The level of alcohol in malt whisky varies significantly, from the minimum bottling strength of 40% ABV (indicating that alcohol accounts for 40 per cent of the contents), up to stalwarts such as 43% and 46% ABV, while cask strength extends way beyond. These numbers clearly confirm that alcohol has a significant presence, and we all know how it can affect our psyche and anatomy. But how does alcohol affect malt whisky?
“Alcohol holds everything together, but as I’ve never tasted an alcohol-free whisky it’s difficult to say exactly what this entails,” says Dr Bill Lumsden, director of distilling, whisky creation & whisky stocks, Glenmorangie.
Consequently, “The role of alcohol is very difficult to deconstruct from all the other influences, such as the ageing process and cask type. Gas chromatography can identify various congeners (flavour compounds) in malt whisky, but can’t isolate the role of alcohol, or tell you how a malt will be perceived on the palate,” says Sandy Hyslop, director of blending, Chivas Brothers.
The role of alcohol is very difficult to deconstruct from all the other influences, such as the ageing process and cask type
So let’s look first at alcohol’s credentials and see where this takes us.
“Alcohol doesn’t really contribute to flavour itself, and is effectively neutral, apart from providing some heat and prickle on the palate, and adding a tiny bit of sweetness, but this is dwarfed by the level of sweetness gained for example from the cask. Alcohol also has a huge impact on the experience and feel of a whisky, adding weight and body,” says Brian Kinsman, master blender, William Grant & Sons.
Meanwhile, alcohol makes another ‘structural’ contribution.
“Alcohol also contributes an element of viscosity to the mouthfeel when mixed with water,” says Rachel Barrie, master blender, BenRiach Company.
In addition to ‘direct’ influences, alcohol makes ‘indirect’ contributions.
“On a chemical level alcohol is a carrier of flavour, providing a medium for the flavours to reach the palate,” says Brian Kinsman.
Meanwhile, “One vital effect is that alcohol intensifies the perception of flavour compounds,” adds Barrie.
The relationship between alcohol and flavour compounds has other facets.
“With a more robust malt such as Glendronach the weight of flavour compounds counter-acts the alcohol, so it seems a remarkably mellow malt. Similarly, when tasting an older, well-matured whisky, you might think there’s less alcoholic strength than there is, due to the accumulation of flavour compounds. It’s all about the balance of characteristics,” says Rachel Barrie.
This also highlights a vital role that alcohol plays during the ageing process: extracting flavour compounds from the oak cask.
New make spirit is typically 63.5% ABV when filled into casks, with the balance essentially water. Flavour compounds in the oak can be classified as alcohol soluble (ie. ‘dissolve’ in alcohol) or water soluble (though there is some overlap between the two).
“Initially the alcohol extracts more alcohol-soluble flavour compounds from the oak such as vanillin and spices. As the alcoholic strength decreases during the ageing process, and the proportion of water increases, the spirit extracts a slightly different profile of flavour compounds. This includes tannins, which are more water soluble (though also alcohol-soluble), which give more colour and a richer mouthfeel. But this in turn also depends on the oak, as Spanish oak has a higher level of tannins than American oak,” says Rachel Barrie.
The time-line involved provides another vital insight.
“The greatest rate of extraction occurs within the first two years of ageing, after which the extraction
rate slows down. Alcoholic strength usually drops by 0.5% ABV per annum, so in 12 years the alcoholic strength declines about 6% ABV, and then more water-soluble compounds start being extracted.
"This means that the flavour profile extracted also depends on the length of ageing,” says Stuart Harvey, master blender, Inver House Distillers.
Filling strengths and bottling strengths are significant considerations, but so is a malt’s ‘serving strength,’ and whether tasted neat or with water (and if so the quantity).
“The higher the alcoholic strength the fewer nuances you pick up, as they’re masked by the intensity of the alcohol. Aberlour A’bunadh, for example, goes from big fruitcake, raisins and Christmas cake, and as you dilute it’s not dissimilar but there is a spectrum change, you get more spice, such as ginger, and orange marmalade. At a lower strength you can also appreciate subtle nutty notes in the oakyness, compared to dry oak notes at a higher strength,” says Sandy Hyslop.
Role of higher alcohols
Alcohol in a malt whisky comprises mainly ethanol but also traces of higher alcohols.
“By definition higher alcohols are a form of alcohol, although they’re considered as flavour compounds, as they’re more about flavour than ethanol. There are different types of higher alcohols and the level varies from whisky to whisky. The level of higher alcohols also changes during maturation, with some losses due to evaporation, and in the right ratio higher alcohols can make a beneficial contribution to a malt,” says Harvey.
However, the role of higher alcohols is difficult to quantify.
“You can look at a higher alcohol in isolation and define its character, but what matters is how a higher alcohol interacts with all the other compounds, which is a far more complex issue. Exactly what each higher alcohol can contribute to the overall character of a malt is still being researched,” Harvey concludes.
Stills play a vital role in alcohol production