The Chemistry of Whisky

All the Colours of Whisky (Part 2)

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September 7, 2022

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

In the previous article, we saw how wood and cask type can influence the colour of the whisky (and its aromas!). However, in reality, things are much (very much) more complicated than that. The maturation temperature, the size of the cask, and even food colouring are all key factors that contribute to the whisky colour. All of these elements are responsible for whether the whisky has that gold or red shade when we pour it into the glass in bright daylight. But let’s go through them step by step, and look at them together.

The size of the cask

The cask maturation is one of the most influential phases that define the colour of the whisky and taste (this phase impacts more than 60% of the final product!). We have already talked (a lot) about it. However, the actual size of the cask can also plays an important role when it comes to whisky colour and taste.

Cask sizes are very difficult to define because there is no real standard. As things weren’t complicated enough, cask size was also a unit of measurement. Take for example the butt. Normally, this cask has a size of 500 litres. But there is also a unit of measurement called a butt, which corresponds to approximately 477 litres. So, when we talk about casks, there are various types.

Generally speaking, a cask is defined as ‘large’ when it contains more than 400 litres of liquid, ‘medium’ when it contains between 200 and 400 litres and ‘small’ when it contains less than 200 litres.

But how does size influence the colours and aromas of whisky?

In a small cask, the ratio of the Whisky to the cask walls is higher than in a large cask. This simply means that the smaller the cask, the more the surface of the liquid is in contact with the wood. Conversely, the larger the cask, the less contact between the whisky and the wood. In the first case, maturation will be faster, and in the second case slower. However, it should be emphasised that a fast maturation process does not automatically translate into a better process.

Below we have listed for you the most common cask sizes in the Whisky industry. So you can brag to your friends at the next tasting you attend together that you are a real cask expert.

Bourbon Barrel (American Standard Barrel) 

Litre: 200

In the USA it is a legal requirement for Bourbon to mature for at least two years in fresh casks made of oak. Once these have been used, they become useless for the American distilleries. And yet, it has become standard practice in Scotland to mature Whisky in these used Bourbon casks for the incredible aromas they provide to the spirit. Typically, such an American Standard Barrel contains about 200 litres, making it one of the smaller ones among the casks.

First fill bourbon casks are perfect for the maturation of Scotch whisky up to a certain age (around 15-18 years). Moreover, a fresh and active cask will also mature quicker. But be careful: whisky left for too long in a first fill cask can become too woody.

The wood of refill bourbon casks is less active than the first fill. However, a refill cask still contains plenty of the natural chemical compounds present in the oak. It will take longer for the new spirit to extract the flavours, and the whisky will mature more slowly, which makes this type of cask more suitable for long maturation. 

Butt 

Litre: 500

In the Sherry industry, 500 litre butt casks are widespread and common. The term ‘butt’ is derived from the Italian word ‘botte’, meaning barrel. In the past, Sherry and Port wine were transported in these casks across the English Channel to the United Kingdom. As with Bourbon casks, the Scots took the opportunity to mature their Whisky in used Sherry casks that give the spirit additional fruity flavours.

First fill sherry butts result in an extremely rich, nutty and often dark-coloured whisky with a lot of flavours imparted from the sherry. Due to the colour, First fill sherry butts are among the most desirable casks available and fetch the highest prices.

A refill sherry cask will mature more slowly, and the sherry influence and the colour will be less intense. However, this is an advantage if the cask is intended for long ageing, and the distillery character will be enhanced.

Port Pipe

Litre: 350 – 650

The casks from the Port Wine industry are very closely related to the Sherry butts. Port pipes also contain up to 650 litres. However, compared to the Sherry butts, Port pipes are a bit more compact. 

Quarter Cask

Litre: 125

Quarter casks are smaller casks in which Whisky often matures to gain more flavour. In the past, these cask sizes used to be very popular because they made it easier to transport spirits. Today, they are known for their capability of making the whisky maturing process faster. Moreover, they are particularly used for secondary maturation.

Hogshead

Litre: 230 – 250

Hogsheads are casks made from the staves of other casks and they are also the most commonly used. Usually, Hogsheads are also made from the staves of former Sherry casks.

Puncheon

Litre: 500 – 700

The puncheon is an old English unit of measurement, after which this type of cask was named at some point. Puncheons are widely used for maturing Sherry. Like a butt, a puncheon also holds 500 litres, but it is shaped in a slightly different way. It is wider and more compact. Some puncheons are also built smaller if they are used for the maturation of Rum. In Whisky production, however, the most common puncheon is the Sherry puncheon, which holds about 500 litres.

Madeira Drum

Litre: 650

These drums are even more compact than the similar Sherry butts or Port pipes. Unlike most other types of casks, the Madeira drum is made of the so-called sessile oak. In Whisky maturation, Madeira drums are particularly popular for finishes, to add the aromas of Madeira Wine to the spirit.

Cognac type

Litre: 300

Similar to Sherry and Wine casks, Cognac casks were also available in Scotland in sufficient quantities due to imports and have a 300 litres capacity. The use of Cognac casks to mature Whisky is not common. However, you can find a Whisky with a finish in a Cognac cask. 

Barrique cask

Litre: 225

Barrique is French for cask. Accordingly, most barriques are made of French white oak and are slightly larger than hogsheads. About 225 litres of Whisky can be stored in one barrique. This Whisky naturally absorbs the aromas of the Wine from the cask.

Bordeaux type

Litre: 225

A Bordeaux cask is also a barrique, but in particular, one that was previously filled with Bordeaux. It can be filled with 225 litres of Whisky

Bloodtub

Litre: 50

It is the smallest of the Whisky casks and can contain a mere 30-50 litres. Today it is no longer used in commercial Whisky maturation, but distilleries often offer it to customers who would like to buy their own cask of Whisky.

Cask Reuse

Another important factor influencing the colouring of whisky is certainly the number of times a cask has been used. The more often a cask is used, the less “active” the wood becomes and the less colour it imparts to the spirit. In short, it is like a felt-tip pen that, as it is used, drains more and more until only a shadow of colour is released. 

Casks are expensive these days. It only makes sense that the Whisky industry matures Whisky in casks more than once. A cask still retains a lot of aromas after 10 years of Malt Whisky maturation and is therefore reused for the next Malt. These types of casks actually have a technical name: they are called ‘refill casks’, and they are reused for up to about 30 years.

Fist Fill Cask VS Refill Cask

A cask used for the first time to mature whisky is referred to as First fill. When it’s referred to it as “refill” or “second fill” etc., it means that they have been reused again and again for ageing whisky. According to how many times it was refilled, the cask plays a different influence on the flavours and colour of the resulting product.

It is clear, however, that in the case of a refill cask, the influence of the cask itself on the taste will get weaker and weaker. That’s why on the labels of some bottles you may sometimes find indications like ‘Refill’ or ‘First Fill’, which stands for the degree of use of the casks. This gives the customer an indication of the approximate intensity of the cask aroma.

Due to their flavour intensity, First Refill casks are perfect for whisky that goes from 15 to 18 years of maturation. Moreover, this type of cask might give 80% of its flavour from the wood and 20% from the distillation process.

Refill casks are commonly used for long maturation periods (from 18 to over 40 years old). This way, the oak flavours will be more subtle, and the distillery character will play a greater part in the overall flavour. To be precise, a refill cask will give closer to 60% of its flavour from the oak and 40% from the distillery.

Single and Double Cask

Whisky is not necessarily matured in one cask. As mentioned in this article, the distillate is sometimes ‘finished’ in a second cask to enhance its flavours and colours. But what does this really mean?

Simply put, a single cask is a whisky bottled from a single cask, while a double cask indicates a secondary maturation, more commonly referred to as a cask finish.

But sometimes, a whisky can be double cask or triple cask, which means that the spirit has spent a period of maturation in one cask, then was poured into another. 

Example of double cask whisky

Here’s a little tip if you are new to whisky. It will probably be easier for you to start with single-cask whisky than double-cask. In particular, Sherry Oak offers a rich sweetness that will appeal to most consumers. Double cask, on the other hand, generally has deeper oak notes and some warmth at the end of the whisky, which makes the spirit more complex to taste.

Temperature

Many other different natural factors can influence the colour of the whisky. Indeed, there is no doubt that the longer a whisky is left to mature, the darker it tends to become.

However, this general rule can vary depending also on the temperature of the whisky during its maturation. 

Indeed, it must be remembered that the colour solubility increases with increasing temperature. This means that the “new make” will absorb the colour (and flavours) more quickly in less time, becoming darker. 

But does darker actually mean better quality whisky? Absolutely not! For the various reasons, we have outlined here and in the previous article. And because sometimes, the hand of man intervenes to make the colour of whisky more appealing to consumers…

Chill-filtering process

Speaking of temperature. Before we go on and discuss the artificial colours added to whisky, let us pause for a moment to discuss chill-filtered whiskies. What exactly does it mean when we see this statement on a label? And how does it affect the whisky?

Have you ever looked at a bottle of whisky and noticed, especially during the winter, that the colour of the whisky has changed? The golden liquid is no longer crystal clear but rather slightly cloudy. Don’t worry. Your whisky has not gone bad. This simply indicates that the distillate was not chill-filtered before bottling. 

In its natural state, whisky tends to form a haze and become cloudy. Over time, some slight sediment may also appear and settle at the bottom of the bottle. This is the result of interactions between temperature and ethanol content: the colder and lower the amount of ethanol, the more turbid the whisky in the bottle can become.

However, it is easy to imagine that consumers seeing their whisky turning turbid would not find it very attractive. To avoid this, the whisky industry solved the problem with the help of the chill-filtering process.

The Process

During the chill-filtering process, the whisky is cooled to a low temperature (around 0°C, sometimes even lower) and the liquid is then passed through a fine filter by means of pressure. During this process, the tiny particles and suspended matter that cause the turbidity of the whisky, are absorbed and filtered out. 

But does this process only affect the aesthetics of the whisky or also the flavour? This a rather difficult question to answer.

While some believe that the chill-filtering process contributes to a somewhat diluted whisky flavour, others question whether any differences in taste are actually perceptible to the human senses. But you know, perception is a rather intimate matter, so there is no correct answer to this question. 

Artificial colouring

Earlier in this article, we said that the colour of whisky can reveal a lot about an expression with just a glance… more or less.

The thing is that a colouring agent is often used in the whisky industry: the E150a, otherwise known as spirit caramel, or caramel colouring.

Why do distilleries use E150a?

It is unavoidable. We make most decisions based on how attractive something looks and feels. This, for many drinkers, means that the darker the whisky, the older and therefore, the better. A misconception that is often wrong for several reasons. For one thing, some ‘young’ and quite pale whiskies can be surprising to the taste and turn out to be much more complex than expected. Secondly, an aged whisky does not automatically mean a high-quality one. In short, as always in life, never judge a book by its cover (well, in this case, don’t judge a bottle by its colour…).

In any case, distilleries choose to add colouring to their whisky to exploit this psychological bias, while also ensuring that each whisky batch has the same colour maintaining brand consistency. That said, the impact that wood, cask and temperature could have on the whisky is completely wiped out by this colouring agent. Everything is coloured in the same way by this element. Not very romantic, we agree.

Effects on taste

Bear in mind, despite using the word “caramel,” to define the E150a, we are not talking about flavour here, as it is virtually tasteless. Though there is a good reason why it is known as “caramel” colouring: it’s basically made by burning carbohydrates (like sugar or corn syrup) into caramel.

Taste tests conducted in recent years seem to suggest that E150a does not alter the whisky’s flavours. But, as we already said, perception is a very subjective matter, thus opinions may vary in the vast world of whisky. In this regard, many consumers and enthusiasts would like the whisky industry to stop using colouring.

Regarding the safety of this colouring agent, The European Food Safety Authority’s scientific Panel on Food Additives and Nutrient Sources added to Food (ANS) has attested that these caramel colours are neither genotoxic nor carcinogenic and that there is no evidence to show that they have any adverse effects. Nevertheless, the Panel also recommended keeping consumer exposure to the caramel colours as low as possible. In short, on the health front you can feel safe if, like everything else, you consume whisky and consequently the colouring in moderation.

But how can you detect a whisky that has added colouring agents?

In general, unless the label explicitly states that the whisky is naturally coloured, it can be assumed that it contains added colouring agents. The rest is up to you. You can decide to buy dye-free whisky or choose that this small detail of appearance will not stop you from buying your next bottle. 

Let us know what you think!

How much are you affected by the colour of the whisky when you buy a bottle? Share the article, tag us on social media and let us know your opinion!

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