After the distillation process, whisky undergoes an important step in the creation of its flavour: aging. For at least 3 years, the whisky is allowed to mature inside oak casks and concentrate the flavours and aromas of both spirit and wood. This delicate harmony is an art that distillers monitor closely to produce the perfect whisky.
Casks: Woods And Fills.
The history of cask usage in Scotland is full of twists and turns. Before whisky distillation was legalized in 1823, whisky distillation and aging was a process shrouded in secret.
In fact, most distillers didn’t age their whiskies, as the only barrels they could find in Scotland were used to contain all sorts of things, from fish to meat and grain. Therefore, distillers and whisky drinkers would enjoy the spirit straight from the still.
But across the Channel, an alcohol armageddon changed things forever. In the mid 1800s, France was hit by the phylloxera blight. This small insect devastated the French wine and cognac industry, ravaging grape crops across the country.
All of a sudden, French vintners and cognac distillers found themselves with an excess of empty barrels and nothing to do with them.
The English and Scottish nobilities, who had thoroughly enjoyed French wine and cognac, found themselves cut off from their supply. To remedy this, they imported sherry, cognac and wine barrels, and started aging the spirits they could find locally.
Chief among these was whisky, whose quality had greatly improved since the 1823 Excise Act legalizing the practice of whisky distillation. By combining Scottish spirit with continental casks, they created the first instance of what we know today as Scotch whisky.
Nowadays, Scottish distillers favour ex-bourbon barrels produced by the American bourbon industry, a supply of casks abundantly available because the laws codifying bourbon production state allow barrels to be used only once for aging. Therefore, American distillers usually sell their barrels to Scottish and international distillers after bourbon production.
Oak casks are one of the most important components in the creation of a fine whisky. After distilling, the whisky will be pumped into a cask, and left to age.
Depending on the region and style, this aging can vary anywhere from 2 to 20+ years, with most whiskies being aged for 3-5 years. During this time in the cask, the whisky concentrates because of angel’s share, and takes on flavours and aromas from the cask.
Given these processes, choosing the right cask for the right whisky is crucial. While theoretically, you could make a cask of any size from any suitable wood, a few types have emerged as gold standards for the industry.
Cask Sizes
Most whisky casks come in one of three sizes : barrels, hogsheads and butts.
- Barrels are the smallest of the three. They are the American standard barrel, used most often for aging bourbon and rye whiskies. They have a capacity of 190-200 liters, and by law must be made of charred new American oak. Because of the laws that codify bourbon production, these casks cannot be re-used for bourbon production.
- Hogsheads contain between 225-250 liters, placing them in the middle of the three types of casks. Hogsheads are the traditional cask used for aging Scotch whisky, along with butts. Most hogsheads in Scotland are actually recycled bourbon barrels. Distilleries will import used bourbon barrels from the US, and have coopers break them down and rebuild them into hogsheads. Because of their size, they are usually used for longer aged whiskies.
- Butts are the biggest commonly used size of cask. Their capacity is usually between 475-500 liters, and they are often used age sherry. After the first fill, they are usually shipped to Scotland to age whiskies. Traditionally, most butts were made from Spanish oak, although today more and more are being made from American white oak.
- Other types of casks include barriques (wine and cognac), puncheons (rum), port pipes (port wine) and Madeira drums (Madeira wine). These are much rarer and more expensive than the three mentioned above, and therefore are more exclusively used to “finish” whiskies, filled in the last period of maturation to add some unique flavours and aromas to the whisky.
Woods
Beyond the size of the cask, the wood from which it is made plays an important part in the final flavour of a whisky. Most casks in the world are made from American white oak, being either bourbon or ex-bourbon. Because of the abundance of this type of cask, they are usually the least expensive.
An estimated 90% of whisky produced in Scotland is aged in American oak (used bourbon) barrels, with the remainder being aged in ex-sherry, ex-cognac and ex-wine/port casks. These are made from Spanish or French oak.
Many ex-bourbon American oak barrels used in Scotland are re-assembled into hogsheads and butts by skilled coopers (barrel-makers). These highly specialised craftsmen ensure no wood goes to waste, and help distilleries maintain casks in good condition to get the most out of each stave of wood.
Each wood has its properties : American oak is known for its light and citrusy aromas and minimal tannins. French oak exhibits stronger tannins and is known for bringing out the flavours in the whisky, along with giving it a silky texture. Spanish oak is the most tannic of the three, and is prized for its smoky, vanilla-like aromas.
As one would expect, most American whiskies are aged in American white oak. This is because the bourbon industry is required to do so by law. However, smaller single-malt distillers are experimenting with different woods and casks.
American oak’s dominance cannot be understated. Because of the massively productive bourbon barrel trade, an estimated 90% of whisky produced in the world is aged at some point in American oak barrels. Even in Ireland, where aging regulations are minimal, an estimated 98% of whisky produced on the Emerald Isle is aged in American oak casks.
Finally, in Japan, wood selection is the most creative. In recent years, award -winning whiskies have come out of Japan using casks made with anything from the highly prized mizunara oak to cedar and pine.
Whiskies that are aged in multiple casks of different woods are often referred to as “”double wood” or “triple wood”, based on the number of casks used.
Fills
Most whisky in the world (outside of bourbon) is aged in ex-bourbon barrels. Most of these are first fill, meaning the cask was used once to age a batch of bourbon, and subsequently sold. These casks are referred to as ex-bourbon (because they were used to age bourbon) first fill (because this fill is the first in a used barrel).
Casks can therefore be classified by the spirit they used to contain (ex-bourbon, ex-sherry, ex-port) and the amount of times they have been used. Note that past the first fill, most casks will label themselves as “refill”. The price of a cask goes down with more fills, and past 3 fills they are generally discarded.
Ex-bourbon and ex-sherry casks are favoured by the whisky industry because of the “classic” flavours and aromas they impart to the whisky. Ex-wine, ex-port and ex-cognac are also commonly used to “finish” whiskies. In recent years, distillers in Scotland, Ireland, the US and Japan have started experimenting with unconventional ex-fill casks, including rum, gin and even sake.
The expert distillers at Ve De Di use primarily new American oak barrels. A few ex-bourbon, ex-sherry, ex-armagnac and ex-rum barrels are also used to create a flavour and aroma that is unique to the distillery.
The Ve De Di Distiller’s Choice whisky, its current release, is a triple wood single malt, using ex-bourbon, ex-sherry and new American oak barrels. Given the climate of Vietnam, this thriple wood casking allows the whisky to extract a rich range of flavours and aromas from the woods in a much shorter time than traditionally expected.
Angel's Share.
When whisky is bottled, water may be added to bring the alcohol level down to the 40-50% range, depending on the whisky. This is because cask strength whisky has a high and variable alcohol level, anywhere from 50-75% depending on the type and batch.
This means that the whisky being aged in casks contains a lot more alcohol, which is a much more volatile substance than water, and therefore evaporates more quickly. However, the higher alcohol content results in a more active chemical interaction between the spirit and the cask, and allows the whisky to extract more flavour compounds from the wood.
This evaporation is called the angel’s share. The rate of evaporation varies depending on the climate in which the whisky is aged. In Scotland, the angel’s share is usually between 2-3% per cask per year, but the warmer and more humid the climate, the faster the evaporation and concentration of the whisky.
In Ve De Di’s case, the warm and humid climate of Hanoi accelerates the aging considerably, the angel’s share being between 10-12%. This makes one year of aging in Vietnam equivalent to 3-4 years of aging in Scotland. This allows Ve De Di to produce whiskies that exhibit characteristics well beyond their age.
This means that for a ten-year aged whisky in a temperate climate, a distiller will lose 20-30% of the original amount of whisky. For highly aged whiskies, distillers will often top-up casks with younger spirits (aged or not). But because whisky age is determined by the youngest spirit in the blend, this means that a 15 year old whisky can contain spirits that are much older.
For example, some 20-year old whiskies contain spirits that are over 40 years old. This is however, extremely rare and expensive, as the amount of whisky required to create such a spirit is huge (if the angel’s share is at 3% per year, a 20 year-old whisky will have lost 60% of its volume).
For those looking to dive into the world of whisky, Ve De Di's Distiller's Choice is a great option. A double-wood whisky, it's aged in ex-bourbon and ex-sherry first fill casks, giving it a nuanced and complex flavour. Order a bottle now on the online store. 18+ only. Drink responsibly.