Now we are able to replicate unaged white spirits and make some basic cocktails in space, we can start to look at the process of artificially aging our spirits to replicate the flavors of aged rums and whisk(e)ys, recreating flavors from aged spirits from two to twenty years as quickly as possible - after all we could age our neutral spirit at the same rate as we do on earth, but who wants to wait around for two years before we can have a proper drink?
Fair warning, this is a very science-heavy post that you'll really love if you are a massive dork (like me), but we'll be getting back to making space-freindly drinks soon.
To investigate how we can speed up the aging process, we first have to look at how spirits are aged now and the factors that effect the finished spirit. The first and most obvious influence to a spirit was the barrel, more importantly the wood from which the barrel is constructed. Over the last five years we've all heard a lot about (and tasted god only knows how many) barrel-aged cocktails and house-aged spirits, but beyond a fairly rudimentary understanding of a barrel's affect on its contents, passed from bartender to bartender like some kind of mildly-intoxicated mondegreen, very little information about how different oaks (or woods for that matter) from different species of tree grown in different parts of the world affect barrel aging differently.
Not all woods are created equal, not all soils are the same - oak selection is as fundamental to spirits as terroir is to wine. So what are the major oaks used by coopers around the world?
French Oak
Major Oak Species:
Quercus Petraea: Durmast Oak, Sessile Oak
Quercus Robur, Quercus Peduncolata: English or Truffle Oak
One of the largest producers of oak staves for coopers (barrel makers) in Europe, French Oak has long been highly sought after for it's consistent quality, mostly due to longstanding control and regulation of the specific regions where the oak suitable for barrels is grown. Below is a map of the major barrel-stave producing oak forests in France, and a table with a brief descriptive of the different characteristics of oaks from different regions.
 |
| -From Nadalie-USA |
As you can see above most French oak is grown primarily for aging wines, with only limousin oak being primarily for the aging of spirits. It's loose grain and the amount of flavor it imparts is undesirable for wine makers but very desirable for spirit producers who are looking at aging a product for longer periods of time.
After they are used to mature wine the casks are often sold on to whiskey producers who use the lingering flavors left in the oak from wine maturation, which are used to provide individual wine finishes to different whiskeys, adding another layer of complexity to the spirit.
A notable difference that French oak has in it's production is the practice of open-air curing of the oak. A (generally) tighter wood grain profile and a less water tight nature means the oak is split down the grown and 'seasoned' for two to three years in open-air wood yards.
This seasoning period helps to leech out unpleasant turpines and aldehydes amongst other undesirable, aggressive flavors, and this is because of a naturally occurring fungi that grows on wood piles during the air-drying period.
As the wood dries it becomes inhospitable to one fungus, which will die and be replaced by another fungus more suited to the wood's current 'environment' of humidity and sugars, and this process is repeated through a variety of fungi until the wood is cured. This series of fungal interlopers release chemicals into the wood which help to introduce oxidization, "softening tannins and caramelizing hemicellulose", as the author of the linked piece puts it.
This mellowing cannot be replicated by the traditional kiln-drying methods employed by the vast majority of American coopers, however the splitting of the wood means that only 20-25% of the harvested wood can be used for barrels, so there is more waste wood created in the French cooperage industry.
American Oak
Major Oak Species:
Quercus Alba: White Oak
 |
| Natural Range of Quercus Alba in the United States |
Before the end of world war two, American oak was widely unused for spirit maturation, with the Volstead act and subsequent American Prohibition almost destroying the coopering industry. It was the American Cooperage Idustries of America, the ACIA, and their lawyers that formulated and lobbied for a law to be passed proclaiming all American whiskeys had to be aged in 100% virgin Quercus Alba to stimulate the coopers industry.
The exact details of this law and how it was formulated are hard to come by, so I have reached out to the modern arm of the ACIA to ask them for information as will update this page with information if and when they reply.
This led to a glut of ex-bourbon barrels that were extremely cheap at a time when spanish ex-sherry casks were becoming extremely expensive in Europe. This led to the Scots and Irish importing these ex-bourbon barrels to mature their spirits.
White oak is relatively fast growing when cultivated, giving straight trunks with a straight grain and a high level of vanillins in the wood, and is seen as a highly desirable wood for aging spirits as opposed to wine, where a tighter grain means more control of flavor development. The loose grain leads to a faster release of flavor into the spirit, and the traditional American barrel size - the ASB or American Standard Barrel - is slightly smaller than the traditional European whiskey hogshead (more about barrel sizes later), leading to a higher wood-to-spirit ratio, leading to faster aging in-barrel.
All these factors have lead to American oak being highly prized for the maturation of spirits worldwide.
Japanese Oak
Major Oak Species:
Quercus Mongolica: Mizunara oak
I was lucky enough to visit Japan as a guest of Suntory a few years ago, visiting the Yamazaki and Hakushu distilleries and learning a lot about Japanese whiskeys, specifically the oak that has typified Japanese single malts, the Mizunara oak.
I was told that they had tried to perfect Mizunara casks for many years, but it was extremely difficult to create a good whiskey from aging in the particular wood. The porous nature of the wood and it's very high levels of vanillin meant it was hard to create a well aged spirit. Most of the Japanese whiskey produced by Suntory is first aged in sherry and bourbon barrel before being either finished in Mizunara or blended with Mizunara cask.
I've got a lot of half-remembered stories and facts about the notoriously tricky Mizunara wood, but unfortunately I have since lost the notebook where I'd written everything down, so I won't give in to the temptation of supplying you with rumors.
Instead, I have come across a very handy study regarding the Mizunara wood and it's flavor characteristics released by the Suntory company in Suntory Information Release No. 10235, however my Japanese is a bit spotty. Luckily the facts have been translated into English over by the folks at Nonjatta, an excellent reference on all thing Japanese whiskey.
The first table below describes the results of a tasting panel measuring a strong coconut odor in whiskey samples aged in both Quercus Alba and Quercus Mongolica.
 |
| Source |
Coconut odor stronger with Mizunara matured spirit, right, so what?
Well the coconut odor indicative of a branched ỿ-lactone, or cis-3-methyl-4-octanolide, also known as whiskey lactone, or more importantly: quercus lactone, a lactone present in all oak species, but in differing amounts.
First identified by Nykänen et al in "Formation and Occurrence of Flavor Compounds in Wine and Distilled Alcoholic Beverages" (1986), trans-oak lactones in low concentrations will produce pleasant woody and sweet aromas, and in high concentrations will produce sweet coconut and tropical notes. Cis-oak lactones have a similar effect, but in higher concentrations tend towards staler, drier flavor notes.
As you can see in the graph below Mizuara has a much higher measurement of trans-oak lactones than in white oak or european oak matured whiskeys. The higher return of these trans-oak lactones give Mizunara matured spirits a fresher, even fruitier finish when combined with other volatile flavor compounds.
 |
| Source |
Spanish Oak
Major Oak Species:
Quercus Petraea: Durmast Oak, Sessile Oak
Quercus Robur: English or Truffle Oak
Those with a keen eye for taxonomy might have noticed the same oak is used in France for barrel staves as in Spain - indeed the oak for barrels does come from the same species of oak as in most of Europe. In fact most of the Quercus Petraea in Europe was bought from Russia and the Baltic states in the 19th century when oak supplies were dwindling.
In fact all three oak genus' referred to commonly as Spanish oak (Quercus Falcata, Quercus Coccinea, Quercus Rubra) are highly unsuitable for barreling, being either far too porous or in some cases legitimately toxic. So Spanish coopers use mostly Spanish-grown European oaks, however most of these European oak barrels are not used by the sherry industry - the vast majority of the wood being used by sherry houses is American white oak, Quercus Alba. Esteemed sherry expert Manuel González Gordon wrote: "In Jerez no other wood has been used for many years, as American oak has given the best results for the fermentation, maturing, ageing and shipping of Sherry." (Sherry, The Noble Wine, 1948)
So Spanish coopers use European oak, and Sherry producers use American oak. So why the whiskey world's obsession with Spanish oak, or more accurately, ex-sherry oak? Originally beginning in the 1860's, the sherry trade from Spain UK bought large quantities of sherry-filled barrels to major shipping ports in the UK, where the barrels were emptied into bottles for retail sale. Bottles could not be shipped on long sea journeys at the time because there would be too much breakage on the rough sea journey. Instead of shipping empty casks back to the producers in Spain, the casks were cheap and plentiful for whiskey producers. Originally sherry-finishing wasn't a matter of choice or flavor preferences, but a cost-saving measure by whiskey merchants; it was simply cheaper to buy up old ex-sherry barrels then pay for virgin oak.
As mentioned earlier, as sherry consumption in the UK dropped after world war two, sherry barrels became scarcer and thus more expensive, whereas the glut of ex-bourbon and American whiskey Quercus Alba from the United States made whiskey producers turn to bourbon casks to finish their Scotch and Irish whiskeys.
In the last decade we have seen a rise again in the use of ex-sherry cask to finish whiskeys, (even though are already White Oak, the same Quercus Alba they were using before in the bourbon casks - the important factor is the spirit that as first impregnated the virgin oak). This is more a stylistic choice than a cost-saving measure, and thus we have seen a greater range of flavor profiles added to a broad style of whiskeys. This is because there is such a wide range of sherry styles and sugar contents that complement different whiskey styles; I won't go too deeply into sherry styles and production as there are many people who have done it earlier and much better than I could (and I highly recommend looking into the subject when you have the time).
So it's not really the oak that effects the final spirit but the wine that has been matured in it previously. Here's a few of the more common sherry types that have been common in the recent sherry-finishing trend:
Pedro Ximenez: Thick, candied fruit, cocoa, very sweet
Amontillado: Nutty, dried fruit, spice
Fino/Manzanilla: Salty, dry, flor (yeast fungus), crisp
The funny thing about the whole sherry-finished spirit trend is that the demand for ex-sherry cask has now outstripped the current supply since global consumption of sherry has dropped. This has led to situations where distilleries are paying sherry producers to produce wines solely so the barrels can be used later for finishing whiskeys.
I remember hearing from one of the aging house stewards at Yamazaki in Japan that they were having to fly to Spain and trying to convince them to produce sherries solely for the barrels, and according to this letter from one of the Macallan ambassadors, they also have sherried barrels specifically made for them.
So ex-sherry barrels are in such high demand that whiskey producers are willing to pay for oak staves to be shipped from the US to be constructed by Spanish coopers and to have sherry aged in them to secure a future supple of sherry finished whiskey. I wonder how widely this is praticed in the sherry industry? If you have any more information on this, please drop a message in the comments.
Scandanavian Oak
Major Oak Species:
Quercus robur (???)
In previous years we have seen the rise of Scandanavian produced whiskeys, particularly Swedish whiskeys like Mackmyra. While they predominantly use American and European oak (virgin and ex-bourbon) they also use Swedish oak, as does Absolut Amber, the aged vodka expression they are promoting at the moment.
As well as this, further investigation finds beers that have been aged in ex-whiskey Swedish oak. However, the information about which oak is used for cooperage is limited - Absolut is keeping schtum about the oak they are using, as is Mackmyra.
What follows is wildly speculative, so don't quote me on this one, but a bit of google-fu revealed that some Swedish winemakers are using Swedish oak from an island called Visingsö. Apparently these oaks had been planted in the 1800's but were only now being used for casks - oaks were vital to the shipbuilding industry under the reign of King Gustav Vasa. Now in the 1800's there was a fear that there would be a lack of oak for shipbuilding materials and there was a massive drive to plant oak - the Swedish navy planted 300,000 trees on the island of Visingsö alone. As technology improved oak was no longer needed, thus the vast spread of oak forest in Sweden today.
But what sort of oak was used? According to Eksog.org, a scientific initiative to map health and mortality patterns in Swedish oak, the vast majority of Swedish oak is Quercus Robur, or the English oak, similar to what is widely used across Europe.
But what makes Swedish oak different? Growing for 200 years in alien soil would have had some effect on the volatile compounds housed int he wood, but so far there is little information publicly available in terms of chromatography and soluble wood compounds. If you do know more please feel free to enlighten us and we can pass on the information.
But wait, why do we have to use oak at all?
What's the deal with this oak boner we have, can't we use another wood in it's place? while it's true that some distillers are experimenting with other wood types like sugar maple, chestnut and cedar, most woods are unsuitable for cooperage. Oak, specifically the species used for making barrels, have the perfect characteristics coopers look for.
Wood must be strong enough to bend and not break, water proof enough to hold it's contents without leaking, porous enough to allow interplay between oak and spirit, have the correct balance of gallic and ellagic acids in the wood to create hydrosoluble tannins, have a reasonably straight grain without knots in the wood to allow for shaping into staves.
A study by the university of Padua revealed in a study of five different common wood types that Oak wood (Q.Robur) has the highest percentage of stable soluble compounds versus oxygen permeability (in regards to both oxidization and the 'angels share', more on those later), making oak the most suitable wood for long-term aging.
Main Volatile Compounds Available in Oak Wood Extract (Q.Robur)
 |
| Source: Mirko et al, Wood Sci Technology (2009) |
Fufural - Oats, burnt oats, 'toast'.
Benzaldehyde - Almond
Cinnamaldehyde - Cinnamon, Cassia
Vanillin - Vanilla
Syringaldehyde - Spicy, smoldering wood, hot
Coniferaldehyde - Sweet, Maple, vanilla (precursor)
Acetovanillone (Apocynin) - Vanilla, waxy, spicy
4-Vinylguaiacol - Buckwheat, wheat, yeast
Eugenol: Spice, clove, menthol
4-Ethylguaiacol - Produced by yeast spoilage bacteria Brettanomyces - smoky, gamey, bacon, leather
Guaiacol - Precursor to Vanillin and Eugenol
3-Oxo-α-ionol - Spicy, dry
cis and trans β-methyl-ỿ-octalactones - Coconut, woody, sweet, rose/celery
This has turned out to be a much more in-depth post then I thought, so I will break it here for now. In part two we will cover the science of toasting, barrel sizes, atmosphere and alcohol percentages, as well as covering exactly how we can speed up the aging process without losing the quality of the final spirit.
Alfa Chemistry offers an extensive catalog of building blocks, reagents, catalysts, reference materials, and research chemicals in a wide range of applications. α-Ionol
ReplyDelete