Boston Sour

Bourbon, lemon, sugar, and egg white — the Whiskey Sour Jerry Thomas codified in 1862 given egg white foam, the Boston name appearing in early 20th-century guides.

The Boston Sour is the egg-white enriched variation of the Whiskey Sour, adding a float of silky protein foam that transforms the standard citrus-and-spirit combination into a more textured and visually striking drink. The Whiskey Sour's foundational recipe — whiskey, lemon juice, and sugar — was first documented in print in Jerry Thomas's Bar-Tenders Guide of 1862, one of the earliest American bartending manuals and the book that established the sour as one of the canonical cocktail categories. The addition of egg white to the sour format was documented throughout Victorian-era American bartending: Thomas himself used egg white in several of his drinks, and the protein foam it creates when shaken — coating the tongue and creating a creamy mouthfeel that extends the flavor — was understood as a qualitative improvement rather than a novelty. The name Boston Sour appeared in early 20th-century bartending guides, though the specific reason for the Boston attribution is not definitively documented in the historical record. The city of Boston had a reputation for sophisticated drinking culture, partly derived from its English colonial heritage and proximity to the rum trade centered on New England's molasses imports from the Caribbean. The contemporary Boston Sour is occasionally served with a red wine float — a thin layer of light-bodied red wine poured over the back of a bar spoon onto the foam — which adds tannin, color, and a secondary flavor layer to the surface of the drink.