The juice of one lemon, an egg white, a bit of sugar syrup and -- most important -- three ounces of pisco: That's what's needed for the drink any Peruvian will tell you is the best thing to come out of this Andean country since the Incas.
"You put all that in a cocktail shaker and out comes the pisco sour," said Mauro Viza, a bartender at El Queirolo, a Lima tavern founded in 1880 where anyone who knows which end of a bottle is up goes to get a mean pisco sour.
"The measurements are exact . . . and the key is the quality of the pisco," Viza said.
The quality of pisco -- and who has the rights to make the grape-based liquor -- is precisely the issue that has sparked debate as both Peru and its southern neighbor Chile seek to make sure their pisco fills cocktail glasses around the world.
Peru celebrates a "Pisco Sour Day," with free cocktails and celebrations in Lima and in southern Peru, where the town of Pisco is located.
Chile, Peru's historic rival, celebrates "Piscola Day" to honor the typical mix of Chilean pisco with Coca-Cola or Sprite.
Pisco is just one more subject for rivalry between the two West Coast South American neighbors, who fought a 19th-century war after which Chile annexed much of southern Peru.
"We are hoping that every Peruvian who has never had a pisco sour will drink one and keep on drinking, honoring our banner drink: pisco," said Eduardo Iriarte, Peru's minister of production.
According to a marketing campaign with the slogan, "Chile, say goodbye to pisco!," Peru wants Chile to stop selling pisco.
But Chileans shrug and say pisco predates either Peru or Chile, having been invented in the 17th century when both were part of a giant Spanish viceroyalty.
"Peru's position is totally unfounded. Peruvian pisco hasn't attained the popularity or acceptance that Chile's has," said one industry executive, requesting anonymity.
Chileans point to pisco's greater success in Chile, which produces about 13 million gallons a year to Peru's 260,000 gallons, even though Chile's population is roughly half of Peru's.
At an outdoor cafe in a wealthy part of Santiago, Mexican psychologist Adolfo Ortega, vacationing in Chile, gazed into the pale yellow, foamy depths of his first pisco sour.
"Some friends who were in Chile told me that pisco sours were really good, and they are," he said, adding that he doubted pisco would win the renown of Mexico's beloved tequila.
Some pisco can be found in the United States, Europe and Japan. But industry officials in Chile hope to make pisco famous worldwide.
"Historically, the industry hasn't put much effort into exporting, but that's changing now. We now have the capacity to produce more than the Chilean market consumes," said Roberto Salinas, deputy managing director for Pisco Capel.
Industry officials in Peru, with minimal exports, admit they have a lot of work to do. "But for the first time, [the government] is ready to deal with the problem . . . and that could help revive this industry," said Pedro Olaechea of the Vina Tacama vineyard.
In one Lima bar, American backpacker Jeffrey Moore brushed aside the Peru-Chile conflict. "I don't care where it comes from," he said. "The point is that pisco should . . . warm up the body and make the soul happy."