A dark and stormy cocktail is made with 1.5 to 2 ounces of Goslings Black Seal rum, 4 to 5 ounces of ginger beer and a squeeze of lime, served over ice. The drink originated in Bermuda and is only considered authentic if Gosling Brothers rum is used.
The Gosling Brothers rum distillery trademarked the name "Dark 'n' Stormy" and considers it the firm's signature drink. The company started brewing the dark, potent liquor in the 1860s, blending a number of dark rums to come up with the Gosling's Black Seal formula. The distillery is located on Ireland Island, the same dockyard used by the British Royal Navy.
Ginger beer is a product of England and was brought to Bermuda by English colonists. The original formula for ginger beer included sugar, ginger, water and a culture to cause the fermentation, which made the drink alcoholic. Most modern ginger beers, which are stronger in taste than ginger ale, are soft drinks. The Crabbie's brand, dating back to 1801 and brewed in Scotland, is an exception.
The Royal Navy added a ginger beer plant to its complex at the dockyards around the turn of the 20th century. The theory was that if sailors drank more ginger beer, which was also good for seasickness, they'd drink less rum. Eventually, the ginger beer and the rum were combined, but since both drinks contained alcohol, it made the mix particularly potent.