EXTRACTION AND ISOMERISATION OF ALPHA-ACIDS FROM HOP EXTRACTS

Abstract: α-Acids are extracted from a crude hop extract (which is itself obtainable from hops by extraction with liquid carbon dioxide) by boiling a mixture of the crude extract with an aqueous alkali, the alkali being present to no more than a slight excess, to form an aqueous layer containing the extracted α-acids and an organic layer containing β-acids, which layers are then separated from one another. The α-acids in the aqueous layer may then be isomerised in the absence of the β-acids by boiling the aqueous layer at a pH of from 7 to 8.5 at a pressure above atmospheric. The β-acids in the organic acid may be oxidized in the ab­ sence of α-acids after extraction thereof from the organic layer.

Description: EXSPACTION AND ISOMERIZATION OF &alpha;-ACIDS @POM HOP EXTRACTS LD OF THE INVENTION This invention relates to te extraction and utilisation of the bitter principles of hops. BACKGROUND OF THE INVENTION It is well known that during the traditional process of brewing, hops are boiled with the wort pricr to the fermentation stave in order to impart bitter flavours. Hops consist of resins, oils, waxes, water soluble raterials (sugars, tannins and proteins) and cellulose. The resins and volatile cil are located in the lupulin glands and it is this material which is of greatest use to the brewer. The resins may be divided into "hard resins" which are almost insoluble in non polar solvents (hexane and liquid carbon dioxide) and are regarded as being of little value in brewing, and the "soft resins". The latter include two important groups of weakly acidic compounds called the &alpha;-acids and acids respectively. The acids, which are distinctly more acidic than the acids, are known generically as "humulones" and are converter by boiling with wort to iso-&alpha;-acids which are primarily responsible for the bitter flavour of beer. The acids, known generically as "lupulones", have little brewing value, if any, as such but the brewer finds use for certain derivatives thereof formed by oxidation. The acids include humulone, cohumulone, adhumulone arc its analogues and are usually referred to collectively aE "humulones". Their isomerized forms, which are the principal bittering agents obtained from hops, are termed herein iso-&alpha;-acids and include isohumulone and its analogues, etc. and are known collectively as "isohumu- lones". Hops are a relatively unstable commodity de to the ease with which the &alpha;-and acids auto-oxidise and are degraded to non-bitter and water insoluble materials (hard resins). Furthermore, the abovementioned process of boiling the hops with the wort is a comparatively inefficient pi@cess since the majority of the potential bittering materials, the &alpha;-acids, are lost du@ing brewing process. The first approach of commerce to the problem, caused by the instability of the dried compressed ho2s, was to extract the useful components using volatile organic solvents, such as methanol , hexane, methylene chloride and trichloroethylene. Hop extracts rnade with such solvents are, in fact, very stable and can be stored in hermetically sealed containers for years without appreciable loss. However, hop extracts although stable when compared to the hops, only marginally increase the utilisation of the potential bittering components during the boiling of the wort. The inefficient conversion of the &alpha;-acids during boiling, and the subsequent absorbtion of both acids and iso &alpha;-acids onto the precipitated wort-insoluble matter, known as "trub" (coagulated proteins, etc.) and absorption onto the yeast during the fermentation process, are responsible for similar losses to those occurring when using hops. To overcome these problems, the next major step forward was the proposal of separately extracting the bitter principles of the hops, isolating the &alpha;-acids, converting these by an isomerisation process to the relatively pure iso-o(-acids and adding these post fermentation to the beer prior to the main filtration stage. GB 855401 describes a process in which hops are (or a hop extract is) boiled in aqueous alkali to simultaneously extract-acids and convert them to iso acids, which are then removed by solvent extraction. The production of isomerised post fermentation bittering materials was not without its on peculiar problems. Early products were crude, containing numerous acidic materials which were not iso-&alpha;-acids. Their solubility in distilled water was poor and their utilisation when added to beer was often in the region of 60-708. A greater disadvantage was that material derived from the hard resin fraction of the hops (hard resins are partly made up of oxidised and degraded q and @-acids) was carried through the varnous processes and was present in the material added port fermentation to beer. These hard resin derived materials have t shown to be responsible for "gushing" or "over foaring" of bottled beer. In order to obtain an iso-c < -acids extract of higher purity, many processes have been developed. In some such known processes, the i-acids are extracted from hops or a hop e::tract, separated fro other undesired products such as acids and thereafter isomerised. Most of these known processes involve the use of solvents at least in the extraction stage (see for example GB 1192681 and GB 1274678). Such processes usually require many elaborate stages of purification, for example, chromatography (GB 1183669) or a long series of separation steps (GB 1404713), or the use Of expensive reagents such as calcium or magnesium salts (GB 1362695). Recently there has been a tendency to avoid using organic solvents, particularly chlorinated hydrocarbons, in the food and beverage industries. Tilts has led to the development of a process in which hops are extracted using liquid (or supercritical) carbon dioxide to provide a hop extract containing unisomerised acids and various other ingredients, including hop oil, fats and waxes, various uncharacterised resins and acids (GB 1575827). Various processes are known in which hops or hop extracts are treated in an aqueous medium to provide an isc-C(-acids - containing product (see, for example, GB 1171021, EP-A-0020087, GB 1575729 and GB-A-2022083). GB 1576729, GB 2022083A and EP-A-0020087 describe respective processes in which extraction of acids from a liquid carbon dioxide extract is carried out by boiling the extract in aqueous sodium or potassium carbonate under an atnosphere of nitrogen, the alkali being present in a large excess with respect to the acids in the extract (Exarple 1 of GB 1576729 uses an equivalent ratio Na2CO3/&alpha;-acids of 15/1, Example 1 of GB 2022083A uses an equivalent ratio K2CO@/&alpha;-acids of 2/L and Example 5 of EP-h-0020087 uses an equivalent ratio K2CO3/-acids of (2/1). Under such conditions simultaneous extraction and isomerisation takes place and a significant quantity of acids are extracted into the aqueous phase. Such acids are difficult to remote fror. the aqueous phase and prevent efficient separation of the pure iso-&alpha;-acids. Furthermore, the product is loaded with large quantities of undesirable organic salts. Such processes may also result in a product in which the iso-O(-acids are partitioned between several distinct phases (see GB-A-2022083). A gum-like precipitate contains most of the iso-&alpha;-acids and this tends to stick to equipment etc. The difficulties associated with handling and treating resins obtained by direct alkaline extraction of &alpha;-acids without the use of organic solvents have been recognised by other workers (see EP-A-0019462) and this has led to the use (as mentioned above with respect to solvent extraction) of expensive complexing agents providing insoluble metal ions such as magnesium (see GB 1395671 and EP-A-0019462). SUMMARY OF THE INVENTION The present invention provides a procedure which allows a hop extract produced, for example, by means of liquid carbon dioxide extraction, to be converted simply and efficiently into a stable isomerised extract which can be added to bright beer without appreciable increase in haze. In contrast to the abovementioned known processes, the procedure of the present invention is simple, direct and may be used to obtain a high conversion of acids into iso-cC-acids of great purity with minirr:rr of degradation. The present invention provides, according to one aspect, a process for the extraction of &alpha;-acids, mainly in unisomerised form, from a hop extract which causes particularly high p@@portions of the &alpha;-acids to be extracted into a single, aqueous phase, leaving most, if not all, of the acids and other unwanted components in an organic phase. These phases can be easily separated from one another. This process provides an aqueous solution of Acids which are at least mainly in unisomerised form, which aqueous solution is a valuable starting material for an &alpha;-acids isomerisation process; the prior removal of a higher proportion of the acids and other impurities by this process, as compared with conventional processes, before isomerisation, enables a more efficient subsequent isomerization process to be carried out. Such an isomerisation process may be carried out by a conventional process. However, the invention provides, according to another aspect, a process for the isomerisation of acids in aqueous solution which can be carried out quickly and easily to give particularly efficient conversion to the iso-&alpha;-acids. The process may be carried out so as to provide an aqueous solution containing the iso-&alpha;-acids, which solution contains only small quantities of inorganic salts and can be easily concentrated for use without the need for expensive and elaborate separation stages. In a preferred procedure in accordance with the invention, a hop extract is subjected to the abovementioned M-acids extraction process according to one aspect of the invention. The resultant orgaric layer is then separated from the aqueous layer containing the -acids, which &alpha;-acids are thereafter isomerised by subjecting the aqueous layer to the abovementioned isomerisation process according to another aspect of the invention. Referring firstly to the &alpha;-acids extraction process of the invention, we find, surprisingly, that if a hop extract, especially a liquid CO2 hop extract, is boiled with aqueous alkali present in an equivalent ratio with respect to the Acids content in the hop extract such that there is no more than a slight excess of alkali (say an equivalent ratio of alkali:acids of no more than 1.2:1) and preferably an excess, more preferably a significant excess ofO(-acids, then a product is obtained which consists of an aquc-ous layer containing mainly unisomerised &alpha;-acids and an oily organic layer which comprises mainly Acids together with uncharacterised resins, fats and waxes. The organic layer can be separated easily from the aqueous layer, and the acids removed therefrom. The p-acids may be oxidized to produce products useful in -he brewing industry as described, for example by P.V.R. Shannon, Chem. & Ind., June 1968, page 720 et seq. The organic layer can be separated easily from the aqueous layer, and is useful as a starting material in a process for oxidizing Acids to produce products useful in the brewing industry. Such a process in which the organic layer can be used as starting material is for example, that described by P.V.R. Shannon, Chem. & Ind., June 1968, page 720 et seq. After this separation, the o(-acids in the aqueous layer can be easily, quickly and efficiently isomerised, preferably in the manner later described. When determining the abovementioned "equivalent ratio", it is assumed that thecµ-acids are dibasic in nature as it is at present believed, though there are doubts about this. Thus when the alkali is dibasic potassium carbonate, an essentially stoichiometric amount of alkali relative to acids will be present when the equivalent ratio is 1/1 and the molar ratio is 1/1. When the alkali is monobasic sodium or potassium hydroxide an essentially stoichiometric amount of alkali relative to&commat;4-acids will be present when the equivalent ratio is 1/1, but the molar ratio is 2/1. A preferred equivalent ratio lies within a range of about 0.4/1 to 0.8/1. In practice, the amount of acids present in a hop extract may be estimated by measuring the lead conductance value (LCV) thereof. The desired concentration of alkali may then be added. Preferred alkalis are potassium carbonate and bicarbonate, sodium carbonate and bicarbonate, though potassium and sodium hydroxides may alternatively be used. Especially preferred are potassium carbonate and bicarbonate. krferring now to the isomerisation process of the invention, we find, surprisingly, that isomerisation of the Of-acids can be very rapidly, easily and efficiently effected with a high degree of process control if the Acids are present in an aqueous solution at a pH of about 7-8.5, preferably about 7.5, and the aqueous solution is boiled under pressure. It was previously thought that isomerisation could be achieved only at high pH levels for example a pH of 10.5 and then only after boiling for a considerable period of time, for example, up to 121 hours. Furthermore, although it may have been appreciated that this time knight be reduced by boiling under pressure, we find that such a process, carried out at high pH levels, is uncontrollable and results in degradation products such as hamulinic acid. It was surprising to us that, by siritaneously reducing the pH and increasing the pressure, conditions would be provided which gave rapid and simple isomerization essentially without formation of degradation products. This process has the significant advantage that it can be carried out without the need for the presence of unwanted inorganic salts which are inevitably present at high pH levels. A preferred pressure is about 20-60 psi (about 1.3 x 105 - 4 x 105 Pa), more preferably about 25-35 psi (about 1.3 x 105 - 4 x 105 Pa), especially about 30 psi (about 2 x 105 Pa). At these pressures, the boiling temperature is about 120-1400C, especially about 135 C. The boiling time may be from about 5 to 50 minutes, but is preferably about 6-15 minutes for most conditions of operation. Conveniently, the pH of the W-acz s - containing aqueous phase produced by an acids extraction prc¯eFs embodying the invention as described above is from about 7-8 and therefore, after separation of the aqueous phase from the organic phase, this aqueous phase may be subjected directly to an isomerisation process embodying the invention without the need for adjustment of pH and without the need to load the solution with unwanted inorganic salts. Although the abovementioned isomerisation process can be carried out with some success anc(-acids extract obtained by conventional processes1 for example, those obtained by solvent extraction processes, a preferred, solvent-free, isomerisation procedure embodying the invention includes both of the abovementioned respective < -acids extraction and isomerisation processes. Such a preferred process may be carried out as follows. The starting material is a typical relatively crude hop extract obtained from hops by extraction with liquid or supercritical carbon dioxide. The preparation of such a crude hop extract is described in GB 1575827. Typically, dry hops are treated with liquid CO2, preferably at a pressure of from about 40 to 60 atm. (about 4 x 105 to 6 x 105 Pa), especially about 50 atm. (about 5 x 105 Pa) and a temperature of from about 3-10 C, especially about 7 C to provide a solution of the crude extract in the liquid CO2. The CO2 may be separated off by evaporation. Such a crude extract contains, in addition to-acids, various ingredients such as hop oil, fats and waxes, various uncharacterised resins and acids. It should not, however, contain appreciable amounts of, for example, tannins, hard resins and chlorophyll. The first stage in this extraction/isomerisation process embodying the invention consists of extraction of essentially unisomerised acids from the crude liquid CO2 hop extract. The hop extract is boiled, more preferably refluxed, with an aqueous alkaline solution, a potassium carbonate or bìcarbonatc solotion bcing especially preferred. A particularly preferred aqueous alkali concentration is about 0.02 - 1, mort preferably about 0.06-0.08M, especially about 0.07M, and a particularly preferred -acids concentration lies within the range of about 2-30 vol% calculated as described hereinafter. As mentioned above, a preferred equivalent ratio of K2C03/c(-acids is about 0.4/1-0.8/1, more preferably about 0.5/1-0.75/1, especially about 0.6/1. This provides the starting mixture with an initial pH of about 9-11. Boiling may be carried out for a time from about 15 minutes to 1 hour, preferably for about 40 minutes. During this process, a small amount of iso- a-acids is formed in the aqueous phase and care must be taken not to conduct the process for too long or at too high an alkali concentration so as to avoid precipitation of an unwanted solid phase containing such iso-&alpha;-acids, and/or breakdown of the -acids with consequent loss of purity. The above extraction process provides (i) an aqueous alkaline layer containing up to 100%, typically about 95%, of theC(-acids in the original crude hop extract (though as mentioned above a small amount of this is present as iso- W-acids), and (ii) an organic layer containing acids and the other ingredients of the crude hop extract mentioned above apart from the hop oils which may be removed by steam vaporisation during the process if desired. This mixture is preferably cooled to between about 40-SO0C before the organic layer is separated off by a conventional method of separating immiscible layers, for example, using a separating funnel This separation constitutes the second stage in the preferred process, and yields the abovementioned aqueous acids - containing layer for providing the iso-C(-acids, and the organic acids containing layer from which the acids may be extracted for oxidation. The final pH of the aqueous phase containing the mainly unisomerised acids formed by the abovementioned extraction step lies in the range of from about 7.0-8.5, preferably about 7-8, especially about 7.5. No adjustment of pH is then necessary before carrying ot to subs qurns isomerisation step. Hence it is not necessary to load the solution with unwanted inorganic salts which are present when operating at conventional pH levels of about 10.5. The third stage consists of directly isomerising the &alpha;-acids in this aqueous phase. The aqueous phase containing the &alpha;-acids is boiled under pressure, preferably under a pressure of about 30 psi (about 2 x 105 Pa), at which pressure the boiling temperature will be about 1300C. A typical boiling time is around 6 minutes as compared with conventional isomerisation processes which can take up to 12 hours. Under such weakly alkaline conditions essentially all of the acids content is simply, quickly and efficiently converted to iso-&alpha;-acids. It is preferred that the amount of hop extract treated in extraction stage 1 above is such that the acids concentration in the aqueous phase subjected to this isomerisation stage 3 is not too high, more preferably not above about 15%, since otherwise longer times and/or higher pressures are required in stage 3. Alternatively the aqueous phase obtained after stage 2 may be diluted. A typical aqueous solution obtained by stage 3 is slightly hazy in appearance and the final stage in the preferred process is to chill, preferably at an iso > -acidsconcentration of less than about 15% (to avoid loss of iso-C(-acid by precipitation), filter and concentrate under vacuum to obtain a product suitable for use. Where the resultant product has a haze value less than about 5 EBC units, as later described, it is suitable for addition directly to a beer after the brewer's final filtration stage. Products having a haze above this value, although suitable for use by the brewer, should be added prior to the final filtration. The absence of high levels of inorganic salts from the aqueous iso-C(-acids solution renders this concentration step particularly simple and efficient because the tendency for the iso-oC-acids to "salt out" is minimised. If desired, the acids may be extracted from the organic layer obtained in the second stage by treatment of the organic layer, conveniently with an alkali solution, usually an aqueous alkali. Since the acids thus extracted are essentially free from acids, they may be easily and efficiently oxidised to produce oxidised acids also useful as bittering agents in the brewing industry. DESCRIPTION OF PREFERRED EMBODIMENTS Especially preferred solvent-free extraction and isomerisation processes embodying the invention, together with less preferred conditions (for the guidance of the reader) will now be described with reference to the following Examples. Determination of various parameters referred to in these Examples was as follows: (i) Equivalent ratios calculated from: average molecular weight of acids = 360 molecular weight of alkali, e.g K2CO3 = 138 (ii) Weight of oils collected (g) = 0.8 X volume of oil collected (mls). (iii) %OC-Acids concentration (W/V) in starting mixture: The amount by weight (g) ofc(-acids in a sarple of hop extract was determined by a conventional LCV method (which involves titration against lead acetate to obtain a conductance curve). Confirmation of the value, to within 0.5%, was obtained by optical rotation value measurement. The "%&alpha;-acids concentration" values merely indicate the amount of water added to a hop extract sample as compared with the amount of acids present in the sample. For example, a "5t acids concentration" means that 20 times as much water has been added. (iv) %o(-acids recovery (stage 1) = wt. of hop extract wt. of (top, organic layer + hop oils) X 100 wt. ofct-acids in hop extract Where the stated %c(-acids recovery values are greater than 100%, this is because of the presence of s311 amounts of acids in the aqueous layer. Where, in the Tables, "B" appears, this indicates that the aqueous phase contains more than 5% acids, such processes being less preferred. Where the stated % &alpha;-acids recovery values are 100% or less, then only &alpha;-acids were present in the aqueous phase; it was confirmed by high performance liquid chromatography (HPLC) that essentially none of the acids component was present. (v) % purity of iso-c(-acids concentration of iso-&alpha;-acids in aqueous = solution (final product) (% W/W) x 100 concentration of total resins in aqueous solution (final product) (t W/W) The concentration of iso-ct-acids in the final product was measured as described in "Analytica EBC", 3rd Edition, 1975, Method 7.5, E60, modified to take into account the absence, from the final product, of interfering substances found in beer (to which this test is conventionally directed). The concentration of total resins in the final product was measured by rendering the solution acidic, retracting the resins into hexane, evaporating and weighing the residue. (vi) t yield of iso- ffi -acids = wt. of iso-QC-acids in final product X 000 wt. ofc < -acids in hop extract (ii) Haze values are measured using a nephelometer, which provides European Brewing Convention (EBC) values. EXAMPLE 1 PRELIMINARY STAGE - PREPARATION OF CRUDE HOP EXTRACT Liquid CO2 hop extracts used in the processes embodying the invention described below were obtained as follows. A commercial hops (as indicated) was formed into pellets, cooled to remove the heat generated during the pelletizing process and again milled to produce a dry powder. The powder was placed in an extractor vessel through which liquid CO2 was passed upwardly at a pressure of about 50 atm (5 x 10% Pa) and a temperature of about 7 C. The resultant solution of the crude hop extract in the liquid CO2 was allowed to issue from an upper region of the vessel to a condenser/evaporator, where the solution was heated and the liquid CO2 allowed to evaporate off to provide the crude hop extract used as a starting material in the processes described below. STAGES 1 AND 2 - EXTRACTION AND SEPARATION Calculated amounts of (a) &alpha;-acids present in a hop extract, (b) alkali and (c) water were refluxed for given times, the hop oils being collected in a cohobation head. Experiments were conducted using an extract obtained by liouid CO2 extraction of the commercial hops "Bullion" (our Batch No. 366) and using varying amounts of hop extracts so as to give varying acids concentrations and also varying base/C(-acids equivalent ratios. The process conditions were as indicated in Table 1. On completion of the reflux time the mixture was cooled to about 80 C, poured into a separating funnel and allowed to stand. The mixture separated into a top, organic, layer and a bottom, aqueous, layer. The bottom, aqueous, layer was run off, leaving the top, organic, layer which was also removed, and then weighed. The bottom, aqueous, layer was used in stage 3 described below. Table 2 shows results of the about and experiments conducted at an o(-acids concentration of 5% for different base/&alpha;-acids equivalent ratios. Similarly, Tables 3 and 4 show results for respective acids concentrations of 15% and 2% including the use of other bases and hop extracts. TABLE 1 %&alpha;-Acids Equiv. ratio pH of Pan concentration K2CO3/&alpha;-acids aq phase No. (W/V) in in starting %&alpha;-acids of prod@@t Time starting mixture mixture recovery of stade) (mons) Q4/115 2 1.0 * -- 30 1.0 ss --- 30 CP4/117 2 0.6 100 7.2 30 CP4/118 2 0.6 P 7.2 30 CP4/120 2 0.4 90.0 7.6 30 CP4/119 2 0.4 76.6 7.6 30 CP4/079 5 0.75 CP4/102 5 0.60 100.0 e.o CP4/094 5 0.50 80.0 7.5 CP4/114 5 0.40 73.3 --- 40 CP4/121* 7.5 1.0 ss 9.4 40 CP4/122 7.5 0.6 97.8 7.8 40 CP4/123 10 0.6 100 7.7 40 CP4/124 15 0.6 105.2 7.9 40 CP4/125 20 0.6 104.3 7.7 65 CP4/127 20 0.6 104.2 8.0 45 CP4/128 30 0.6 ss 8.0 60 *This run gave an aqueous solution containing, in addition to the &alpha; ;-acids, too high an amount of acids for use in stage 3. TABLE 2 (5%&alpha;-ACIDS SOLUTION) EQUTVALENT NOP EXTRACT WT. &alpha;-ACIDS MLS. OIL. @ &alpha;-ACIDS RATIO K2CO3/ WT. (g) (g) WT. TOP LAVER COLLECTED BY BECOVURY &alpha;-ACIDS (g) VAPORIZATION 2.0 100 40 26.0 2.0 ss 1.0 50 20 - - ss 0.5 50 20 32.2 - 89.0 0.5 50 20 31.7 - 91.5 0.5 50 20 30.9 2.9 83.9 0.75 50 20 24.0 - ss 0.5 50 20 31.2 - 94.0 0.5 50 20 32.1 2.7 78.7 0.5 100 40 64.3 3.4 82.4 0.5 100 40 71.6 3.4 64.2 0.6 100 40 55.9 3.6 103.0 0.5 100 40 64.1 3.2 83.3 0.6 100 40 55.3 3.6 104.5 0.6 100 40 57.4 3.0 100.5 0.6 100 40 56.6 3.0 102.5 0.6 100 40 56.8 3.4 101.2 0.6 200 80 112.9 5.0 103.8 0.6 200 80 114.0 6.6 100.8 0.6 203 81.2 116.0 5.8 101.4 0.6 200 80 109.2 7.0 106.0 0.6 200 80 112.7 6.0 101.0 0.6 200 80 112.8 7.0 102.0 0.4 100 40 68.1 3.2 8.8 TABLE 3 15# &alpha; ;-ACIDS SOLN Equivalent ratio %&alpha;-Acids Source of crude alkali/&alpha;- acids recovery extract (1)/Alkali 0.6 105.2 Bullion 366/K2CO3 0.78 ss Bullion 366/Na2CO3 0.6 p Target 338/K2CO3 0.6 82.9 Bullion 365/Na2CO3 0.6 ss Bullion 3 < 1/K2CO3 0.5 99.0 Bullion 341/K2CO3 0.5 83.3 Bullion 123/K2CO3 0.6 83.8 Bullion 366/Na2CO3 0.75 p Bullion 366/NaOH 0.25 26.9 Bullion 366/NaOH 0.25 30.a Bullion 366/KOH 0.6 95.5 Bullion 366/KOH (1) The name, e.g. "Bullion", represents a commercial hops and the number, e.g. "366" represents our Batch No. for the crude extract used as starting material for Stage 1. TABLE 4 2% &alpha;-ACIDS SOLN Equivalent ratio %&alpha;-Acids K2CO3/&alpha;-acids recovery Crude extract 1.0 ss Bullion 366 0.6 101 Bullion 366 0.4 76.6 Bullion 366 0.g 90.0 Bullion 366 From thc above results it can be seen that quantitative extraction of-acids is possible if the equivalent ratio of base/q-acids is adjusted to ensure that no acids are extracted and that maximum yield is obtained. By experiment using K2CO3 an equivalent ratio of 0.6/1 was found to be the optimum for some resins; higher ratios may result in extraction of some acids while for other resins a ratio of 0.5/1 was found to bc the optimum. Lower ratios resulted in loss of yield in both cases. This variation seems to be due to different amounts of acidic substances present in different batches of hop extracts. Although not wishing to be bound by theory, it is believed that the particularly efficient separation of the < -acids and acids into the respective aqueous and organic phases occurs because of the competition between theCC-acids and acids for the available alkali; the alkali prefers to react with the more acidic O;-acids, rather than with the less acidic acids, to form water-soluble acids salts, leaving the acids essentially in their free, waterinsoluble, state. The effect of &alpha;-acids concentration did not at first seem to have any effect on extraction, but it was found that at high concentration (30%) uncharacterised resins were extracted. This is clearly shorn when purities of the final products are studied. At lower concentrations ( < 15%) no uncharacterised resins were present. Another disadvantage appears at higher concentrations ( > 15%); on chilling larger losses occur than for the more dilute solutions. Use of NaOH and KOH is possible in which case a 0.6/1 equivalent ratio (1.2/1 molar ratio) seems to be the optimum. When corresponding tests were carried out using sodium and potassium carbonate respectively, potassium carbonate tended to give better yields. This is possibly because the potassium salts of the &alpha;-acids are more soluble than the sodium salts. In this first extraction stage some isomerisation does occur. Iso-oC-acids are known to be monobasic. This therefore affords possible e;planation as to why relatively small amounts of K2CO3 give quantitative extraction. Once some of thec(-acids have been isomerised, thus releasing more K+ ions, these "excess" K+ ions extract the remainingCX-acids, but conditions now are such that no further isomerisation takes place. The mixture obtained by stage 1 consists of two phases, a top, organic layer and a bottom, aqueous layer. In stage 2, as described above, these layers are separated from one another. STAGE 3 - ISOMERISATION The aqueous phase from stage 2 was then charged into a pressure reactor and the pressure increased by increasing temperature. Table 5 shows times for completion of reaction at given pressures andC(-acids concentrations in the aqueous phase obtained from stage 2 (Run Nos. in Table 5 correspond with those of Table 1). The &alpha;-acids concentrations given are those before extraction stage 1 was carried out, but since acids recovery values for stage 1 were high, these give an approximate indication of &alpha;-acids concentration in the aqueous phase obtained from stage 2. TABLE 5 RUN PRESSURE ALXALI TIME &alpha;-ACIDS CON NO. P.S.I. (Pa x 105) MIN CENTRATIO@ % CP4/102 30-35 (2.1-2.4) K2CO3 6 5.0 CP4/106 30 (2.1) " 15 5.0 CP4/107 30-40 (2.1-2.8) " #15 5.0 CP4/116 30-35 (2.1-2.4) 6 6 5.0 CP4/118 30-35 (2.1-2.4) ' 6 2.0 CP4/120 30-36 (2.1-2.6) 10 2.0 CP4/122 30-35 (2.1-2.4) 6 7.5 CP4/123 30-38 (2.1-2.6) 6 10 CP4/124 30-38 (2.1-2.6) n 7 15 CP4/125 30-40 (2.1-2.8) 40 20 CP4/127 60-67 (4.1-4.6) " 6 20 CP4/128 60-67 (4.1-4.6) " 6 30 CP4/133 30-35 (2.1-2.4) " 10 5.0 CP4/142 30-38 (2.1-2.6) KOH 14 15.0 As can be seen from Taboo 5 the rcact2on w:r to completion within minutes once a pressure of about : :D psi was reached at acids concentrations of 15% or less. At higher concentration either longer times were required or higher pressures. Products obtained from isomerising for longer times were inferior in haze characteristics. From this, it can be seen that, if solutions containing high Or-acids concentrations ar2 to be isomerised then pressures should be increased to about 60 psi whereby the reaction goes to completion in 6 minutes and a highly satisfactory product is obtained. At these higher pressures,hence higher temperatures, the necessary energy required to overcome the activator energy "hump" for the reaction is readily achieved. In cc-:-entional isomerisation procedures this is cvercore by raking use of higher quantities of base. The excess base has then got to be removed by further processing. Isomerising under pressure means that low levels of base can be used throughout the process. This eliminates extra stages in the process. Another advantage of isomerising under pressure is the control afforded once the reaction is completed. Cooling gives a rapid drop in pressure and hence a fast quenching of the reaction. In conventional refluxing procedures for isomerising, it tales longer to quench the reaction and so the possibilities of further reactions such as iso-&alpha;-acids to humulinic acids are increased. STAGE j - FILTRATION/CONCENTRATION The solution from stage 3 was cooled rapidly to auench the reaction and further chilled in a refrigerator to about 80C. Chilling of the isomerised solution results in cloudiness for dilute solutions ( < 158) and precipitation of resins for concentrated solutions ( > 15E). On analysis of resin precipitated out of concentrated solutions it was found to consist mainly of iso-&alpha;-acids; hence a loss in yield. In dilute solutions very sr-ll quantities of resins precipitate out, which Or were shown to consist mainly of p-acids, the ss-acids having been extracted in trace quantities in stage 1. These chilled solutions were then filtered through kieselguhr, giving a bright filtrate which was then concentrated to the required specification. gain due to 1 low levels of base the solutions could be concentrated up to about 45' iso-d.-acids without "salting out" occurring. The final products obtained by the Runs listed in Table 5 were analysed for various parameters as shown in Table 6. TABLE 6 1% SOLUTION EMI24.1 RUN <SEP> @ <SEP> &alpha;-ACIDS <SEP> EQUIVALENT <SEP> CONCN <SEP> OF <SEP> TOTAL <SEP> PURITY <SEP> YIELD <tb> NO. <SEP> CONCN <SEP> IN <SEP> AQUEOUS <SEP> RATIO <SEP> ISO-&alpha;-ACIDS <SEP> RESINS <SEP> OF <SEP> ISO- <SEP> OF <tb> SOLUTION <SEP> FROM <SEP> WT/WT <SEP> TO <SEP> WHICH <SEP> WT/WT <SEP> (%) <SEP> &alpha;-ACIDS <SEP> pH <SEP> OF <SEP> HAZE <SEP> ISO-&alpha; <tb> STACE <SEP> 3 <SEP> SOLUTION <SEP> IS <SEP> % <SEP> CONCEN- <SEP> UNITS <SEP> ACIDS <tb> TRATED <tb> ADJUSTED <SEP> AFTER <SEP> EBC <SEP> % <tb> ISO-&alpha; ; COMPLETION <SEP> OF <tb> ACIDS <tb> ISOMERISATION <tb> SOLUTION <tb> CP4/102 5.0 0.6 21.8 23.28 93.7 7.6 1.6 84.0 CP4/106 5.0 0.6 25.6 24.80 103.2 7.0 5.5 84.1 CP4/107 5.0 0.6 21.5 22.40 95.9 7.2 8.0 80.8 CP4/116 5.0 0.4 17.6 18.70 94.1 6.5 2.1 53.4 CP4/118 2.0 0.6 16.7 17.90 93.0 6.9 6.5 86.3 CP4/120 2.0 0.4 27.6 27.40 100.0 6.4 6.0 45.4 CP4/122 7.5 0.6 34.0 35.00 97.0 7.1 5.5 77.2 CP4/123 10.0 0.6 38.4 40.73 94.3 7.7 8.0 76.0 CP4/124 15.0 0.6 35.4 35.49 99.7 7.8 11.5 68.1 CP4/125 20.0 0.6 13.9 15.52 89.5 7.2 62.5 74.8 CP4/127 20.0 0.6 13.7 15.25 89.8 8.9 1.6 73.8 CP4/128 30.0 0.6 17.6 19.52 90.2 8.7 4.2 71.4 CP4/133 5.0 0.5 16.33 16.46 99.2 7.4 2.0 80.8 CP4/142 15 1.2 31.17 32.3 96.7 7.5 8.7 67.7 EXAMPLES 2-14 Thcsc Examples wcrc carricd out in essentially the same manncr as that described in Example 1, except wre stated. In each case, the aqueous layer containing acids produced by stage 1 had a pH between 7.5-8.5. The various parameters were as defined and calculated with reference to Example 1. EXAMPLE 2 0.6/1 equivalent ratio of alkali/O(-acids at 5% W/V acids concentration. A crude liquid CO2 extract of hops (from the Bullion hops variety, weighing 200 gms, and containing 40% acids as determined by LCV) was added to a stirred solution of potassium carbonate (18.4 gms in 1600 mls deionised water). This mixture was refluxed for 30 mins, the steam volatile hop oils being collected in a cohobation head (6.6 mls collected). The mixture was then transferred into a separating funnel while still hot and the two phases separated off. The upper, organic, layer, containing mainly the acids, amounted to 114 gms. The lower, aqueous, phase, containing mainly the C(-acids, was separated from the upper layer and transferred to a pressure reactor. The Acids were then subjected to boiling at about 135 C for 6 mins under a pressure which as initially about 30 psi (2.1 x 105 Pa), but rose to about 40 psi (2.8 x 105Pa) during the reaction. This resulted in complete isomerisation to iso-GU-acids. The reaction mixture was quenched rapidly by reduction of pressure and cooled. The cooled iso-oC-acids solution was then chilled by refrigeration, filtered through kieselguhr and concentrated up under vacuum to give a pale yellow isomerised extract (308.5 gms). The product was analysed, as previously described, to provid the following results:- Concentration of iso- W-acids 21.8E w/w Total resins 23.3s w/w % Purity 93.7% Overall yield 84.0% pH of 1% solution 7.6 Haze value " " " 1.6 EBC units EXAMPLE 3 0.6/1 equivalent ratio of alkali/&alpha;-acids at 5% W/V acids concentration. A crude liquid CO2 hop extract resin (200 gms) of the type used in Example 2 was added to a stirred solution of potassium carbonate (18.4 gms in 1600 mls water). The mixture was refluxed (30 min), steam volatile oils being collected in a cohobation head (7.0 mls collected), and finally transferred into a separating funnel. The lower, aqueous, phase was removed for further processing, leaving an upper, organic, phase amounting to 112.8 gms. The aqueous phase was boiled at 40 psi (2.8 x 105 Pa) pressure for 6 mins, cooled, chilled and filtered through kieselguhr followed by concentration under vacuum, to give a final product (301 gms). Product analysis: Concentration of iso-C(-acids 21.5% w/w Total resins 22.4% w/w %Purity 95.9% Overall yield 80.8% pH of 1% solution 7.2 Haze value " II 8.0 EBC units The use of a higher pressure in the isorerisation stage than that of Example 2 led to a lower amount of residual CC-acids. The amount of residual acids was double-checked by HPLC. EXAMPLE 4 0.4/1 equivalent ratio of alkali/&alpha;-acids at 5% W/V acids concentration. A crude liquid CO2 hop extract resin (200 gms) of the type used in Example 2 was added to a solution of potassium carbonate (12.26 gm in 1600 ml water). The mixture was refluxed with stirring for 40 mins, the steam volatile oils being collected in a cohobation head (oils collected - 6.0 mls). The mixture was transferred to a separating funnel. The top, organic, layer amounted to 136.8 gms and the bottom, aqueous, layer was removed and boiled at 30-35 psi (2.1 x 105 - 2.4 x 105 Pa) for 6 mins, cooled, chilled, filtered through kieselguhr and concentrated up to give a final product (243 gms). Product analysis: Concentration of iso--acids 17.6% w/w " Total resins 18.7% w/w % Purity 94.1% Overall yield 53.4% pH of 1% solution 6.5 Haze value " " " 2.12 EBC units The use of a lower equivalent ratio of base/C(-acids in the acids extraction process than that of Example 2 resulted in a loss in overall yield of iso-CX-acids. EXAMPLE 5 0.6/1 equivalent ratio of alkali/c(-acids at 7.5% W/V acids concentration. A crude liquid CO2 hop extract resin (300 gms) of the type used in Example 2 was added to a solution of potassium carbonate (27.6 gms in 1600 ml water). The mixture was refluxed for 40 min with stirring, the steam volatile hop oils being collected in a cohobation head (10.7 mls collected). The mixture was finally transferred to a separating funnel and the aqueous, bottom, layer removed for further processing. The top, organic, layer amounted to 174.0 gms. The aqueous phase was boiled at 30-35 psi (2.1 x 105 Pa) for 6 mins, chilled to 10C, fired through kieselguhr and concentrated up to give 272.5 gm isomerised extract. Product analysis: Concentration of iso-&alpha;-acids 34.G w/w Total resins 35.0! w/w t Purity 97.0 Overall yield 77.2% pH of 1% solution 7.1 Haze value " " " 5.5 EBC units EXAMPLE 6 0.6/1 equivalent ratio of alkali/&alpha;-acids at 10% W/V acids concentration. A crude liquid CO2 hop extract (400 gms) of the type used in Example 2 was added to a stirred solution of potassium carbonate (36.8 gms in 1600 mls water) and refluxed for 40 mins, the steam volatile oils being collected in a cohobation head (12.5 mls collected). The mixture was then transferred to a separating funnel and the bottom, aqueous, phase removed for further processing. The top, organic, layer amounted to 228.6 gms. The bottom, aqueous, phase (pH 7.7) was boiled at 30-38 psi (2.1 x 105- 5 2.6 x 10 Pa) for 6 mins, cooled, chilled and filtered through kieselguhr and finally concentrated under vacuum to give 316.8 gms of an isomerised extract. Product analysis Concentration of iso-&alpha;-acids 38.4% w/w Total resins 40.73% w/w % Purity 94.3% Overall yield 76.0% pH of 1% solution 7.7 Haze value " " 8 8 EBC units EXAMPLE 7 0.6/1 equivalent ratio of alkali/&alpha;-acids at 15% W/V acids concentration. A crude liquid CO2 hop extract (600 gms) of the type used in Example 2 was added to a stirred solution of potassium carbonate (55.2 gms in 1600 mls water). The mixture was refluxed for 40 mins, the steam volatile oils being collected in a cohobation head (19.0 mls collected). The mixture was then transferred to a separating funnel and the bottom, aqueous, layer removed. The top, organic, phase amount to 332.2 gms while the bottom, aqueous, phase (pH 7.9) was boiled at 30-38 psi (2.1 x 105 - 2.6 x 105 Pa) for 7 mins, cooled, chilled, filtered (kieselguhr) and concentrated under vacuum to give an isomerised extract (462.2 gms). Product analysis: Concentration of iso-c(-acids 35.4% w/w Total resins 35.49% w/w % Purity 99.7% Overall yield 68.1% pH of 1% solution 7.8 Haze value II II 11.5 EBC units EXAMPLE 8 0.6/1 equivalent ratio of alkali/C(-acids at 20% W/V Oc-acids concentration. A crude liquid CO2 hop extract resin (800 gms) of the type used in Example 2 was added to a stirred solution of potassium carbonate (73.6 gms in 1600 mls water). The mixture was refluxed for 45 mins, the steam volatile oils being collected in a cohobation head (20 mls collected). The mixture was transferred to a separating funnel. The upper, organic, phase amounted to 450.0. The lower, aqueous, phase (pH 7.7) was boiled at 30-40 psi (2.1 x 105 2.8 x 105 Pa) for 40 mins. The resulting iso-DC-acids solution was cooled and filtered to give a product that was not concentrated up (1722 gms). Product analysis: Concentration of iso-C(-acids 13.9t w/w " Total reins 15.528 w/w % Purity 89.5% Overall yield 74.8% pH of 1% solution 7.2 Haze value " " " 62.5 EBC units For a given isomerisation pressure, solutions of acids containing higher concentrations require a longer isomerisation time and give products having higher haze values (but compare Example 9, where a higher pressure is employed). The longer isomerisation time of 40 mins required in this Example still compares favourably with the period of about 121 hours required for conventional isomerisation processes. EXAMPLE 9 0.6/1 equivalent ratio of alkali/&alpha;-acids at 20% W/V &alpha;-acids concentration. A crude liquid CO2 hop extract resin (800 gms) of the type used in Example 2 was added to a stirred solution of potassium carbonate (73.6 gms in 1600 mls water). The mixture was refluxed for 45 mins, the oils being collected in a cohobation head (22.0 mls collected). The mixture was transferred to a separating funnel. The upper, organic, layer amounted to 449.1 gms. The lower, aqueous, phase (pH 8.0) was boiled at 60-67 psi (4.1 x 105 - 4.6 x 105 Pa) for 6 mins. The resulting iso-CX-acids solution was cooled and filtered to give a product that was not concentrated up (1725 gms). Product analysis : - Concentration of iso-&alpha;-acids 13.7% w/w " Total resins 15.25Ew/w % Purity 89.8% Overall yield 73.8% pH of 1% solution 8.9 Haze value " " " 1.6 EBC units At higher acids concentrations, higher pressures but lower times gave a product low in haze characteristics. EXAMPLE 10 0.6/1 equivalent ratio of alkali/O(-acids at 30% W/V W-acids concentration. A crude liquid CO2 hop extract (1200 gms) of the type used in Example 2 was added to a stirred solution of potassium carbonate (110.3 gms in 1600 mls water). The mixture was refluxed for 1 hour, the steam volatile oils being collected (31.5 mls). The mixture was then separated off, the top, organic, layer weighed (634.1 gms), and the bottom, aqueous, phase (pH 8.0) boiled at 60-67 psi (4.1 x 10 - 4.6 x 10 Pa) for 6 mins. The resulting iso-o < -acids solution was then cooled, chilled and filtered but not concentrated to give an isomerised extract (1583 gms). Product analysis: Concentration of iso-CX-acids 17.6% w/w Total resins 19.52% % Purity 90.2% Overall yield 71.4% pH of 1% solution 8.7 Haze value " " " 4.2 EBC units. EXAMPLE 11 0.5/1 equivalent ratio of alkali/OC-acids at 5% W/V acids concentration. A crude liquid CO2 hop extract (from the Target hops Variety, weighing 147.3 gms, and containing 54.3% acids as determined by LCV) was added to a stirred solution of potassium carbonate (15.3 gms in 1600 mls water) and refluxed for 40 mins. The steam volatile oils were collected (6.7 mls) and the reflux mixture transferred to a separating funnel. The upper, organic, layer amounted to 61.6 gms. The bottom, aqueous, layer (pH 7.6) was boiled at 30-35 psi (2.1 x 105 - 2.4 x 105 Pa) for 10 minutes. The resultant iso-o(-acids solution was cooled, chilled and filtered (through kieselguhr) and concentrated up to 396.2 gms. Product analysis: Concentration of iso-c(-acius 16.338 w/w " Total resins 16.46t w/w % Purity 99.2% Overall yield 80.8% pH of 1% solution 7.4 Haze value " " " 2.0 EBC units EXAMPLE 12 0.6/1 equivalent ratio of alkali/ct-acids at 15% hl/V &alpha;- acids concentration. A crude liquid CO2 hop extract (600 gms) of the type used in Example 2 was added to a stirred solution of sodium carbonate (42.4 gms in 1600 mls water) and refluxed for 40 mins. The steam volatile oils were collected and amounted to 14.0 mls. The reflux mixture was finally transferred to a separating funnel. The upper, organic, phase (389.8 gms) was removed and the bottom aqueous phase (pH 7.6) was boiled at 30-35 psi (2.1 x 105 - 2.4 x 105 Pa) for 7 mins. The resultant iso-O(-acids solution was then chilled, filtered and concentrated up. An organic phase separated out due to "salting out". This would not redissolve in water indicating the lower solubility of the sodium salt of the iso-&alpha;-acids. The aqueous phase after concentration had the following analysis: Concentration of iso-Ct-acids 9.7% w/w Total resins 9.8% w/w % Purity 98.9% pH of 1% solution 7.2 Haze value " " " 1.4 EBC units The yield of iso-X-acids was difficult to measure because of the abovementioned salting out and was not recorded. EXAMPLE 13 1.2/1 Molar (0.6/1 equivalent) ratio of alkali/ &alpha;-acids at 15% W/V acids corcentration. A crude liquid hop extract (600 gms) of t type used in Example 2 was added to a stirred solution of potassium hydroxide (44.9 gms in 1600 mls water) and refluxed for 40 mins. The steam volatile oils were collected and amounted to 15.5 mls. The reflux mixture was finally transferred to a separating funnel. The upper, organic, phase amounted to 358.5 gms. The bottom, aqueous, phase (pR 8.1) was boiled at 30-38 psi (2.1 x 105 2.6 x 105 Pa) for 14 mins. The cooled, chilled solution was then filtered (through kieselguhr) and concentrated to give a final product (521.5 gms). Product analysis: Concentration of iso-Q(-acids 31.178 w/w Total resins 32.23% w/w % Purity 96.7% Overall yield 72.0% pH of 1% solution 7.5 Haze value " " " 8.7 EBC units EXAMPLE 14 (Best Method) 1/1 Molar (0.5/1 equivalent) ratio of alkali/-acids at 15% W/V a-acids concentration. A crude liquid CO2 hop extract (from the Target hops Variety, weighing 400 gms and containing 43.1% acids as determined by LCV) was added to a stirred solution of potassium bicarbonate (47.8 gms in 1149 mls water) and refluxed for 1 hour. The steam volatile oils were collected (7.6 mls) and the reflux mixture finally transferred to a separating funnel. The top, organic, layer was removed (223.7 gms). The bottom, aqueous, layer was boiled at a pressure of 30-35 psi (2.1 x 105 - 2.4 x 105 Pa) for 30 mins, cooled, filtered (through Hyflo) and concentrated up to give product (554.9 gms). Product analysis: Concentration of iso-c(-acids 24.2e w/w Total resins 23.89 w/w % Purity 101.6t* pH of 1% solution 6.5 Haze value " " " 7.2 EBC units *This value represented about 100% purity within the limits of experimental error, and this Example shows the excellent purity achievable using potassium bicarbonate. As can be seen from the above, processes embodying the invention allow a particularly simple and efficient extraction and isomerisation of &alpha;-acids from crude hop extracts. No use of organic solvent need be made. The process employs only low concentrations of alkali relative to the acids concentration during all stages. Indeed, it is preferred to operate also at low aqueous acids concentrations and low aqueous alkali concentrations throughout both the extraction and isomerisation stages. An isomerised product of high purity that can be added to beer with no significant increase in haze can be obtained.

Claims: CI.AMs :- I. A process for the extraction of -acids from, a crude hop extract, which process comprises boiling a mixture of the crude extract with an aqueous alkali, the equivalent ratio, in the mixture, of alkali: acids in the crude hop extract being no more than 1.2:1, to form an aqueous layer containing extracted &alpha;-acids and an organic layer containing acids, and separating the aqueous layer and the organic layer from one another. 2. A process according to claim 1, wherein the crude hop extract is an extract obtained by treating hops with carbon dioxide in liquid form or at a supercritical pressure. 3. A process according to claim 1 or claim 2, wherein the equivalent ratio of alkali: acids in the crude hop extract is such as to provide an excess of acids. 4. A process according to claim 3, wherein the equivalent ratio of alkali: acids in the crude hop extract is from 0.4:1 to 0.8:1 inclusive. 5. A process according to any preceding claim, wherein the alkali is potassium carbonate, bicarbonate or hydroxide, or sodium carbonate, bicarbonate or hydroxide. 6. A process according to any preceding claim, wherein the concentration of alkali in the said mixture of the crude hop extract and aqueous alkali is from 0.02 to 1 M inclusive. 7. A process according to any preceding claim, wherein the &alpha;-acids concentration in the said mixture of the crude hop extract and aqueous alkali is from 2 to 30 grams inclusive per 100 mls of aqueous alkali. 8. A process according to any preceding claim, wherein the said mixture is boiled for a period of from 15 minutes to 1 hour inclusive. 9. A process according to any preceding claim, wherein the separation of the aqueous and organic layers from one another is effected at a temperature of from 40 to 800C inclusive. 10. An aqueous extract derived from hows, which extract contains acids at least a major proportion of which o(-acids are unisomerised and which extract is essentially free from acids. 11. An organic extract derived from hops, which extract contains acids and is essentially free from acids and iso-C(-acids. 12. A process for preparing iso-O(-acids, which process comprises boiling an aqueous medium containing unisomerised &alpha;-acids in solution in the aqueous medium characterised in that the aqueous medium has a pH of from 7-8.5 inclusive and the process is carried out at a pressure above atmospheric pressure. 13. A process according to claim 12, wherein the pressure is from 1.3 x 105 to 4 x 105 Pa inclusive. 14. A process according to claim 12 or 13, wherein the pH is 7-8. 15. A process according to any one of claims 12 to 14, wherein thec < -acids concentration in the aqueous medium is not more than 15 grams acids per 100 ml. of aqueous medium. 16. A process according to any one of claims 12 to 15, which includes the additional step of increasing the concentration of the iso-C(-acids in the resultant product by concentration thereof under reduced pressure to provide an iso-O(-acids concentrate. 17. A process for the preparation of iso-&alpha;-acids from a crude hop extract, which process comprises (i) boiling a mixture of the crude extract with an aqueous alkali, the equivalent ratio, in the mixture, of alkali: Cc-acids in the crude hop extract being no more than 1.2:1, to form an aqueous layer containing extracted Ct-acids and an organic layer containing acids, (ii) separating the aqueous and organic layers fro one another, (iii) optionally diluting the aqueous layer, and (iv) boiling the aqueous layer at a pressure above atmospheric pressure and a pH of from 7 to 8.5 inclusiv isomerise the said extracted acids therein. 18. A process for extracting acids from hops and iso ising the extracted acids, which process comprises, (a) treating the hops with carbon dioxide, which carbon dioxide is in liquid tory, to form a solution of a c.d hop extr-:t in the carbon dioxide, (b) separating the crude hop extract from the carbon dioxide, (c) boiling a mixture of the crude hop extract with an aqueous alkali, the equivalent ratio, in the mixture, of alkali: -acids in the crude hop extract being no more than 1.2:1, to form an aqueous layer containing extracted &alpha;-acids an an organic layer containing p-acids, (d) separating the aqueous and organic layers from one another, (e) optionally diluting the aqueous layer, and (f) boiling the aqueous layer at a pressure above atmospheric pressure and a pH of from 7 to 8.5 inclusive to isomerise the said extracted O(-acids therein. 19. A process for the preparation of oxidized p-acids from a crude hop extract, which process comprises (i) boiling a mixture of the crude hop extract with an aqueous alkali, the equivalent ratio, in the mixture, of alkali: Cc-acids in the crude hop extract being no more than 1.2:1, to form an aqueous layer containing extracted o(-acis and an organic layer containing acids, (ii) separating the aqueous and organic layers from one another, and (iii) extracting the acids from the organic layer by treatment thereof with an alkaline solution, and (iv) oxidizing the p-acids by treating them with an oxidizing agent. 20. A process for extracting acids from hops and oxidizing the acids, which process comprises, (a) treating the hops with carbon dioxide, which carbon dioxide is in liquid form, to form a solution of a crude hop extract in the carbon dioxide, (b) separating the crude hop extract from the carbon dioxide, (c) boiling a mixture of the crudc hop extract with an aqueous alkali, the equivalent ratio, in the mixture, of alkali: acids in the crude hop extract being no morc than 1.2: :1, to form an aqueous layer containing extracted CX-acids and an organic layer containing acids, (d) separating the aqueous and organic layers from one another, (e) extracting the acids from the organic layer by treatment thereof with an alkaline solution, and (f) oxidizing the acids by treating them with an oxidizing agent.

Inventors: PATEL, CHANDRAKANT CHHAGANBHAI
Applicants: THE ENGLISH HOP PROCESSING COMPANY LTD
Application year: 1985
Main classification: C12C9
IPC codes: C12C3