From oak variety to shape, soleras to seasoning, there are a huge number of variables to be considered when trying to understand the world of the sherry cask – not to mention a few centuries of history and a slew of very recent regulations to get to grips with. Further muddying the waters, many decades worth of marketing on the part of the Scotch whisky industry has played up the perceived value of ‘sherry cask’ whiskies, while simultaneously perpetuating a general lack of clarity about exactly what the term means.
In order to demystify the sherry cask, over the coming issues we will dismantle the topic stage by stage until there’s no corner of the forest, cooperage or bodega (warehouse) left unexamined. But before we can understand the sherry cask, we must first ask ‘what is sherry’? And that question demands a history lesson.
According to the writings of Greek geographer Strabo (c.63BC-AD23), wine production in the region surrounding the town now known as Jerez de la Frontera, in the southern Spanish region of Andalucía, can be traced back as far as 1100BC.
Physical evidence supporting claims of this ancient history was recently discovered by archaeologists working just 4km from Jerez at Castillo de Doña Blanca, in the form of Phoenician wine presses that have been dated to the 4th century BC. Though the style of wine produced in the area has undoubtedly changed much over the centuries, it has nevertheless long held a reputation for ‘travelling well’ and was widely appreciated across the Roman empire.
By the time of the Moorish conquest of Spain in the early 8th century AD, it is known that the area they called ‘al-Andalus’ (from which we get the modern-day name of Andalucía) was a well-established wine producing region. Though Islamic scripture forbids consumption of alcohol, grapes continued to be cultivated in decent numbers during 500 years of Moorish rule. It is understood that the wine, some of which was also distilled into a grape spirit, was produced for ‘medicinal’ purposes, though this may just have been a convenient loophole.
Regardless, it seems that none of the Islamic rulers felt it necessary to dismantle the local wine industry and, though the sale of alcohol was illegal, it was nevertheless still taxed. Further reluctance to damage the industry is seen in AD966 when Caliph Al-Hakam II ordered for just one third of the region's vines to be destroyed on religious grounds, while the remaining plants were to be left untouched on the basis of a somewhat dubious claim that they played an important role in supplying soldiers’ raisin rations.
By the 12th century, wine from ‘Seris’ (the Moorish name for Jerez and pronounced ‘sherish’) was being exported regularly to England. The Christian ‘reconquista’ (reconquest) of Jerez in 1264 saw the city become the southern frontier of the Kingdom of Castile and was thus dubbed ‘Jerez de la Frontera’, a name it retains to this day. Following the reestablishment of Christian rule, British appreciation for wine exported from Andalucía grew ever more rapidly and as trade increased the locals recognised that a degree of official control would be required to protect the industry. This resulted in the publication of the Regulations of the Guild of Raisin and Grape Harvesters of Jerez on 12 August 1483, which is the earliest known document to lay down rules governing the production of the region’s wine.
Direct supply to Britain was disrupted by the Anglo-Spanish war (1585-1604), so English crews would instead loot defeated Spanish ships that were laden with wine destined for Habsburg Spain’s colonies. Such was the wine’s significance that when Sir Francis Drake attacked Cadiz in 1587, part of an operation known as ‘Singeing the King of Spain’s beard’, his forces thought it worthwhile to bring back more than 3000 plundered casks filled with Jerez wine.
The 17th and 18th centuries saw continued growth of sherry’s popularity in Britain and this prompted now-famous names such as Gordon, Mackenzie, Harvey, Williams, Humbert and Sandeman to establish businesses in Jerez to secure the steady and legitimate supply required to satisfy a thirsty public. The Napoleonic Wars (1803-1815) saw the imposition of high duties on French wine, which made sherry an even more attractive proposition. Its competitive edge was honed further, when British wine merchants succeeded in convincing the Government to further lower excise duties on sherry in 1825.
By 1838, there were more than 40 registered companies shipping sherry wine to Britain and between 1825-1840 sales of sherry increased four times over. Importantly, large quantities were landed in the Port of Leith, on the east coast of Scotland, which was by then a bustling wine-trading port and also known for its role in the whisky industry, after being granted a license to store whisky under bond in 1822.
It was during this time that fortification using grape spirit came into its own as a key element of the sherry production process, which allowed for the styles recognisable today to emerge. Up until this point, fortification was a technique that had been used solely to preserve wines, which were almost always unaged, for transport to far-off markets. The strict regulations of the Gremio de la Vinatería (Vintner’s Guild) prioritised the selling of young wines over ageing to protect the commercial interests of growers, but this in turn stifled wine merchants’ ability to react to changing tastes and made it difficult to sell a consistent product. The slow dismantling and eventual abolition of the guild in the 1820s led to the development of the famous Criaderas and Solera ageing system.
Even the scourge of phylloxera, which devastated most of Europe’s vineyards in the late 19th century, didn’t keep the sherry industry down for long, but a big challenge was presented by the sale of fake sherry that imitated the region’s style and was labelled along the lines of ‘British sherry’ or ‘Australian sherry’.
In order to protect sherry’s unique identity, the first Spanish wine law was enacted in 1933. This established the region’s official Denomination of Origin (DO) and led to the founding of the Consejo Regulador, the regulatory body that today defends the legal rights of the ‘Jerez-Xérès-Sherry’ and the ‘Manzanilla-Sanlúcar de Barrameda’ DOs, along with an important new classification that regulates what can legally be called a ‘sherry cask’ by third parties such as whisky companies.
So that’s the history. But what exactly is sherry today? For whisky drinkers, the term is perhaps best compared to that of ‘Scotch whisky’, in that it describes a drink produced in line with strict regulations and within the boundaries of a designated geographical area, but not one specific style or flavour profile. The term 'sherry' can only be applied to wines produced using grapes grown within the boundaries of a 7000-hectare region near Jerez and its neighbouring towns. Cruicially, the grapes used must also be grown ‘on land which the Consejo Regulador considers suitable’.
A second geographical limitation regulates the ‘Ageing and Maturation Zone’, which comprises the boundaries of Jerez de la Frontera, El Puerto de Santa María and Sanlúcar de Barrameda, which together form the famous ‘Sherry Triangle’. A final boundary regulates only Manzanilla sherry, which is exclusively aged in the coastal town of Sanlúcar de Barrameda.
Though other varieties of grape are grown in the region, only wines made from the Palomino, Pedro Ximénez and Moscatel grapes, all of which are white, may go on to be called sherry.
Though most are matured for much longer, sherry must also be aged for at least two years and undergo a transformation driven by oxidisation, anaerobic biological action under a layer of yeast called ‘flor’ or both.
For whisky drinkers, the important thing to note here is that casks are used purely as containers and sherry producers do not want any influence from the wood during the maturation process – which is at odds with the desires of the whiskymaker. Because of this, regardless of whether a sherry is aged ‘statically’ (in a single cask) or in the more common solera system, the wood must be inactive in terms of additive impact. Tannin is particularly undesirable, as it is detrimental to flor development and extracted tannic elements are not desired in any sherry wines. For this reason, local timber such as pine and chestnut was historically favoured over tannin-rich European oak (Quercus robur or Quercus petraea).
Today, butts made from American oak (Quercus alba) are most commonly used, a practice that emerged during centuries of trade between Spain and the New World that brought vast numbers of casks to Andalucía.
It is worth noting that the neutralisation and acclimatisation process required for introducing a new cask to a solera is long, so it is avoided. Because of this, casks will be used until they disintegrate and single staves will be replaced to extend a cask’s lifespan. What this all means is that it is very unusual for a bodega to replace or sell off its precious casks in large quantities.
So, between inactive wood, inconsistent provenance and short supply, the solera casks pictured in the marketing materials of many Scotch whiskies over the years don't, on paper at least, look like very viable options for maturing Scotch whisky. Indeed, by and large solera casks have not been the kind used to produce the ‘sherried’ style known and loved by so many – though there are a few exceptions. So where did whisky drinkers get their taste for sherry casks? To find out, we must look to a different type of cask entirely. And it's not one that's found in a bodega.
The Solera System
The solera system is a dynamic method of ageing and essentially a process of fractional blending that concentrates flavours and wines of greatest average age in the lowest row of casks. This bottom tier is also called the ‘solera’, a name that derives from the Spanish word for floor (suelo), and it is from these casks that wine will be periodically taken for bottling. Arranged in tiers called nurseries (criaderas), each level contains wine of the same average age. At various points during the year, wine will be drawn (saca) from casks in the bottom row and those same casks will be topped up (rocío) with wine from the tier above in a process called 'running the scales' (correr escalas). This is repeated up the levels until the top, into which fresh wine (‘sobretabla’) from the most recent harvest is introduced. No more than a third of the wine in a cask is transferred at a time, though this process will often be repeated many times during a year.