Despite the name, this style of gin doesn’t have to be made in London. It is linked with the British capital because of Aeneas Coffey, who patented a design for a column (or continuous) still in 1830.
Column stills were a game-changer in the distilling world, enabling the production of a pure spirit, without foul-tasting impurities such as methyl alcohol and acetone. These types of stills can also sustain continuous distillation, enabling large-scale production.
Although Coffey was an Irish distiller, he moved to London when whisky producers complained that his still was too efficient and produced bland spirits, stripped of all flavour. In London Coffey set up his business as a still manufacturer and local gin producers started using his column stills.
The new, purer, column-distilled gins they produced earned the name London Dry. But today the term London Dry or ‘London gin’ distinguishes gins that contain only distilled botanicals from those which have flavours added after distillation.
All gin starts life as a neutral base spirit (usually distilled in a column still) which needs to be flavoured with botanicals: berries, herbs, spices. Juniper must be the main botanical; according to the legal EU definition of gin, juniper must be its predominant flavour.
Distillers put their botanical mix in a still to macerate in the neutral spirit. A pot still is preferred by craft distillers and is always used to produce ‘small-batch’ gins. This mixture is then distilled to produce a high-strength spirit, which is diluted with water to at least 37.5% abv.
If nothing else is added to the gin, it is a London Dry Gin or ‘London gin’. If flavours are added after distillation, it’s labelled ‘distilled gin’ or simply ‘gin’.
For more on gin history read London Dry: The Real History of Gin by Ted Bruning.