Viognier can be a difficult grape to grow because it is prone to powdery mildew. It has low and unpredictable yields and should be picked only when fully ripe. When picked too early, the grape fails to develop the full extent of its aromas and tastes. When picked too late, the grape produces wine that is oily and lacks perfume. Winemakers in the Condrieu often pick the grapes with a level of sugar that will produce wine with alcohol in the 13% range. When fully ripe the grapes have a deep yellow color and produce wine with a strong perfume and high in alcohol . The grape prefers warmer environments and a long growing season, but can grow in cooler areas as well.