Tunnel-like cave at Stag's Leap Wine Cellars, one of the most highly regarded wineries at Napa Valley. Photo provided to China Daily

Apart from quality, another label that Napa growers happily attach to their wines is one of exclusivity. That is because Napa wines are so rare, accounting for just 4 percent of the entire California wine production and only 0.04 percent of worldwide wine production.

"This exclusivity and rareness makes them more attractive to the Chinese market than an easy-to-get cheap wine," Meadows said.

Walker noted at the wine-tasting seminar that she occasionally sees fake Napa Valley wines on the Chinese market.

"If the front label of the bottle does not indicate the origin of Napa Valley, then it is probably not Napa wine," she said.

For most Californian wineries it is much less profitable to ship wines to China than to sell them domestically. This is mainly because historically US winemakers have relied less on exports because of high domestic demand.

But there seems to have been a subtle change of heart in recent years as US vintners have begun to realize the huge opportunities China's booming wine market holds.

"Only five percent of our wines were shipped outside US," Huneeus said. "So only a modicum of wine went to China, but we are investing on China's future market."