天堂宝 Aging and Heaven’s Treasures
Some thoughts on whisky aging:
Why in the world is this meaningful for looking into Japanese whisky? Well, nothing I write here will be as useful or prescriptive as a good distillery. However, with multiple new distilleries, blends and storage places coming to market, this can be overwhelming and information is not likely to be easily available. In Scotland, the aging process and how geography impacts it is mostly standard. It’s a fairly small, hilly but not mountainous piece of land, all with a high humidity from both the proximity to the North Sea and the frequent rains brought in with the higher temperature water via the Gulf Stream in the Atlantic. Islay and Speyside are positively tiny as a proportion even of Scotland, so some of the more famous whiskies you have probably heard of were produced in the general area equivalent of a large global city centre. (For example, Islay is 15 x 15 km, effectively.)
This is not a particularly apt description of Japan, and hence the location of a distillery and the weather characteristics it offers can be a meaningful choice in whisky production. Combining this with what we know of some blenders or companies will be helpful and the location will definitely not tell the whole story. Good craft can completely change how something is expressed, but from the perspective of putting a finger in the air to see where the wind is blowing and to start thinking about what features are likely to be imparted and the constraints the distillers are working within, this is a good start.
Note on Angel’s Share
Angel’s Share is basically an effect of other things such as temperature and pressure, which I will cover my thoughts on below. However, I’ve seen people equate the overall share to the level of aging of the whisky, which is not really the whole story. The barrels can be slightly leaky, the humidity could simply have been very low, there can be high temperatures, etc. If aging was equivalent to angel’s share, inland Texas would produce the best aged whiskies ever!
水分 What does play a role then? Vapour pressure!
After the barrel, the only play in the whole game of aging is really in vapour pressure. What… is vapour pressure? It’s the relative abundance and volatility (how likely they are to turn into gas) of vapours (liquids that have turned to gas) in a mixture of gasses. If you only have one vapour - like in normal air where you have water vapour which can condensate in lower temperatures - then this constitutes all the vapour pressure of a gas mixture - air in this example. Of course, if you include other vapours like ethanol (alcohol), then this changes the game and you will have partial vapour pressures for each vapour. Multiple factors play a role with vapour pressure in the context of whisky aging, and I will go through them below:
Temperature Swings
Average Temperature
Humidity
Pressure
Barrel
熱 Temperature Swings
Changes in temperature will drive the wood that the barrel is made from to expand and contract. When the wood expands, this creates bigger pores in the wood, which will soak up, leak and vapourize some of the distillate. Think of it as an accordion - when you pull at it the accordion grows and pulls in air. Now we are working with whisky instead. Once you compress it, the accordion expels the air and generates notes. Our whisky will also generate notes when expelled back into the barrel! The more we allow this to happen, the more character we get from whatever was in the barrel before along with some of the flavour of the wood. Let the music play! Keep in mind though, doing this a lot over a long period of time might take a whisky from having great pleasant wood aromas to simply… feeling like drinking boozy sawdust.
A small secondary effect is lignin breakdown - the higher level of saturation the barrel gets with alcohol, the more wood is exposed to breakdown. Lignin makes up the cell structure of the wood. If a higher amount of alcohol is absorbed into the wood, the lignin breakdown also will not consume the same amount of alcohol relative to what is absorbed in the wood, allowing higher concentrations to be kept and the lignin breakdown to go on longer. However, this effect is minor compared to the overall aging factor.
What is a good temperature swing? One that is meaningful! Distilleries that tout having swings within the day probably are… trying to play up the aspect a bit. Water takes a lot of effort to heat up or cool down, and when we have multiple barrels stored in a protected storeroom environment, a couple of minutes or even a day of sunshine won’t get you a temperature swing for the barrel that has any effect. One good example: in frigid climates (think -30 C), one trick we would do to keep a cellar or storehouse above freezing was to keep 2-3 buckets of water, at 20 L each, in the place. The extra cold it took to freeze that water would be unlikely to flow into the cellar in any reasonable amount of time, hence it would easily cover a few days worth of the worst deep freezes. Looking at a 169 L barrel at 60% ABV and 40% water gives us… 67.6 L of water - per barrel! This obviously should never freeze, but taken 10 barrels I’d say it takes at least a week of significantly different temperatures (up or down 5C / 9F) to impact any storehouse temperatures enough that “it counts” from the perspective of changing the size of the barrel and hence the whisky.
For a normal warehouse, especially around the top barrels in a storage rack, one can probably get a swing of temperature in within 1 week which would change the temperature enough to drive the size of the barrel. A dunnage (the primary type used in Scotland traditionally) would probably be closer to two or three weeks. Double this to let the whisky return back and you will get about 25 possible temperature cycles in a year for a standard warehouse, and 10-ish for a dunnage. But mostly weather doesn’t come that consistently, so for most distilleries in Japan you would be lucky to get 10 cycles in of wood absorbing and expelling liquor within a year, and it’s more likely that you are in the 5-7 range.
This also depends a lot on location - a mountain location in Saitama prefecture or Gifu will have much bigger temperature swings during the year and definitely between seasons than a seaside venue like Hakone. Northern Japan will have more pronounced temperature swings than a southern location, so a storage facility on Hokkaido will probably see more wood flavours for the aging time than the same facility would in Kyushu.
地 Average Temperature Baseline
Average temperatures will impact how much of the distillate dissipates to evaporation over longer time periods and what evaporates, primarily. There is a bit of a secondary effect on lignin in the wood and alcohol saturation, but this is fairly minor. Also, any other chemical reaction happening over longer times will generally be accelerated. A good rule of thumb is often that an added 10 degrees C (18 F) will halve the reaction time.
Temperature will really impact how much of the relative gasses there are in your in-barrel air mixture at any given time, which really matters. Alcohol becomes liquid at -114 C, but boils at 78 C. Water you hopefully know. Hence there is a lot more relative alcohol vapour in cold climates around 0 C since there will only be minimal water vapour, and alhocol’s vapour pressure proportionately does not change as much as the water vapour pressure when you go from 5 C to 25 C! Also, the temperature variability means that an even swing over 5 to 25 and back over the year is going to help you evaporate a higher fraction of water and more distillate overall than a barrel kept closely at 15.
Here, you’ll generally get a higher temperature the further south and closer to the equator you go, and given that the ocean circulation is taking heat away from Japan, you’re likely to find temperature relations closer to east coast North America than those of the west coast, or Europe’s Atlantic shores. A bit more on the aggressive temperature differential side where you are about as likely to see blizzards in a year as you are tropical cyclones!
湿 Humidity
Ah, the most difficult to understand since this really impacts the vapour pressure. A higher humidity will do a couple of things: 1) It will “cake” the barrel on the outside, forcing it to expand a bit if the barrel is not fully saturated with the prior spirit. Hence, we will have water covering the outermost layer of the barrel, or at least a higher percentage of water in the last couple of millimetres of the wood. It will swell the wood as well. 2) It will impact the fractional vapour pressure differential in the barrel. What, what, did a lot of science just happen in a short time?
The water vapour pressure in a dry climate is much lower (no vapour) than it is in a humid climate. From the perspective of a barrel, if there is relatively more water vapour in the air outside the barrel than there is water vapour in the air inside the barrel, by the universe’s efforts to smooth differences out (entropy), water will migrate in. Say that the overall amount/density of vapour in the barrel is 10 units (Pascal for those of you keeping count), made up with 5 units of ethanol vapour and 5 units of water vapour. If the air outside has 7 units of water vapour density as its only vapour, over time your barrel will lower its ABV given that water will migrate in. Even though there is less overall vapour outside the barrel. The air mixture inside the barrel will literally push ethanol out, while pulling water in. If the water vapour pressure on the inside and outside are more even or lower on the outside, water will be pulled out of the distillate at a higher rate.
縦 Altitude (affecting multiple factors: Temperature + Humidity + Pressure)
Altitude affects all of temperature, humidity, and air pressure, bringing all of them lower in general. Lower pressure means higher vapour pressure differential. Lower humidity means lower amounts of water vapour, making it easier to scale the proof with age if desired as a higher proportion of water can escape the barrel compared to what would be the case in a humid clime. Lower overall temperature will make for an overall slower aging process from both a lower angel’s share (lower pressure in the barrel) and temperature at which the chemical reactions take place.
Pressure has not been listed before because the only realistic way of adjusting the average air pressure at the scale needed for whisky storage is in increasing or decreasing the height above the sea where the distillery is placed. But each gust of wind will contain less air, and hence the air humidity and other vapours that come with it. There will be less water being pushed into the barrel and less surrounding air to do the actual pushing, meaning that the relative pressure inside will be higher. This forces more of your distillate out during aging, and what comes out largely depends on the temperature of your distillate.
材 Barrel
What barrel is being used? How dry is it when filled with distillate? Is it porous or highly dense oak wood? What is the thickness? How many times has the same barrel been used? What did it contain before? Barrels are a science all in their own, and there are multiple ways to get good insight into what makes for a good barrel and what will make things differ. Combine this with the other variables being looked at, and things start getting very interesting very quickly! What temperature would be ideal for a first fill port barrel? Are we storing a high or low ABV distillate in the barrel and which ones are best for this? How long are we looking to age this product for and do we have strong wood or earth notes in the distillate itself that might risk overtaking the rest of the whisky if we go for an early fill? Barrels matter, and they are the easiest variable to play with - a distillery can buy any barrel but will have to store it onsite with the humidity, pressure, and temperature they have!
木版 Lignin breakdown
You can’t really rush this process, it’s one of the few things that comes with age. However, a higher alcohol content will more aggressively eat away at the wood! (This is the reason why corks should be wet for wine, and moist at most for whisky!) Hence, knowing more about the barrel ABV levels and what is likely to happen can tell us a bit more about the impression of the age of the whisky overall. Higher ABV will mean a faster level of aging inside the oak, releasing more subtle wet tobacco, fig and vanilla notes. This also adds some of the esters - or aromas - to the whisky as it reacts with some of the aldehydes contained in the distillate, on top of the esters already in the distillate.
To achieve this marginally faster we want a higher alcohol content, and a higher saturation level of alcohol in the wood, even though the process is primarily governed with time. Throw out the halving of a chemical reaction time guideline I gave you before, in this particular instance. This has to then be balanced with fewer temperature swings as it is a longer process (in order to avoid the sawdust sensation).
To achieve the higher alcohol content within those constraints you should ideally have a lower humidity, and a slightly higher temperature. However, be careful with what the whisky itself and the barrel will do with the higher temperature! You don’t want day-to-day swings in temperature, but what makes sense is rather pronounced swings across the year, allowing longer periods of higher alcohol saturation in the barrel wood to be re-expressed and refreshed on an annual basis.
濃度 On Proofing
Basically, to make a higher alcohol barrel (if that is your only goal) go for a lower-humidity, lower pressure, higher average temperature location. This will press out the water in higher proportion, and make the Angel’s share overall higher. Add in temperature swings, and the whisky will quickly - less than 5 years - gain character, while still being recognizable as a younger whisky due to the lack of some of the finer aging notes.
For making a slightly lower-proof whisky designed to age for a long time (30+ years, the way the Scots did their most valued work), go for higher humidity, lower temperature, and higher pressure environment. The temperature is less impactful here if you get the higher humidity, but will play an absolutely crucial role if the humidity or pressure is not as high.
余韻 Finishing Note
This is going to be a relatively important piece of reference going forwards in my whisky journey as I see new independent distillers come around, and explore where more established companies are locating their new distilleries as their companies grow to meet market demand. If you ever see a link on the words “Angel’s Share” or “Aging”, know that this is where I will be directing you.
