GB2177693A - Method of producing an iso-humulate concentrate - Google Patents

Abstract

A method of producing a concentrate for use in providing a bitter flavour for beer, comprising acidifying a solution of iso-humulate to form iso-humulone, separating the isohumulone from the residual reaction mixture and reacting the separated iso-humulone with an aqueous alkali at a concentration sufficient to produce a final concentration of iso-humulate of over 20%. <IMAGE>

Description

SPECIFICATION Method of producing a concentrate This invention relates to a method of producing a concentratefor use in providing a bitterflavourfor beer.

Hops are used in the manufacture ofbeerfora variety of reasons, notably to produce certain distinctive elements oftasteforthe beer. The hops contain acids or humulones, which on isomerisation to isohumulones produce a bitterflavourforthe beer, p-acids or lupulones, which are currently not actively used in the manufacture and do not appear in the final form ofthe beer, and essential oils which impartother distinctive flavours to the beer.

It is desirable to separate the humulonesfromthe lupulones during the isomerisation stage, and this has been described for example in UK Patent No. 1,576,729 in which a liquid carbon dioxide extract of hops is treated with potassium carbonate to provide an alkaline medium, boiling the resulting reaction mixture is boiled and then the pH is lowered with carbon dioxide. The lupulones precipitate out from the isomerised humulone solution and can then be separated.

The free iso-humulone solution can be added directly into the brewing process, butthe presentapplicants have recognised that it could be sold commercially if it could be concentrated. Afterthe separation of lupulonesthe iso-humulones are in about 3% solution in aqueous potassium carbonate, in the form of potassium iso-humulate, but itwould be impractical fortransport and storage reasonsto offersuch a dilute solution for sale.

The obvious step in concentrating the solution would be to evaporate the unwanted bu I k of the water, but on attempting this it was found that when the iso-humulateswere at 10-12% concentration separation took place into an aqueous phase and an oily phase. The latter contained a high concentration of iso-humulate, buta considerable volume of iso-humulate remained in the aqueous phase sotheyield at that point ways not acceptable. Further evaporation of the water resulted in the potassium carbonate being driven into the oily phase thereby reducing the purity of the product.

On a laboratory scale it was possible to obtain 30-40% concentration of the iso-humulate at reasonableyield when the aqueous and oily phases were of equal volume, but the conditions were stringent and could not be reproduced consistently on a large scale.

Another method of concentrating the iso-humulate solution is by ion exchange whereby the iso-humulate is adsorbed from its solution onto an ion-exchange resin and then recovered by elution. However, the counterion foreluting the iso-humulate, namely nitrate, was not acceptable as a constituent of beer, and the process was not successful with other counter-ions such as chloride and hydroxide.

Concentration was also attempted using a semi-permeable membrane, but of those tried a suitable membrane could not be found which would allow migration ofthe iso-humulonewithoutthe undesired carbonate.

It was eventually suggested that the iso-humulate be treated with acid to produce free iso-humulone,which couldthen be separated from the aqueous solution. Iso-humulone itself is not soluble in water or beerand could not be used directly for producing the required bittertaste, so would not be acceptable for commercial sale in concentrate form. By following this route, however, the applicants struck upon the idea of obtaining the iso-humulone and then treating itwith alkali to reform it into the iso-humulate salt which could be diluted to the required concentration. Thus, instead of starting with the dilute iso-humulate and concentrating it,they converted itto iso-humulone and then diluted the product during a further reaction.

According to the present invention, therefore, there is provided a method of producing a concentrate for use in providing a bitterflavourfor beer, comprising acidifying a solution of iso-humulone to form iso-humulone, separating the iso-humulonefrom the residual reaction mixture, and reacting the iso-humulonewith an aqueous alkali at a concentration sufficientto produce a final concentration of iso-humulate of over20%.

Preferably the starting solution of iso-humulate is pre-treated to remove or reduce the contentofhumulate which may be present in non-isomerised form. This may be performed after separation of acids from the isomerisation mixture, the separation being described for example in our European PatentApplication Number 0,161,806. The residual solution containing iso-humulate and a lesseramount of humulate istreated with mineral acid, preferably hydrochloric, sulphuric orphosphoric acid, to reduceth pH ofthe solution to not less than 5, and preferably 5.5-6.75. This causes humuloneto precipitate from the solution, leaving the isomerised form in solution.

The pH is maintained atS or more during this process in orderto prevent precipitation of iso-humulate. An organic buffer material such as acetic acid can, if desired, be included in small amountto preventthe pH dropping too rapidly on addition of the mineral acid, thereby providing practical control overthe procedure.

The removal or reduction of non-isomerised humuloneallows a purerconcentrateto be produced, and reduces the likelihood of haze being present in beer made from the concentrate.

The concentration of iso-humulate in the product solution is preferably 20-50%, most preferably 20-30%.

The starting iso-humulate is preferably acidified using a mineral acid, preferably sulphuric, phosphoric or hydrochloric acid.

The acidified solution should have a pH of not more than 4, at which about 50% ofthe iso-humulone is recoverable. Preferably the pH is less than 3 ( producing about 98%) and most preferably less than 2(99.9%).

The iso-humulone precipitates from the aqueous acidified solution as an oil.

The temperature at which the acidification is carried out is not critical. However, at low temperatures the iso-humulone oil is viscous and bubbles of carbon dioxide liberated in the reaction can become caught up in the thick oil globules and carry them to the surface, thus interfering with the effective separation; in orderto avoid the need for centrifugation, therefore, it is better to perform the reaction at a temperature of 50-60" or higher, atwhich the oil is less viscous.

An organic solvent such as hexane may be added at the acidification stage to extract the iso-humulone as it is formed, the solvent subsequently been driven off after separation from the aqueous reaction mixture.

However, it is undesirable to have organic solvents in a beer-making process, so the applicants prefer to allow the iso-humuloneto separate out without extraction.

The alkalising step is preferably carried out by running the free iso-humulone into a stirred solution of potassium hydroxide or potassium carbonate (although other alkalis may be used).The concentration ofthe alkaline solution is selected to give the desired final concentration of the iso-humulate.

Examples are: (1 ) a 10% solution of potassium hydroxide gives a 20% iso-humulate solution art a final pH of 8; (2) a 20% solution of potassium hydroxide gives a 50% iso-humulate solution at a final pH of 8; (3) a 22% solution of potassium carbonate gives a 50%iso-humulate solution at a final pH of 7.5; and (4)a 6.5% solution of potassium carbonate gives a 21% iso-humulate solution atafinal pH of 9.

Care must be exercised in this reaction as the use of an alkaline solution oftoo high a concentration can resultin the iso-humulone being hydrolysed to humulinic acid which is useless to the brewing process.

The iso-humulone and alkali are preferably reacted in equivalentquantitiesforfull reaction oftheisohumulone; thus 2 moles of iso-humulone react per mole of potassium carbonate while 1 mole of isohumulone reacts per mole of potassium hydroxide.

Afterthe reaction between the alkali and the iso-humulone is complete the reaction mixture is readyfor packaging and commercial sale, but it may be considered advisable to filter prior to packaging.

A particular embodiment of the invention will now be described by way of illustration in the following Example.

Example A starting solution of iso-humulate was obtained as described for example in UK Patent No. 1,576,729.

A batch of 3360 litres of de-ionised waterwas introduced to a jacketed fermentation vessel and heated two 90"C. In order to remove dissolved oxygen periodic nitrogen sparging took place in 10-15 second bursts.

Previously melted hop extract (189 kg liquid CO2 extractfrom Pride of Ringwood Hops) was then added to the vessel to give a final concentration of 2-3% of a-acids (83 kg total).

1.54% weightlvolume potassium carbonate (an hydrous) was added slowly with nitrogen sparging taking place during addition to ensure quick mixing and solution. This avoided the formation of local high pH areas which could result in humulinic acid formation.

The vessel was then steam heated to boiling (101-1 02"C) and boiled gently to allow full isomerisation ofthe a-acids to take place. The duration of boil for 1.54% potassium carbonate was 90 minutes. The isomerisation process was monitored by HPLC analysis and the boil continued until all the a-acid was isomerised, without significant humulinicacid being formed. Mild conditions were deliberately chosen to avoid this.

After the boil the vessel was allowed to stand hot for approximately 10 minutes two allow waxes and uncharacterised resins to form a dense surface layer with a sharp interface, and the contents of the vessel were then transferred to another vessel containing sufficient cold, de-aerated water to cool the reaction to 800C. Care was taken towards the end ofthe transfer to ensure that no waxes were carried forward. With care and attention a good separation was achieved and the hot waxes and other residual materials were run into cans or buckets at the end oftransfer (54kg of "wax" was obtained containing about 40% p-acid and 0.2% iso-a-acid.

The remaining material was uncharacterised but contained the hop oils).

The pH ofthe isomerised mixture was then lowered by sparging with CO2 to about 8 to bring p-acids out of the mixture as a discrete fluid layer. The vessel was then allowed to stand overnight at 80 C to allowthe acids to coagulate and settle in a conical lower portion ofthevessel. Itwas important to maintain an elevated cone temperature to enable the p-acids to be run-offthrough atap at the bottom ofthevessel asa mobile liquid.If the p-acids were allowed to cool in the vessel separation was impossible as crystals were formed which adhered to all the internal surfaces of the vessel.

The lower liquid layer of p-acids was then run off from the vessel (approximately kg containing 70% p-acid and 0.4% iso-a-acid) leaving the upper liquid layer of iso-humulate (iso-a-acid) solution containing 1.8% wlv iso-a-acid and approximately 1000 ppm of non-isomerised humulone.

Concentrated sulphuric acid (approximately 10.6 litres) was added to this solution ro reduce the pH to 6.25 and precipitate the non-isomerised material. The precipitate was removed by continuous centrifugation at 14,000 g and 30"C. 16 keg of solid was collected, containing approximately 8% iso-a-acid, 12% a-acid, and 18% acid. (This material can be recycled to give improved overall yields of isomerised a-acids). The supernatant solution of iso-humulate contained 1.8% w/v iso-a-acid and < 0.01% w/v a-acid with no detectable p-acid.

The present analytical systems for residual a-acid at this concentration is not precise. However the effect of the final pH of the iso-humulate solution during clarification (by centrifuge orfilter), and hence the amountof residual a-acid, on the haze formed on addition ofthe clearsolution to beer is shown in Table 1 .These results illustrate that the greatest'purity' is achieved at low pH. In practice the 'purity' must clearly be balanced against the loss of iso-a-acid in the precipitated material.

Table 1 Haze formed in beer on addition of iso-humulate solution clarified at different pH values. (Final iso-a-acid concentration in beer is 50 ppm).

pH at Clarification Increase in Haze ("EBC) 6.92 0.7 6.75 0.3 6.25 0.1 5.5 0.1 The clarified iso-humulate solution obtained was warmed to 44"C and acidified to pH 2 with concentrated sulphuric acid (approximately 9 litres) to precipitate the free acid. The vessel was allowed to stand overnight at 44"C to allow the iso-a-acid to coagulate and settle in one cone. It was important to maintain an elevated cone temperature to enablethe iso-a-acid to be run-off as a mobile liquid. (71.7kg of concentrated iso-a-acidwere recovered). The supernatantfluid containing 254 ppm of residual iso-a-acid was centrifuged to recover further 2 kg of concentrated iso-a-acid.

Free iso-a-acid was converted to potassium iso-humulate in batches of 20 kg by reaction with potassium carbonate. 3.4 kg of anhydrous potassium carbonatewas dissolved in a minimum of de-ionised water. This solution was added slowly in portions with vigorous mixing to the precipitated iso-a-acids (20 kg). The pH of the solution was measured and a quantity of aqueous carbonate (approximately 0.6 kg) added in orderto achieve a pH of 8.0.

The resulting mixturewas diluted furtherwith de-ionised water until the required concentration was achieved (total volume approximately 60 litres at 30% iso-a-acids). The pH of the solution was then adjusted to 9.0 with the further addition of solid potassium carbonate.

Care must be exercised to this reaction as the use of an alkaline solution oftoo high a concentration can result in the iso-humulone being hydrolysed to humulinic acid which is useless to the brewing process.

It is recommended to use de-ionised water atall stages of the process in order to minimisethe contentof metal ions, especially calcium and magnesium, and to keep oxygen levels low by frequent sparging with nitrogen.

The method described in the above embodiment of the invention allowed easy and effective separation of the p-acids and iso-a-acids from the bulk solution by maintaining these acids in liquid form and simply running them off from the bottom of the vessel. This transformed the practical usefulnessoftheCO2 hop extract as a starting material in the brewing process, and a very high yield was obtainable, especially on the addition ofthis material into the brewing process to enhance the bitterness of the beer.

Afurther considerable advantage of the method described in this Example is that no organic solvents or reagents were used, the materials being potassium carbonate (although other alkalis such as potassium hydroxide may be used), water, carbon dioxide, and mineral acid, all of which are presently used in conventional brewing processes.

Modifications and improvements may be made without departing from the scope of the invention.

Claims (14)

1. A method of producing a concentrate for use in providing a bitterflavourfor beer, comprising acidifying a solution of iso-humulate to form iso-humulone, separating the iso-humulonefromthe residual reaction mixture, and reacting the iso-humulone with an aqueous alkali at a concentration sufficient to produce a final concentration of iso-humulate of over20%.

2. A method according to Claim 1, wherein the starting solution of iso-humulate is pre-treated priorto acidification to remove or reduce the content of non-isomerised humulate.

3. A method according to Claim 2, wherein the pre-treatment to remove or reduce the content of nonisomerised humulate is performed after separation of acids.

4. A method according to Claim 2 or 3, wherein said pre-treatment of the starting solution comprises reducing the pH to within the rangefrom 5to 6.75.

5. A method according to Claim 4, wherein the pH is reduced to within the range from 5.5 to 6.75.

6. A method according to any one of the preceding Claims, wherein the solution of iso-humulate is acidified to a pH of4or less.

7. A method according to any one of the preceding Claims, wherein the final concentration of iso-humulate is within the range from 20 to 50%.

8. A method according to Claim 7, wherein said final concentration is within the range from 20to30%.

9. A method according to any one of the preceding Claims, wherein the acidification is conducted at an elevated temperature.

10. A method according to Claim 9, wherein the acidification is conducted at a temperature within the range from 50" to 60 C.

11. A method according to any one of the preceding Claims, wherein the acidification is performed using a mineral acid selected from hydrochloric, sulphuric and phosphoric acids.

12. A method according to anyone ofthe preceding Claims,whereinthe aqueous alkali is potassium hydroxide or potassium carbonate.

13. A method of producing a concentrate for use in providing a bitter flavourfor beer, substantially as herein before described with reference to the Example.

14. A concentratefor use in providing a bitterflavourfor beer, whenever produced by the method according to any one ofthe preceding Claims.