled and optimised conditions
about 85%; with unisomerized extracts added to the copper
utilization is typically 27 to 35% compared with about 25 to
~/g when the hops are used without extraction. We have had
no signi~icant difficulty in obtaining utili~ation values of
better than 8~/o, without specifically optimizing the conditions,
and believe that values of 9~/o and more will be obtained by
optimizing the methods o~ addition.
When commercial isomerized extracts are used to bitter
beer there are sometimes problems with gushing~ The main
gushing promoters are oxidation products of hop resins which
are present in the hops and/or formed during processingO
~nother advantage of our new process is that the resulting
isomerized extracts show no tendency towards gushing. Hence
gushing promoters are not extracted Xrom the hops or formed
during processing~
The quality of the iso-a-acid preparations of this
~ tion is evidenced by analysis. Examination by column
chromatography, as described by O~ter, Silvester and ~aylor,
J. Inst. ~rew~ ~ (1972) 57, on typical samples produced as
described above shows the presence of iso-a-aoids but fails
to show any u-acids~ ~-acids or humulinic acids~ ~hese
- compcnents are generall~ just detecta~le ~y thin l~yer
-29-
.
chromatography. Commercially available iso-extracts
generally r-eveal much higher levels of these undesirable
compounds. Further the iso-~-acids of the present invention
do not contain any detectable amounts of polyphenolic
com~oulld~. These are usually present in commercial extracts
and are thou~ht to contribute to the inferior properties of
the prior art materials, particularl~ with regard to haze
formation.
The invention will be descr-ibed further in connection
with the accompanying drawings, in which :-
~igure 1 illustrates apparatus for batch extraction of
hops with liquid C02, and
Figure 2 schematicall~ illustrates apparatus for semi-
continuous extraction of hops with liquid C02~
Figure 3 schematically illustrates apparatus for con- -
- verting a primary extract into an iso-~-acid preparation
suitable for addition to beer.
In Figure 1, hops 1 are contained in a press~re cell
having inlet 3 wlth associated tap 4, outlet 5~ including
sintered metal filter 67 with associated tap 79 observation
windows 8 and press~e gauge 9. To extract the hops, tap 7
is closed and liquid C02 is introduced into the cell ~ by way
of inlet 3 and tap 4. ~ap 4 is closed and the cell 2 rocked
to mix the hops and liquid C02 to extract the soft resins
(~-acids and ~-acids) into the liquid C02, When extractio~
is completed the extract can be transferred to a second
pressure cell 10 containing flask 11 and including observatio~
-3-
, .
7~
wi~dow 8 and exhaust line 12 provided with heater 13 and
tap 14~ ~o transfer, the extract tap 14 is closed and tap 7
is open and the extract flows through filter 6 (thus prevent-
ing any fi.nes being carried with the extract) into flask 11
in cell 10. After completio.n of the transfer, tap 7 is
closed. This extraction and transfer procedure can be
repeated as necessary or desired to extract the hops. ~he
extract can be separated from the liquid C02 by opening tap
14, thus controllably venting cell 10 to the atmosphere by
way of heater 13.
In ~igure 2, liquid C02 in storage tank 20 is pumped
by pump 21 at a pressure monitored by indicator 22 through
heat exchanger 23 in which the temperature of the liquid C02
is adjusted to that desired for extraction~ In a com~ercial
extractor the storage tank 20 will normally be refrigerated
to a temperature of between -15C and -20C. ~or small scale
extraction.s the storage tank can conveniently be replaced b~
a number of liquid C02 cylinders arranged in parallel~ When
C2 cylinders are used, because of the small scal.e 9 these will
~` 20 nQt usually be deliberately cooled and, being at ambient
temperature~ they will have an internal pressure greater than
. the vapour pressure o~ liquid C02 at the extraction tempera-
tur~ and this excess pressure in the cylinders can be used to
force the liquid C02 through the system at a ~uitable flow
- 25 rate thus obviating the need for a pump.
As a practical matter it is convenie~t to adjust the
:, .
temperature of the liquid C02 at the outlet of the heat
. -31-
; . :
.,. , ~.
., .
,:
'' ~: . '
exchanger 23 to allow for any temperature differences
between ambient temperature and the actual temperature of
extraction. lJe expect that the extraction in 11 generally be
carried out at sub-ambient rather than super-ambient temper-
atures and the liquid C0~ will thus be cooled to compensate
for the absorption of heat from the environment, which being
at ambient temperature, ma~ be up to 20C warmer than the
liquid C02 in the extraction column. To minimize such
undesired heat transfer to the liquid C02, the extraction
column and associated pipework valves etc~ will normally be
lagged to give a suitable degree of thermal insulation~ With
a suitably insulated column the liquid C02 will not usually
need to be more than about 2~ or 3C cooler than the desired
e~traction temperature. We have fo~nd that about 3C is
generally a suitable margin in small scale extractio~ apparatus
where heat pick up problems are more likely to arise tha~ orL
commercial equipment because of the proportionately larger
surfa&e area.
~rom the heat exchanger 23 the liquid C? is passed
through the extractio~ column 24 containing hops in suitable
form, e.g. as a powder or crushed pellets~ In the apparatus
illustrated the colu~n is arranged vertically with the liquid
C2 passing upwards through the column.
Although onl~ one extraction column is illustrated in
~igure 2, others may be placed in parallel with it~ e.g.
between B and B' and by switching the flow of C0~ through
such a plurality o~ columns (the neeessary taps etc. ~re not
-32-
shown) it is possible to run the apparatus semi-continuous~J,
e.g. when columns containing spent hops are isolated from t~e
pressuxe circuit to refil them with fresh hops whilst con-
tinuing the extraction through the other column(s) thus
enabling extract to be obtained continuously.
From the top of the extraction column the liquid C02
containing the extract is fed to an evaporator 25 where the
C2 is boiled off through pipe 28~ The evaporator is heated,
e.gO by warm water entering at 27a and leaving at 27b. This
warm water can conveniently be at 40C, although the temper-
ature of the heating medium will depend to some extent on the
extraction temperature and will be chosen to ensure adequate
heat transfer and to avoid isolation of the extract at a
temperature so low that it is very viscous of solid or so
high that it may be degraded or decomposed. The ex~ract,
which will typically be a liquid at the contac-t -temperature
within the evaporator, is collected within the evaporator
or a collecting vessel connected thereto and can be removed
from time to time via tap 26.
r~he ~a~eous C02 coming from the evaporator Z5 at outlet
28 i5 passed to condenser 29 in which the gaseous C02 is
cooled to reliquefy it. The liquid C02 is passed to storage
- tank 20. From tank 20 the liquid C02 is pumped by pump 21
through heat exchanger 25 and thus recycled through column 24
to evaporator 25. Fresh liquid C02 can be introduced into the
circuit via valve 30 to replace C02 lost when removing ex-
~ract via valve 26 or when refillinc extraction collunns~
.
~33~
-
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' ~
i. , : : ~
In ~iKure 2 the liquid C02 is showrl as passing npward1y
through extraction column 24. Whilst we prefer for engineer-
ing reasons to pass the liquid C02 upwardly it is possible
to pass it downwarclly through a column of hops if desired.
Other forms of equipment m~y be used to effect the ex-
traction with liquid C02 and the extraction step of the inven-
tion is not limited by the particular form of apparatus in
which the e~traction is performed.
In ~igure 3 high quality primary liquid C02 hop extract
40~ e.g. that produced using the apparatus of ~igure 1 or 2
as des~ribed, is fed together with ~n alkali, e.g. sodium or
potassium carbonate solution, of a suitable concentration,
e~g. 0.01N to 0.5N~ into a vessel 4~ provided with heating
coil 4~ and condenser 44. ~he solution of hop extract in
al~ali t~pically containing from 0.5 to 2 gl 1 of o-acids at
pH 8 to 11 is boiled, eO~. for from 5 minutes to 2 hours, to
isomerize the o-acids in the extract to iso-o-acids. The steam
evolved during~this boiling carries with it hop oil present
i~ the primary extract~ ~he water vapour and hop oil are
condensed in condenser 44 and can be collected at 45. After
completion of the isomerisation the alka~i~e solution is
removed from vessel 42 ~ia valve 46 and passed through Gooler
47 where the solution is preferably cooled to between 0 and
10C. hfter cooling the solutio~ 48 is fed to vessel 49
equippea with stirrer 52 and p~ meter 51~ Acid 5Q~ e~g. hydro-
chloric acid at a suitable concentration is fed into vessel
49 to acidify the isomerized extract, e.g. to a p~ of from
.
7~
2.5 to 5O The acid mixture is stirred and the ~-acids
precipitated. The mixture, containing a filter aid such
as kieselguhr if desired is then passed via valve 53 through
fil-ter or centrifuge 54. ~he filtered or centrifuged
solution 55 is then fed to vessel 56 equipped with stirrer
59 and pH meter 58. Alkali 57, e.g. sodium and/or potassium
hydroxide and/or carbonate is fed into vessel 56 to make the
solution of iso-~-acid alkaline, e.g. to a pH of from 8 to
10. ~his alkaline solution is then passed via valve 60 to
concentrator 61 which may co~veniently be a flash evaporator
pro~ided with heating coil 62, vapour trap 63, vacuum pump
64 and condensate collector 65. ~he temperature inside the
evaporator is preferably not more than 40C in order to avoid
degradation of the iso-~-acids. The concentrat'ed iso-~-acid
preparation can be removed from collector 65 via valve 66
Although the apparatus illustrated in Figure 3 is
described as producing a concentrated iso-a acid prepara-tion
it will be appreciated that, if desired~ the isomerized ~-acid
solution may be taken from a previous stage of the prepara-
tion, e.~ after filter ~ or from valve 60 if desired.
~urther, the apparatus has been described in batchwise
operation; iX desired continuous or partly continuous
operation may be effected if desired.
~he design of the individual pieces of equipment for
use in such apparatus is straightforward; indeed suitable
(although perha~s not optimum equipment) will, we expect, be
available "off the shelf". ~ruly co~tinuous operation may
-~5-
'
, :
require custom built equipment but we believe that design
of such equipment would not present any subst~ntial diffi-
cultry to the skilled chemical engineer. Equipment other
than as illustrated may be appropriate to sui-t particular
needs and the isomerization step of the method of the inven-
tion i5 not limited by the particular form of appara-tus in
which it is performed.
~he invention ~ill be described further in the follow-
i~g examples.
EXAMPIE 1
Extraction of Hops~ Batch Process~ and Conversion to an
Ir~ri~ei ~xtr~ ~.
100 g~ of powdered Wye Northdown hops, which contained
7O3% ~-acid~ were extracted in the apparatus shown in ~igure 1
generally as described below.
1.0 litre of liquid carbon dioxide was introduced to
the cell 2 via inlet 3 and associated valve 4 at a pressure of
730 p.s.i.g. At this pressure the temperature inside the
cell was about 16C. ~he cell was rocked for 15 minutes,
during which the pressure increased to 745 po S~ g~ ~ap 7
was opened and the liquid was then passed through sintered
filter 6 into flask 11 standing in second cell 10. Tap 7
was closed and tap 14 was the~ opened and the liquid carbon
dioxide was evaporated as gas which was vented to the atmos-
phere over a period of 45 minutes~ ~he hops were extracted
a further seven times using this procedure and the extracts,
which contained residual solid carbon dioxide, were bulkedr
, .
-~6-
"~ ,
.
. ' :
The flask was removed from the pressurized vessel and the
residual solid carbon dioxide was evapora-ted, via a bunsen
value, to leave a yellow viscous extract (15.8 g.).
The extract was examined by thin layer chro~atography
using the procedure described by the European Brewery Co~ven-
tion (J. Illst. ~rewi~g 1970~ ~, 386) and the presence of onl~
~-acids and ~-acids were revealed as two distinct spots when
the plate was sprayed with ferric chloride reagent. ~en
products obtained by extractin~ hops with organic solvents
are examined by this technique, the chromatogram is normally
complex and often consists of more than ten spots.
The extract was ~ho~n to contain 40,~/o of ~-acid when
estimated by a conductometric procedure (J. Inst. ~rewi~g
1970, 76, 343) using methanolic lead acetate. ~ence 88.1% of
the available a-acids were extracted from the hops using
liquid carbon dioxide. Examination of the extract by col1~mn
chromatography on Sephadex (J. Inst. Brewing, 1972, ~8, 57)
revealed that 70.~/o of the ~-acid present in the hops had
been extracted.
~ 10.0 portion of the extract was steam distilled using
the procedure similar to that described by ~oward (J. Inst.
Brewi~g, 1979, 76, 381) and a total of 450 mg. of hop oil was
collected. In this experiment the liquid carbon dioxide
had extracted 83% of the available oil ~rom the hop~
Similar yields of oils a~d resins were obtained when
powdered Wye Challenger hops were extracted by this process
usin~ liquid carbon dioxide~ ~his solvent was used to
-37-
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.
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i ' :'
~ ~8~
.
extract whole hop cones from the variety Wye Challenger
and also cones which had not been dried, iOe. green hopsO
Hop resins and oil were successfully extracted from these
samples.
A 1~1 g. portion of the extract obtained from Wye
Northdown hops and containing 40.~ acid was placed in a
flask fitted to a condenser via a cohobation head. 500 ml. of
0.1~ sodium carbonate was added and the mixture was boiled for
15 minutes under an atmosphere of nitrogen. ~he hop oil was
discarded and the mixture cooled to ~0C and the p~ was
adjusted to 4.0 by the addition of 2N hydrochloric acid.
~he mixture was stirred at constant pH for 100 hour, kieselguhr
~10 g.) was added and a stream of nitrogen was passed througk
the mixture for 5 minutes to aid flocculation of the a-acids.
The mixture was filtered through a bed of kieselguhr (40 gD )
which was washed with water. ~he filtrate and washings were
combined and the p~ of the solution adjusted to 9~0 by the
addition of 2~ potassium carbonate to give a dilute solution
of the required isomerized extract. A qualitative examination
of the extract by thin layer chromatograph~ showed the
presence of iso-~-acids together with only trace quantities
of ~-a~ids and ~-acids. ~ quantitati~e analysis of this
extract using the method of Otter et al (J~ Inst. Brewing,
1972, 78~ 57) revealed that the yield of iso a-acids obtained
from the hop extract was 79.~/o. Hence 70.4% of the available
~-acids present in the Wye ~orthdown hops were converted into
iso-a~acids.
~38-
~he extract was concentrated to 15% iso-~-acids
(W/V) usiIl~ a rotary evaporator (both tempera.ure 35C,
15 mm/~lg) without loss of iso-~-acids.
EX~LE 2
PreParation of ~n Isomerlzed Extract (Semi-Continuous
~xtraction of Hops).
= ~ . . .
200 gO of powdered Northern Brewer hops which contained
6.1% of ~-acid were placed in the column of the semi-continu-
ous extractor shown in ~igure 2. ~iquid carbon dioxide was
circulated through the system at a pressure of 890-910 p.s~i.g.
for 5 hours. The pressure in the system was released and the
extract which had collected in the evaporator (temperature
40C) was recovered.
A further five 200 g. samples of hops were extracted in
the same manner and the extract obtained from the six extrac-
tions bu7ked (15708 g.). ~he extract was examined using
the procedures described in Example 1 and the following
results were obtained:~
a) only ~-acid ~-acids could be detected by thin layer
~0 chromatography 9
b) 93% of the available ~-acids and 6~/o of the avail-
able ~-acids were extracted by -the liquid carbon
dioxide, and
c) 70% of the available hop oil was present in the
extract~
28.0 g. of the hop extract which contained 43% o-acid
were isomerized in a similar manner to that described in
. . .
, ~9
,, .
:
;" . . : -
,, .
-
Example 1 and a yield of 98% iso-~-acid was obtained af~er
filtration through kieselguhr. Only trace amoun-ts of ~- and
~-acid were detected in the extract.
~he volume of the aqueous iso-extract at pH 4 (8.2 l)
was reduced to below 1 litre by eva~oration at 50/15 mm of
Hg~ ~he pH was then adjusted to 9 with 0.2N sodium carbonate
solution and the volume made up to 1 litre to give isomerized
extract as a pale yellow solution (overall yield of iso-~-acid
88%, i.e. 1.06% W/V ) .
Additions were made to an l1n~opped beer by adding the
isomerized extract (diluted to 0.5~/o w/v iso-~-acid) prior to
racking at a rate of ~0 mg. iso-~-acid per litre of beer.
~he bitterness of the resultant beer measured by the recom-
me~ded method of analysis (J. InstO Brew~, 1971, 77, 181) was
26 EBU. ~he utilization of iso-~-acid in the beer was thus
~6%.
Isomeri~ed extract was also added to beer in the bright
beer tank prior to bottling at a rate of 42 mg~ iso-~-acid
per litre of beer. ~he bitterness of the bottled beer
measured as above was ~5 E3U. ~he utili~ation of iso-~-acid
in the beer was thus 83%.
A commercial isomerized hop extract was added to another
batch of the same beer in the bright beer tank at the same
dilution and ra-te of addition as that used with the abo~e iso-
extract. ~1he initial haze readings of the resultant bottled
beers, as measured by the recommended methods o~ analysis
(J. Inst. ~rew~ 1971, ~, 181), were 0.60 E~C units for the
1~0_
:
'
beer bittered ~ith the iso-extract prepared in this ~xP~ple
and 4~42 ~BC units for the beer co~taining the commercial
isomerized hop e~tract. ~he haze reading of the beer bittered
with iso-extract prepared by this Example did not exceed
105 EBC units after 15 wee~s storage. ~eer is reckoned to
have satisfactory storage stability with reference to haze
formation if the haze reading is not more than 205 ~B~ units
after 12 weeks storage. Induced gushing tests ~Jere carried
out on the bottle beers by the method of Laws and McGui~ness
(J. Inst~ Brewing, 1972 7 78, 30~) when the ]oss of beer
recorded was 0.4 g/~ pint for the beer containing iso-extract
prepared in this Example and 117.~ g/~ pint for the beer
containing -the commercial isomerized hop extract. For
comparison, an equivalent traditionally brewed (i.e. not
involving addition of extract or iso-extrac~ after brewin~)
bottled beer loses typically from 005 to 5 g/~ point under
similar testing~ Hence the beer bittered with the new
isomerized extract did not have a tendency to gush.
~ s on the Pllot Plant Scale.
830 g. of powdered W~e Northdown hops containing 701% of
o_acid were placed in the colum~ of the semi-continuous extrac-
tion apparatus illustrated in ~igure 2. Liquid carbon di-
o~ide was circulated through the system at a rate of 6,4
litres/hour and pressure o~ 870 p~s~i~go for 5 hours. ~he
pressure in the system was released usin~ the vent valve ~d
the ~xtract (114~8 g~) which had collected ln the evaporator
~1 -
was isomeLiz~d using the procedure described in Example 1
and an.alysis of the product revealed. that the overall effi-
ciency of tke extraction of ~-acid and isomerization was
88%
EX~MPLE 4
Samples of a variety of hop cultivars were extracted
with liquid C02 and issmerized according to the procedures
described in Example 2 above. ~he extracts and isomerize~
extracts were of a similar high purity. ~he results of the
extractions and isomerizations are summarised in ~able 3 and
the results of tests on haze formation, gushing, bitterness
and utilization of these isomerized extracts when added to
beer are given in Table 4.
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