The switch to metal tops was not good for Portugal, which provides more than half the global cork supply. It launched a campaign to tout cork's sustainability (it's an easily renewable resource), and it worked on the quality of its product.
The efforts may be starting to pay off. Even in Australia, which took screwcap wine mainstream, at least one winery has switched to cork. Shannon also became a convert. "The retail customer started pushing back on some of our wines, I believe, because they weren't cork-finished."
When he went back to cork, he discovered they'd improved: "We have zero problems right now."
Merlot back from the 'sideways' curse
This year marks the 10th anniversary of the film "Sideways," which made pinot noir a hero and merlot a zero. "If anyone's drinking merlot, I'm leaving," said Miles Raymond, portrayed by Paul Giamatti, before shouting the film's most famous line: "I am not drinking any (unprintable) merlot!"
In the years that followed, merlot sales plummeted.
"Merlot is definitely back," said Duncan. In addition to running Silver Oak, he is also a managing partner at Twomey Cellars, where the 2013 merlot has been described as the best ever produced in California.
(Read more: Wine Balloon: No regrets after rejecting $400,000)
Merlot is "absolutely" in favor again, said Jennifer Putnam, executive director of Napa Valley Grapegrowers. "Merlot's delicious." She noted that some wineries are planting the varietal again.
But when you ask Shannon if merlot is back, he scoffs.
"No, what makes you think that?" He has some merlot vines that he may soon pull out. "I grow merlot, and I don't have a home for it."
Merlot has always been an important grape in Napa, and the sting of criticism from "Sideways"—which takes place further south, along the Central Coast—is still felt. Duncan poined out that in the film, Giamatti's character ends up drinking his treasured bottle of wine at a burger joint. That wine, cheval blanc, is a merlot blend.
"Miles was right in the movie a little bit in that there were some not-very-good merlots being made," he said. That's changed, Duncan added. The wines are better. "It's OK to drink merlot again."
—By CNBC's Jane Wells. Follow her on Twitter @janewells