mid-15c., "act or business of grinding (grain) in a mill," verbal noun from mill (v.1). In reference to shaping metals by 1610s; in coin-making by 1817.
mid-15c., malten, "to convert grain to malt," from malt (n.). Meaning "to make with malt" is from c. 1600. Related: Malted; malting. Malted (n.) "a drink with malted milk" is by 1945.