The Chemistry of Whisky

All the Colours of Whisky (Part 1)

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September 1, 2022

How Wood and Casks types can influence the colour of a whisky.

Have you ever looked at a whisky and imagined even before tasting it the complexity of its aromas and the richness of its flavours? You’ve probably been influenced by that dark caramel colour. The more intense the colour of the whisky, the better, right? Well, more or less.

Whisky colours can say a lot about an expression: the type of cask it was probably matured in, how long it was aged, its aromas, and much more. However, it is not an exact science. Colours can reveal all this information about an expression, but it says nothing about the quality per se. Moreover, there are several factors that influence the final colour of the whisky that must also be taken into account.

Many people are surprised to learn that, in most modern distilleries, the “new-make” spirit emerges from the still as clear as spring water. Where does it get its colours then? Well, everything starts from the cask…

The image is from Whisky Flavour Wheels and Colour Charts

Oak Casks

Aside from very few rare cases, whisky usually ages in oak casks. Indeed, Oak’s chemical composition removes impurities and sour notes from newly distilled whisky, while infusing it with other favourable aromas and flavours, such as vanilla, caramel and leather. 

Other woods such as maple or hickory are sometimes used. However, most of the whisky production worldwide specifies the use of oak as a legal requirement. 

Why Oak? This type of wood is abundant, strong, flexible and waterproof. It also has the right amount of bitter tannins and acidic vanillins to ensure a balanced flavour profile. Although, not all oak species are suitable for whisky ageing. The most common varieties are Quercus Alba, or American White oak, Quercus robur, or European oak, and Quercus Mongolica, or Japanese Mizunara oak.

  • American Oak: It gives a softer, sweeter taste with notes of vanilla and caramel to the whisky, colouring the whisky with a slight reddish nuance.
  • European Oak: It is spicier and has a stronger wood input on the whisky. Moreover, it brings notes of vanilla, pepper and subtle spiciness, while colouring the spirit with a strong golden shade. 
  • Mizunara Oak: The use of casks made from Mizunara oak is widespread in the production of Japanese whisky. This wood lacks oily waterproofing enzymes, so during the ageing process, the whisky evaporates much more than whisky stored in more traditional American or European oak casks. To avoid this, most Japanese whiskies are matured in American or European oak casks and then later finished in Mizunara casks. Nevertheless, Mizunara oak gained popularity for whisky ageing due to the special aromas it imparts to whisky: reminiscent of sandalwood, coconut and oriental spices, and pale amber colour.

Toasting and Charring

All casks are toasted, but not necessarily charred. A new oak cask goes through heat treatment – toasting. The process will caramelise the wood sugars, helping the wood to release those vanilla and caramel notes from American oak and more tannins and spices from European oak. 

The next step is charring the casks. The charcoal inside the cask will help to mellow the sharp flavours from the distillation. There are different levels of toast and charring, and each distillery has its own preferences. As a general rule, a higher charring level allows the spirit to get into the pores of the oak. Obviously, these casks will have a different impact on the flavour and on the colour. 

Previous liquid

The question of what influences the colour of whisky becomes even more complex depending on the liquid initially contained in the cask used to mature the whisky.

The casks can come from a number of different spirits. Former sherry or bourbon casks are incredibly popular, but distillers are always trying to experiment to innovate their production. Thus, it is possible to find whisky matured in wine casks…and even tequila! 

Let’s see together how the different types of casks used in the whisky industry can influence the whisky colour and flavours. 

The Most Popular Type Of Casks in the Whisky Industry

Bourbon Cask

Bourbon casks are made from American white oak. Then, they are toasted before being used for the first time. The wood infuses the whisky with its aromas, along with the characteristics of the bourbon itself: notes of vanilla, butter and caramel, and that unmistakable colour that turns to light golden.

Whisky Examples

Sherry Cask

Ex-sherry casks are the second most used cask type in the industry. Traditionally, this cask is made with Spanish oak, which is responsible for the dark and spicy flavours to the whisky. However, sherry casks can also be made of American oak, which results in sweeter characteristics such as vanilla and fresh fruit.

In any case, this type of cask tends to give the whiskies matured in it that lovely coppery colour.

Whisky Examples

Other Casks

As mentioned earlier, ex-sherry and ex-bourbon casks are the most widely used in the whisky industry. But this has not stopped distilleries from experimenting with other cask types! What happens if we put a new whisky in a Bordeaux or a Marsala cask? Read more to find out!

Fino Sherry Cask

The Fino Sherry is a light type of Sherry. Actually, maturation in a Sherry Fino cask greatly increases the dryness of the whisky. But it also adds some floral or other fruity notes.

Since Fino is a light wine, the effect it has on the colouring of whisky is almost none. However, most of the hue comes from the oak of the cask wood. 

Oloroso Cask

Oloroso Sherry originates in southwest Spain. It is a fortified wine with 17-22% ABV and a sugar content of 0-5 grams per litre. It is precisely these characteristics that give the whisky matured in these casks those sweet flavours of figs, sultanas and nuts, making the distillate softer than other whiskies. 

Whisky matured in oloroso is very dark and for this reason, some distilleries tend to subject the whisky produced to a process of ‘lightening’ the colour to make it more amber-coloured. 

Bordeaux Cask

This famous French wine is named after its region of origin. The many appellations and grape varieties result in many different aromatic expressions. In general, whisky matured in this type of cask has strong tannins, fruity notes and a full-bodied character. In addition, it gives the whisky that typical dark ruby red hue, which can also turn purple.

Burgundy Cask

The Burgundy casks come from the Burgundy Wine. Most of the whisky matured or finished in this type of cask gain fruity and fresh aromas, and sometimes can become a little bit dry. As for the colour of the distillate, it tends to acquire dark red tones. 

Madeira Cask

Madeira Wine is a fortified Portuguese Wine, and it comes from the Madeira islands, in front of the African continent.

Whiskies matured in Madeira casks usually take on the spicy and fruity flavour typical of the wine itself, with slight hints of spiciness. Usually, all fortified Madeira wines have a dark colour. This results in a darkening of the whisky matured in these barrels, with some red hues.

Port Cask

As a general rule, the sweeter and less dry the port stored in the cask, the greater its impact on both the flavour and colour of the whisky.

The typical aromatic characteristics of whiskies matured in ex-port casks are plum, blackberry, strawberry jam, cherry and sultana. All accompanied by that beautiful colour tending almost to pink when the bottle is kissed by the light.

Pedro Ximenez Sherry Cask

The Pedro Ximenez originated from the southern regions of Spain and it is a very sweet fortified Dessert Wine with a very dark colour. 

Maturation in Pedro Ximenez gives the whisky an additional Sherry-like sweetness. It also adds flavours of dried grapes and a softness reminiscent of syrup.  Also considering its very dark colour, whiskies matured in these casks turn almost dark brown. If, on the other hand, the whisky is only finished in the casks, it turns a light amber or golden colour.

Manzanilla Sherry Cask

The Manzanilla Sherry is a subcategory of the Fino Sherry. 

Whiskies matured in these casks achieve a greater dryness, if not slightly acidic with a slight hint of marine. As the Manzanilla is a clear wine the effect on the whisky colour is practically non-existent.

Amontillado Sherry Cask

The Amontillado is an intermediate between the Fino and the Oloroso. Indeed, whiskies matured in this type of cask have the sweetness of Oloroso and the more typical dryness of Fino, with an added hint of hazelnut. The Amontillado Sherry cask turns the whisky into a nice amber colour liquid, with a golden shine to it.

Palo Cortado Cask

The Palo Cortado is a special kind of Sherry: a mixture of Amontillado and Oloroso. However, the fresh, dry, crispy notes of the Amontillado develop more in the nose than the taste. The general flavour is dominated by the dark, fruity Oloroso aromas. 

The whiskies matured in this type of cask are usually darker and comparable to an Oloroso.

Sauternes Wine Cask

The Sauterne Wine comes from the Sauterne region, a subregion of the Bordeaux Wine region. This type of cask enriches the whisky with sweetness, making it fruity, with distinct notes of apricots and peaches, accompanied by a slight hint of honey and nuts. Finally, it imparts amber colour tones to the whisky. 

Tokaji Cask

The Tokaji is a Sweet Wine made out of white grapes and produced in Eastern Europe.

Tokaji cask offers many aromatic nuances due to the mix of different grape varieties. The main types ‘Furmint’ and ‘Hárslevelű’ create a balanced dry and floral aroma. To these are added the typical notes of Muscat and ‘Zéta’. Overall, Tokaji has honey and fruit aromas, which influence the whisky. 

With regard to colour, since the grapes are white, a Tokaji cask does not affect the colour of the maturing whisky.

Ruby Port Cask

This port is the most popular port wine available on the market. Ruby is mostly stored in airtight tanks to avoid oxidative maturation of the wine. This means that there are no casks in this case. However, a few Ruby ports are still matured in oak barrels. As a result, the whisky matured in these barrels is a sweet distillate with a wine pale colour. 

Barolo Cask

This wine is produced in North Italy. Barolo cask matured whisky has a slightly red hue, with intense fruity aromas of blackberry, in combination with dark chocolate, tobacco and wood.

Chardonnay Cask

Chardonnay is a famous French wine. Due to the maturation in Barriques, in which the Chardonnay was previously stored, the whisky obtains light and fresh aroma. Moreover, it can also give the whisky a dry taste with a hint of tropical fruit. The whisky matured in Ex-Chardonnay casks has a light colour between yellow and amber.

Muscat Cask

Muscat is named after the grape from which the wine is made. The effect on the taste is much like a Sherry or a Port: it makes the Whisky sweeter and fruitier. The Colour alteration of the Whisky matured in the cask solely depends on the type of Muscat Wine stored in the cask before. Usually, for whisky making Muscat fortified wines are preferred.

Rum Cask 

The finish in Rum casks underlines the fruity notes of a Whisky. This includes sweet aromas like vanilla and caramel. Additionally, it provides the Whisky with spice, also making it smooth. As for the colour, the amber tint of the whisky does not come from the rum per se, but from the cauterised casks.

Amarone Cask

Amarone is an Italian Red Wine from Veneto. This type of cask amplifies the bitter notes of the whisky, also giving the distillate a particularly dark colour that leans towards red. 

Marsala Cask

The Marsala Wine is a fortified Italian Wine that comes from the city of Marsala, Sicily. The Marsala wine has a sweet, spicy and sometimes nutty aroma. This is also reflected in the whisky that had a Marsala wine maturation or finish. The result is a dark spirit with a dark reddish colour.

Virgin Oak Cask

Fresh white oak casks, or ‘Virgin Oak’ casks, are mainly used for Whiskey maturation in the USA. A freshly toasted cask gives off particularly many vanilla and clove aromas to the Whisky, with a hint of sweet ginger and coconut. This kind of cask gives the whisky a  caramel colour, created by the roasting and charring of the same. 

In Conclusion

In this article, we learned how wood and casks affect the final flavour and colour of the whisky. To be precise, these factors contribute 60% of the final result! But there are certainly other criteria to take into account when it comes to colour. If you are curious to know more, don’t miss the second part of this article!

In the meantime, share the article and tag us so we can know which type of whisky maturation is your favourite. And of course, what is your favourite whisky colour? 😉

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