This part 3 of the article about sherry and fortified wines.
Climate and soil characteristics of Jerez
The Jerez area has a characteristically warm climate with minimal cloud cover; mean monthly temperatures vary from 25°C in summer to 10.5°C in winter. Rainfall is varied, mostly occurring in the winter, and approximately 600mm per year . Wind factors significantly influence the local climate, the prevailing south westerlies increase relative humidity’s and cool temperatures , which may delay harvest, while the south easterly wind increases temperatures and decreases humidity’s, producing early harvests . The time of harvest has a significant influence upon the resulting wine, as is described in a subsequent section.
Soil is generally of poor quality, however it is capable of absorbing and maintaining moisture well, the latter an essential characteristic as irrigation of vines is not permitted. The most appropriate soils for viticulture are those found in the low hills of the region, which have high calcium carbonate (chalk) contents, a clay consistency and alkaline pH levels, between 7.5 – 8.5.
Grape Varieties
Four types of grape are permitted in the production of sherry:
Palomino fino is the primary type utilized, as varietal character of this cultivar is low, which is a prerequisite for the production of subtle flavours in the wine during maturation and blending. This variety also produces wines low in acid and sugar, which are essential characteristics for the maturation process.
Palomino de Jerez is an old cultivar no longer in use, due to low yields in comparison to Palomino fino vines.
Pedro Ximinez varieties, which may be sourced from outside the Jerez region, are sometimes incorporated in the musts for sweetening purposes.
Muscatel types are only used in small amounts, primarily for flavoring of the wine.
Viticulture and Harvesting
The majority of vines are trained upon wires and pruned low, leaving two fruiting branches, which have maximum exposure to the sun, thus ensuring grapes ripen to optimal conditions (i.e. contain maximum sugar and juice concentrations to assist in achieving wine with high alcohol levels and low acidity) prior to picking.
Due to the uniformity of grape variety (Palomino fino) and soil conditions, vines present optimally ripened fruit at the same time, usually the first week in September. Thus harvest is completed quickly, within 3 weeks, to preserve optimal juice/sugar levels.
European regulation states that sherry must is required to contain a natural alcoholic strength of no less than 10.5% by volume, although optimal must conditions are often defined as 11.5% by volume of potential alcohol, with 2.75g l-1 of total titratable acidity (as tartaric acid). However, titratable acidity is not accurate in defining must acidity, as high levels of potassium and polyphenol compounds may falsely elevate pH levels. Thus, further define must qualities, as represented by °Brix × (pH)2. Values between 270 – 295 indicate optimum quality grapes, in terms of alcohol and acidity.
Harvesting of the fruit is primarily by hand, as mechanical pickers may damage grapes. Fruit damage is undesirable, as it leads to enzymic browning (via polyphenol oxidase action) and may inhibit the metabolism and growth of flor yeasts during maturation. Small containers of 15 – 20kg capacity are used for harvested grapes, to minimize damage. Traditionally, post harvest, grapes were left to dry for 24 – 48hrs on mats in the sun to further concentrate sugars within the grape. This procedure is now only utilized in the production of sweet wines from Pedro Ximinez grape varieties. Modern practices ensure crushing occurs within four hours of picking.
A point of note is the fact that the prevailing environmental conditions during growing season dictate the sherry style that is produced that year: states that humid seasons delay ripening and lead to the production of predominantly fino types; early vintages produced by hot, dry conditions, favor the production of oloroso type wines. The characteristics of both of these styles are defined elsewhere in this paper.
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Wine has traditionally been produced in the Jerez area of Spain since the time of the Romans, however sherry in its present form seems to have evolved at some point during the mid 1700s to early 1800s , after the commercialization of distillation , although Voss (1993) and Reader and Dominguez (2003) indicate its origins may extend beyond this time period. The primary reason for fortification of this style (with a neutral grape spirit) seems to lie in the fact that the hot climate of this region, coupled with comparatively poor soils, created wines of poor quality . Fortification with a spirit served to significantly improve the quality of this wine . However some authors, Halliday and Johnson, (1992) and Jackson, (1994) indicate fortification was utilized to offer microbial stability to such wines during often lengthy ocean voyages to England (a primary consumer of such wines) in the 1700s.
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