Lactose cannot be fermented by brewers' yeast (Saccharomyces cerevisiae), and the residue adds sweetness, body and calories to the finished beer.

In 1875, John Henry Johnson first sought a patent for a milk beer, based on whey, lactose and hops.

[3] By the 1950s it accounted for half of Whitbread's production, and was brewed at Chiswell Street in London, Stockport, Kirkstall and Hythe.

A 4.9% Mackeson's XXX is brewed by Carib Brewery in Trinidad for the local market where it is targeted at young men, with the advertising slogan "king of the night".

[8] The Trinidadian version is a popular import into Hong Kong, and is among the top twenty highest-selling beers there, selling over 500,000 litres a year.