The 37-year-old Kurniawan, once considered one of the top-five wine collectors in the exclusive world of fine vintage wine, faces up to 40 years in jail if convicted of wire and postal fraud.
It is unclear how many bottles of fake blended wine the Indonesian-born dealer allegedly put on the market during his 10-year career until his arrest in California in 2012.
But Michael Egan, a wine expert who worked more than 20 years for auction house Sotheby's in London, was clear about one thing.
"The vast majority I found to be counterfeit," he told the 12-member jury on day six of the trial at a US federal court in Manhattan.
He said he examined "very carefully" the 267 bottles allegedly credited to Kurniawan's kitchen laboratory.
Kurniawan, wearing a suit and tie, sat expressionless in court.
From 2002 to 2007, when Kurniawan enjoyed a meteoric rise selling millions of dollars of wine each year, the market grew from $90 million to over $300 million, Egan said.
In 2006, two auctions in New York that offered Kurniawan wine fetched $35 million.
In the first auction, clients "purchased 39 lots that contained counterfeit wines for a total of $1,291,450," Egan said.
"This represents a sizeable proportion of the auction," he stressed.
Egan also said he had examined "1,433 counterfeit wines since 2006 -- from seven clients. And 1,077, or 75 percent, of those counterfeit wines were from Rudy Kurniawan."
Egan testified about files found on Kurniawan's computer and counterfeit labels in the process of being prepared.
He explained the different stages of production, how Kurniawan worked from an authentic label but changed the year, added a stamp and a serial number, then printed it in high resolution.
The nearly 19,000 labels found in Kurniawan's home represented 27 of the very best wines in the world, including 40 from a Romanee-Conti 1945 Burgundy -- so rare it no longer exists.
Kurniawan copied and made stamps used by the large Burgundy and Bordeaux wineries, Egan explained. Sometimes the accused aged them and also bought large quantities of wax to make old-style corks, he said.
Kurniawan, who is understood to have an exceptional palate, has been living illegally in the United States since 2003 when his asylum bid was rejected.
The defense has portrayed a young man who desperately wanted to fit into the richer, older world of rare wine collectors, and painted a picture of a man being made a scapegoat.