They were French winemakers of the highest caliber, from a narrow strip in Burgundy, France, from families who for generations have produced some of the world’s most sought-after wine.

They took the witness stand in Federal District Court in Manhattan on Thursday, holding aloft purportedly rare bottles, decades old, from their vineyards that fetched tens of thousands of dollars at auction and in private sales. And then they described how the wines were counterfeits.

Fake labels. The wrong corks. Mysterious wine.

This was the testimony in the fraud trial of Rudy Kurniawan, a mysterious man from Indonesia who prosecutors say worked his way into the most rarefied circles of the superrich and made millions selling them counterfeit wine. The trial, which opened this week, has been a crash course in fine wine, a display in how people assign value to things they do not even understand, and a how-to, as in how to make fake wines.

Mr. Kurniawan, described by his lawyers as the son of a wealthy Chinese family, burst onto the fine wine scene in the early 2000s. He quickly developed a reputation as a wealthy prodigy with an unmatched palate, able to blindly identify the vintage and provenance of some of the world’s finest wines. He showed up at auctions in Beverly Hills, Calif., and in New York and helped drive the prices of many wines skyward.