When in Scotland, you can visit a working cooperage and take a tour to discover what it takes to produce produce this age-old product, still using traditional methods and tools. speysidecooperage.co.uk
How are whisky casks made?
The art of making whisky casks is a highly skilled and traditional practice called coopering. Nowadays, modern machinery aids the cooper (the name given to someone who makes casks and barrels) but it still takes years of training to reach the required industry standards.
Whisky cask types and capacities
When you buy a bottle of whisky it may state the type of cask or barrel that has been used during maturation on the label. This is especially likely on an independent bottling company’s label. But what does the type and size of the cask really tell us? The most basic thing to remember is that the smaller the cask, the more contact the whisky inside has with the wood.
It can be very confusing if you are not sure of the terms, so we have compiled a quick guide to the ten main types of cask used within the whisky industry, starting with the largest.
The influence of wood on whisky
Many of the flavours and characteristics of whisky are picked up from the wooden casks that it spends its time maturing in. Historically any type of wood could be used to make casks but now, by law, they now must be constructed of oak. Oak is selected for its toughness and yet easy to work with, has tight grain that prevents leaking, is porous and allows oxygen in and out of the cask and it can be bent by heat without splitting.
Wood is full of naturally occurring oils called vanillins. It is these oils that are drawn out of the cask by the spirit and over the period of maturation they add to the whisky’s flavour profile. So if all whisky is matured in oak casks, then how can they all be different when tasted? The character of the distillery, the ingredients used, the size and shape of the stills and its location are all important but the major factor is the type of oak cask used for maturation. There are three main types of wood used by the whisky industry.
European oak (Quercus robur)
This type of oak has traditionally been used to mature whisky in Scotland and Ireland for nearly two centuries. The first casks were made from English or Scottish oak but these species of tree were slow growing with twisted trucks and grain and this made the casks prone to leaking. Later Russian oak was imported as this gave more consistent wood structure due to the trees being fast growing with straight trunks.
In the 1860s, the importing of sherry from Spain to the UK started. The casks used to mature and transport the sherry were made from Spanish oak and had similar properties to Russian oak but were much cheaper. This oak is traditionally grown in the Galicia region of northern Spain and although the sherry industry has declined since the 1970s, Spanish oak is still commonly used and sought after. This is despite the price of a sherry cask costing nearly 10 times as much as a bourbon cask.
The other type of European oak commonly used in modern whisky maturation is French oak. This is traditionally made into casks for the wine industry and these are mostly used by distilleries to give a different ‘finish’ to their whiskies.
Flavour key words - sherry, dried fruits - sultanas, raisins, candied peel, spices - cinnamon, nutmeg, wood, caramel, orange, Christmas cake.
American oak (Quercus alba)
This has only been used in the whisky industry since the end of the Second World War. At that time, the Cooper's Union and lawyers formulated the law that stipulated that all American whiskey had to be matured in new wooden casks. This was done to boost the coopering industry that had collapsed during Prohibition in the 1920s and 30s. As a result, there was a massive increase in the number of casks available. The American bourbon whiskey industry slowly recovered from Prohibition and the Scots and Irish began using their casks for maturation. This was due to the good availability and price of bourbon casks compared to the more traditional sherry casks, whose numbers were declining and becoming more expensive.
American oak is seen as perfect for whisky cask construction as the trees are fast growing with tall straight trunks, giving good quality wood and high levels of vanillins. The size of cask produced (known as an ASB - American Standard Barrel) is also considered to mature whiskey at the optimum rate as there is the perfect ratio between the amount of liquid and the surface area of the inside of the cask. The result of this is that nearly 90% of all the world's whisky is now matured in American oak bourbon casks.
Flavour key words - vanilla, honey, nuts - coconut, almonds, hazelnuts, butterscotch, fudge, spices - ginger.
Japanese oak (Quercus mongolica)
Also known as mizunara oak, this type of wood is used in the Japanese whisky industry. Mizunara has been used since the 1930s and gives the whisky a unique set of flavours. The wood has extremely high levels of vanillins but is soft and very porous, making the casks made from mizunara oak very prone to leaking and easily damaged. As a result, the practice of maturing whisky was modified in order to reduce these factors. Now most Japanese whisky is matured in either bourbon or sherry casks and then transferred to mizunara casks to gain its flavoursome characteristics.
Flavour key words - vanilla, honey, floral - blossom, fresh fruit - pears, apples, spice - nutmeg, cloves, wood.