Charles Krug is one of the most visible wineries in Napa Valley, but it’s hiding a secret: In an obscure building across the tracks from its two historic stone buildings, C. Mondavi & Family makes 1.4 million cases a year of its CK Mondavi wines, a popular wine sold in supermarkets for $6.99 or even less. A Napa Valley Cabernet for $6.99 retail? And a good one at that? Yes, but there’s a catch. The CK Mondavi wine is made in Napa Valley but not from expensive Napa grapes. They come from family vineyards in the Sacramento Valley and independent growers in Lodi, and the grapes are turned into wine in St. Helena. The family recently refreshed the labels of their wines to emphasize their heritage, adding the words “and ...