For many restaurateurs in New York, the guide to these nuances has been Mr. Beckwith, who founded In Pursuit of Tea in 1999 and now supplies more than 180 restaurants, a number that he said has accelerated in the last year. “It does seem like there’s a tide changing,” he said.

Customers trust their palates more, he believes, and so they are asking for higher quality tea. Restaurants, in turn, are responding both to the demand and to the competition: “Everyone else has better tea, so I better up my game,” as he put it.

Mr. Beckwith, an engaging, unpretentious and encyclopedic tea maven, presides over tea tastings in a spare, serene apartment and office in the Flatiron district. On one wall is an oak pharmacy chest with dozens of small drawers containing tea samples. On the other, a glass container of water supplies his bubbling teapot.

One recent morning, he set out the elements of a Chinese style of tea service known as gong fu cha: a slatted wooden tea tray to catch excess water and tea, a lidded dish called a gaiwan for steeping, a pitcher to hold the steeped tea, and a few small porcelain teacups. As he deftly poured, steeped, discarded and resteeped, he provided a guided tour of tea, describing how it is grown, picked, processed and tasted.