If we have previously identified the type of ageing system (biological or oxidative) and the type of vinifiaction (total or partial fermentation) as being key factors in differentiating different types of sherry, it is no less certain that there remains another parameter of crucial importance when it comes to determining the quality of our wines: time.
Prolonged ageing intensifies the typical characteristics of certain types of sherry wines as a consequence of the permanent process of concentration made possible by the use of wooden casks. In other cases, however, this combination of time and wood confers new characteristics and sensations, bestowing a singularity and roundness upon the wine which can only be achieved after long years of ageing. Biological ageing, by its own very nature, cannot be prolonged over an excessively long period of time.
After an average of seven or eight years, depending upon the microclimatic conditions within the bodega itself, the yeast grows weak having consumed practically all of the nutrients in the wine which provide its sustenance. The film of yeast is thus unable to continue protecting the wine from direct contact with the oxygen in the surrounding air. When we therefore speak of very old sherry wines we always refer to wines which have undergone, or at least most of them, an oxidative or physico-chemical ageing process.
The Consejo Regulador certifies three special categories according to the peculiarities of their ageing:
Sherries of Certified Age
The Consejo Regulador only certifies sherries of the highest quality which have been aged for an extraordinary long time. Additionally, in order to comply with the terms of Certified Age, said sherry wines must also belong to one of the following types: Amontillado, Oloroso (sweet or dry), Palo Cortado or Pedro Ximénez.
Those sherry firms belonging to the Denomination de Origin are custodians of authentic oenological treasures. Their tasters frequently select lots of wine which, due to their special qualities, are deemed fit to join the criaderas reserved for the most special of sherry wines. Wines that form a part of a solera ageing system whose origins normally reach back to the very origins of the firm itself, usually the nineteenth century but in some cases as far back as the eighteenth. These centuries-old wines are of such exceptional quality that they are rarely put on sale to the public.
Enjoyment of these wines was traditionally the reserve of a privileged few: members of the owner's family or trusted employees who had access to the so-called "sacristies" where they were stored.
They were also served to local dignitaries or personages visiting the Jerez region. It was in the year 2000, however, that the Consejo Regulador of the Denomination of Origin Jerez-Xérès-Sherry created two special categories of Sherry Wines of Certified Age with the aim of awarding these wines an official certification which would enable them to accredit their age and extraordinary quality: Sherry Wines of over twenty years of age (V.O.S.) and Sherry Wines of over thirty years of age (V.O.R.S.).
One of the key factors which characterises Sherry Wines is the ageing method known as "de Criaderas y Soleras". This is a marvellous, perfect dynamic ageing process, but one which makes it impossible to ascertain the exact age of sherry wines, only enabling us to refer to this in average terms.
The age certification system developed by the Consejo Regulador is based upon the individual lots (known as "sacas") of this type of wine issued by the different sherry firms. The certification of the Consejo is granted not to a specific commercial brand or type of wine from a particular firm, but to each individual batch drawn from the corresponding solera, with an average age of over twenty years, or of over thirty years.
Tasting Committee and analytical parameters
In order to obtain this certification of quality and age, bodegas have to submit their wines to the judgement of an independent Tasting Committee. This is made up of specialists of accredited expertise and reputation who have no connection of any kind with sherry firms in the Jerez Region. Together with personnel from the Consejo Regulador itself, committee members include academics, technicians and other experts considered to be authorities on sherry tasting. The Tasting Committee analyse and taste samples of sherry from each saca with two distinct aims in view: not just to certify a specific average age, but also to verify that they meet the exceptional standards of quality expected of wines of such special characteristics.
In order to carry out its work the Committee has the complete support of the Estación de Viticultura y Enología de Jerez, one of the best equipped wine laboratories in Spain, which among other tasks analyses those parameters specifically related to the age of the wine samples it receives, such as Carbon 14, ester content, ash or dry extract. Even so, the results of these analyses alone are not considered sufficient to merit the certification of the Consejo if the wine in question fails to satisfy the demanding qualitative standards set by the team of expert tasters.