Today in 1990, US Patent 4915959 A was issued, an invention of Esko Pajunen, Veijo Makinen, Heikki O. Lommi, and Markku S. Loisa, for their “Method for the Continuous Maturation of Fermented Beer” or the “Decarboxylation of Acetolactate to Diacetyl, Enzymatic Reduction to Acetoin.” Here’s the Abstract:

Beer is fermented by the use of yeast and after fermentation the yeast is removed and the maturation or lagering of the beer is accomplished by a continuous maturation process which involves heat treating the beer to convert all or substantially all the alpha acetolactate and other diacetyl precursors present to diacetyl, cooling the beer, and feeding the heat treated fermented beer through a reaction column packed with immobilized yeast cells at a flow rate which effects the conversion of said diacetyl to acetoin in order to lower the concentration of said diacetyl to levels which do not result in tastes normally considered unacceptable for a beer.