Boston Sour Recipe: The Whiskey Sour with Egg White

A Boston Sour is a Whiskey Sour with egg white. That is the whole definition — Difford's Guide puts it in one line, "a Boston Sour is simply a Whiskey Sour with egg white" — and PUNCH, which prefers its Whiskey Sour with egg, uses the same name. Egg white is optional in a Whiskey Sour; in a Boston Sour it is the point. The half-ounce of white turns the sharp, bright classic silky, with a meringue-like cap that holds a lemon twist and a few dashes of bitters.

Below is the spec, the dry shake and reverse dry shake explained, what the name does and doesn't tell us, how the drink compares with the classic rye Whiskey Sour, and which ryes have the presence to come through the foam.

What a Boston Sour Is

The spec above is Difford's. Strip out the egg white and you have a Whiskey Sour; put it back and the drink changes in texture more than in taste — the same sweet-sour balance, softer acidity, and a foam that sits on top like a cap.

The half-ounce is the agreed amount — PUNCH, Difford's and Jeffrey Morgenthaler all use ½ oz of white per drink, roughly one small egg's worth, while the IBA's Whiskey Sour calls for only "a few drops." Difford's specifies pasteurized egg white, and so does RyeCentral: the FDA warns that fresh eggs may carry Salmonella and advises pasteurized eggs for raw-egg recipes, especially for children, older adults, pregnant women and anyone immunocompromised.

Why It's Called a Boston Sour

Nobody knows. Difford's and PUNCH both define the drink and neither explains the name; etymologist Barry Popik's entry on the term has no dated first citation. What the record does show is when egg white arrived in sours generally: Robert Vermeire wrote in 1922 that "a few drops of white of egg improves all Sours," the Oxford Companion to Spirits & Cocktails dates egg white in the Whisky Sour to the 1920s, and the 1887 Whiskey Sour in Jerry Thomas's guide has none.

So the egg-white Whiskey Sour is a 1920s development that at some point picked up a Boston name no one has traced. The Ward Eight, this corner's other Boston drink, is unrelated beyond the city. The longer arc is in the Whiskey Sour history hub.

Boston Sour vs the Classic Rye Whiskey Sour

The two sweeteners are the same dose expressed two ways — Difford's conversion is 20 ml of 2:1 for 30 ml of 1:1, so ½ oz rich and ¾ oz simple land in the same place. The classic rye Whiskey Sour page covers the base build; Whiskey Sour ratios covers the alternatives.

PUNCH's 2017 judges split on whether egg belongs at all — Willey preferred the drink without it but conceded egg white is "really showy"; Fu called it "a good way to experience that texture and foam and mouthfeel that sours call for." Both wanted egg versions up in a coupe, because foam on the rocks breaks down quickly. That is why the Boston Sour is served up.

The Dry Shake, Explained

Egg white has to be emulsified into a foam, and ice gets in the way. There are two accepted orders, and the research splits between them.

Standard dry shake: shake everything without ice first — Julie Reiner's rule is about ten shakes, roughly ten seconds — then add ice and shake again, then strain. Reiner tried the reverse method and went back to this one for finer bubbles and better mouthfeel.

Reverse dry shake (the order in the recipe card, and Difford's order for its Boston Sour): shake with ice first, strain the ice out, then shake again without ice and pour. Because ice breaks foam down, building it last gives the firmest, most meringue-like head — Tales of the Cocktail found exactly that in a side-by-side test. The trade-offs are larger bubbles (Reiner) and foam that settles faster (Ray Keane). Either way, don't over-shake without ice. Some bartenders skip the step: Rob Krueger relies on proper ice and a hard shake, and Morgenthaler froths the white with an immersion blender. Full technique in how to shake a Whiskey Sour.

Choosing the Rye

Difford's writes the Boston Sour on bourbon. RyeCentral makes it on rye, and the research agrees: PUNCH's 2017 judges found rye the stronger choice against egg white, and the 2017 winning Whiskey Sour was built on Rittenhouse Rye 100. Egg white mutes whatever is under it, so proof matters more here than in the plain sour.

Rittenhouse Bottled-in-Bond Rye (100 proof, guide price $26.99, RyeCentral Consensus Score 4.0/5 · Strong confidence) is the default — bonded strength, a 51% rye mash bill with enough corn to stay round under the foam. Old Forester Kentucky Straight Rye (100 proof) is a drier, 65%-rye alternative at a similar price; Sazerac Rye Full Proof (125 proof) pushes orange peel and black pepper straight through the foam; Old Overholt Straight Rye (86 proof) makes a gentler, cheaper version. The Bottle Library ranks the full shortlist.

Garnish, Glass and the Aquafaba Option

Difford's finishes its Boston Sour with an expressed lemon twist and nothing else. Nearly every entry in PUNCH's 2024 Whiskey Sour contest dashed Angostura onto the foam (the judges said it masks egg aromas), so a few dashes of Angostura dragged across the top is a fair addition. More in Whiskey Sour garnish and best Whiskey Sour glass.

For an egg-free version, replace the white with about 1 oz of aquafaba (low-sodium chickpea liquid) and dry shake 10 to 12 seconds rather than roughly six; Tales of the Cocktail reports it "changes the character of the cocktail slightly," and bitters on top help. Fee Foam and Ms. Better's Miraculous Foamer are the bottled alternatives. Details in the egg white guide; every other riff is in Whiskey Sour variations and the Recipe Room.

Frequently Asked Questions

What is a Boston Sour?

A Whiskey Sour with egg white: 2 oz whiskey, ¾ oz fresh lemon juice, ½ oz rich 2:1 syrup and ½ oz pasteurized egg white, shaken, dry shaken and served up in a coupe with a lemon twist.

Why is it called a Boston Sour?

No one knows. Difford's and PUNCH define the drink without explaining the name, and etymologist Barry Popik's entry has no dated first citation. Egg white in sours is attested by 1922 (Vermeire).

What is the difference between a Boston Sour and a Whiskey Sour?

Only the egg white. The Boston Sour makes it mandatory and is usually served up in a coupe; the Whiskey Sour may be made with or without it and is often served over ice.

How much egg white goes in a Boston Sour?

About ½ oz per drink — roughly one small egg's white. PUNCH, Difford's and Jeffrey Morgenthaler all use ½ oz; the IBA's Whiskey Sour calls for only a few drops.

Do I have to dry shake a Boston Sour?

You need some way to emulsify the egg white: a dry shake first (about 10 seconds, then ice), the reverse (ice first, then without), or an immersion blender as Morgenthaler uses.

Is raw egg white in a Boston Sour safe?

The FDA warns fresh eggs may carry Salmonella and advises pasteurized eggs for raw-egg recipes, particularly for higher-risk groups. Use pasteurized egg white, or substitute about 1 oz of aquafaba or a few dashes of Fee Foam.