Boston Sour Recipe: 3 Tips for Making a Boston Sour

The Boston Sour is a cocktail variation on the classic Whiskey Sour that features an egg white, served in a chilled cocktail glass. The velvety variation is made with two parts rye whiskey or bourbon, to one part each of lemon juice and simple syrup, topped with egg white foam, and garnished with lemon zest or a maraschino cherry. Like the New York Sour, the Boston Sour adds an egg white for a lighter, frothy mouthfeel.

The cocktail belongs to the family of classic sour cocktails—alongside the Gin Sour, Whiskey Sour, or Amaretto sour—which typically call for two parts of a spirit, and one- to three-quarters parts each of sweetener and citrus (like lemon or lime).

Like all mixed drinks in the sour cocktail family, the Boston Sour is straightforward to bring together. The egg white is the star of this drink—here are a few tips to help you achieve the ultimate foamy topper:

1. 1. The “dry shake” is key. Any cocktails using egg whites require a “dry” shake (shaking the ingredients without ice), which helps produce a thick foam with ingredients like cream and egg whites. Agitating the ingredients without ice allows the egg white to emulsify without dilution from the ice. Learn more about shaking cocktails in our complete guide.
2. 2. Use fresh eggs. Like any recipe using raw egg, ensure your eggs are fresh, undamaged, and kept in the refrigerator before use to prevent any food-borne illness. If you want to omit egg whites from the recipe, substitute 2 tablespoons of aquafaba, the liquid from canned chickpeas. This vegan substitute will foam up the same way as a standard egg.
3. 3. Switch up the sweetener. To adjust the flavor of the Boston Sour, experiment with different sweeteners, like maple syrup or agave, to complement the flavors in the bourbon whiskey or standard whiskey.