Light-stable hop extract

Abstract

The invention relates to a method of preparing a light-stable hop extract, said method comprising: providing a pre-isomerised hop extract comprising at least 10% of iso-alpha acids by weight of dry matter, and illuminating the pre-isomerised hop extract, optionally after dilution of the pre-isomerised hop extract.

Claims

1. A method of preparing a light-stable hop extract, comprising: (a) providing a pre-isomerised hop extract comprising at least 10% of iso-alpha acids by weight of dry matter, the iso-alpha acids being selected from the group consisting of isohumulone, isoadhumulone, isocohumulone, pre-isohumulone, post-isohumulone and combinations thereof; and (b) illuminating the pre-isomerised hop extract, optionally after dilution of the pre-isomerised hop extract, with an illumination intensity of at least 50 W/m.sup.2 for at least 30 minutes, wherein the pre-isomerised hop extract when diluted has an iso-alpha acid content in the range of 0.2-200 g/l.

2. The method according to claim 1, wherein the pre-isomerised hop extract is illuminated with light having a maximum intensity at a wavelength in the range of 200-800 nm.

3. The method according to claim 2, wherein the pre-isomerised hop extract is illuminated with light having a maximum intensity at a wavelength in the range of 250-600 nm.

4. The method according to claim 3, wherein the pre-isomerised hop extract is illuminated with light having a maximum intensity at a wavelength in the range of 300-500 nm.

5. The method according to claim 1, wherein the pre-isomerised hop extract is illuminated with an illumination intensity that exceeds 100 W/m.sup.2.

6. The method according to claim 5, wherein the pre-isomerised hop extract is illuminated with an illumination intensity that exceeds 200 W/m.sup.2.

7. The method according to claim 1, wherein the pre-isomerised hop extract is illuminated with the specified illumination intensity for at least 1 hour.

8. The method according to claim 1, wherein the temperature of the hop extract remains within the range of 0-100 C. during the illumination.

9. The method according to claim 1, wherein the diluted pre-isomerised hop extract is diluted with water to produce a diluted pre-isomerised hop extract.

10. The method according to claim 9, wherein the diluted pre-isomerised hop extract has an iso-alpha acid content in the range of 0.5-70 g/l when the illumination starts.

11. The method according to claim 10, wherein the diluted pre-isomerised hop extract has an iso-alpha acid content in the range of 1-25 g/l when the illumination starts.

12. The method according to claim 9, wherein the diluted pre-isomerised hop extract contains at least 80 wt. % water.

13. The method according to claim 12, wherein the diluted pre-isomerised hop extract contains at least 90 wt. % water.

14. The method according to claim 13, wherein the diluted pre-isomerised hop extract contains at least 95 wt. % water.

15. A light-stable hop extract that is obtained by illuminating a pre-isomerised hop extract comprising at least 10% of iso-alpha acids by weight of dry matter at an illumination intensity of at least 50 W/m.sup.2 for at least 30 minutes, wherein the iso-alpha acids are selected from the group consisting of isohumulone, isoadhumulone, isocohumulone, pre-isohumulone, post-isohumulone and combinations thereof, and wherein the pre-isomerized hop extract is optionally diluted prior to illumination, and wherein the pre-isomerised hop extract when diluted has an iso-alpha acid content in the range of 0.2-200 g/l.

16. The light-stable hop extract according to claim 15, comprising at least 1% of iso-alpha acids by weight of dry matter.

17. The light-stable hop extract according to claim 15, comprising alpha-acids in a concentration of 0-10% by weight of dry matter.

18. The light-stable hop extract according to claim 15, comprising beta-acids in a concentration of 0-10% by weight of dry matter.

19. The light-stable hop extract according to claim 15, comprising reduced iso-alpha acids in a concentration that does not exceed 10% by weight of the iso-alpha acids; the reduced iso-alpha acids being selected from the group consisting of dihydro-iso-alpha acids, tetrahydro-iso-alpha acids, hexahydro-iso-alpha acids and combinations thereof.

20. A process of preparing a beer, comprising introducing a light-stable hop extract according to claim 15 to the beer.

21. The process according to claim 20, wherein the hop extract is introduced at a concentration of at least 2 mg/l.

22. The process according to claim 21, wherein the hop extract is introduced at a concentration of 5-200 mg/l.

23. The process according to claim 22, wherein the hop extract is introduced at a concentration of 10-150 mg/l.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Accordingly, a first aspect of the present invention relates to a method of preparing a light-stable hop extract, said method comprising: providing a pre-isomerised hop extract comprising at least 10% of iso-alpha acids by weight of dry matter, illuminating the pre-isomerised hop extract, optionally after dilution of the pre-isomerised hop extract, with an illumination intensity of at least 50 W/m.sup.2 for at least 30 minutes.

(2) The term iso-alpha acids as used herein refers to substances selected from the group of isohumulone, isoadhumulone, isocohumulone, pre-isohumulone, post-isohumulone and combinations thereof. The term iso-alpha acids encompasses different stereo-isomers (cis-iso-alpha acids and trans-iso-alpha acids).

(3) The term alpha acids as used herein refers to substances selected from the group of humulone, adhumulone, cohumulone, prehumulone, posthumulone and combinations thereof.

(4) The term beta acids as used herein refers to substances selected from the group of lupulone, adlupulone, colupulone, prelupulone, and postlupulone and combinations thereof.

(5) The term beer as used herein encompasses both alcohol-containing and alcohol-free beer.

(6) According to a particularly preferred embodiment of the present method, the pre-isomerised hop extract is illuminated with light having a maximum intensity at a wavelength in the range of 200-800 nm, more preferably in the range of 250-600 nm, most preferably of 300-500 nm.

(7) The illumination intensity employed in the present method preferably exceeds 50 W/m.sup.2. More preferably, said illumination intensity exceeds 100 W/m.sup.2, most preferably it exceeds 200 W/m.sup.2.

(8) The pre-isomerised hop extract is typically illuminated with the aforementioned illumination intensity for at least 30 minutes, more preferably for at least 1 hour and most preferably for 2-48 hours.

(9) During illumination the temperature of the hop extract typically remains within the range of 0-100 C., more preferably of 15-80 C.

(10) The inventors have found that particularly good results can be obtained if the pre-isomerised hop extract is exposed to illumination after being diluted with water. Accordingly, in accordance with a particularly preferred embodiment, the present method comprises the steps of: diluting the pre-isomerised extract with water to produce an aqueous solution; and illuminating an aqueous solution of the pre-isomerised hop extract.

(11) The aqueous diluted solution of the pre-isomerised hop extract typically has an iso-alpha acid content in the range of 0.2-200 g/l, more preferably of 0.5-70 g/l and most preferably 1-25 g/l when the illuminations starts.

(12) The aqueous diluted solution of the pre-isomerised hop extract typically contains at least 80 wt. % water. Even more preferably said dilution contains at least 90 wt. % water. Most preferably, at least 95 wt. % water.

(13) Another aspect of the present invention relates to a light-stable pre-isomerised hop extract that can be obtained by the method described herein. Preferably, the light-stable pre-isomerised hop extract is actually obtained by said method.

(14) The light-stable hop extract of the present invention typically contains at least 1%, more preferably at least 2% and most preferably at least 3% of iso-alpha acids by weight of dry matter.

(15) Alpha acids are typically contained in the light-stable hop extract in a concentration of 0-10%, more preferably of 0-3% and most preferably of 0.01-2% by weight of dry matter.

(16) The light-stable hop extract of the present invention typically contains 0-10% beta acids by weight of dry matter, more preferably 0-5% beta acids by weight of dry matter.

(17) The amount of reduced iso-alpha acids (dihydro-iso-alpha acids, tetrahydro-iso-alpha acids and hexahydro-iso-alpha acids) in the light-stable hop extract preferably does not exceed 10% by weight of the iso-alpha acids. Even more preferably the amount of reduced iso-alpha acids does not exceed 3% by weight of the iso-alpha acids.

(18) The light-stable hop extract preferably is a hop extract that has been isolated from hop by means of extraction of with liquid or supercritical carbon dioxide.

(19) The light-stable hop extract of the present invention preferably is a pre-isomerised hop extract, more preferably a pre-isomerised hop extract containing iso-alpha acids and alpha acids in a weight ratio that exceeds 10:1, most preferably in a weight ratio that exceeds 20:1.

(20) The light-stable hop extract preferably has a water content of at least 30 wt. %, more preferably a water content of at least 50 wt. % and most preferably of at least 70 wt. %.

(21) Yet another aspect of the present invention relates to a process of preparing a light-stable beer, said process comprising introducing the hop extract of the present invention.

(22) As explained herein before, riboflavin plays an important role in the light-induced formation of 3-MBT in beer. Riboflavin is naturally present in beer and undergoes extremely rapid photolysis. As a matter of fact, in ordinary beer riboflavin is photolysed much more rapidly than iso-alpha acids. Thus, in light-struck beer riboflavin content is usually reduced to only a fraction of the original content even before a significant fraction of the iso-alpha acids has been photolysed.

(23) The riboflavin content of the light-stable beer that is produced in the present process preferably is at least 60 g/l. Most preferably, the riboflavin content is in the range of 80 to 2,000 g/l.

(24) The present process preferably yields a light-stable beer that contains at least 0.1 mg/l, more preferably at least 0.3 mg/l, even more preferably at least 0.6 mg/l and most preferably at least 1 mg/l of iso-alpha acids. Typically the level of iso-alpha acids in the beer will not exceed 30 mg/l.

(25) The present process typically produces a light-stable beer that contains less than 100 ng/l 3-methyl-2-butene-1-thiol (3-MBT). Even more preferably the 3-MBT content is less than 50 ng/l, most preferably less than 30 ng/l. The concentration of 3-MBT can suitably be determined by means of the method described by Hughes et al. (Hughes P. S., Burke S. and Meacham A. E. (1997) Aspects of the lightstruck character of beer. Institute of Brewing, Proceedings of the 6th Central and South Africa Section, pp. 123-128).

(26) In the present process the light-stable hop extract is preferably added to wort or beer before clarification, i.e. before removal of entrained solids and yeast from the fermented beer. Typically, clarification of fermented beer is achieved by means of filtration.

(27) In the aforementioned process the light-stable hop extract is preferably introduced into the wort or beer in a concentration of at least 2 mg/l, more preferably in a concentration of 5-200 mg/l, most preferably in a concentration of 10-150 mg/l.

(28) Following addition of the light-stable hop extract to the wort, the wort is subjected to further processing steps, including: fermenting the wort with the help of brewer's yeast; clarifying the fermented beer; and packaging.

(29) The invention is further illustrated by the following non-limiting examples.

EXAMPLES

Method of Determining the Concentration of Riboflavin

(30) The concentration of riboflavin in beer can be determined by means of UPLC-FLR using equipment, materials and conditions as described below.

(31) Equipment:

(32) UPLC system: Acquity UPLC (Waters) equipped with a BEH C18 column (1.7 m, 2.1 mm150 mm; Waters product number: 186002353) Detector: Acquity Fluorescence (FLR) detector (Waters)
Chemicals: Milli-Q Ultrapure Water Acetonitrile99.9% (Sigma Aldrich product number: 34998) Phosphoric acid85.0% (Sigma Aldrich product number: 30417) Riboflavin (Sigma Aldrich product number: R-7649) Sodium dihydrogen phosphate monohydrate (Merck product number: 106346) pH buffer 2.7 (7.5 g sodium dihydrogen phosphate monohydrate in 200 mL Ultrapure water+1 mL Phosphoric acid in 1000 mL Ultrapure water)
UPLC Instrument Conditions: Column temperature: 40 C. Injection volume: 10 L Sample temperature: 10 C. Run time: 15 min Eluens A=pH buffer 2.7 Eluens B=acetonitrile
Gradient:

(33) TABLE-US-00001 Flow Time (min) (mL/min) % A % B 0.00 0.20 95 5 10.0 0.20 95 5 10.5 0.20 15 85 12.0 0.20 15 85 12.2 0.20 95 5 15.0 0.20 95 5
Detector Conditions: .sub.ex=444 nm .sub.em=525 nm

(34) Samples are degassed prior to analysis.

Example 1

(35) A pre-isomerised hop extract (so-called Isohop obtained from Barth-Haas Group) was used as a starting material. This hop extract had the following characteristics (according to the product description sheet from Barth-Haas Group): contains 300.5 wt % iso-alpha acids contains <0.7% alpha acids contains <0.3% beta acids

(36) The pre-isomerised hop extract was diluted with Milli-Q Ultrapure Water (1:50 w/w). 16 mL of the diluted hop extract was introduced into a glass tube with screw cap (Duran glass, tube diameter is 16 mm, tube length is 160 mm). 30 of these glass tubes were simultaneously illuminated for a period of 32 hours inside a Suntest XLS+ device (ATLAS), using a Xenon lamp. During illumination, the following conditions were applicable: Power of Xenon lamp is 1700 W Tubes were horizontally positioned inside the Suntest XLS+ device Distance between glass tubes and lamp is 25 cm Amount of irradiance at sample level was set at 765 W/m.sup.2 Temperature of diluted hop extract increases from ambient to circa 50 C. (no cooling nor heating was intentionally applied during illumination)

Example 2

(37) The illuminated and non-illuminated hop extracts of Example 1 were added to unhopped beer (300 mL unhopped beer in green bottle). A first beer (reference beer) was prepared by adding 20 mg/L of the non-illuminated hop extract. A second beer (light-stable beer) was prepared by adding 60 mg/L of the illuminated hop extract. The illuminated hop extract was applied in a higher concentration in order to compensate for the loss in bitter intensity that had occurred as a result of the illumination. The flavour profile of the beer containing the illuminated hop extract had a flavour profile that was very similar to that of the beer containing the non-illuminated hop extract.

(38) Both beers were exposed to artificial sunlight by putting the bottles horizontally in the Suntest XLS+ device and illuminating them for a period of 24 hours. During illumination, the same conditions were applied as in Example 1.

(39) Before and during exposure to the artificial sunlight the concentrations of the following substances were determined in both beers: iso-alpha acids, riboflavin, and 3-MBT.

(40) Determination of iso-alpha acids in beer was performed according to the method described by the American Society of Brewing Chemists (ASBC) in 2009 (Methods of Analysis, 14th Edition): Method Beer 23 (section E: Iso-alpha acids in beer by HPLC). The 3-MBT content was determined using the method described by Hughes et al. (Aspects of the lightstruck character of beer. Institute of Brewing, Proceedings of the 6.sup.th Central and South Africa Section (1997), pp. 123-128).

(41) The results of these analyses are summarised in Table 3:

(42) TABLE-US-00002 TABLE 3 Iso-alpha acids Riboflavin MBT (mg/L) (g/L) (ng/L) Reference beer 0 h illumination 19.2 318 7 2 h illumination 18.8 16 309 6 h illumination 17.8 2.8 660 24 h illumination 16.0 0.3 2072 Light-stable beer 0 h illumination 4.5 313 8 2 h illumination 4.4 15 74 6 h illumination 4.2 2.0 137 24 h illumination 3.6 0.4 506