Brew me a glass of grog, i.e. mix one for me. Brew me a cup
of tea, i.e. make one for me. The tea is set to brew, i.e.
to draw. The general meaning of the word is to boil or mix; the
restricted meaning is to make malt liquor.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894