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
Fortified wine wine that is both sweeter and stronger, normally containing about 20% alcohol by volume (ABV). During the fermentation process, yeast cells in the must continue to convert sugar into alcohol until the must reaches an alcohol level of 16%–18%. At this level, the alcohol becomes toxic to the yeast and kills it. If fermentation is allowed to run to completion, the resulting wine will (in most cases) be low in sugar and will be considered a dry wine. The earlier in the fermentation process that alcohol is added, the sweeter the resulting wine will be. For drier fortified wine styles,