Tonic

Quinine is extracted from the bark of the cinchona tree, and it is what makes tonic bitter rather than merely sweet. Tonic water began as a way of taking quinine in liquid form, and the story of how it travelled from a medicinal preparation to a bar mixer is told in several versions, most of them tidier than the surviving record supports. What is not in dispute is that the bitterness is the entire point of the category, and that a tonic without it is just sweetened fizzy water.

Indian tonic is the original, plain style, and it is the benchmark the others are sold against. Light versions carry less sugar, which leaves the quinine more exposed and the finish drier. Flavoured tonics add a botanical or fruit note, and they push a gin in a particular direction rather than sitting neutrally underneath it.

A wedge of lime, a slice of grapefruit or a strip of cucumber peel is not decoration. Citrus oils sit on the surface of the drink and reach your nose before the liquid reaches your mouth, and a squeezed wedge adds acid that shifts the balance against the sugar. Match the garnish to the gin rather than to habit: sharp citrus for classic dry styles, something softer for the floral ones.

One part gin to three parts tonic is the common starting point, stretching to one in four in a tall glass. Push past that and the quinine flattens the botanicals it is meant to frame. Pull it back below one in two and the tonic stops carrying aroma out of the glass. Adjust with ice.

Three things flatten it: a warm mixer, too much agitation and too little ice. Gas leaves solution faster in warm liquid, and pouring from a height knocks more of it out on the way down. Pour the tonic gently down the side of a glass that is already full of ice, and then leave it alone. Stirring is what turns a lively drink into a dull one.

Not watery, drier. Taking out sugar removes the sweetness that was covering the quinine, so a light tonic reads as more bitter and shorter on the finish. That suits a rich, sweet-edged gin and can be severe with a very dry one. If it tastes thin rather than dry, use less of it and more ice.