After the grapes destined for Vin Santo are harvested in September or October, they are laid out on straw mats, often under rafters or staircases. They are kept in warm, well ventilated rooms that allow the moisture in the grape to evaporate. This process of desiccation allows the sugars in the grape to be more concentrated. The longer the grapes are allowed to dry and desiccate, the higher the resulting residual sugar levels will be in the wine. Depending on the style of wine desired, the grapes may be crushed and the fermentation process started after a few weeks or not till late March. Producers may use a starter culture of yeast known as a "madre" that includes a small amount of finished Vin Santo from previous years production. It is believed that this older wine can help jump start the fermentation process and also add complexity to the wine.