Green’s Dictionary of Slang

to drink.

1813		P. Hawker Diary (1893) I 22 Feb. 68: We [...] stopped to malt it at all the hedge alehouses.
1829		Hants. Chron. 28 Sept. n.p.: Never ‘malt’ whilst ‘at feed’ though you’ve but wine as you please.
1834		Marryat Jacob Faithful 171: ‘Well, I malts,’ said Tom, reaching a pot of porter, and taking a long pull.
1859		Bell’s Life in Sydney 10 Sept. 3/3: Josh [...] had evidently been ‘malting’ too much.
1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant.
1890–1904		Farmer & Henley Sl. and Its Analogues.