Larkmead Vineyards in Calistoga, California, embodies the Napa Valley of popular imagination. At the beginning of harvest, vines heavy with inky clumps of grapes stretch out in perfect rows, their leaves showing the faintest yellow tinge of autumn’s impending turn. The grapevines run for 110 acres to the base of the Mayacamas and Vaca Mountains, interrupted only by the occasional service road and a quaint white farmhouse. But picturesque landscapes are not what Dan Petroski, Larkmead’s winemaker, wants to show me when I arrive at the 124-year-old vineyard at the end of August.