Today in 1986, US Patent 4610888 A was issued, an invention of James Teng and John H. Dokos, assigned to the Anheuser-Busch Companies, Inc., for their “Beer Foam Enhancing Process and Apparatus.” Here’s the Abstract:

A beer foaming process and apparatus in which a smooth stable foam is formed by intimately admixing a nitrogen containing gas, preferably air, by a Venturi effect in a nozzle positioned on the beer tap. The nozzle has a mixing chamber with a perforated plate at its intake end to divide the flow of beer from the keg into smaller streams of higher velocity in the mixing chamber, intake ports in the side walls of the chamber for admitting gas into the chamber, and a screen of 30 to 200 mesh at the discharge end of the nozzle to form the stable foam discharged from the chamber.