Today in 1975, US Patent 3891781 A was issued, an invention of Kurt Bauer, Helmut Findeiss, and Alfred Krempel, for their “Process For The Extraction Of Hops.” Here’s the Abstract:

Process for extracting from hops the essential brewing ingredients thereof, viz., neutral substances, bitter substances and tannin, which process comprises subjecting a primary extract solution of hops, e.g., in alcohol or hydrocarbon solvents, said solution containing as ingredients the neutral substances, bitter substances and tannin, to a first liquid-liquid extraction, wherein either (i) the tannins or (ii) the neutral substances are separated off, leaving a solution of (i) neutral and bitter substances or (ii) tannins and bitter substances, and subjecting the latter solution to a second liquid-liquid extraction to separate said solution into its components; the first extractant is desirably an aliphatic, cycloaliphatic or aromatic hydrocarbon when the primary extract solvent is an alcohol or aqueous-alcoholic solution, to result in extraction of the neutral and bitter substances in a hydrocarbon phase and leaving of the tannin in the alcoholic phase, whereafter the neutral and bitter substances are separated from each other by treating the extract with a second extractant, desirably aliphatic alcohol containing water.