The earliest whisky distillers aged their whisky in whatever barrels happened to be available. In Scotland, that often meant whisky maturing in a fishing barrel. One sip of a powerfully fishy and briny scotch told them all they needed to know about how casks can influence a whisky’s flavor.
Fortunately, the days of using fishing barrels are long gone. In fact, it was almost 193 years ago when The GlenDronach discovered which barrels lead to the most robust Highland single malt: Pedro Ximénez and oloroso sherry casks from Andalusia, Spain.
There are some major differences between Pedro Ximénez and oloroso sherry. Pedro Ximénez casks impart rich, deep fruit flavors and an intensely dark color, while dry and nutty notes come from oloroso casks. But they share one common trait that makes their casks perfectly suited for robust and flavorful single malts.
The GlenDronach only uses Pedro Ximénez and oloroso sherry casks.
Pedro Ximénez and oloroso are both aged oxidatively, which means that the top layer of yeast (called the flor) is removed so that the sherry can interact with oxygen during the maturation process. This adds complexity to the sherry itself, but whisky drinkers will be more interested in the way it influences the casks.
The natural spice of single-malt whisky brings out flavor compounds naturally found in the wood. This is where The GlenDronach gets its notes of vanilla, coconut, nutmeg and clove. The sherry also transforms the natural oak compounds in the staves (the pieces of oak that make up the cask) to feature flavors commonly associated with wine, such as dark fruits and nuts. This combination of flavors balances the natural spice of Scotch whisky and results in complex and flavorful expressions like The GlenDronach 12.
However, not just any Pedro Ximénez and oloroso cask is going to have this effect on whisky. First-fill sherry casks (ones that have only been used to age sherry) will impart the full force of flavor that the whisky needs during the maturation process. Because every time you use a sherry cask, its effect on the whisky diminishes.