If you have been drinking whiskey for a while now you will be familiar with sherry maturation. In fact, you may likely be a fan of this rich, deep and spicy style. When whiskey and sherry come together it is a beautiful thing. Last time on the blog we took you through the origins of sherry. This week we look at the horticulture of sherry: the earth, the grape, the method. We answer the question: how do they make sherry?

The White Soils of the Andalucian Vinyards; Shutterstock

Little White Houses, Chalky White Soil

As we touched on last time, the soil and climate in the Jerez region impacts the final product immensely. Three soil types; Albariza, Barros and Arenas, are unique to the area Around 90% of vineyards grow in albariza. Chalky and with low organic matter, composed mainly of the remains of fossilized sea creatures! The results of 5 million years of geological shifts, when at one stage, half the Iberian Peninsula was completely underwater. This soil possesses high water retentive properties. Perfect for the long summer months, especially considering the area of Andalucia is the driest in Europe. The high chalk content also makes the soil absurdly white, reflecting sunlight back onto the vine aiding photosynthesis.

Grapes pressed and ready to ferment; Shutterstock

The Wine

Sherry is a fortified, or dessert wine much like port, marsala and madeira. Like any wine, the juice is pressed from grapes, fermented, and aged in oak barrels. The flavour will range from being bone dry to cloyingly sweet, depending on the style winemakers are looking to achieve. Along with choosing the right grape variety, this variance is accomplished by the management of the naturally occurring yeast known as ‘flor’. This is a style of winemaking unique to Spanish sherry, French Jura and Hungarian Tokaj wine.


Sometimes to make things a little special you have to get a little biological. The aim here is to create a biofilm, or layer of yeast that grows atop the wine, sealing it from any exposure to air. Flor is a living organism that consumes air, alcohol and sugar to survive. The longer a wine remains under flor, the dryer, crisper and more delicate the wine becomes. To provide airflow, the bung of the cask, normally hammered shut, is left slightly ajar. Flor can only survive between 15% and 17% alcohol by volume. Therefore it is necessary to ‘top-up’ the cask with fresh wine to replenish the levels consumed by the flor. This produces the driest styles of sherry, Fino and Manzanilla.

The Types of Sherry, with Dark, Viscous Oloroso in behind.


For the purpose of whiskey making however, one style dominates. Oloroso. This is produced from the same grape variety as it’s dryer cousins but the flor is absent during maturation. Winemakers create this different style of sherry by maintaining an alcohol  content above 18%, a level resistant to flor growth. The liquid therefore retains it’s sugar content, is exposed to air and prone to evaporation. This produces a sweeter, more viscous wine often with darker notes of walnuts, figs and tea. This style was the classic ‘sack’ sherry enjoyed during Elizabethan times (1558–1603), and the first style to mature whisky.

Pedro Ximenez

The pre-eminent style of the sherry world. Pedro Ximenez is produced from the grape of the same name, and falls under the niche straw wine category. Production of which initially involves sun-drying the harvested grapes for up to 4 weeks, essentially producing raisins. The raisins are then subjected to high pressure, extracting the treaclesque juice, before being fortified with brandy and casked to mature. Similar to oloroso, no flor is present. Different from oloroso, pedro ximenez possesses 100 times more sugar content. The resulting liquid is richer, leathery, almost tarlike. Proving itself the perfect, luxurious companion for lengthy whiskey maturation.

Casks of Sherry in Andalusia; Shutterstock

Worlds Collide

Moving casks is an expensive and precarious practise. Prior to shipping, empty casks are broken down into their staves, saving on volumetric shipping, being rebuilt at their next destination. During the peak of sherry consumption in the 17th century, Irish whiskey makers were hard at work honing their craft. Fortunately for them the wine was shipped still in their cask! Instead of returning the empty butts to their respective Spanish bodegas, whiskey makers in Ireland seized upon them. The fruity sweetness of the sherry butts mellowed the spicy whiskey distilled at the time, in particular the style produced by Dublin distillers. Although a myriad of other wines were available at the time, it was sherry that reigned supreme.


Thus sherry maturation of Irish Whiskey was born! From chalky marine soil, through rich, treacly grapes to a cask steeped in flavour. Just another sheet of light in the spectrum of Irish Whiskey. There is so much to creating a whiskey, no wonder it demands to be savoured.