The Bartender’s Bible By Simon Difford Firefly, 350 pages, $40 THIS scholarly book explains how gin is made. It has detailed profiles of 18 leading distilleries and tasting notes for 175 brands from around the world. The writer, Simon Difford, a Glenfiddich food and drink award winner and a lifelong resident of London, England, also gives us a fascinating history of gin, iincludingl di theh ddays ini 1750s when it was the crack cocaine of the poor in London’s east end. Also covered: the role of the gin and tonic in the British Empire; the first known recipe for the martini in O.H. Byron’s 1884 The Modern Bartender; the bathtub gin of Prohibition and the “new cocktail boom” starting in the 1990s.