Despite what you may hear about a proper Old Fashioned, it is perfectly fine to use either bourbon or whiskey, as they both offer a smoky, sweet, and strong kick to the drink. While you can customize your Old Fashioned to fit your taste, you might want to know the difference between whiskey and bourbon.

Whiskey is an internationally manufactured liquor with various techniques and combinations of flavors. Distilled whiskey comes from a blend of different grains, such as rye, wheat, corn, or barley, and is aged in wooden barrels before being bottled and distributed. Canadian whisky is typically a light liquor with caramel and citrus-like notes, while Jameson and other Irish whiskeys lean more towards sweet and spicy tones made from malt and barley.

For a whiskey to be considered bourbon, Food & Wine reports that it must be made from a grain blend of 51% corn, aged for two years in an unused charred oak barrel, and manufactured in America. Bourbon is sweeter and oak-flavored, without the use of added flavors or coloring agents, and contains 10% higher alcohol levels as it is normally required to be 160 proof.