The texture (or ‘mouthfeel’) of a malt is determined by a number of factors, including alcohol, water and various flavour compounds such as vanillin (which is extracted from the cask during aging, and contributes vanilla notes). Even small differences between the proportions of each influencing factor will result in one malt having a slightly, or significantly different texture from another. This explains why there is such variety in the texture of malt whiskies, from delicate, silky and velvety, to luscious, creamy and full-bodied. However, research into texture is still at an early stage, which means that exactly how the texture is determined is one of the least understood aspects of whisky.
Of all the factors that influence texture, alcohol and water are present in the greatest quantity. For example, a malt whisky bottled at 40% abv (alcohol by volume) comprises 40 per cent alcohol, and the balance of 60 per cent is almost entirely accounted for by water (with flavour compounds only accounting for a tiny fraction of this balance).
Malts are of course bottled at a wide range of strengths, which includes plenty of expressions at 43% and 46% ABV. The alcoholic strength is significant because this determines the proportion of alcohol to water, which in turn influences mouthfeel, as water and alcohol molecules have a different effect on the palate, and consequently promote a different texture. Alcohol has a ‘prickly,’ puckering and drying effect, whereas water has the opposite effect, being cooling, hydrating and soothing. However, as alcohol and water are integrated, this ensures a homogenous texture.
Although water and alcohol are the dominant ‘components’ of a malt whisky in terms of volume, they are not actually the most significant factors in establishing a malt’s individual texture.
“Most malts are bottled at 40-43% ABV, so they have pretty much the same quantity of water and alcohol. This means that an awful lot of the differences in texture between malts are due to other flavour compounds, such as tannins. Even though these flavour compounds may only be present in trace amounts, they are very influential,” says Dr Bill Lumsden, head of distilling and whisky creation, Glenmorangie.
Tannins are extracted from the oak cask by the maturing spirit during the aging process, and the level extracted depends principally on the type of cask used. Sherry casks and bourbon barrels are the standard choice, with Sherry casks usually made from European oak, which contains several times more tannins than American oak, from which bourbon barrels are made. This means that malt aged in a sherry cask generally acquires a higher level of tannins than malt aged in a bourbon barrel.
Meanwhile, tannins are extracted from the cask at the greatest rate during the first few years of aging, after which the extraction rate slows down significantly. Consequently, longer aging doesn’t result in tannin levels increasing at the same rate each year.
“Tannins definitely affect mouthfeel, promoting a mouth-coating velvety texture. Additionally, tannins generally give dryness, which isn’t really a texture, but dryness gives a sensation that could be described as mouthfeel, and this also lingers in the aftertaste, like a mouth-coating residue on the palate,” says Brian Kinsman, master blender, William Grant & Sons.
However, the benefits that tannins contribute to mouthfeel also depend on the level extracted.
“In the right quantity tannins give structure and body to the mouthfeel, but there is definitely a tipping point, and the level can get to a stage where the effect of tannins is very drying, with tannins also contributing astringency and bitterness,” says Dr Bill Lumsden.
Vanillin is another flavour compound which contributes to mouthfeel, as the vanilla flavour includes a creamy texture. Moreover, vanilla notes also have a significant interaction with other flavours in a malt whisky. In the same way that adding salt when cooking can ‘focus’ different flavours, in a malt whisky vanilla has the ability to make other flavours seem richer, smoother and rounder; which in turn influences the perception of mouthfeel.
Meanwhile, longer aging doesn’t result in a continually escalating level of vanilla flavour and creamy texture, because the extraction rate of vanillin from the cask is greatest during the first few years of aging, and then slows down significantly.
Esters are renowned for contributing fruity notes, such as apples and pears, but esters are also another example of a flavour compound that contributes to the texture. Esters are created when alcohol and acid molecules interact and integrate with each other, the majority being formed during fermentation, with smaller amounts formed during distillation and the aging process. Different types of esters are formed, including short chain esters (typically comprising a couple of linked units), medium chain (up to several linked units) and long chain esters (in excess of several linked units).
“Long chain esters are present in tiny quantities, but they contribute oily, silky, rich notes which are not so much a flavour but a mouth-coating texture,” says Brian Kinsman.
And that takes us to a recurring theme when discussing texture. To what extent do characteristics such as creamyness, oilyness and silkyness play a more comprehensive role in the wider scheme, by also contributing to the perception of flavour?
With some malts you can feel a rich, honeyed texture on the palate, which is certainly mouthfeel, though richness can also be described as part of the flavour. You cannot separate the texture from aroma and flavour, they are all part of the same whole.
Despite numerous technological advances, the greatest authority in discerning texture continues to be an experienced palate.
“When you use technology to analyse malts you can measure differences in the level of various flavours, but you can’t pick up any real differences between malts in terms of viscosity. It’s only when you actually taste these malts that you see how different the mouthfeel of each malt can be,” says Brian Kinsman.