Green’s Dictionary of Slang

a consumer of alcohol; thus a drunkard.

1913		Sport (Adelaide) 25 Jan. 11/2: They Say [...] That Scrubbet B., known as the champion beer shifter, has tossed up crabbing.
c.1916		Daily Liar 3/1: Cheap line of Wobbly ones. Very good Beer Shifters. Good at resting.
1933		‘William Juniper’ True Drunkard’s Delight 233: A term for a drunkard [...] shifter.
1937–84		Partridge DSUE (1984) 1050/1: from ca. 1896.