The process of liquor distillation is centred around separating alcohol – or ethanol – from water and other substances through vaporization and condensation. Since the former has a relatively low boiling point compared to many other compounds in the liquid, the separation that occurs during distillation enables impurities and many of the compounds that contribute to colour and flavour to be expelled. The by-product of this distillation is relatively pure in the context of alcohol content, and appears clear, as a result.
However, the clarity does not necessarily mean that the absence of all compounds other than ethanol exist since there continue to be trace amounts of other compounds that contribute to the purified liquor’s aroma and taste. A great example of this is vodka – which is distilled multiple times to achieve a high level of purity, with the resulting liquid being exceptionally clear and almost flavourless. In contrast, spirits like gin or rum might use botanicals or undergo aging in barrels, adding to their flavour and colours post-distillation.
The signature amber colour that many liquors such as whiskeys or dark rums possess, primarily comes from the aging process in wooden barrels. During this course, the liquor interacts with the wood – specifically compounds present in oak barrels, that are responsible for its taste and appearance. Natural compounds like lignin and tannins in the wood break down and leach into the liquid over time. On one hand, lignin facilitates the disintegration into various complex molecules, which contributes to the liquor's flavours, whereas tannins add depth and complexity. In addition to this, the chemical reactions that take place between the alcohol and the wood, further influence the colour and taste of the aging liquor.
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The longer liquor continues to remain in the wooden barrels, the richer the hues become for aged spirits. Moreover, the oxygen in the atmosphere also interacts with the alcohol, leading to controlled oxidation, which helps in the development of flavour notes and the mellowing of harsh compounds in the liquor. Furthermore, the process also involves the liquor undergoing esterification – where the liquor obtains its fruity and floral notes. Over time, as some of the liquid evaporates through the barrel – or what is known as the ‘angel’s share,’ it results in the concentration of flavour and enhances the richness of what remains.
While both – distilled and aged liquors start off with similar base ingredients like grain or fruit, clear liquors typically emphasize the purity of the base ingredients whereas aged spirits enhances the complexity through interaction with the wood and other environmental factors. Clear liquors like vodka or gin are often chosen for their neutrality – making them ideal for cocktails, since the emphasis is on other flavours and ingredients. Barrel-aged liquors, on the other hand, tend to have more of a distinct taste that is developed through aging, and hence is often enjoyed neat or with minimal mixers to appreciate their nuanced taste.