(WSJ) - When Mark Bright attends wine events in China, he says, people often complain that California wine is overpriced and of poor quality. The San Francisco-based winemaker and sommelier blames that reputation on vendors who have flooded China with cheap "plunk" wine that they sell at prices normally charged only for better vintages. "It's horrible for California," says Mr. Bright, who laments that if this continues, "we're never going to be able to build a business in China."

California winemakers—in particular those in Bay Area counties like Napa and Sonoma—have spent decades establishing their wines as some of the best in the world. But in China, where drinking wine is a more recent phenomenon, these well-constructed wines compete with bulk wine from the state that is bottled, branded and sold at prices they could never command elsewhere.