Roll Out The Barrel

Aging cocktails has proved to be one of the biggest trends in contemporary mixology. Bars around the globe buy and stock barrels in the dozens. Philip Duff explains where the aging craze originated and how it works.
We discovered aging by accident. Long before Coffey patented or nicked the idea for a continuous still to make neutral alcohol, our forefathers found a way to make rough liquor taste better: barrels. Barrels which were exclusively what you used to store and transport spirits, unless you count the leather bottles of Jamaica – smoothed out harsh liquor. Or, alcohol was being distilled from excess grain and stored in a barrel, because whisky keeps good while grain spoils, and you could keep the whisky until you could get a good price for it. Barrels are usually oak. Oak is common and great barrel-wood, and oak is specified in several national and European and American laws as being the wood for aging. In Appreciating Whisky, Phillip Hills points out that many English politicians at the time of the American War of Independence would have been happy to write America off as a loss-making venture, if it hadn’t been for the fact that America had a vast supply of oak for Royal Navy ship building.
America influences us to this day: because U.S. laws specify that oak whiskey barrels be used, and used only once for bourbon, ex-bourbon barrels made of oak are the cheapest and most common around. A bourbon barrel can be had for €75 or so, while an ex-cognac barrel may cost ten times more. American oak (quercus alba) is harder to penetrate than European oak (quercus robur and quercus petraea), which is the stuff used in Spain, and France’s famous Limousin and Troncais oak. Oak hybridises very easily, so an oak barrel might be made up from ten different types of quercus, prompting Hills to observe on oak aging: “It’s like hiring a hippogriff to look after your kids.”
Aeration for Green Apple and Nutty Flavours
So you make the booze and you stick it in a barrel. Usually at a higher strength than you’ll need to bottle it at, because you’ll lose some strength through evaporation, and you can always dilute it down anyway. The drink has changed even before you seal the cask, though – just pouring it in exposes the liquid to a lot of oxygen, and as anyone who’s decanted a heavy red wine will know, just this aeration can already have a large effect. In a  recent Art of Drink posting, the always-excellent Darcy O’Neil points out that aeration oxidises the liquid, converting ethanol (alcohol) to aldehydes, which give green apple/nutty flavours. What have you done to the barrel? Char the inside, as with bourbon, and you’ll change what it is: you’ll add a layer of carbon (and vodka fans will recall that carbon itself is an excellent filter, smoothening out rough edges of liquor), and you change the chemistry of the wood.
Phenols decrease when you char, as do tannins, while concentrations of aldehydes and acids rise. And then we wait. And wait. And wait. Extremes of temperatures are probably best avoided, hence some Kentucky distilleries aircondition their rickhouses, but in general it’s best to just let time do it’s work. The barrel breathes, in and out, hence Islays whiskies have a tang of salt and brine, and Linie Aquavit has all sorts of exotic seafaring scents, because it crosses the equator twice in barrels before being bottled, echoing it’s original use as ballast, on trading ships. About 2% or so of the liquid evaporates each year, named the Angel’s Share: more, in hot climates. Visit Cognac in France and you’ll see a tell-tale black stain on many buildings; this is a fungus that lives on cognac fumes, and the stain was once used to track down illegal distilleries.
Colouring Whiskey With Caramel
Colour leaches into the liquid. I spent almost two hours on the phone with Ireland’s Cooley Distillery master blender/distiller Noel Sweeney last week. He told me categorically that you cannot get a dark whiskey through aging in bourbon barrels. You have to colour it. No harm there. Spirit caramel is used, which does not affect taste unless you really go overboard. He once made a light-coloured whiskey he describes as “great”*, with no colouring caramel added, that encountered a problem. When served hot whiskies with this spirit, guests complained that the drink contained no booze, because it did not darken significantly. And flavour transfers from the wood to the liquid. Lots of flavour. Phenols are a woody plant’s last line of defence: pungent chemicals deep in the heartwood designed to discourage burrowing insects. Phenols include eugenol (cloves) anethol (anise), cinnamaldehyde (cassia/cinnamon) and their superstar in the whiskey world, vanillin, which comes from the lignin in the wood.  When we taste vanilla we automatically think of the food or drink we are ingesting as being sweeter, because we almost always taste vanilla in conjunction with a sweet food or drink, although vanilla itself is not sweet.
What else? Tons of stuff. Cocktail blogger Darcy O’Neil points to a theory that acids in anything alcoholic will extract hemicellulose from wood barrels,  and hemicellulose is a polysaccharide, which will make the taste of the liquid sweeter.  Tannins, lactones (coconut-y aroma), glycerol, fatty acids (remember chill-filtering?) and furfural all come from the wood, and are gently extracted by the aging alcohol, because alcohol is a solvent. This is why vodka is excellent for stain removal, by the way. Aldehydes and esters in the liquid, fruit, floral aromas, increase in concentration over the length of aging, which is why whisky, barrel-aged for a good long time, has more of these aromas than shorter-aged spirits.
The Finishes
And what of the famous finishes? You cannot add flavouring to most whiskies and still sell them as whisky, but you can age the whiskey for a short time in a barrel previously used for something else: sherry or rum, or port or the like. In Scotch, using casks other than the traditional ex-bourbon or ex-sherry was first popularised by Glenmorangie in 1995, with Port, Madeira and Sherry finishes. Now it’s a bit of a game, and lots of people in the whisky industry regard the explosion of finishes the way most cocktailians regard yet another “new” flavour of vodka. And what of when a barrel is used up? Ah, now you’re talking. The most honest thing is to scrape off a layer of the wood inside, and perhaps re-char it.
Results are good, but the barrel does not last twice as long, just a little longer. Least honest are paxarette (or wine treatment) and boise. Never heard of them? I’m not surprised. Paxarette was outlawed in Scotland years ago: it is a boiled-down wine-sherry-flavourings liquid that was forced into worn-out empty casks, under pressure, to rejuvenate them. We’re still drinking whisky today aged in such casks. Paxarette gives a lot of colour to the whisky, so distillers can honestly say they haven’t added any caramel, and all the colour comes from the cask. Boise – woodchips in water boiled down to a concentrate – does the same for cognac,  and (shamefully) may to this day be added to any cognac, of any grade.
Cocktail Ageing the Watermelon Breezer
But cocktails? Tony Conigliaro aged them in bottles. Ingenious idea. Jeffrey Morgenthaler aged them in wood barrels. Also very cool. Indeed you can now buy, and I am not joking, ready-aged bottled cocktails from The Handmade Cocktail Company. It’s not a new idea. In the 1800s bartenders made bottled cocktails for their guests to enjoy while travelling. Starting in the 1900s, drinks firms marketed bottled cocktails large-scale. Arguably, RTDs are bottled cocktails. The difference between Morgenthaler’s 6-week Negroni and a Watermelon Breezer is this: bottle and barrel-aged cocktails aim to improve the flavour of the liquid because they are aged in a bottle or barrel, whereas RTDs aim to taste exactly like a fresh-made cocktail even though they are bottled.
It is a great idea! Barrels are not so expensive: you can get a 5 or 10 liter barrel for €80. Age 5 liters of, say, Negroni in one, and you can make 50** barrel-aged Negronis. Ask €1 extra for each Negroni, and after less than two 6-week aging cycles the barrel has paid for itself, all future barrel-aged cocktails are pure profit, you should get some great attention from the media, and you can serve the cocktails much, much quicker. Just pour from the barrel, add ice, stir and garnish. Cool!
In the same article referenced above, Darcy deals further with the chemistry of bottle- and barrel-aging, and introduces a new concept: aging cocktails with citrus ingredients, by substituting acid phosphate or Lactart for the lemon or lime juice. This is really ground-breaking: as we speak, I have  two barrels aging (one new, one ex-cognac) with White Ladies using Lactart. Want to taste them? Me too! We’re serving them up for the first time at the Manhattan Cocktail Classic…
* Noel is not given to exaggeration.
** 5 liters should equal 55.5 Negronis, but 10% of barrel-aged Negronis seems to mysteriously evaporate. I am told this is called the Bartender’s Share.
This article was first published in MIXOLOGY Issue 3/2011.