Enjoying whisky in the form of a long, refreshing drink, or a sophisticated cocktail, certainly has its appeal. But to savour a malt whisky a typical recommendation is diluting with water, on the basis that it ‘opens up’ the character.
While this implies that the existing aromas and flavours will simply become more accessible, adding water actually initiates a series of complex changes within the whisky. As these changes are still not fully understood, opinions on this subject inevitably vary.
However, diluting can significantly alter a malt’s balance and intensity, which in turn affects the aroma, flavour profile and mouthfeel. So, while still the same whisky, it can show different nuances.
Malt whisky already contains a certain amount of water, with an alcoholic strength of 40% ABV for example meaning that approximately 60 per cent is water (a combination of ‘process water’ added during mashing, and ‘reduction water’ added to reduce the strength for barrelling and bottling, as required).
An initial consequence of adding water is lowering the alcoholic strength. This sees a reduction in any possible pungency or ‘alcohol tingle’.
A related factor is that alcohol at a certain strength can overwhelm some taste buds on the tongue, which limits the detection of particular characteristics. This effect peaks of course in cask strength whisky, when the palate has to deal with a significant or excessive level of pungency, and diluting is required in order to assess the flavours.
However, exactly what happens on the tongue when tasting whisky is so complex that it’s still in the process of being fully understood.
It’s easier to quantify certain reactions taking place within the whisky.
Adding water makes some compounds come out of solution (ie. come out of a liquid form), and show primarily as an aroma rather than as a flavour. For example, adding water sees esters come out of solution, and vapourise into the headspace. This creates the sense of a sudden release of esters, typically showing as fruity, floral notes.
Meanwhile, small ‘clusters’ of esters remain in solution and continue to show as a flavour, but in a milder manner. Consequently, the level of esters on the nose will not necessarily be replicated on the palate, and a urther consequence could be a noticeable increase in the way other characteristics, such as oaky and cereal notes, show on the palate.
Adding water also creates a certain temperature change in the whisky, with this release of energy effectively confirming that the balance of the malt is changing. However, if served within a typical range of between 20%-40% ABV, an increase in temperature is not sufficient to influence the malt’s flavour delivery.
Diluting results in a certain degree of bonding between the water and the alcohol (a process which happens more rapidly at a lower strength).
Meanwhile, another factor is that at a higher strength alcohol molecules are grouped around water molecules, whereas at a lower strength the reverse occurs, with water molecules grouped around alcohol. Although this may also effect a minor change in mouthfeel, texture stems from water and alcohol each having a different mouthfeel. Consequently, dilution alters the balance by increasing the influence of water on the texture, and simultaneously decreasing the influence of the alcohol, resulting in a more ‘watery’ mouthfeel.
Moreover, water has a greater surface tension than alcohol, and as they don’t mix homogenously, there are micro-zones within the whisky that have different concentrations of alcohol and water. It’s these ‘irregularities’ that contribute subtle texture and mouthfeel. Adding more water sees these micro-zones begin to break up and become more uniform, which in turn changes the mouthfeel.
An additional, though subtle influence on mouthfeel are other compounds within a malt, such as tannins, though trying to quantify the exact influence of tannins is another matter.
Similarly, why the texture of older malts is mellower than younger malts is still not entirely understood, though one theory attributes this to a particular alignment of all the various components. What’s clear is that diluting an older malt entails a significant risk of the whisky simply ‘collapsing’ possibly due to this particular alignment being altered by a reduction in alcoholic strength. After all those years of aging to acquire a certain mouthfeel, that would be really tragic.