From Zimri-Lim to Uisce Beatha

Whiskey! Enigmatic, the spiritual spirit. The taste experience; our language ill-equipped to describe what our palate experiences. Shrouded in mystery, legend, folklore. Mesopotamia and King Zimri-Lim’s perfumery. Arrack distilled in India. Aristotle noted the exhalations from wine. Alexandrian Greek alchemists. Al-Kuhl – powdered antimony used in cosmetics; alcohol. Stills excavated from 12th century China. Persians and Arabs refining perfumes and essences. The alchemy eventually gave us liquid gold, uisce beatha! From the alembic to the pot still. Irish monks bringing Christianity around Europe and the miracle of distillation back to Ireland. No grapes, so cereal used. Barley worked best, and the rest is history, mystic and mystery. Queen Elizabeth I liked her Irish whiskey. The very sun, contained in a glass. Ireland; island of saints, scholars – and stills.

Whiskey, Oak and Cooperage

When whiskey was first made, it had to be stored somehow. Wooden barrels worked and they seemed to add flavours and colour. Oak worked best, a hardwood. Softwoods were resinous, and both leaked and ruined the flavour. Gradually, a whole craft, art and science developed around the storage. It was as important to the finished product as its initial distillation, and the craft of the cooper developed.

Gallons and Galleons

Oaks in Europe and America are different species. American oak (Quercus Alba) grows faster and can be used younger (70 years) than European oaks (150 and more). American oak imparts a mellow aroma, Europeans a fuller, more intense one. The huge oak forests of Ireland were stripped in Elizabethan times to make galleons, though Irish oak is making a comeback.

Grains, Veins and Staves

Oak has to be cut in a special way for use in making whiskey barrels. The tree’s veins cannot connect the inside surface of the staves – the side in contact with the whiskey – to the outside, else there will be excessive evaporation, even liquid leakage. Whereas a plank is simply cut, a cask stave has to be crafted.

Toasting, Wood Sugars and Vanillin

Cut staves are then dried to 10% residual moisture. Heating the wood makes it pliable and amenable to bending into a cask shape. This “toasting” – to 200° for half an hour – also changes the chemistry of the wood, probably a chance discovery long ago. The cellulose breaks up into wood sugar which caramelises, and lignin turns to flavoursome vanillin. The wood is now ready, when assembled as a cask, to interact with the whiskey. An extra step, charring the inside for a few minutes, is favoured of bourbon makers, as the resulting charcoal coating acts as a filter which removes tangy flavours, leaving the mild and mellow taste they seek.

Size Matters, Saving Staves, Staving off Fatigue

The size of a cask or barrel (usually we say “bourbon barrel” but “whiskey cask”) is important. If you regard a cask as more or less cylindrical, then the ratio of surface area to volume (S/V) is = 2/H + 2/R, where H is height and R radius. So smaller barrels have greater contact with their contents and maturation is faster. A sherry butt is 500 litres, hogshead 250, wine hogshead 240, bourbon 200. Whiskey matures in a hogshead and so when, eg a bourbon barrel is used for whiskey maturation, it is taken apart, rejuvenated and reassembled to the smaller capacity. By USA law, bourbon casks are used once, so they are then available to whiskey makers. Just about all hogsheads are assembled from staves of used bourbon, sherry and port barrels. Producing these accounts for 10-20% of the cost of whiskey production. The “first fill” of these reconstituted casks produces the strongest flavours, but after continued use, they can be further rejuvenated, eg by scraping the inside and toasting and charring again. With all of these variables and strategies, there is unlimited potential for whiskeys of many noses, tastes and finishes.

What Happens in the Barrel in a Nutshell

In the barrel, first off, a good 2% (more if the temperature is higher) of the alcohol is lost every year through evaporation – the angels’ share. Oak allows this breathing, whereas resin-containing softwoods don’t, and many other woods impart undesirable flavours. All kinds of chemical reactions happen between the whiskey and the wood (usually oak) of the bourbon or sherry barrels (depending on their first use), though not a whole lot until or unless the temperature is above 6°C. A good 200 or so compounds in the wood interact with the whiskey. Esters, tannins, lactones are amongst the many that appear in the maturing liquid, and their concentrations, measured in parts per million ppm, even parts per billion ppb, shape and finish the precious whiskey over years.

Timing is Everything

Just as timing is everything in the distillation process – sampling every 15 minutes for oiliness – it is also critical to maturation and finishing, albeit the timeframes are longer. For about the first 8 years in a cask, whiskey undergoes “subtractive maturation”; the tangy metallic taste goes. For the next years – the number depending on the desired end-taste, and the age and prior use of the cask staves – there is “additive maturation” as the whiskey assumes flavours from the cask. The last phase of “interactive maturation” is when the distillery character (determined by the malt and the many distilling processes and decisions) harmonises with the cask character to produce the desired result. It’s all about balance and consistency, consistency and balance.