Green’s Dictionary of Slang

(US black) beer.

1908		in New Broadway Mag. July 34: I’d rather have foam that bubbles any day [HDAS].
1916		in Editor 20 May 535: Foam – beer [HDAS].
1944		Cab Calloway New Hepsters Dict. in Calloway (1976) 256: guzzlin’ foam (v.): drinking beer.
1946		C.S. Montanye ‘Don’t Meddle with Murder’ in Thrilling Detective May 🌐 I finished the rest of my foam.
1955		‘Ed Lacy’ Best that Ever Did It (1957) 29: He’s buying me a can of foam.