In Australia, the law states that whisky must be aged for a minimum of two years. At Sullivans Cove, our whiskies are aged for a minimum of nine years, and up to twenty one, being bottled only when they're at the peak of flavour and character. But where does that flavour and character come from? What happens to the whisky while it’s sitting in the cask?
When an unaged, or “new make”, whisky goes into the cask for ageing,
it already has an amazing array of naturally occurring flavours and aromas. But most whiskies get the majority of their flavour and character from the casks they’re aged in.
Whisky casks can range in size, oak species and style. In Australia, it’s common to use American oak ex-bourbon barrels, as well as casks from the Australian wine industry (usually French oak) that have previous been used to age Apera (Australian sherry-style wine) or Tawny (Australian port style wine). Increasingly, Australian distilleries are also experimenting with other kinds of wine barrels, especially Shiraz and Pinot Noir. Various cask sizes are also employed across the industry, and the ageing conditions will vary from place to place based on climate. All of these factors will have an influence over the flavour and style of the final aged whisky.
Species of Oak
The kind of oak the cask is made from will have an impact on how it flavours the final whisky. American oak tends to lend flavours of vanilla, caramel, cherries and bananas, while French oak tends to have more tannin, spice and herbal notes. The American oak casks generally used in Australia for ageing whisky tend to come from the American whisky industry, but they’re also common in the Australian wine industry.
What each cask was used for previously will also have a big impact on the flavour of the final whisky. Virgin (never used before) oak casks will be intensely oaky, ex-bourbon casks will have lots of stone fruit and vanilla character, and ex-tawny or port casks will impart notes of dried fruit and Christmas spices, for example. While ex-bourbon and fortified wine casks are by far the most common styles used for ageing whisky, red wine casks are used frequently in Australia, and it’s possible to find whiskies aged in everything from ginger beer to brandy casks.
How the cask is treated by the cooperage before being filled with new make will also impact the flavour of the whisky. Some distilleries have the barrels scraped and charred to create a new layer of charcoal and caramelised oak, while others use the cask as-is, allowing whatever was in the cask previously to be more dominant.
The size of the barrel will make a big deference in how the whisky ages over time. Many Australian distilleries use smaller 20, 50 or 100 litre casks to age their whisky. The increased surface area of the cask for every litre of whisky inside means the oak will impart more flavour in a shorter period of time, often resulting in a richly flavoured whisky in a fraction of the time of a full-sized cask. Australian distilleries have employed this technique with some excellent results, releasing whiskies as young as two years old that are dark, oaky and rich. However, larger casks tend to produce more consistent whisky, and although they take longer to reach maturity, the increased ageing time can result in wonderful textures and flavours that are hard to replicate with smaller casks.
Australia’s hot climate also helps to accelerate the rate of influence from the oak. Low average temperatures in places like Scotland and the mountains of Japan mean a whisky might need to age for at least ten years in a full sized cask before it’s mature enough to bottle. But in places like Kentucky and Australia with very hot summers, the oak influence is also accelerated. Tasmania is a bit of a middle ground – not nearly as cold as Scotland, but not as hot as the Australian mainland. This is an important factor for Sullivans Cove where we’re able to age whiskies for well over ten years without becoming too oaky.
If you want to know the exact age of any bottle of Sullivans Cove Whisky, just check the distillation and decanting dates on the side tag of every bottle. They show you down to the day exactly how long every whisky we release has been aged.
While the flavours generated from the oak itself are a major factor in every whisky, it isn’t the only thing that happens in the cask over time. If a whisky is aged for many years, each summer, the increased pressure inside the barrel pushes the whisky into the wood grain, filling it with flavour. In the winter, the whisky filters back out of the wood, brining that flavour with it, while the char on the inside of the barrel also acts as a filter for harsher notes in the whisky.
Other chemical reactions also occur throughout the ageing process, like oxidation and the formation of new esters (flavour and aroma molecules), among many other. Sometimes these reactions are compounds breaking down, and other times bonding together, but all the while new aromas, flavours and texture are being created. There is a flurry of oak extraction that occurs in the earlier years of ageing when the new make spirit is still pretty raw. So even though you can get a lot of oak flavour in a short time, there’s a lot that needs to happen inside a barrel to see these compounds soften and marry into a mature, complex and balanced whisky. This is why older whiskies tend to be creamier and more textural, with long, lingering finishes and a greater degree of complexity and integration.
At Sullivans Cove Distillery,
all of our whiskies are aged in full-sized 200 and 300 litre casks. Our standard release whiskies are by far the oldest in Australia, aged between nine and fifteen years, and our Old & Rare and special releases are up to 21 years of age, an unprecedented achievement in the Australian whisky industry.
Our single malts are un-rushed, allowed to mature slowly over many years in the unique Tasmanian climate. The result is textural, complex and nuanced whisky that lingers on the palate long after your glass is empty.