Acid-Phosphate Cocktails: Whitehall Mystery Recipe

One of the most unequivocal laws of the Boston shaker set is clear: There can be no sour without citrus.

But thanks to the new ingredient, acid phosphate, bartenders can throw out that rule book.

Actually, it's an old ingredient, a onetime staple of soda fountains that was prized for imparting the dry tartness of lime juice without the overt sugar of actual citrus, ideal for balancing drinks with other sweet components.

Darcy O'Neil, a chemist, cocktail blogger and author, first heard about acid phosphate through legendary New Orleans bartender Chris McMillian. Intrigued, he began researching. He realized that thoughtful modern bartenders could have a field day with the stuff, so he began selling it in liquid form online.

He was right: At Leon's Full Service in suburban Atlanta, Miles Macquarrie uses it in an Old Tom gin-based drink called Whitehall Mystery, which combines the silky, boozy heft of a stirred cocktail with the subtle zing you'd expect from something shaken with citrus.

In Houston, Bobby Heugel of Anvil matches it with aged rum, maple syrup, seltzer and house-made sarsaparilla syrup. The bartenders at 47 Scott in Tucson harness Lactart–a close relative to acid phosphate–in the Beetnik Fizz, a high-wire combination of beet-infused gin, lime juice, orgeat and egg whites.

Move over lemon: There's a new sour squeeze.

Whitehall Mystery

Recipe adapted from Leon's Full Service, Decatur, Georgia

Makes 1 drink

Ice

1½ ounces Hayman's Old Tom Gin

½ ounce Plymouth Sloe Gin

½ ounce Cocchi Americano

½ ounce Pommeau de Normandie (or Calvados)

¼ teaspoon (15 drops) acid phosphate

In a pint glass, combine all of the ingredients. Stir briskly until very cold, then strain into a chilled cocktail glass and serve.