GB1597703A

GB1597703A - Hop extracts

Info

Publication number: GB1597703A
Application number: GB2521278A
Authority: GB
Original assignee: Albright and Wilson Ltd
Current assignee: Solvay Solutions UK Ltd
Priority date: 1978-05-31
Filing date: 1978-05-31
Publication date: 1981-09-09
Also published as: DE2836823A1

Description

(54) HOP EXTRACTS

(71) We, ALBRIGHT & WILSON preferably obtained as a solution in an LIMITE, A British Company of Albright & essentially non-aqueous solvent. The solution 5 Wilson House, Hagley Road West Oldbury, may be prepared in any of the known ways, Wailey West Midlands, do hereby declare the such as those described in our aforesaid patent 5 invention, for which we pray that a Patent may or in B. P. 1161787. be granted to us and the method by which it is The hops, or lupulin resin physically -"*rformed to be particularly described separated thereform may optionally be ground swing statement :- and extracted with the solvent, and insoluble -hoD extracts and is material separated thereform. Alternatively, in in our the hops may be extracted with any other convenient solvent for alpha-acids, the extract P E- from the extracting solvent, e. g. by c 1nend, nent. EtS c'-tfer and redissolved in the ou General, C'FIC . ;-. c, Tn rez salt. 1 ne,. ~ metric amounts. to patent IVO 1597702.

25 We have now discovered Tlla. 702. of hop extract in an essentially non-aqur+ phase may most conveniently be effected tl. ~ means of a small stoichiometic excess of absence o, Bas 9406313 anvdrous alkali, especially potassium hydro-is sufficiently volas 3/3 xide or preferably carbonate, which permits the product to be recovered substantially free from beta-acids.

According to this invention an alpha-acidscontaining hop extract is isomerised by contacting the extract or a solution thereof in an essentially non-aqueous water-immiscible solvent with an essentially non-aqueous alkali to form essentially non-aqueous, resinous alkali metal salts of the alpha-acids or an essentially non-aqueous solution thereof, heating the alpha-acid salts to form iso-alphaacid salts, and recovering the iso-alpha-acid salts by partitioning the isomerised extract between a water immiscible substantially non polar solvent and an aqueous phase having a pH of from 8.2 to 9.5.

The alpha-acid-containing extract is by evaporation, without subian... degradation of the. extract. rt is preferreu that neither the hops nor the extract should be exposed to any strong aqueous alkaline solvents at this stage. Acidic extracting solvents may be used but are generally inconvenient.

The extract may be subjected to one or more purification stages, such as have been proposed in the prior art such as chilling the solution in the extracting, or any other, solvent to precipitate waxes, or redissolving the extract in aqueous methanol to reject fixed oils, however such pretreatment are not essential.

The partitioning step is carried out with a partitioning solvent which is water immiscible and has a general non-polar (54) HOP EXTRACTS (71) We, ALBRIGHT & WILSON LlMrrED, A British Company of Albright & Wilson House, Hagley Road West Oldbury, Wailey West Midlands, do hereby declare the invention, for which we pray that a Patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement :- This invention relates to hop extracts and is a modification of the method described in our British Patent No. 1423129, and is divided out of our application No. 31619/76. (Serial No.

1597702) Our aforesaid specification claims a method for isomerisation of alpha-acids which comprises contacting a solution of a hop extract in a water immiscible organic solvent with a base such as an oxide, hydroxide or carbonate of an alkaline earth metal or zinc to form the corresponding alpha-acid salt and heating the alpha-acid salt in the water immiscible solvent to form an iso-alpha-acid salt. The base is used in substantially stoichiometric amounts.

We have now discovered that isomerisation of hop extract in an essentially non-aqueous phase may most conveniently be effected by means of a small stoichiometic excess of anydrous alkali, especially potassium hydroxide or preferably carbonate, which permits the product to be recovered substantially free from beta-acids.

According to this invention an alpha-acidscontaining hop extract is isomerised by contacting the extract or a solution thereof in an essentially non-aqueous water-immiscible solvent with an essentially non-aqueous alkali to form essentially non-aqueous, resinous alkali metal salts of the alpha-acids or an essentially non-aqueous solution thereof, heating the alpha-acid salts to form iso-alphaacid salts, and recovering the iso-alpha-acid salts by partitioning the isomerised extract between a water immiscible substantially nonpolar solvent and an aqueous phase having a pH of from 8.2 to 9.5.

The alpha-acid-containing extract is preferably obtained as a solution in an essentially non-aqueous solvent. The solution may be prepared in any of the known ways, such as those described in our aforesaid patent or in B. P. 1161787.

The hops, or lupulin resin physically separated thereform may optionally be ground and extracted with the solvent, and insoluble material separated thereform. Alternatively, the hops may be extracted with any other convenient solvent for alpha-acids, the extract recovered from the extracting solvent, e. g. by evaporating the latter, and redissolved in the essentially non-aqueous solvent.

Suitable extracting solvents include aromatic hydrocarbons such as benzene, toluene, or xylene, halohydrocarbons such as methylene chloride or trichlorethylene, and aliphatic hydrocarbons such as petroleum or hexane. It is also possible to use alcohols such as methanol or ethanol, ketones such as acetone, or any other organic liquid capable of dissolving alpha-acids from hops, or liquefied carbon dioxide. Preferably, if the extracting solvent is different from the solvent with which the base is contacted, or the contacting step is to be performed in the absence of a solvent, the extracting solvent is sufficiently volatile to permit its removal by evaporationrwithout substantial degradation of the extract. It is preferred that neither the hops nor the extract should be exposed to any strong aqueous alkaline solvents at this stage. Acidic extracting solvents may be used but are generally inconvenient.

The partitioning step is carried out with a partitioning solvent which is water immiscible and has a general non-polar character so that it dissolves alpha-acids and iso-alpha-acids, but dissolves their salts less readily than does water. The solvent may be any of those described in our aforesaid British Patent, and is preferably a hydrocarbon, most preferably an aliphatic hydrocarbon, e. g. a petroleum or terpene hydrocarbon. Hop essential oils are particularly preferred. Usually on technical grounds saturated hydrocarbons are preferred, but olefins are operative and may sometimes be the solvent of choice on economic grounds. Alternatively, aromatic hydrocarbons or halohydrocarbons may be used.

It is preferred to contact the alkali with a solution of the alpha-acid-containing extract in an essentially non-aqueous, water immiscible, substantially non-polar solvent, which is most conveniently the same as the partitioning solvent. In particular, it is preferred to isomerise in the presence of the solvent and recover the iso-alpha-acids by adding water to the mixture. Where the isomerisation is performed in the presence of a solvent, the solvent preferably has a boiling point greater than 100 C and usually less than 200 C, most preferably 105 C to 150 C e. g. 110 to 130 C.

Solvents boiling below 1 00gC are not recommended, since it is preferred to isomerise at temperatures above 100 C, however, solvents boiling above 80 C could be used if heating under pressure is feasible, or if a slow rate of isomerisation can be tolerated. Solvents boiling above 200 C are operative, but are less readily recoverable, and usually less convenient.

Typical examples of suitable solvents include paraflns, e. g. petroleum fractions having the desired boiling point, aromatic hydrocarbons such as toluene or more preferably xylene, and terpene hydrocarbons such as limonene or hop oils. Generally speaking any liquid, saturated or aromatic hydrocarbon having a boiling point in the preferred ranges may be present during isomerisation. Olefinic hydrocarbons may cause difficulties.

Halocarbons such as tetrachloroethane or chlorobenzene are operative but less preferred.

The proportion of the hop extract to the essentially non-aqueous solvent is not critical provided that there is sufficient solvent to dissolve the beta-acids and other less water soluble hop resins, but generally speaking the higher the concentration, the more commercially attractive is the process.

The isomerisation is preferably effected with an essentially non-aqueous alkali, preferably potassium hydroxide or most preferably potassium carbonate. Sodium alkalis are less preferred. Most preferably an anhydrous alkali is used.

The isomerisation is preferably performed at temperatures above 100 C e. g. temperatures at or near the boiling point of any solvent which may be present. Lower temperatures are possible, but are commerically unattractive due to the length of time required. Preferred temperatures for isomerisation are 100 to 150 C e. g. 110 to 140 C. At such temperatures the reaction can usually be taken to completion within 30 minutes.

The isomerisation is effected under essentially non-aqueous conditions. It will be understood that some water will inevitably be present, since water is evolved when the base reacts with the alpha-acids, however, at our preferred isomerisation temperatures evaporation will prevent the formation to any significant extent, of a separate aqueous phase, at normal or reduced pressures. We do not, however, exclude the possibility of carrying out the reaction in an autoclave, under which conditions a separate aqueous phase may be present, provided that there is no sufficient water to dissolve more than a minor proportion of the alpha-acids salts, so that the isomerisation proceeds substantially in the resin phase or in its organic solution.

The presence during the isomerisation of traces of excess moisture up to about 3% by weight, typically 0.5 to 1.5% by weight, is not appreciably disadvantageous, but the benefits of the invention are progressively reduced as the amount of water is increased sufficiently to form a distinct aqueous layer into which significant proportions of alphaacid may be extracted. The term"essentially anhydrous"as used herein means that the amount of water present should not be such that the isomerisation occurs while a substantial proportion of the alpha-acids are in aqueous solution.

The amount of anhydrous alkali added is at least stoichiometric and not greater than 140% of stoichiometric amount. It is preferably such as to produce a pH, when the isomerised solution is subsequently washed with water, sufficient to extract the isoalpha-acids into the aqueous phase, but is not sufficient to extract the weaker beta-acids.

The optimum pH required depends on the affinity of the isomerising solvent for the iso-alpha-acids and the proportion of other hop resins and oils'present. Pure iso-alphaacids can be extracted from petroleum at pH's between 7 and 8. However, we have now discovered that in the presence of substantial amount of other resins, or in stronger solvents, higher pH's of at least 8 are required. In practice we usually prefer to achieve a final pH of 8.2 to 9.5, preferably 8.5 to 9.2. Typically an excess of the alkali is used over the stoichiometric amount based on the alpha-acids, preferably 20 to 40% excess e. g. a 30 to 35% excess.

If sufficient alkali is not added during isomerisation, and the subsequent aqueous washing does not efficiently extract the isoalpha-acids, additional alkali is added at that stage to bring the pH to the required level.

Excessive amounts of alkali cause extraction of relatively insoluble resinous material on subsequent washing, so negating the benefit of this invention and also may cause degradatio of the iso-alpha-acids and generation of off flavours, In calculating the stoichiometry of the alkali, carbonates should be regarded as diacidic bases.

According to the preferred method of carrying out our invention a solution of the hop extract in a non-polar (e. g. hydrocarbon) solvent is contacted with from 100 to 140% of the stoichiometric amount of an anhydrous alkali, to precipitate an alkali metal salt of alpha-acid as a resin phase which is isomerised by heating in the presence of the solvent and the absence of a separate aqueous phase, and the mixture of resin and solvent is then washed with sufficient water to dissolve the resin, and the pH, if necessary, is adjusted to between 8.2 and 9.5.

It will be obvious to those skilled in this art that a similar result can also be achieved, without departing from the invention by the equivalent method of heating the resin separately from the solvent or by including a minor amount of a polar solvent such as methanol or ethanol in the solvent so as to maintain the alpha-acid salts in solution in the solvent during the isomerisation, or by heating with a minor amount of water present. It is also possible to prepare a resinous hop extract comprising free alpha-acids, by extracting hops with a volatile solvent such as liquid carbon dioxide and evaporating off the solvent, and dissolving the substantially non-aqueous alkali, such as anhydrous potassium carbonate, in the resinous extract. The alkaline extract may then be heated to isomerise the alphaacids and finally partitioned between a water immiscible substantially non-polar solvent, such as hop oil, and an aqueous phase having a pH from 8.2 to 9.5.

The preparation of the final product from the isomerised resin may be carried out in two stages, the first stage using sufficient water to recover substantially all the iso-alpha-acids as a dilute aqueous solution of their salts and the second comprising precipitating the iso-alphaacids from the aqueous solution with an alkaline earth metal, zinc or aluminium or preferably extracting them with a polar water immiscible solvent such as isobutanol, ethyl acetate or methyl isobutyl ketone in order to transfer them to more concentrated aqueous solution as described in B. P. 1161787. The final product is preferably an aqueous solution of potassium iso-alpha-acid salts, preferably having a concentration of from 10% to 70% by weight of the iso-alpha-acid salts, most preferably 20% to 60% by weight.

Preferably the final product has a pH of from 8.8 to 9.0.

Aqueous extracts prepared according to our invention can be stored, and are preferably used by diluting them to less than 5% e. g. about 2% by weight of iso-alpha-acid, with distilled water. The diluted extract is then dispersed into cold fermented beer to provide the desired degree of bitterness.

The invention is illustrated by the following examples :- 'EXAMPLE 1 275 gm of methylene chloride extract of hops (containing 100 gm alpha-acids) was dissolved in 700 ml limonene. The solution was decanted off the residual solid which was washed with 100 ml limonene. The combined solutions were acidified by shaking with a solution consisting of 100 ml methylated spirit, 50 ml water and 50 ml concentrated hydrochloric acid, and the mixture was allowed to separate. The lower layer was discarded. The limonene solution was heated with 25.6 gm of dry potassium carbonate (a 35% excess) at 100-200 C for 30 minutes, traces of water and methylated spirits being allowed to distill off. One litre of water was added over 30 minutes, the mixture was brought to the bofl and allowed to separate.

The aqueous layer was recovered, backwashed with 100 limonene, and filtered. 5 gm oleic acid was added to suppress gushing and the pH of the solution was raised to 10.3 with potassium carbonate. The solution was then extracted with three portions of ethyl acetate (500 ml, 300 ml, 200 ml) and the combined extracts desolventised by adding water while evaporating off the solvent to provide an aqueous solution containing 30% iso-alpha acid at a pH of 8.8.

The product weighed 240 gms representing a yield of 72% by weight.

EXAMPLE 2 232 gm of methylene chloride extract of hops (43. 2% alpha-acids) was dissolved in 700 ml limonene. The solution was decanted off the insoluble residue, which was washed with 100 ml limonene. The combined limonene solution was stirred with 25.6 gm of solid potassium carbonate (a 35% excess over the alpha-acids present). The mixture was heated at 120'C for 20 minutes and allowed to coolto 100 C. I litreofwaterwasadded, while the temperature was maintained at 100 C. The mixture was allowed to separate and the aqueous layer (pH 9.2) was recovered, washed with 100 ml limonene and filtered.

5 gm oleic acid and 50 ml of 25% potassium carbonate solution were added, raising the pH to 10.4, and the solution was extracted with ethyl acetate (500 ml, 300 ml, 200 ml).

The extract was distilled under reduced pressure to remove the solvent. The residue was dissolved in water and 1. 5 ml of 25% potassium carbonate was added so that the pH of a 5% solution was 8.8. The product was concentrated to 142 gm. It contained 37.6% iso-alpha-acids i. e. a yield of 53.3%.

Claims

WHAT WE CLAIM IS :- 1. A method for the preparation of isomerised hop extract which comprises contacting an alpha-acid containing hop extract or a solution thereof in an essentially nonaqueous water immiscible solvent with an essentially non-aqueous alkali to form essentially non-aqueous, resinous alkali metal salts Qf the alpha-acids or an essentially non-aqueous solution thereof, heating the alpha-acid salts to form iso-alpha-acid salts and recovering the isoalpha-acid salts by partitioning the isomerised extract between a water immiscible sub stantially non-polar solvent and an aqueous phase having a pH from 8.2 to 9.5.
2. A method according to claim 1, wherein the isomerisation occurs in the absence of a separate aqueous phase.
3. A method according to either of claims I and 2, wherein the alkali is contacted with a solution of the alpha-acid containing hop extract in a water immiscible non-polar solvent to precipitate salts of alpha-acids therefrom.
4. A method according to claim 3, wherein the solvent is a hydrocarbon solvent.
5. A method according to either of claims 3 and 4, wherein the precipitated resin is isomerised in the presence of the solvent.
6. A method according to any of claims 3 to 5, wherein the solvent has a boiling point between 100 and 200 C.
7. A method according to claim 6, wherein the solvent has a boiling point of between 105 and 150 C.
8. A method according to either of claims 6 and 7, wherein the isomerisation is affected at a temperature of from 100 C to the boiling point of the solvent.
9. A method according to any of the claims 3 to 8, wherein the partitioning of the isomerised extract is effected by adding water to the mixture of isomerised resin and water immiscible solvent.
10. A method according to any foregoing claim, wherein the proportion of alkali is from 100 to 140% of the stoichiometric amount based on the proportion of alpha-acid.
11. A method according to any foregoing claim, wherein the alkali is potassium carbonate.
12. A method according to any foregoing claim, wherein the partitioning is effected at a pH of between 8.5 and 9.2.
13. A method according to either of claims 11 and 12, wherein the amount of alkali contacted with the alpha-acids is from 120 to 140% of the stoichiometric amount, and the pH during the partitioning step is adjusted if required by addition of further alkali.
14. A method according to claim I, which comprises extracting hops with liquid carbon dioxide recovering the hop extract from the carbon dioxide, contacting the recovered extract with alkali to form alpha-acid salts, isomerising the alpha-acid salts by heating and partitioning the isomerised extract between water and a water immiscible non-polar solvent.
15. A method according to claim 14, wherein the solvent is hop oil.
16. A method according to either of claims 14 and 15, wherein the amount of alkali is from 100 to 140% of the stoichiometric amount based on the quantity of alpha-acid.
17. Isomerised hop extract prepared by the method of any foregoing claim.