The prevailing climate of the Jerez region is warm as a direct consequence of its low-lying latitude, it being one of the most southerly winegrowing regions in Europe (the town of Jerez sits on latitude 36º North). Summers in the region are dry and marked by high temperatures, thus provoking equally high levels of evapotranspiration, though the proximity of the Atlantic Ocean has an important role to play in maintaining levels of humidity and moderating temperatures, something that is more evident at night.
Spring and summer, the seasons which mark the growing cycle of the vine, are characterised by two prevailing winds known as the Poniente (from the west) and the Levante (from the south-east). The former is cool and humid (humidity levels can reach ninety-five percent), whilst the latter is hot and dry (with humidity levels of around thirty percent). The average annual temperature is 17.3ºC with very mild winters, during which temperatures rarely drop below zero, and very hot summers where temperatures frequently rise above 40ºC. The region enjoys a very high average of between 3,000 and 3,200 hours of effective sunlight.
Levels of rainfall are quite high, on average six hundred litres per square metre per year, usually falling in autumn and winter. With certain exceptions, this amount of water is sufficient for the correct evolution of the vines, supplemented as it is by the all important nocturnal humidity provided by the nearby Atlantic Ocean.
It should be noted, however, that the climate is not the same for all the vineyards of the region. There are marked climatic differences between the different sub-zones, districts and pagos which make up the sherry-growing area known as the Marco de Jerez.
The Sherry Region of Jerez is an area of open, gentle rolling hills or slightly sloping knolls - with gradients of between 10 and 15 per cent - covered by a limestone soil known as albariza, characterised by the extreme, dazzling whiteness it takes on during the dry months. This soft loam of chalk and clay comes to the surface on the tops of the hills, thus giving rise to the characteristic Sherry vineyard landscapes. It is rich in calcium carbonate (containing up to forty percent), clay and silica from the diatomite and radiolite shells present in the sea that once covered the region far back in the Oligocenic period. The finest albariza soil, with the highest proportion of limestone and elements of silica produces the most select and sought after sherry wines in the Marco de Jerez.
Its main characteristic from a wine-growing point of view is its high moisture retaining power, storing each winter's rainfall in order to nourish the vines during the dry months. Its leafy structure opens up like a sponge during the rainy season and absorbs immense quantities of water. Later the upper levels of soil bake hard under the heat of the summer, thus preventing the evapotranspiration produced by the region's high levels of sunlight.
Albariza soil is easy to work and, being very moisture retentive, facilitates an excellent distribution of the root system. Roots up to twelve metres in length have been found at depths of up to six metres in albariza soil.
Within the region there are also other types of soil used for the production of Sherry Wines, though in a lesser percentage, known as "barros" (clays) and "arenas" (sands). The former are predominant in lower-lying regions at the foot of hills and valleys. Sands are more commonly found in coastal areas.
The wine-growers of the region have traditionally divided the production zone into smaller areas known as "pagos": a term used to refer to small areas of vineyard delimited by topographical features and possessing homogeneous soils and mesoclimate. Famous pagos inlcude Carrascal, Marcharnudo, Añina, Bilbaina, etc... Up to 70 different pagos have been identified within the sherry region.
The Regulations of the Consejo Regulador indicate the following varieties of vine as being suitable for the production of Sherry: Palomino, Pedro Ximénez and Moscatel. All three are white-grape varieties.
The three varieties mentioned above, traditionally used throughout the Jerez Region, belong to the Vitis vinifera species, which gives grapes of the quality required to produce Sherry. The most widely favoured variety is that of the Palomino grape, together with others such as Pedro Ximénez, Mantuo, Albillo, Cañocazo, Perruno, Moscatel, etc... all of which were grown on their won rootstock. In the years 1894, however, destructive insect known as phylloxera (Daktulosphaira vitifolii) made its first appearance in Jerez and in many other parts of the world, the worst scourge in the history of viticulture which destroyed the vast majority of European vineyards by attacking the roots of the vine. The only possible solution was to plant American varieties of rootstock with phylloxera-resistant roots and then graft onto them the vines traditionally grown in the area. In such a way that the plant, from that period onwards, is always made up of a subterranean section (American rootstock) and an above-ground section, or vine stock, which produces the fruit. Both parts are joined at what is known as the graft union point.
Apart from natural factors and varieties used, the way in which the vine is cultivated has a decisive effect both upon the yield of the vine and the characteristics of the grape produced. The vine-growing techniques used for making sherry have always had the historical distinction of being committed to quality in a very specific kind of wine, developing idiosyncratic practices which over the years have been adapted to current technological advances.
The vine-growers of the Jerez region exemplify the symbiotic relationship between man, plant and soil.
Preparing the terrain
Preparatory work for planting is carried out in the summer, once the area in which the vineyard is to be planted has been selected, in an intense operation known as "agostado" (from the Spanish word for August). Ploughing up the land to a depth of 60cm oxygenates the albariza soil which is then manured as it is extremely poor in organic matter.
Once the land has been flattened, in December, the specific points where the each rootstock will be planted are clearly marked. These plantation marks indicate the distance at which each vine should be planted from the other. The traditional planting pattern used in the region used to be the "Marco Real" (a 1.50 x 1.50 metre grid). Due to the progressive mechanisation of the vineyards, however, a rectangular pattern with a 1.15 x 2.30 metre grid is now normally employed.
The rows of vines, or "liños", are planted from north to south in order to facilitate the maximum exposure to sunlight during the day, also taking into account the inclination of the land. On a vineyard in the Jerez Region the density of vines is usually of between 3,600 and 4,200 vines per hectare.