GB2072657A - Process for obtaining hulupones from lupulones - Google Patents

Abstract

A process for obtaining hop extracts comprises adding adsorbents to hop products which contain alpha-acids and ground, crushed or ruptured lupulin seeds, or such hop products which are in the form of extracts, treating the mixture obtained with CO2 in a closed pressure vessel at a supercritical temperature and under a pressure of from 50 to 600 bars, reducing the pressure of the CO2 leaving the pressure vessel whereby a base extract comprising hop oils and lupulones is precipitated, mixing the lupulones with adsorbents, converting the lupulones to bitter-tasting hulupones by oxidation and treatment with CO2 under pressure, and removing undesirably accompanying substances to purify the thus obtained hulupones. Hulupones obtained by the process, optionally in combination with isohumulones provide a beer-soluble product which, as a bitter constituent, has all the taste properties of natural hops.

Description

SPECIFICATION Process for obtaining hulupones from lupulones The present invention relates to a further development of the process described in British Patent Application No. 7921290, with the object of obtaining bitter-tasting hulupones from lupulones. In accordance with British Patent Application No. 7921290, an isomerised hop product may be obtained by adding adsorbents to hop products which contain alphaacids and then treating the mixture in a pressure vessel at a supercritical temperature and under a pressure of from 50 to 80 bars. The isomerised product thus obtained is withdrawn from the pressure vessel in a dry form and the carbon dioxide, which causes the isomerisatin also acts as a solvent and purifying agent.The carbon dioxide issuing from the pressure vessel contains, as dissolved substances, hop oils, soft hop resins, in particular beta-acids, and other indistinguishable soft resins.

Under unfavourable operating conditions, it is also possible for small quantities of alpha-acids which have not been isomerised, to be removed from the pressure vessel in dissolved form with the carbon dioxide.

According to the present invention it has now been found that, by reducing the pressure of the COs which is led off from the pressure vessel, a pure, bitter-tasting hulupone product is obtained from the base extract which is precipitated in the pressure reduction vessel and of which about half consists of lupulones, by the addition of an adsorbent and an oxidising agent in conjunction with a further pressure treatment with CO2, and also that this pure, bitter-tasting hulupone product can be added directly to beer or other beverages, including alcohol-free beverages, which are to be made bitter either on its own or together with other bitter constituents, such as isomerised alpha-acids which have been obtained by the process of British Patent Application No.

7921290.

The lupulones or beta-acids are those hop resins which do not have a bitter taste, which are not isomerised in the brewing process and which are discarded thereafter, unused, together with the spent hops. From a quantitative point of view, the lupulone fraction of hops is as large as the humulone# fraction thereof, and there has, therefore, been no lack of attempts to isolate the lupulones, either in the brewery itself or in conjunction with the preparation ofisohumulones with the aid of organic solvents, and then to convert them into bitter-tasting hulupones.

German Patent Specification No. 941,965 describes a process in which after the customary boiling of hops with wort, the spent hops which have been removed are oxidised with a controlled quantity of oxygen and are thereby converted into a bitter-tasting soft resin.

German Auslegeschrift No. 1,300,485 is concerned with the conversion of lupulones into hulupones, and the hop resins, which have been dissolved in an organic solvent, are separated by means of a dilute aqueous alkaline solution into a lupulone-containing phase and then oxidised by the passing in of oxygen.

In accordance with the disclosure of German Offenlegungsschrift No. 2,217, 135, hulupones may be obtained from lupulones by oxidising the hop resins contained in a liquid alkaline medium with gases containing oxygen under the influence of visible light.

In accordance with the disclosure of German Auslegeschrift No. 2,244,895, lupulones are oxidised catalytically to give hulupones by using finely divided noble metals or noble metal oxides as catalysts.

In the procedure suggested here, an acceleration of the oxidation reaction was also observed in an alkaline, polar solution by increasing the pressure to 60 atmospheres gauge and also raising the temperatureto approximately 100 C. However, because of the uncontrolled reaction, a yield of unpurified hulupone of only approximately 20% was obtained.

All the processes mentioned above have the disadvantage that in addition to the desired end product, the resulting oxidation products contain undesirable by-products and therefore cannot be added directly to beer.

It is the object of the present invention to obtain a bitter-tasting hulupone product in improved yield and without the disadvantages of undesirable byproducts, so that it can be added directly to beer or to other beverages.

According to the present invention there is provided a process for obtaining hop extracts which comprises adding adsorbents to hop products which contain alpha-acids and ground, crushed or ruptured lupulin seeds, or hop products which are in the form of extracts, treating the mixture obtained with C02 in a closed pressure vessel at a supercritical temperature and under a pressure of from 50 to 600 bars, reducing the pressure of the COP leaving the pressure vessel whereby a base extract comprising hop oils and lupulones is precipitated, mixing the lupulones with adsorbents, converting the lupulones to bitter-tasting hulupones by oxidation and treatment with COP under pressure, and removing undesirable accompanying substances to purify the thus obtained hulupones.Preferably, hop products in the form of extracts are used, these extracts most preferably being obtained by a process which comprises extracting hops or a hop product with COP at a temperature up to its critical temperature and at a pressure above its critical pressure and subsequently evaporating the CO2 from the extract obtained.

In detail, the process according to the present invention may be carried out as follows: The base extract obtained on the pressure reduction side in the isomerisation of humulones in accordance with British Patent Application No.

7921290 essentially consists of hop oils, beta-acids and indefinable soft resins, esters and waxes. By removal in stages, the hop oils are separated in a nearly pure form from the other constituents of this base extract.

This separation is appropriately effected in a second pressure reduction vessel which is placed downstream, and which reduces the pressure of the circulating COp by means of a suitably adjusted pressure reduction valve, to a lower pressure than that in the first pressure reduction vessel.

After isomerisation of the alpha-acid in accordance with the process of British Patent Application No.7921290 and also removal of the hop oils in the second pressure reduction vessel are complete, the base extract is removed from the pressure reduction vessel.

Instead of a base extract obtained by CO2 extraction, it is also possible to use extracts obtained in another manner, for example those produced in the isomerisation process with the aid of organic solvents.

In order to enlarge the surface area of the resin-like base extract and also to promote the formation of hulupate salts, the base extract is mixed with adsorbents, as a result of which a pulverulent extract is formed. Suitable adsorbents for use in the present invention are all conventional adsorbents, such as, for example, activated charcoal, activated aluminium oxide. Fuller's earth, sodium bentonite, calcium bentonite, silica gel, kieselguhr and the like and also the known alkali and alkaline earth metal salts and their oxides or hydroxides, which are fixed by lupulones andlor hulupones by adhesion, with salt formation. These include, in particular, Na2CO3, MgCO3, CaCI2, calcium oxide, magnesium oxide, sodium hydroxide and also potassium hydroxide.

The base extract which has been mixed with one or more of the aforementioned carriers is also treated with one or more oxidising agents. Oxidising agents suitable for use in the present invention are, besides pure oxygen and the oxygen of the atmosphere, all known oxidants which can be used without leaving a detrimental residue in an end product which is intended for food purposes.

It should be understood that the term liquid CO2 as used herein means not only carbon dioxide which is subcritical with respect to pressure and temperature, but also carbon dioxide which is sub-critical with respect to its temperature only (that is to say at or below 31.3 C), and which can also definitely have higher pressures than the pressure corresponding to the critical pressure of about 73 bars (for example, a pressure of 200 bars and a temperature of 28 C).

The term supercritical CO2 as used herein means carbon dioxide which has a temperature higher than 31 .3CC and at the same time a pressure higher than 73 bars.

It was surprising to find that the formation of bitter-tasting hulupones, associated with a purification of these hulupones from the aforementioned undesirable and indefinable soft resins, esters and waxes takes place only as a result of the action of liquid orsupercritical CO2.

This conversion into bitter-tasting hulupones and the purification of the same by means of CO2 under the conditions of the present invention would not have been expected, since hitherto it was only known that crude hulupones are formed from lupu lones in the presence of an alkali and/or oxidising agents. This is especially unexpected since CO2 is neither an oxidising agent nor a substance with an alkaline reaction.

The pressure treatment with CO2 according to the present invention therefore constitutes a conversion of the lupulones into bitter-tasting hulupones and includes the purification of the hulupones thus obtained.

The base extract which has been pretreated by the process of the present invention is conveyed into the extraction vessel of a CO2 high-pressure apparatus and is there treated with CO2, e.g. liquid or supercritical CO2. Excess CO2, which is charged with the undesirable soft resins, esters and waxes, is continuously discharged into a pressure reduction vessel through a pressure controlled pressure reduction valve.

The action of the circulating.C02 ensures that, at the end of the extraction, only the bitter-tasting hulupones and/or salts thereof, together with the adsorbents used, are still present in the extraction vessel in the form of a pulverulent substance. The pulverulent hulupones which are removed from the pressure vessel are then subjected to a process of fine comminution and can subsequently be added directly to the finished beer either on their own or else mixed with isoalpha-acids which have been obtained in accordance with the process of British Patent Application No.7921290.The addition of quantities of hulupones, as compared with the addition of equivalent quantities of isohumulones to beer which was ready for drawing off showed no significant differences in the purity of the odour of the beer, in the purity of its taste, in the intensity and quality of its bitter taste nor in the body of the beer.

In terms of the intensity of the bitter taste, the addition of hulupones obtained in accordance with the present invention leads to a saving in the quantity of isohumulones added as a bitter constituent which corresponds to the amount of hulupones added.

The hulupones obtained in accordance with the present invention, in combination with the isohumulones obtained in accordance with the process of British Patent Application No.7921290, provides a beer-soluble product, as a bitter constituent, which has all the taste properties of natural hops.

Example 500 g of base extract which is freed from oil ( -acid content 49% on an anhydrous basis) is mixed with 500 g of sodium bentonite, and the mixture obtained is then treated for 2 hours in a pressure vessel under a- pressure of 250 bars by sucking in and blowing out air through two interposed pressure reduction valves.

Subsequently to the above oxidative treatment, the pulverulent base extract present in the pressure vessel is treated for 3 hours by passing there in supercritical CO2 at 70 C and under a CO2 pressure of 350 bars.

During this treatment time, the undefinable resins (soft resins and hard resins), waxes and esters which are charged with CO2 are separated off in portions at a time interval of about every 7 seconds through a pressure reduction valve into a pressure reduction vessel at a pressure of 50 bars and a temperature of 21 CC.

The yellow, resin-like mass obtained in the pressure reduction vessel is nearly free from acids, while the pulverulent product remaining in the pressure vessel is also free from acids.

When dissolved in water, the filtrate from the pulverulent product exhibits an intense and agreeably bitter taste. The substances having the taste have been identified as hulupones by means of thin layer chromatography.

Claims (16)

1. A process for obtaining hop extracts which comprises adding adsorbents to hop products which contain alpha acids and ground, crushed or ruptured lupulin seeds, or such hop products which are in the form of extracts, treating the mixture obtained with CO2 in a closed pressure vessel at a supercritical temperature and under a pressure of from 50 to 600 bars, reducing the pressure of the CO2 leaving the pressure vessel whereby a base extract comprising hop oils and lupulones is precipitated, mixing the lupulones with adsorbents, converting the lupulones to bitter-tasting hulupones by oxidation and treatment with CO2 under pressure, and removing undesirable accompanying substances to purify the thus obtained hupulones.

2. A process as claimed in claim 1 wherein hop products in the form of extracts are used.

3. A process as claimed in claim 2 wherein the extracts are obtained by a process which comprises extracting hops or a hop product with CO2 at a temperature up to its critical temperature and at a pressure above its critical pressure and subsequently evaporating the CO2 from the extract obtained.

4. A process as claimed in any of claims 1 to 3 wherein the hop oils contained in the base extract are separated from the lupulones by reducing the pressure of the CO2 in stages.

5. A process as claimed in claim 4 wherein in a first stage the COP pressure is reduced to from 15 to 50% of the pressure prevailing in the pressure vessel, and in a second stage the CO2 pressure is reduced to from 50 to 80% of the pressure in said first stage.

6. A process as claimed in any of claims 1 to 5 wherein atmosphere oxygen is used as the oxidising agent in the oxidation stage.

7. A process as claimed in any of claims 1 to 5 wherein a suitable oxidant (as herein defined) is used as the oxidising agent in the oxidation stage.

8: A process as claimed in any of claims 1 to 7 wherein adsorbents are added to the base extract for purifying the bitter-tasting hulupones.

9.t A process as claimed in any of claims 1 to 8 wherein a pressure treatment with CO2 in which the pressure of the CO2 is reduced continuously is carried out for converting the lupulones into bittertasting hupulones and for the purification thereof.

10. A process as claimed in any of claims 1 to 9 wherein the conversion of the lupulones into bittertasting hulupones and the purification thereof is carried out in the pressure vessel using liquid CO2, the pressure of the CO2 being reduced continuously.

11. A process as claimed in any of claims 1 to 9 wherein the conversion of the lupulones to bittertasting hulupones and the purification thereof is carried out in the pressure vessel using CO2 above its critical point, the pressure of the CO2 being reduced continuously.

12. A process as claimed in any of claims 1 to 11 which further comprises the step of adding the hulupones obtained, optionally together with isomerised alpha-acids to an alcohol-containing or an alcohol-free beverage which is to be made bitter.

13. A process for obtaining hulupones substantially as herein described with reference to the Example.

14. Hulupones whenever obtained by a process as claimed in any of claims 1 to 12.

15. Substances whenever obtained bya process as claimed in any of claims 1 to 13.

16. Beer containing hulupones as claimed in claim 14.