The unparalleled success of sherry is largely due to the perfect conditions for making fortified Spanish wine. Vineyards soak up the sun from early morning until late evening (3,000 sun hours or 290 sun days per year) within the triangle formed by Sanlcecar de Barrameda, Jerez de la Frontera and El Puerto de Santa Maria, between the rivers Guadalquivir and Guadalete.
The only cooling comes from a little early morning shade and some gentle sea breezes. The climate is wholly Mediterranean in nature, with hot summers and mild winters. The soil appears to be ideal for making sherry type wines. The large but undulating albariza hills of white organic marl, high in chalk, clay, and silica dioxide, absorb water during the short rainy seasons in winter and spring. During the hot summer and autumn these minerals form a hard white crust on the surface which reflects sunlight while the water absorbed in the ground remains trapped so that the vines are prevented from drying out. This mineral mixture known locally as albariza is only found in this particular triangle of towns, forming the area known as Jerez Superior.
Beyond El Puerto de Santa Maria, to the east, is another zona, or area with less ideal clay (barros) and sandy soil (arenas), which produces Spanish wine of lesser quality.
The classic grape variety of the Jerez area is the Palamino Fino or Listan. The Palomino is an old traditional grape variety which has been grown since the start of viniculture in this area and which is perfectly adapted to the climate conditions it encounters and it thrives on albariza. The second grape variety that is important for sherry making (especially of sweet Oloroso) is Pedro Ximenez, often abbreviated to PX. This variety has also been here for as long as anyone can remember. The experts consider that both varieties of grape vine originated in the region around the Caspian Sea. It is probable that they were brought here by the Phoenicians.
The final variety of grape permitted here is the Moscatel de Alejandro (Muscat of Alexandria), which was brought from Egypt to Spain by either the Phoenicians or ancient Greeks.