When choosing a malt whisky there are various factors to consider: the distillery, the age and the style, not to mention the price. The alcoholic strength is also significant, being one of the factors that determines a malt’s flavour profile. Consequently, perceptions of the same malt at different strengths can vary, which includes the intensity and range of flavours.
The bottling strength is either pre-determined, and reached by diluting the whisky with the required amount of water, or, in the case of cask strength bottlings this depends on the alcoholic strength a whisky reaches as a consequence of the ageing process.
The vast majority of malts are bottled at 40% ABV (the EU minimum for Scotch whisky). Another established bottling strength is 43% ABV, also referred to as ‘export strength,’ as Scotch whisky was traditionally dispatched around the world at this strength (and regulations in South Africa, for example, continue to stipulate 43% ABV as the minimum).
Meanwhile, Scotch whisky is increasingly exported at a range of strengths. This includes 46% ABV, which has more recently become a key bottling strength, as it is considered the lowest strength at which malt whisky can be bottled without chill-filtering (ie. chilling the whisky, then passing it through a filter). Whiskies bottled below this strength are chill-filtered in order to prevent the possibility of a ‘cloudy haze’ forming when the whisky is exposed to lower temperatures. Opinions on the effects of chill-filtering vary, particularly as there are different ways of approaching this process, including the temperature to which the whisky is chilled (this needs to be the subject of a separate article).
Cask strength bottlings span a broad range of alcoholic strengths, and depending on the length of ageing this won’t necessarily be higher up the scale, as the strength gradually decreases during ageing. But whatever the ABV, this style has a particular appeal.
“A cask strength bottling means getting whisky exactly as it was in the cask. Nothing’s been done to it, and more people are becoming aware of that, which has resulted in a big increase in demand for cask strength whiskies,” says Gordon Motion, Edrington’s master whisky maker.But what about the influence of alcoholic strength on the actual flavour profile itself?
“The higher the strength the more intense and concentrated the flavour, rather than the myriad of flavours at a lower strength,” says Sandy Hyslop, Chivas Brothers master blender.
Brian Kinsman, master blender, William Grant & Sons, adds, “Alcohol is a carrier for flavour compounds, and alcohol itself contributes very little to the character of a malt, but a lot to the experience. As the alcoholic strength reduces, various flavours can show more readily.”
So, what can we expect to see as the strength of a malt decreases ?
“Different flavour compounds show at different strengths. Richer flavours, such as dried fruit, tend to come over at relatively higher strengths, and can dominate lighter notes such as citrus, which show more at a relatively lower alcoholic strength. But this also depends on each individual malt whisky, as some have more ‘top notes’ such as citrus, while others have a higher proportion of richer notes,” says Stuart Harvey, master blender, Inver House Distillers.
This naturally leads to the subject of adding water to a glass of malt whisky (and so lowering the alcoholic strength).
“I actively encourage people to experiment with the strength at which they drink malts. If you have a cask strength malt, such as Glenlivet Nadurra or Aberlour A’bunadh, you can add a drop of water, try it, and then continue adding another drop of water and re-tasting, until you find the strength that you like best. Tormore at cask strength, for example, shows intense orange marmalade, while at 40% ABV the orange notes are sweeter and accompanied by soft caramel and vanilla,” says Sandy Hyslop.
Brian Kinsman provides another example, together with a note of caution. “Adding water to The Balvenie Single Barrel 12-years-old, bottled at 47.8% ABV, accentuates the fruit, honey and sweetness. But this only works up to a certain point of dilution, after which dilution takes all the body out of a malt.” Timeline Of Alcoholic Strength
The alcoholic strength of new make spirit is typically around 70% ABV, which is usually diluted with water to reach a strength of 63.5% ABV before being filled into casks for ageing. During the ageing process water and alcohol evaporate from the cask (oak being porous).
“The annual evaporation rate is around two per cent of the contents of the cask per annum, for the first 12 years or so. After this time the evaporation rate slows down to about one per cent per annum, and after about 20 years ageing this decreases further, to below one per cent, and possibly even 0.5 per cent per annum,” says Brian Kinsman.
This, in turn, promotes another significant change.
“Evaporation is a principal reason for the reduction in alcoholic strength during ageing. Up to 12 years ageing, the reduction is generally around 0.5% ABV per annum, after which this rate slows down in line with the decreasing rate of evaporation,” adds Brian Kinsman.
A cask strength sample from Glenrothes