GB1597702A - Hop extracts - Google Patents

Description

(54) HOP EXTRACTS (71) We, ALBRIGHT AND WILSON LIMITED, a British Company of P.O. Box 3, Oldbury, Warley, West Midlands, England do hereby declare the invention, for which we pray that a Patent may be granted to us and perrformed 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.

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 an oxide, hydroxide or carbonate of an alkaline earth metal or zinc to form the corresponding alphaacid 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 alpha-acids dissolved in a water immiscible solvent may most conveniently be effected by means of a particular stoichiometric excess of anhydrous alkali, especially potassium hydroxide or preferably carbonate.

According to this invention alpha-acids are isomerised by contacting a solution thereof in a water immiscible, substantially non-polar, solvent (hereinafter referred to as the isomerisation solvent) with a substantially anhydrous alkali to form alkali metal salts of the alpha acids,heating the substantially anhydrous alphaacid salt to form iso-alpha-acid salts, and recovering the iso-alpha-acid salts by aqueous extraction, at a pH of from 8.0 to 9.5.

The solution of the alpha-acid containing extract in the isomerising solvent may be prepared in any of the known ways, such as those described in our aforesaid patent or in BP. 1161787. The hops, or lupulin resin physically separated therefrom may optionally be ground and extracted with the isomerising solvent, and insoluble material separated therefrom. Alternatively the hops may be extracted with any other convenient solvent for alphaacids, the extract recovered from the extracting solvent, e.g. by evaporating the latter, and redissolved in the isomerising solvent.

Suitable extracting solvents include aromatic hydrocarbons such as benzene, toluene, or xylene, halo-carbons 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. Preferably, if the extracting solvent is different from the isomerising solvent, the former is sufficiently volatile to permit its removal by evaporation, without 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 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 isomerising solvent to precipitate waxes, or redissolving the extract in aqueous methanol to reject fixed oils, however such pretreatments are not essential.

The isomerising solvent is water immiscible and has a generally non-polar character so that it dissolves alpha-acids and iso-alpha-acids, but dissolves their salts less readily than does water.

The isomerising 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. 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 halocarbons may be used. Preferably the solvent has a boiling point greater than 80 C and usually less than 2000most preferably between 1000C and 1500Ce.g. 110 to 1300C. Solvents boiling below 80"C are not recommended, since it is preferred to isomerise at temperatures above 80"C, however they 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 isomerising solvents include paraffins, e.g. petroleum fractions having the desired boiling point, aromatic hydrocarbons such as toluene or more preferably xylene, and terpene hydrocarbons such as limonene. Generally speaking any liquid saturated or aromatic hydrocarbon having a boiling point in the preferred ranges may be used as the isomerising solvent. Olefinic hydrocarbons may cause difficulties. Halo carbons such as tetra chloroethane or chlorebenzene are operative but less preferred.

The concentration of the hop extract in the isomerising solvent is not critical, but generally speaking the higher the concentration, the more commercially attractive is the process.

The isomerisation is effected with substantially anhydrous alkali, preferably potassium hydroxide or most preferably potassium carbonate. Sodium alkalis are less preferred.

The isomerisation is preferably performed at temperatures above 100 C e.g. temperatures at or near the boiling point of the isomerising solvent. Lower temperatures are possible, but are commercially unattractive due to the length of time required. It is even possible to isomerise very slowly at ambient temperature. Preferred temperatures for isomerisation are between 100 and 1500C eg. 110 to 1400C. At such temperatures the reaction can usually be taken to completion within 30 minutes.

The presence during the isomerisation of traces of moisture up to about 3% by weight, typically 0.5 to 1.5% by weight, is desirable, but the benefits of the invention are progressively reduced as the amount of water is increased sufficiently to form a distinct aqueous solution containing significant proportions of alpha-acid salts. The term "substantially anhydrous" as used herein means that the amount of water present should not be such that the isomerisation of a substantial proportion of the salts of the alpha-acids occurs in solution in water.

The amount of substantially anhydrous alkali added 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 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-alpha-acids can be extracted from petroleum at pH's between 7 and 8. However in the presence of substantial amounts of resin, or in stronger solvents, higher pH's are usually required. In practice we usually prefer to achieve a final pH of 8.0 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 50% excess e.g. a 30 to 40% excess.

If sufficient alkali is not added the isomerisation is slower and may not go to completion, and the subsequent aqueous washing does not efficiently extract the iso-alpha-acids unless additional alkali is added at that stage. Excessive amounts of alkali can cause degradation of the iso-alpha-acids, generation of off flavours and extraction of relatively insoluble resinous material on subsequent washing, as well as negating much of the benefit of this invention.

In calculating the stoichiometry of the alkali, carbonates should be regarded as diacidic bases.

The preparation of the final product may be carried out in two stages, the first stage using sufficient water to recover substantially all the iso-alpha-acids as a dilute solution of their salts and the second comprising precipitating the isoalpha-acids with an alkaline earth metal, zinc or aluminium or extracting them with a polar water immiscible solvent such as isobutanol, ethyl acetate or methyl isobutyl ketone in order to transfer them to a more concentrated aqueous solution as described in BY. 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 provided 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 - 2000C for 30 minutes, traces of water and methylated spirits being allowed to distil off. One litre of water was added over 30 minutes, the mixture was brought to the boil 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 1 200C for 20 minutes and allowed to cool to 100 C.1 litre of water was added, 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 A, 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%.

WHAT WE CLAIM IS: 1. A method for the isomerisation of alphaacids which comprises contacting a solution thereof in a water-immiscible substantially nonpolar solvent with a substantially anhydrous alkali to form alkali metal salts of the alphaacids,heating the substantially anhydrous alphaacid salts to form iso-alpha-acid salts and recovering the iso-alpha-acid salts by aqueous extraction at a pH of from 8 - 9.5.

2. A method according to claim 1 wherein the solvent is a liquid hydrocarbon.

3. A method according to claim 2 wherein the solvent is an aliphatic solvent.

4. A method according to claim 3 wherein the solvent is a petroleum or terpene hydrocarbon.

5. A method according to any foregoing claim wherein the solvent boils between 80" and 2000C.

6. A method according to claim 5 wherein the solvent boils between 100" and 1500C.

7. A method according to any foregoing claim wherein the substantially anhydrous alkali is a potassium alkali.

8. A method according to claim 7 wherein the substantially anhydrous alkali is potassium carbonate.

9. A method according to any foregoing claim wherein the isomerisation is effected at a temperature between 1000 and 150"C.

10. A method according to any foregoing claim wherein the isomerisation occurs in the presence of from 0.5 - 1.5% by weight of water based on the total reaction mixture.

11. A method according to any foregoing claim wherein the amount of alkali added to the alpha-acids is sufficient to produce, on subsequent contact with water a pH sufficient to extract the iso-alpha-acids into the aqueous phase but not sufficient to extract beta-acids.

12. A method according to claim 11 wherein the iso-alpha-acids are extracted by washing with water and the amount of alkali added to the alpha-acids is sufficient to produce a pH in said water after said washing of from 8.5 - 9.2.

13. A method according to any foregoing claim wherein the alkali is potassium carbonate which is added in an excess of from 20 - 50% over the stoichiometric proportion based on the alpha-acids calculated on the assumption that carbonate is a di-acid base.

14. A method according to any foregoing claim substantially as described herein with reference to either of the examples.

15. Hop extracts whenever prepared by the method of any foregoing claim.

16. Beer containing a hop extract according

Claims (1)

1. to claim 15.