What is the main spirit used in an Old Fashion?

The primary spirit used in an Old Fashioned cocktail is bourbon. This classic cocktail highlights the flavors of bourbon through its simple and elegant preparation, which typically includes just a few additional ingredients such as sugar, bitters, and a twist of citrus. The bourbon provides a rich, caramel-like flavor that pairs exceptionally well with the sweetness of sugar and the aromatic qualities of bitters, making it the foundational element of the drink.

Bourbon's unique characteristics, such as its sweetness from the high corn content and its aging process in charred oak barrels, contribute to the Old Fashioned's overall profile. In contrast, the other spirits listed—gin, vodka, and rum—do not traditionally play a role in this particular cocktail. Each of those spirits lends a different flavor and character to drinks that may share some similarities with the Old Fashioned, but they do not align with its classic recipe or flavor expectations.