Patent GB-896567-A (GB)
Title: Improvements in or relating to the manufacture of bittering agents for malt beverages
IPC: C07C49/743
Filed: 1960-02-08
Abstract: Iso-humulones are reduced by metal borohydrides such as sodium or potassium borohydride, or lithium aluminium hydride; it is stated that the carbonyl group of the iso-hexenoyl side chain is reduced to a secondary alcohol.  Examples, in each of which potassium borohydride is employed, are directed to (1) isolating pure humulones, isomerizing them to their respective iso derivatives and subsequently redusing the iso-humulones, (2) combined isomerization and reduction of pure humulones through suitable adjustment of temperature, concentration and pH, (3 and 6) extracting ground, dried hops and isomerizing and reducing the resulting hop extract including in (4) a preliminary extraction of lupulone or, alternatively, in (6) removal of lupulone after the isomerization and reduction of the humulones, and (7) the isomerization and subsequent reduction of an extract of fresh, undried hops.  Petroleum ether or iso-octane are mentioned as suitable solvents for the preparation of the extracts. According to Example 1, ground, dried hops are extracted with low boiling petroleum ether; the oily residue obtained by evaporating off the petroleum ether, was taken up in absolute methanol and, after chilling to remove hop waxes, the humulones are precipitated as a lead complex by the addition of methanolic lead acetate solution. The humulones are freed from their lead complex by slurrying in p  90% methanol and adding a molar solution of sulphuric acid in methanol until precipitation of lead sulphate is complete; after centrifuging, the humulones are recovered by petroleum ether.  A solution of re-purified humulones in ethanol are treated with normal sodium hydroxide, and phosphate buffer and water are added; this mixture is then boiled under reflux to effect isomerization. The chemical reduction of the iso-humulones is accomplished by adding potassium borohydride to the iso-humulone solution and stirring at room temperature; at this point the excess borohydride is decomposed by acidification with 6N hydrochloric acid and the reduced iso-humulones are recovered by extraction with petroleum ether.  The bitter product remaining after evaporation of the petroleum ether is light-stable in the presence of sulph-hydryl-containing compounds, such as those arising in the production of malt beverages.  The reduction can be accomplished in non-aqueous solvents such as alcohols, amines and glycol ethers.ALSO:A bittering agent for a fermented malt beverage such as beer or ale is prepared by treating hops to render bittering constituents, normally chemically reactive with the sulphhydryl groups normally present as a component in the malt beverage, chemically inactive towards the sulph-hydryl groups, so that the bittering constituents when combined with the ingredients of the malt beverage provide a light-stable product.  The inactivation may be effected by chemical reduction of the iso-humulones formed during brewing.  Examples are directed to (1) isolating pure humulones, isomerizing them to their respective iso-derivatives and subsequently reducing the iso-humulones through the addition of sodium or potassium borohydride; (2) combined isomerization and reduction of pure humulones through suitable adjustment of temperature, concentration and pH, (3 to 6) extracting ground, dried hops and isomerizing and reducing the resulting hop extract including in (4) a preliminary extraction of lupulone or, alternatively, in (6) removal of lupulone after isomerization and reduction of the humulones; and (7) the isomerization and subsequent reduction of an extract of fresh, undried hops (see Group IV (b)).  Petroleum ether and iso-octane are mentioned as suitable solvents for the preparation of the extracts.  An ethanolic solution of the reduced iso-humulones may be added to unhopped wort, or at any other stage of brewing.