The Chemistry of Whiskey

Via the Dish, lulucrumble highlights some of the 300 or so chemical compounds that make up whiskey:

Some chemical compounds sneak in at birth. The first stage of whisky-making, malting, requires fire to dry the barley. Peat is one fuel for this fire, and peat contains phenols. These aromatic hydrocarbons produce the rich, smoky flavours of whiskies made in peat-fired distilleries like those on the small Scottish island of Islay. When you sip an Islay whisky, you can almost feel the peaty smoke fill your mouth.

Distilling adds chemical fire to the wash. It captures the strong, burning ethanol, but also the buttery diketone, diacetyl, and the fruity acetals. Distillation also produces fusel oils. In small quantities, these higher-order, oily alcohols round out a whisky, giving it body. In excess, fusel oils are toxic. The stillman who brings the whisky through this adolescence is a Goldilocks figure, cutting off the distillation at precisely the point where the concentration of fusel oils is just right.

And so we have a teenage spirit, grown up from its babyish beginnings in a warm bath. What our 12th century monks did not know is that uisge beatha is not the end game. Place the young spirit in a wooden womb and something really comes to life. After three years or more in an oak cask, the water of life is reborn.

“We do not know exactly what happens in the cask, it is still a mystery that science is yet to fully understand,” says Professor Paul Hughes, Director of the International Centre for Brewing & Distilling, Edinburgh. What the Centre’s scientists do know is that chemical compounds in the oak enrich and transform the spirit.

Tannin, which makes tea brown, gives whisky its golden glow. Oak lactones also mingle in, giving a hint of sweet coconut. The carbon lining of charred whisky helps to release vanillin from the oak. The active carbon filters out undesirable substances like sulphur that cause an eggy taste. Gaps and pores in the cask’s wood let in air. Gently, gently, this air oxidises the alcohols, breathing new life into the spirit. Ethanol reacts with acids during this maturation process, giving rise to zesty esters – more commonly found in pear drops.

The change from white liquor to brown is rather astounding, and as the author notes, drinking an Isley whisky, or another peat-smoked malt, is a very unique experience.  I would liken it to drinking smoke.