The science of whisky

I entered the piece below into the Wellcome Trust Science Writing Prize. It didn't quite make the shortlist, but I'm really proud of it and wanted to share it with more than the two shortlisters who read it for the competition. I hope you enjoy reading it as much as I enjoyed writing it.


You would not expect the scent of whisky to waft from a chemistry lab. You certainly wouldn’t hope to smell it around working scientists. But with 300 detectable chemical compounds, whisky is more complex than human blood. It is made by the standard scientific technique of distillation and it has a very scientific life.

This life begins as a simple beer. To make whisky, first, malt some barley. Next, add yeast, and let it devour the sugars released by the malted barley. This sweet fuel is energy for the yeast to produce alcohol by fermentation. Together, the alcohol, yeast and sticky barley form the beery “wash”.

Scottish monks were making whisky in the 12th century, by condensing the vapours of boiled “wash” to drink. This distilled spirit was named uisge beatha, the water of life. It was clear like vodka, twice as strong, and drunk without adulteration. Darren Rook of http://thewhiskyguy.co.uk explains, “The Scottish monks learned the method of whisky making from European counterparts who called the spirit aqua vitae – a little like scientists share their methods today.”

In the 18th century someone discovered something magical: if you pour this strong, clear, distilled alcohol into a large barrel and leave it a while, you will discover an amber, smooth drink that seems to cleanse the soul. Now, with modern techniques of mass spectrometry and chromatography, scientists can explain the magic that makes the whisky we know.

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 final result is an aged concoction so loved worldwide that in 2010 Scotland’s whisky exports earned the UK £109 a second. That’s a staggering 1060 million bottles sold. And while the chemistry of whisky-making stops at bottling, the science is far from over. Whisky is made for tasting, not examination under the spectrometer. The human brain is possibly the most remarkable detector of all.

The moment whisky enters the mouth, our salivary glands spring into action and one little sip sloshes around ten thousand taste buds. Volatile compounds like the esters travel up the nasal passages. The brain’s olfactory and gustatory areas (for sensing smell and taste) light up. Our remarkable minds discover and describe flavours that are often unbelievable. Members of the Scotch Malt Whisky Society (SMWS) sometimes describe the taste of iodine to SMWS Ambassador Craig Johnstone, although, “there is no iodine in the whisky. But aromas are very strong triggers for memories and phenols do give an antiseptic smell to whiskies, much like iodine in old antiseptics.”

As the last traces of a whisky die from the tongue, its long and complex life ends. It is a life of evolution and metamorphosis, of meetings between chemicals with long and complicated names. But what a life.