The current island of Santorini is the crescent-shaped remnant of an ancient volcano whose caldera erupted and collapsed into the sea in 1500 BCE. Because of this unique geology, the soils are a mixture of young volcanic material overlaying older schist and limestone. The lack of meaningful groundwater on the island not only restricts human habitation but leaves very little water or organic material to nourish the grapevines. Vineyards are planted in extremely low densities to not increase the competition for already scarce resources between vines. Even the wind conspires against the vine grower, slowing flowering in the spring and delaying maturation at harvest when stress from drought can be multiplied by the dry breezes. The local response has been to train vines low to the ground with the canes woven into circular basket shapes referred to as kouloura or stefani. This allows the vine’s own branches to protect the leaves and fruit in the interior of the basket from the winds. The low clay and moisture levels of the soils of Santorini also prevent phylloxera from invading, and as a result, vines can still be found whose root systems are several hundred years old, though their branches must be regrafted in hundred-year intervals.
Four grapes compose most plantings on Santorini: Assyrtiko, Mavrotragano, Athiri, and Aidani, though the production is focused on wines made from Assyrtiko. Assyrtiko may be Greece’s most recognized grape variety regardless of color, making a distinctive style of wine marked by high acidity, high levels of dry extract (which can be confused for tannins), full body, and elevated alcohol. Flavors of lemon and green apple are given depth by the marked mineral character of the wine, and wines made from Assyrtiko have the longevity that is uncommon for white wine. This expression of Assyrtiko is unique to those wines made from Santorini, where stress from drought delays ripening and dehydrates berries, thereby increasing acidity and simultaneously increasing the potential alcohol level of the finished wine. Difficulties at flowering and the low soil fertility of Santorini further lower yields, resulting in an increased concentration of dry extract and texture on the palate.
A historic variation of Assyrtiko, called Nykteri, is made from grapes that are harvested at night, and barrel fermented. This results in a full-bodied wine that achieves the highest alcohol levels of all Santorini wines. A small amount of dessert wine is made, called vinsanto. This wine, not to be confused with the Italian vin santo (a term the Italians borrowed from the Greeks), is made from overripe grapes that have been partially dried in the sun before being fermented as raisins left in contact with their juice. After aging for multiple years in oak barrels, the vinsanto is then considered ready for consumption, with the high acidity of the Assyrtiko grape and volatile character from sun drying distinguishing it from its Italian counterparts.