Different viticulture techniques and later picking times – rather than climate change – have caused alcohol levels in Californian wines to rise, according to Christopher Howell, winemaker and general manager at Cain vineyard and winery.Speaking at the Napa Valley Climate Seminar at Vinexpo in Bordeaux yesterday and referring to data collected since 1991 in Napa and Sonoma, Howell (left) said: “Temperatures have changed but nothing like as dramatically as the [grape] sugars… just over a period of two decades we have seen a huge increase in sugars and our claim is that most of this is due to fashion and winemaker choice.”