Barley-broth; that is, malt liquor brewed from barley ( Scotch).
The cock may craw, the day may daw, And aye we'll taste the barley-bree.
Burns: Willie Brew'd a Peck o' Maut.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
More on Barley-bree from Infoplease: