Whisky begins as grain. After milling, fermenting and distilling, the result is left to sit in oak barrels where it transforms into the richly flavoured liquid we all love. In the previous feature I introduced some of the sometimes surprising ways grain and yeast create whisky flavours.
Canadian whisky is ideal for studying the sources of flavour because each component of the whisky is processed individually. This makes it easier to tease out their special contributions. Additionally, Canadian whisky is made from two different kinds of spirit. One, 'base spirit', is distilled to high ABV. This removes many of the flavours generated during fermentation, making it much easier to identify the flavours that develop later, during maturation.
Dr Don Livermore is the master blender at Hiram Walker distillery in Windsor, Canada. His Heriot-Watt PhD in brewing and distilling examined the influence of wood on maturing whisky. With two decades of distilling experience behind him, Livermore knows his whisky. To learn about the flavours that arise after distillation, he matures base spirit in three ways: in new wood, in used wood, and in seasoned wood. Who better, then, to help us take a closer look at where in the whisky making process the various flavours of whisky arise?
What we taste in whisky results from the presence of chemicals called congeners. Any chemical that contributes flavour - good or bad - is a congener. Some are so potent that we can taste them in concentrations of parts per billion or even parts per trillion.
Using gas chromatograph mass spectrometry (GCMS), Livermore identifies the various congeners that develop while the whisky matures. This information guides him as he tailors individual whiskies to exhibit specific flavour characteristics. Three different processes produce the flavours that arise during maturation. First, some flavours leach out of the barrel wood itself. Second, air seeping into the barrels leads to oxidation reactions, primarily oxidation of alcohol, creating the classic flavours often associated with long-aged whisky. And third, some of the previous contents that have been absorbed by the barrel seep into the maturing whisky. Let's take a closer look.
"If you really want to know what wood does to whisky," says Livermore, "try Wiser's Red Letter. Good quality virgin oak barrels contribute the dominant characters of this whisky. It begins as a light, smooth, double distilled spirit, and is aged in brand new virgin oak barrels." Since it is made from base whisky, there is no yeast character or grain character to distract from the wood flavours. "If you want to understand what wood tastes like, this is it."
He's right. Red cedar and fresh-cut lumber notes are followed by classic rye spices of cloves, pepper, and ginger, which quickly interrupt the typical caramel start. As there's no rye grain, where did those spices come from? He smiles. Of course! The wood!
"Lignin is the most underappreciated flavour molecule in whisky," explains Livermore. "Think of all the flavours that come from it." This key flavour precursor is found in grain, peat, and wood. Lignin is the main source of wood congeners, including 4-ethylguaiacol and that is what gives rye its signature flavour. "The question people should be asking," he reiterates, "is not 'How much rye,' but how much 4-ethylguaiacol."
Heating breaks down the cellulose, hemicellulose and lignin that wood is made up of, into smaller, more flavourful compounds. Winemakers have known for generations that toasted wood barrels often produce more flavourful wine than charred wood barrels. Livermore's experiments help us understand this effect in whisky. Charring to a depth of 2mm, he discovered, leaves more flavour components in the wood than does charring to twice that depth. With more charring, many wood chemicals that would otherwise contribute flavour and colour to the whisky are incinerated, leaving little flavour behind.
Grain contains sulphur though, and this has a tendency to create off flavours in the whisky. Malting the grain can make the negative influence of this sulphur even more noticeable. However, charcoal, created when the barrel is charred, has the ability to remove these off flavours. Deep charring is preferred when the spirit contains a lot of sulphur, while lighter charring works best for producing typical woody notes such as vanilla. The most surprising thing his instruments reveal though, is that after about 200 days very little additional flavour comes from the barrel, regardless of how it was prepared.
Livermore dismisses the whisky web's current obsession with whisky's age. "How the barrel is prepared is more important than age, except for acetaldehyde and ethyl acetate." Those are the flavours of age, or as Livermore explains, "The taste of the angel's share." To know what really happens in a barrel, he suggests drinking Wiser's 18 Years Old. This whisky comes from high ABV base spirit that is matured for 18 years in barrels that have already been used several times, leaving little wood flavour in them. Air seeps into the barrel over time and reacts with ethanol to create acetaldehyde and ethyl acetate: the green apple notes (some liken them to acetone) that denote long-aged whisky. Since all other potential sources of flavour have been minimized we finally discover the taste of age.
To my palate, Wiser's 18 Years Old is clean, sweet, woody, and ever so complex with hot pepper, baking spices, tobacco, cigar box, and, yes, little green apples. Wiser's 18 Years Old has been a consistent connoisseur's favourite for decades, a reality that might cause those who believe grain and wood are the biggest contributors to flavour, to reconsider their assumptions. Certainly, grain and wood can influence the flavour, to a greater or lesser extent depending on how the whisky is distilled and matured. But in the case of this multi-award-winning whisky, they make virtually no contribution at all.
"The barrel is like a sponge," Livermore explains, before offering his final example. A dry wine barrel typically has several litres of wine soaked into the wood, and an empty Bourbon barrel contains several litres of 'in-drink' Bourbon, hidden in its staves. "What was in the barrel before comes over into the spirit," he says.
Ethereal, estery flavours found only in long-aged whisky, on the other hand, have nothing to do with the wood. These are the products of long slow oxidation that occurs as air seeps into the barrel to replace the angel's share - the spirit that evaporates out. And those ripe fruity notes in sherry malts and wine-finished whiskies? They are there because the whisky contains, yes, significant amounts of sherry or wine. The more you know, the better any whisky tastes.
Red Letter 45% ABV
Waves of crispy oak and fresh-cut firewood, and the vanilla caramel sweetness of new oak. Complex, elegant and superbly balanced. Gingery finish with citrus pith.
18 Years Old 40% ABV
Ever so complex with hot pepper, baking spices, butterscotch, vanilla, cigar box, Granny Smith apples, and dried baking fruits ending in a citric zestiness.
10 Years Old 40% ABV
Spicy dark fruit, poached pears, gingery spice, sherry malt and clean oak. Nutty and fruity with cleansing bitter grapefruit pith on the finish.