Mint julep is a mixed alcoholic drink, or cocktail, consisting primarily of bourbon, sugar, water, crushed or shaved ice, and fresh mint. As a bourbon-based cocktail, it is associated with the American South and the cuisine of the Southern United States in general, and the Kentucky Derby in particular.
A mint julep is traditionally made with four ingredients: mint leaf, bourbon, simple syrup, and crushed ice. Traditionally, spearmint is the mint of choice used in Southern states, and in Kentucky in particular. Proper preparation of the cocktail is commonly debated, as methods may vary considerably from one bartender to another. The mint julep may be considered a member of a loosely associated family of drinks called “smashes” in which fresh mint and other ingredients are muddled or crushed in preparation for flavoring the finished drink. The step further releases essential oils and juices into the mixture, intensifying the flavor from the added ingredient or ingredients.
Traditionally, mint juleps were often served in silver or pewter cups, and held only by the bottom and top edges of the cup. This allows frost to form on the outside of the cup. Traditional hand placement may have arisen as a way to reduce the heat transferred from the hand to the silver or pewter cup. Today, mint juleps are most commonly served in a tall old-fashioned glass, Collins glass, or highball glass with a straw.
Information from Wikipedia. Image from Food and Wine