Solera by the producers of sherry. In a Spanish sherry "solera", the vintner may transfer about a third of each barrel a year. A solera sherry has to be at least three years old when bottled. A quite similar process is called sostrera, used to produce fortified wines in the Mediterranean regions of France. In Sicily, where Marsala wine is made, the system is called "in perpetuum". Solera vinification is used in the making of Mavrodafni ("Black Laurel"), a fortified red dessert wine made in the Northern Peloponnese in Greece. Exceptional "Mavrodafni" vintages are released every 20 or 30 years: they
Sweetness of wine Aszú dessert wines: In Spain, the rules applicable to the sweet and fortified Denominations of Origen Montilla-Moriles and Jerez-Xérès-Sherry In the United States, the wine industry measures the sweetness of must and wine in degrees Brix. Sweetness of wine The subjective sweetness of a wine is determined by the interaction of several factors, including the amount of sugar in the wine, but also the relative levels of alcohol, acids, and tannins. Sugars and alcohol enhance a wine's sweetness; acids (sourness) and bitter tannins counteract it. These principles are outlined in the 1987 work by Émile Peynaud, "The Taste of Wine".