Today in 1968, US Patent 3364033 A was issued, an invention of Lars O. Spetsig, assigned to Sweden’s Stockholms Bryggerier Ab, for his “Method of Preparing Hop Extracts.” There’s no Abstract, but here’s his introduction in the description. “This invention relates to a new and improved method of preparing hop extracts for flavoring beer and other fermented malt beverages, in which a more complete utilisation of the hop constituents is achieved.” And further along there’s this:

It has now been discovered that better utilisation of the valuable substances is achieved if the hops are extracted in the following manner. The hops are first treated with Warm water to obtain a tannin extract. This is followed by leaching out the readily soluble bitter substances (among them hulupones) and isomerizing the relatively insoluble humulones to readily soluble isohumulones: by boiling the hops in an aqueous solution of neutral pH to yield a first bitter extract. Rapid boiling at this stage is preferred to counteract oxidation. The vapour boiling off is condensed to form an aromatic extract. Since the most valuable aromatic substances are the last to be distilled off, however, fractionation may be employed to collect two or more separate fractions. Finally, the partially spent hops are oxidised by customary means, e.g. see Swedish Patent No. 150,997, to form a second bitter extract.