Without wanting to get too technical, it’s all to do with the interaction between compounds in the wood and the water and alcohol in the liquid. You’ve got all sorts of different compounds that will affect the colour of the whisky – tannins come into it, as do sugar-type compounds. When the cask is first made by the coopers, the wood inside is toasted (heated low and slow without igniting the wood) or charred (burnt in high heat for a short blast), or sometimes both. That process caramelises the sugars present in the wood – creating those lovely toffee and caramel flavours so central to whisky, and additionally giving some brown colour too as the colour compounds are extracted from the wood by the spirit.
Different types of cask give different colours too, and extract colour at different rates. The spirit maturing in our ex-bourbon casks is the colour of light straw, whereas the STR red wine casks give a much darker, amber hue. Port casks produce a deep ruby red colour to begin with, although as oxidation occurs, that deep red will turn to a more brick-red and then steadily browner. There really are lots of variations out there.
Now, where it gets slightly muddier (the topic, not the colour of the whisky) is that some whisky producers will ‘top up’ the naturally occurring caramel, with not-so-naturally occurring caramel, known as E150a, or spirit caramel. This is a processed caramel made by burning sugars under controlled conditions to create a thick, black, tarry substance. This substance can be added to whisky in order to iron out differences in colour between batches.
Batches of whisky are matured in different casks, and colour development in a cask is almost impossible to predict or control, so the whisky that comes out of the casks will be different colours. The blenders mix different casks together to make sure the flavour of that batch matches the flavour of the batches before – so the consumer is buying a consistent product. But even if they get the batches tasting the same, they may be different colours.
The industry argues that adding a tiny amount of spirit caramel allows them to give colour uniformity between batches, which is what the consumer wants. A tiny, tiny amount is enough to turn a clear liquid into a deep brown one, so not very much is needed – and the argument goes that these tiny amounts are ‘organoleptically inert’: you can’t smell or taste them in the whisky.
This would all seem fairly problem-free, except that spirit caramel makes a liquid darker. You won’t find blenders taking steps to match the colour of batches by making some lighter, because subconsciously darker whisky = older whisky, and older whisky (according to the industry) = better whisky. So the added benefit to using E150a is that the whisky is more attractive to consumers because it looks older. And that’s why purists object to the use of spirit caramel – it’s seen as misleading, deceptive even. Some also argue that they can actually taste the added caramel – it is not necessarily unpleasant and might help mask the differences between casks. But in these instances, it would then represent an artificial flavour additive, which is supposed to be outlawed in whisky making in this country.
So, where do we stand? Unsurprisingly we’re in the ‘no artificial colour’ camp. We just don’t think it’s necessary – whisky drinkers embrace the magic of cask maturation, they know that each cask is a unique vessel. Why should tiny differences in colour put them off? Interestingly, because part of our Cotswolds Single Malt Whisky is matured in STR red wine casks, the whisky itself has a much darker colour than a whisky matured solely in bourbon casks – but we can assure you, no caramel trickery here, it contains 100% naturally occurring colour.