Today in 1957, US Patent 2789654 A was issued, an invention of David Zurit, for his “Apparatus for Filtering Air or Gas That Enters Beer Kegs.” There’s no Abstract, but in the description summarizes it thusly. “This invention relates to apparatus for filtering the air or compressed gas supplied to a beer keg, and the invention relates more particularly to a construction in which a separate filter, with a replaceable filter cartridge, is connected with each individual beer keg from which draft beer is drawn.”