GB2224513A - Isomerised hop preparations - Google Patents

Abstract

A method of producing isomerised hop preparations comprising admixing hops with a solid or aqueous alkali or alkaline earth metal salt and subjecting the resultant mixture to a pressure of at least 2 kg/cm<2> at an elevated temperature in a closed vessel. The hops are in the form of a hop extract coated onto a biologically acceptable solid support such as starch, cellulose, barley, husks or kieselguhr.

Description

IMPROVED HOP EXTRACTS The present invention relates to improved hop extracts.

Dried hop cones (approximately 1,.- moisture) are used in brewing to provide beer with both a bitter taste and hoppy aroma. The essential oils, which comprise of 0.5 to 2% of the weight of hops, are responsible for aroma whilst beer bitterness is derived from transformation products of hop resins and in particular the alpha-acid fraction (4S to 12sic of the weight of hops). These alpha-acids are only slightly bitter and their solubility in beer is low (2 ppm to 5 ppm). When hops are boiled in brewers wort the alphaacids are converted, as a result of an isomerisation reaction, into the much more bitter and soluble isoalpha-acids.This reaction is very inefficient in wort although the yield of potential bitter substances can be increased by boiling under pressure.

In addition losses of bitter substances occur during the brewing process and only 25 to 40T of the alpha-acids in hops are found as the corresponding iso-alpha-acids in the finished beer. Hence the overall utilisation of the bitter principles is low when hops are used conventionally in brewing. Hops slowly deteriorate on storage because they lose both alphaacids and essential oils as a result of oxidative degradation leading to a further reduction in brewing value.

Various methods are used to improve hop utilisation and minimise losses of hop components which occur on storage. Extracts produced by treating hops with hexane, methylene chloride or more recently liquid or supercritical carbon dioxide all show improved storage characteristics.

Pelletised hop powders are produced by a process which involves milling hops, thoroughly mixing the resulting powder and then feeding it into a pellet press. Heat is generated during this process so that the pellets have to be cooled prior to packaging.

Pellets packaged in partially evacuated packs, made from suitable plastic laminates, can be stored at ambient temperature for up to 12 months without significant reduction in their bittering potential. However, if pellets are stored in air, oxidative degradation is very rapid. When extracts or pellets are boiled in wort there is only a small increase (about 10sic) in utilisation since bitter substances are lost with the break (proteinaceous precipitates formed during wort broiling and subsequent cooling) and also with the yeast removed at the end of fermentation.

Hop utilisation can be substantially improved by adding isomerised hop extracts to beer after fermentation when losses of bitter substances during wort boiling and yeast removal are avoided. These extracts are usually produced by converting the alpha-acids present in solvent extracts of hops into iso-alpha-acids by boiling with dilute aqueous alkali such as sodium or potassium hydroxides or carbonates for 30 to 60 minutes. The isomerised extract, containing soluble sodium or potassium salts of iso-alpha-acids, is then added to beer towards the end of processing when 80 < c to 95 of the iso-alpha-acids survive into the packaged beer.

An alternative method of making these extracts involves precipitating the magnesium or calcium salts of the alpha-acids from a solvent extract of hops . The moist salts are then heated to effect the isomerisation reaction and give a product consisting of the calcium or magnesium salts of iso-alpha-acids. (See Hildebrand, R.P., Clarke, B.J., Lance, D.G. and White, A.W. Proceedings of the European Brewery Convention Congress, Salzberg, 1973, p.125), Such salts are not very soluble consequently long contact times are necessary and they have to be added to beer in conditioning vessels to achieve high utilisations of bitter substances.

Addition of isomerised extracts to boiling wort in the kettle also results in a marked improvement in hop utilisation. For examplet if the utilisation in a brewery is 3051 using hops this could be increased to 50%G to 60Fc by using isomerised extracts in the kettle.

However, when producing isomerised extracts processing costs are high and it is not usually economically attractive to use such products in this way.

Cheaper ways have been sought of benefitting from the improvement in utilisation when using isomerised hop preparations in the kettle. Hop pellets showing improved storage characteristics can be prepared by mixing magnesium or calcium hydroxide with powdered hops, and pelleting the mixture (See Grant, H.L., United States Patent 4 123, 561). During this process most of the alpha-acids are converted into their more stable salts, heat is generated and some isomerisation occurs.

Subsequent anaerobic heating of these pellets in a controlled manner results in the production of "isomerised hop pellets" which are claimed to contain a high proportion (over 90çv) of the initial alpha-acids as the corresponding magnesium or calcium salts of the iso-alpha-acids.

Use of such isomerised hop pellets in the kettle can result in an improvement in hop utilisation and in one commercial trial the pellets gave a utilisation of 55 whilst the corresponding value for the control was 415G. (See Grant H.L., Proceedings of the European Brewery Convention Congress, Berlin, 1979, p.441) Extrusion cooking is widely used by the food industry for the production of breakfast cereals, pet foods and various snack foods. In its simplest form an extrusion cooker is an Archimedian screw rotating inside an enclosed cylindrical barrel which can be heated in a controlled way. The feed is often moistened and propelled along the flight of the screw where it is cooked by a combination of pressure, heat and mechanical shear and then forced through a restricted opening or die at the opposite end of the barrel.A characteristic of this process is the immediate expansion of the product on exit from the cooker due to the flashing of steam.

The extrudate usually appears as a ribbon which can readily be cut into pellets using a revolving knife.

The extrusion process is simple to operate, rapid, versatile and economical because it makes efficient use of energy. Extrusion cookers have also been used as continuous chemical/biochemical reactors for the enzymatic hydrolysis of starch to give glucose syrups (see Linco, P., Hakulin, S. and Linco, Y.Y., Journal of Cereal Science, 1983, 1, 275) and also for the production of sodium caseinate by treatment of casein with sodium bicarbonate (Linco, P., Lecture read at a Royal Society of Chemistry Symposium on extrusion cooking held at the University of East Anglia on 19th and 20th September, 1985).

In recent work on the possibilities of extrusion cooking of hops, we have discovered a means of converting a high proportion of the alphaacids present in hops to the metal salts of corresponding iso-alpha-acids. In this process, powder hops are mixed with solid alkali or alkaline earth metal salts and extruded at a maximum temperature between 120-1800C and moistures generally in the range of 10-25'. The resulting extrudate cKr. contain up to rC; of the alpha-acids isomerised into their corresponding isoalpha-acids. Tests of such extrudates in brewing has resulted in an increase in utilisation of over 100 (typically 32S to 65c/o) .

We have now found that the extrusion cooking of hop extracts can provide an improved isomerised hop preparation. Accordingly, the present invention provides a method for the production of isomerised hop preparations which comprises admixing hops with a solid or aqueous alkali or alkaline earth metal salt, subjecting the resultant mixture simultaneously to a pressure of at least 2 kg/cm at an elevated temperature in a closed vessel, characterised in that the hops are in the form of a hop extract coated onto a biologically acceptable solid support. Preferably the support is selected from starch, cellulose, barley, husks, or kieslguhr.

In a preferred form of the invention the closed vessel is an extrusion cooker and the admixture is additionally subjected to shear and to a sudden release of pressure Go form expanded coherent friable pellets. The dwell time in the closed vessel is preferably from 1 - 5 minutes at a pressure of from 3.5 - 25 kg/cm. The temperatures to be utilised may be any temperature over 800C, and preferably a temperature in the range of 120 - 18O0C.

The salts in accordance with the present invention msy be selected from cabonates, bicarbonates, oxides or hydroxides of sodium, potassium" magnesium or calcium.

In accordance with the present invention the hop extracts which may be obtained by treating hops with hexane, methylene chloride, or liquid or supercritical carbon dioxide, are coated onto a biologically acceptable solid support and mixed with the solid or aqueous alkali or alkaline earth metal salts prior to extrusion.

During extrusion some of the alpha-acids are converted to metal salts of the corresponding isoalpha-acids. There is no need to heat the product after extrusion cooking to effect further isomerisation.

The product can be in the form of pellets or a fine powder which have a hoppy aroma and readily disintegrate when added to the boiling wort. This contrasts with isomerised pellets made by the prior art (see Grant, H.L., Proceedings of the European Brewery Convention Congress, Berlin, 1979 p.441). Usually isomerised pellets are compact and do not completely break up in boiling wort, which results in a reduced utilisation.

The invention will now be described, by way of illustration only, with reference to the following Example.

Whole wheat grain was ground using a condux mill and then coated with liquid C02 hop extract (485c alphaacids) to give a wheat:extract ratio of 10:1 and then mixed with sufficient solid potassium carbcnate to give an alkali:alpha-acid ratio of 2:1. The mixture was fed into a Baker-Perkins twin screw extrusion cooker at a rate of 20 kg per hour. The barrel was divided into five zones for the purpose of heating and during the run the temperatures of the first to third zones remained steady at 25"C, 65"C and 130"C, respectively.

The e fourth and fifth zones were both held at the same temperature, either 1600C or 180"C. The screw speed was 300 r.p.m. and sufficient water was added via the barrel to maintain the moisture content of the mixture at a desired level, usually 25. Under these conditions the residence time of the preparation was approximately 130 seconds and the pressure at the dies was 117 p.s.i.g.

The extrudate was in the form of a pale-brown expanded product of diameter lOmm which can readily be cut to desired lengths.

The extrudate was analysed for alpha-acids and iso-alpha-acids using a modified method (see Buckee, G.K., Journal of the Institute of Brewing, 1985, 91, 143) employing high performance liquid chromatography (Note:- The same (lOg) was shaken with a (70%) aqueous solution of methanol (lOOml) for 10 minutes. 4ml aliquots of this solution were taken and analysed according to the published procedures). The analytical results (e.g. sample 3) in Table 1 show that the conversion of alpha-acids to iso-alpha-acids was over 76-. The Table also shows analytical values obtained for products produced under different extrusion conditions.

Table 1 - Preparation of Isomerised @op Extradate Max. Barrel Barrel Alpka-acid Iso-alpha-acid Conversion of Toip ( C) moisture Content Content (% dry alpha-acids to (%) (% dry wt) wt) iso-alpha-acids Sample (%) 1 120 25% 0.5 2.6 58.8 2 140 25% 0.3 3.1 68.9 3 160 25% 0.1 3.4 76.5 4 180 25% 0.1 3.3 75.S 5 160 30% 0.4 3.3 73.5 6 160 20S 0.1 3.3 74.6 Alpha-acid content of the coated wheat at the time of extrusion (4.4C0 w/w) Our work to date has revealed that the yield of the desired product depends on the molar ratio of alkali:alpha-acids, the temperature in the various zones of the extrusion cooker and the residence time, moisture content and shear of the feed within the cooker.

Table 1 shows that using solid potassium carbonate with an alkali:alpha-acid molar ratio of 2:1 it is possible to isomerise over 75% of the alpha-acids using a maximum temperature in the final two zones of the barrel of 1600C and a barrel moisture of 25%. A very simple method of effecting the reaction involves metering aqueous potassium carbonate or hydroxide into the feed during passage along the barrel of the cooker, thus providing the necessary moisture and alkali in a single operation.

Claims (10)

CLAIMS:

1. A method for the production of isomerised hop preparations which comprises admixing hops with a solid or aqueous alkali or alkaline earth metal salt, subjecting the resultant mixture to a pressure of at least 2 kg/cm2 at an elevated temperature in a closed vessel, the hops being in the form of a hop extract coated onto a biologically acceptable solid support.

2. A method according to claim 1 in which the support is selected from starch, cellulose, barley, husks or kieselguhr.

3. A method according to claim 1 or claim 2 in which the closed vessel is an extrusion cooker.

4. A method according to any of the preceding claims in which the admixture is additionally subjected to shear and to a sudden release of pressure to form expanded coherent friable pellets.

5. A method according to any of the preceding claims in which the mixture remains in the closed vessel for from 1 to 5 minutes at a pressure of from 3.5 - 25 kg/cm2.

6. A method according to any of the preceding claims in which the elevated temperature is a temperature greater than 5000.

7. A method according to claim 6 in which the temperature is in the range of 120 - 18000.

8. A method according to any of the preceding claims in which the salt is selected from one or more of carbonates, bicarbonates, oxides or hydroxides of sodium, potassium, magnesium or calcium.

9. A method according to claim l and substantially as herein described.

10. A method for the production of isomerised hop preparations substantially as described in the Example.