Protein Shakes: the science behind making the perfect foam on your cocktail.

In certain cocktails, a foam can be the essential ingredient that turns an otherwise flat and uninteresting drink into a textured and complex tipple, a light and fluffy introduction onto your palate of the flavors waiting underneath, the gentle kiss before the punch as it were. What would a Clover Club be without that silky sensation, the density of weight giving way to the well-chilled drink beneath, giving a luxurious texture to what could otherwise be an unremarkable drink?

But how and why do these layers form? The answer is protein; egg whites are around 92% water, and 8% protein, tightly bonded spirals that contain amino acids. By emulsifying an egg white via whisking or dry-shaking, you break this protein shell and expose the amino acids, some of which are hydrophillic and some of which are hydrophobic, that is, some are attracted to water and some are repelled by it. 

As such, the rapid agitation introduced by your emulsification causes the hydrophillic amino acids to gather close to water, and the hydrophobic ones to gather  close to the air introduced into the mix. This causes the protein strands to unfold and bond to other adjacent proteins, forming a network of bonds that make up the body of the foam.

The more you emulsify the stiffer the foam will get until all the proteins have unfurled. In a solution (say, a cocktail for example), the linked proteins will rise to the surface of the drink due to the air bubbles being lighter than the liquid surrounding it. Protein will continue to bond with adjacent protein, so after 30 seconds there will be a layered separation of liquid and bonded proteins, i.e. the foam.

Simple, right? Well not so much. Egg white isn't the only ingredient in your drink that can contain the combination of protein and acids that can create a foam, and there are myriad reasons that can lead to your foam being too thin, dissolving too quickly, or just looking sad and flaccid.

The higher the alcohol content in the cocktail, the lower the ratio of bonds formed so less foam; this will also create weaker bonds that will break apart much quicker than in a solution with lower alcohol.

Likewise, the ratios of sugar and acid in the solution will affect how well your bubbles form - consider the drink as you would consider a delicate meringue; sugar acts as a stabiliser while emulsifying, creating stronger, but smaller bonds. The higher the sugar content, the denser the foam will be. Acidity is another variable - if a solution is too acidic then bonds will begin to weaken and collapse very quickly after settling, leaving you with a deflated and unpleasant looking foam.

Another factor is the freshness and temperature of the egg white used in the recipe.  Refrigerated whites will be slow to emulsify, taking much longer than with room temperature whites, and the ideal age of an egg will be 2-3 days after laying. Eggs that are too fresh will produce a white that visibly separates when cracked: a thin, watery liquid will separate from the jelly-like inner white, known as the ovomucin. Ovomucin acts as a trypsin inhibitor, trypsin being a enzyme that breaks down proteins and occurs naturally in digestion and is present in the egg when it is laid.

The older an egg is the weaker the proteins become as the ovomucin degrades and the trypsin starts to break down the proteins in the albumen, and the weaker and thinner the resultant foam will appear. For long term storage pasteurisation works as a solution to denaturalise the enzymes in egg white, however the egg white can still spoil for bacterial reasons.

An ideal solution for any high-volume usage of egg white would be the use of dehydrated albumen, as it takes up less space, does not spoil in it's dry form and is consistent in it's protein content across a batch - eggs are of course, at the end of the day an organic product and never consistent from egg to egg. Just place egg white in a shallow pan and put it into a dehydrator (under 65c, or else you'll end up with a large omelette) and blend it once dried - store somewhere dry.

A bar spoon per drink is about perfect, and just dry shake and wet shake as you would using egg white. The only thing you have to adjust for using this method is the liquid volume you are losing without hydrated egg white - remember your wash lines before spinning this method out.

It goes without saying but of course you shouldn't be using cage eggs - poor nutrition in the chickens mean a low protein count and a watery egg white and a poor foam. Also it's incredibly cruel.

Egg white isn't suitable for every drinker however, as people with dietary concerns or squeamish individuals shy away from a drink when they see egg white going into the mix. Therefore it is worth investigating other options to create the same affect in a cocktail.

One such option is pineapple juice - pineapple has a high level of protein and creates a thick, foamy head when emulsified as a result of the high level of fruit sugars in ripe pineapple acting as a stabiliser for the foam.

However in the core of pineapple exists an enzyme called bromelain, which is a digestive enzyme similar to trypsin in the way it attacks proteins. If you have ever sliced up a load of fresh pineapple and felt a tickling sensation on your fingers that is bromelain digesting your skin; it's a commonly used ingredient as a meat tenderiser. To avoid the proteins in your pineapple juice from breaking down, one you have juiced the pineapple flesh, bring it quickly to boil to denaturalise the enzymes. Once cooled, the juice will last for two days and provide a gorgeous head every time.

Another option is to use a soy-derived protein - soy lecithin will give you the same result in terms of creating protein strands when emulsified - however a higher sugar content in a drink will make a more stable foam in the finished product as soy proteins create a weaker bond and require more stabiliser.

In terms of methods of emulsification, there are a few methods to properly activate the proteins for a final drink:

- The classic dry shake: shaking the cocktail without ice first to aerate and blend the mix. (A common question is why is it called a dry shake when the shaker contains liquid? The answer of course being that it is shaken without ice first so no dilution is achieved - hence keeping it dry.)

-A whipping article added to the shaker: classically the spring from a hawthorn strainer added to a shaker and dry shaken, although this is messy and somewhat of a ball ache. Other items that can assist are the metal balls from protein shakers, while Alcademic's Camper English suggests cat toys.

-Immersion blender: A stick blender can do wonders in quickly whipping proteins into light, fluffy piles before shaking, and removes the hassle of a double shake.

-The inverse dry shake: friend and occasional nemesis Jay Gray espouses the benefits of the inverse dry shake; that is, shaking with ice first, fine straining the mix, then dry shaking it before serving. I'm not 100% sold on the science of this, as diluting the mix first would in theory result in weaker protein bonds  in the final solution. He swears by it's efficacy however, and I swear against it, and then we both swear at each other.

-The crushed ice time saver: Popularised at Bulletin place, this method does away with the dry shake, with crushed ice pulling double duty as both a diluter and emulsifier, which is then fine strained out of the final drink and resulting in a consistent and silky smooth finish to the drink.

Finally, I thought I'd add a recipe from a few months ago for a vegan-appropriate amaretto sour using soya lecithin extract; it is distressing how many people enjoyed this one

The Lagomorph

nb: Lagomorph being the genus name for rabbits. No, my jokes aren't funny in person, either. 

45ml Amaretto

15ml Amaro Averna

30ml Blanched carrot juice

20ml lemon juice

1 bsp soya lecithin

Dry shake vigorously, wet shake and strain into a chilled sour glass. 

Garnish with dehydrated "Rabbit Ears"

In Defence Of Artificial Aging Pt.3

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We've covered the various factors in aging spirits that affect the final taste of a product as it comes off cask. But know we know how the flavors in an aged spirit are made, can we manipulate these factors to speed up this process without losing the final quality of an aged product?

Before we get started I want to address the obvious taboo im sure that we are about to breach, the one that has been preached to us for many years, that age in spirits automatically equates to a superior product. 

If you look at the history of advertising for spirits,  the aged spirit as a luxury item has onoy really been advertised since the late 1960s. In fact the best source of advertising for spirits, to see the rise of aged spirits and vodka in popularity in the American market (at the time the biggest global spirits consumers), is the most popular mens magazine of the time- Playboy. If you can get your hands on a wealth of vintage magazines it is interesting to track the development of advertising over a generational timeline (honest honey, I omly read them for tbe vintage rum advertisements!).

Aging for extended periods of time was never a viable economic option for small producers, and it still isn't today - it takes an incredible amount of capital to be able to put a large amount of distilled spirit down for 18-odd years, especially when even in the hands of the best cellar masters and blenders there is no guarantee it will taste good.  

Sure, the ability of wood to strip out negative flavor compounds in a spirit was recognized, as it had been by winemakers for generations, but the marketing of age as defining a premium product is only a relatively new development, as we have come to realize that extended barrel interaction means more extraction of these tasty flavors consumers love so much.

A lot of purists will be quick to claim that messing with the aging process is verboten, lest we mess with the delicate craft of the cellar master. However large suppliers have already begun experimentation into how controlling and manipulating conditions can speed up the aging process.

At the end of the day the spirits business is a business at heart, and long aging times do not make for a happy accountant. Any method by which to increase aging without compromising quality can and will be explored.

One of the most traditional examples of manipulating the aging process is found in the Norwegian Aquavitt Linie. As the story goes, casks of the spirit were shipped to either Batavia (Indonesia today) or Australia from Norway in ex-sherry casks, with some merchant or another hoping to sell the spirit there. 

No-one seemed to care for the spirit though, so the casks were shipped back to Norway, where the proprietor found the spirit had taken on a sweet, woody character from the casks, and thus Linie was born. Today the spirit still crosses the equator twice, going into barrel at 60% abv in 500 litre ex-oloroso casks strapped to the deck of a container ship. 

The 19-week passage takes the aquavitt through fluctuating temperature, humidity and pressure zones, while the constant movement of the boat means the spirit is constantly washed against the oak of the barrels, increasing the percentage of spirit to wood surface area contact. This is a great example of manipulating variables to increase aging; 5 and a half months aging in Norway would not yield the results that the constant agitation and changing atmospheric conditions that Linie goes through on it's voyage.

Speaking of ships, Jefferson Bourbon recently released an extremely small batch (200 litres!) expression of Ocean-Aged Bourbon. Interested to see what effect the constant agitation, salt air and atmospheric pressure would have on barrel aging, he aged three 200-litre barrels on the deck of a...shark chasing research vessel?

Insert 'Jaws' reference here

So after four years of following sharks around the pacific, we can see the effect the agitation had on the spirit below - bear in mind the standard Jefferson's to the left and right of the bottle have been aged for eight years, not four.

Wow

So manipulating these factors can have an effect. But both of these methods still provide too many uncontrolled variables. How much agitation is applied? What if one batch goes through a particularly stormy month and the other suffers the doldrums of flat seas? What is the temperature fluctuation, the salt content of the air, how much do these change as the ship travels?

A better way to impart woody flavors to a spirit quickly and with much more control over variables would be to use gas pressure to force a 'flash' infusion. This requires an isi canister, or cream whipper, your white spirit, a gas canister, and wood chips. Wood chips have the added benefit of having a much higher surface area, so it is much easier to extract flavor from the wood. 

While I went into further detail regarding the exact mechanics of how this process works in an earlier post, the basic science is that when released into the chamber, the gas forces its way into whatever porous material it can find as pressure increases. As the pressure is released so is the gas, and flavor compounds are quickly forced out of the material and into the spirit, instantly giving a cold infusion of sorts. 

A plus side to this is you can infuse spirits with many types of wood that would otherwise be too porous for use for barrel aging. I've listed below a few different types of wood and their properties for aging. 


Acacia - Robinia Pseodoacacia

Hard wood, low pore count on the oak; would require extended aging to extract any flavors. High in aromatic aldehydes: Vanillin, syringaldehyde (spicy, smoky, hot and smoldering wood aromas), dihydroxybenzaldehyde (cork must, organic matter). 
No presence of eugenol (That spicy clove & menthol note)

Mulberry - Morus Alba 

Tender, elastic wood. Too soft to construct barrels from, low organic compounds, low eugenol content. High in fatty acids (creates unpleasant esters)

Chestnut - Castanea Sativa

Too porous for barrel aging, but excellent for flash infusing. Contains very similar volatile compounds to Quercus Robur, namely vanillin, syringaldehyde, eugenol, and alpha terpineol (floral, similar to lilac; present in Lapsang Souchong teas). Notably lacks any of the whiskey lactones (cis- or trans-).



Cherry - Prunus Avium

Again too porous for barrel aging, but excellent for flash infusing. Low aromatic compounds, low eugenol, low fatty acids. No real draw to this wood, except for something called trimethoxyphenyl, which I can only find described as 'bland'. 

One downside of flash infusing is that it does not have the effect as extended barrel-aging, that of the evaporation of either water or ethanol, the "angel's share" we discussed last time, does not occur when the effects of the wood are meted instantaneously. By equal parts, you also avoid the potential development of unpleasant esters and acetone odors that can be present in spirit aged for longer periods.

One Last Thing...

A few months ago the story of Miami Club Rum, a rum that aged it's rums by playing Cuban Salsa at the barrels during the aging process, made the rounds to differing reactions of bemusement and derisiveness. At first I gave little thought to this very unique method, as it sounds at best like a marketing gimmick, and at worst like the sort of psuedo-scientific claptrap that drives me to drink.

It wasn't until later (in the pub, of course) that I started to give the idea some more thought, specifically the science behind the idea. You see, sound travels in waves by creating pressure in the medium through which it travels, decreasing in pressure and intensity as it propagates.

However, when a sound wave intersects with another sound wave, there is no affect on the propagation of the wave, but if pressure is measured at the point of wave intersection, there is a change of pressure. If two low points in the wavelength intersect, they end up with a higher pressure reading, and if a high and low point collide they cancel each other out and no change in pressure is recorded.

The first time I came across this particular occurence was when I was introduced to something called "Tibetan Bowl Therapy", a particular theory wherein several copper bowls are placed on various parts of a patient and rung at certain tones to illicit a muscular response. 

I originally approached this method with a healthy dose of skepticism, partly because it was being administered to me by an old man in the attic of a church in eastern Switzerland who didn't seem even slightly Tibetan. It was a...strange time.

Anyway, it did do wonders for relieving muscle strain, and I later contemplated the science beyond the mysticism that these treatments are often presented with. By creating low-frequency vibrations in a circular arrangement, the bowls created an intersecting point of increased pressure within muscle tissue, effectively 'massaging' with sound.

Propagation of Sound Waves Intersecting on Barrel

As you can see in the diagram above, if you were to arrange speakers around a barrel as above and constantly play music at it, the sound waves would intersect at multiple points on and inside the barrel, creating pressure around the staves and inside the barrel content, agitating the liquid contents in a similar method as leaving it on a sea-bound boat, and forcing liquid into the wood faster than it would if left alone. 

Moreover, if you were to play music that had high shift between low-frequency high pressure notes and higher, less decibel heavy notes (like for example, Cuban Salsa music) the effect would be similar to the capillary effect in the wood caused by day-to-night atmosphere transitions experienced by traditionally aged barrels.



So is the method employed by the Miami Rum Company a legitimate attempt at artificial aging based on sound science, or just a marketing gimmick? Well, I'd tend toward the latter myself, but this is all conjecture.   

What we have now however, is the potential for two experiments to test the theories and science we have discussed in this series.

Experiment 1:
Does playing sound at barrel-aged spirits affect their maturation speed?

By setting up a control and a few test cases, we can see if there is any reality behind these claims, and more importantly, which type of music makes liquor mature faster and by extension taste better?

And the big one:


Experiment 2:
By manipulating atmospheric conditions, can we reduce the maturation time of a spirit?

We've talked a lot about the different atmospheric conditions that affect the aging of a spirit in wood. But by taking a barrel and filling it with new make spirit, can we recreate an equivalent quality of an aged spirit in a fraction of the time? 

So here is the challenge we set ourselves:

Can we mature and recreate the quality of a 3-year aged spirit in only one week?

We will keep the blog updated with progress on each of the experiments as they happen, but follow us on twitter @Zero_G_Drunk to keep up to date with this and our other news.

Thanks for reading this series as it's progressed, it's been fun. 

See you next time Space Cowboys.

BG

In Defence of Artificial Aging pt.2 - It's Not the Size of Your Stave, It's What You Do With It.

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Previously on Bottlestore Galactica we looked at the different types of wood from around the world that go into making barrels, and the complex ways their character makeup can effect your finished spirit. So you've chosen your wood type, now you're ready to make your barrel; but how big should you make your barrel, and how does that change taste? What's the difference between toasting and charring? What about temperature? Humidity? Atmosphere? And what about that very bugbear we are trying to banish, time?


In Defence of Artificial Aging, pt.2
It's Not the Size of Your Stave, It's What You Do With It.

The Grain

One factor that was discussed in the previous entry was that of wood with a loose vs tight grain, with the postulation that barrels made up of tightly-grained wood were better suited for wines, whereas looser grained wood was better served aging spirits. But how do you know if your barrel is tight or loose grained?

Well on the off chance you are not a fourth generation French cooper, an easy method to ascertain a barrel's grain is simply by looking at the stave at the end of your barrel and counting.

A French cooperage places the following designation on grain grading:

nb: GPI= Grains per inch

>17 GPI: Extra Fine Grain
12-16 GPI: Fine Grain
8-11 GPI: Medium Grain
8Coarse Grain


Now grain size depends on how fast a tree grows during summer - so trees growing in warmer climates will have a broader, looser grain - see Quercus Alba, the American White oak. 

Barrel Size

The size of the barrel a spirit is aged in has a huge affect on how much of the barrel's character is absorbed into the wood; that is, how many of the wood solubles are dissolved into the spirit and at what concentration. Smaller barrels have a higher ratio of oak in contact with the contents of the barrel and therefore will release a higher concentration of flavors and colors into the the total content of the spirit than would occur in a larger-size barrel.

In this way a smaller barrel can give the desired effects of long-term maturation faster than a barrel with greater volume, assuming the spirit is maintained in identical conditions in both cases. A smaller barrel can therefore 'age' a spirit faster than a large barrel: keep this fact in mind for later.

Another way that a producer can speed up the 'aging' process is to increase the surface area of oak exposed to the wood without increasing the overall volume. One such way to do this is to use corrugated staves, a practice that is used at Maison Vicard in Cognac.

In order to calculate the interior surface area of a barrel you can follow this formula below: 

SA = (2 x Pi x r x (A-(L+I)) + (2 x Pi x (r x r)) 

Where SA: Surface area,

             Pi: 3.14

              r: Radius of the barrel top

              A: Actual Length

              L: Lip of Barrel (Stave Width)
              I: Interior Lip 

Regularly to calculate the surface area of a cylinder you would use the following:

SA = (2 x PI x r x H) + (2 x PI x (r x r))

But this doesn't take into account the irregular shape of a barrel, nor does it take into account the thickness of the staves, and it would only give you the outside surface area of the barrel.

When measuring your barrel, be sure to measure the Actual Length (A) and not the Height (H) of the barrel; the barrel's irregular shape means that the height measurement will give you an innacurate measurement, whereas Actual Length will account for the shifting exterior circumference of the barrel as an average (assuming the stave width, L, is a uniform constant).

Once you have your interior surface area in square units (cm or inches, we don't discriminate), you can do a quick calculation of your liquid volume divided by the surface area to see how large a percentage of your liquid comes into contact with the oak.

Percentage of liquid in contact with oak = ((volume/interior surface area)/volume) x 100

LC(%)=((V/SA)/V) x 100

Once you have this figure you can start to get an idea of how increased contact with oak can speed up the maturation process, and affect the concentration of wood flavors. I haven't done it myself yet but it would be and interesting experiment to take a series of different sized barrels and age identical lots of spirit under controlled conditions. This way you will be able to demonstrate how much of an effect spirit-to-wood contact has on the final spirit.

Below is a table of the most common barrel styles used in the global liquor industry, and their characteristics:

Barrel Name	Capacity	Wood Type (Traditional)	Characteristics & Notes	Used For (Traditional)
Gorda	700 Litres	American Oak	Large size and low wood-to-oak ratio means this size is seldom used for maturing whiskey, intended instead for marrying blended whiskeys.	Blended/Vatted Malts
Maderia Drum	650 Litres	French Oak	Short, fat barrel. Very Thick staves.	Madeira Finishing: whiskey
Port Pipe	650 Litres	European Oak	Tall, thin barrel.	Port Finishing: whiskey
Butt	500 Litres	European Oak	Popular in the Spanish sherry industry – tall, thin design.	Sherry Finishing: whiskey
Puncheon	500 litres	Spanish Oak	Thick staves, short fat barrel design.	Rum, Sherry Finishing: whiskey
Barrique	300 Litres	European Oak	The traditional use of barrique casks by the wine industry has led to the spirits industry using this barrel type to give a wine finish.	Wine Finishing: whiskey
Hogshead	225 Litres	Traditional: European Oak Contemporary: American White Oak	Barrel size derives from 15th century brewers-unit. While traditionally made of European oak, the shift in demand and oak prices sees most contemporary hogshead made from American oak.	Scotch, Irish Whiskey
American Standard Barrel (ASB)	200 Litres	American White Oak	Smaller barrel size and wide-grain Quercus Alba meant faster spirit maturation vs. traditional hogshead	Bourbon, Irish & Scotch whiskey (ex-bourbon)
Quarter Cask	50 Litres	No standard	Also known as a firkin.	Small batch whiskeys, dodging the tax man.
Blood Tub	40 Litres	No standard	Long, oval shape designed to be carried on horseback. Awesome name.	Brewing beer, small batch whiskeys.

Information from whiskeyforeveryone

In the last few years we've also seen the rise of the personal barrel, popular in bars and with home distillers. For the most part they are American oak (although certain French vodkas are starting to hand out 3 liter barrels of Quercus Petraea) and come in variations of 1, 2, 3 and 5 liters and have no specific title. 


Charring and Toasting

Once the wood is chosen and the barrel has been constructed, coopers can further adjust flavor profiles that can be extracted from the wood by charring and toasting the barrels, using a range of methods from flash-toasted to naked flame to 'cook' the wood.

We've already discussed how the American coopers industry would dry and cure their oak by kiln as opposed to the traditional French air-drying industry. The process by which the French shape their actual barrels is by bending their staves by heating them with the use of a wood-fired brazier, before heating to either light (5-10min), medium (10-15min), or heavy (15-20min) toasting. American barrels are shaped by using a steamer to soften the oak staves, then using a gas torch to char the interior of the barrels, grading as light (15s under torch), medium (30s), or heavy char (45s), with even heavier char (1min<) available to craft distillers.

There is no definitive proof of who begun charring oak barrels and when they did, although plenty of bourbon producers have claimed that they begun the trend that now defines the category.

In fact the earliest record of charring barrels comes from a book stored in the United Distillers archive in Louisville, Kentucky. Unfortunately, there is no cover to the book or author listed, just an uncredited, handwritten note that references the year 1854. It appears to be in the common style of farmer's almanacs of the times, which would provide a wide variety of information on everything from when to plant crops to how to cure meat, usually including information on home-made tinctures and tonics.

It includes this passage:

“Q: Why are water and wine casks charred on the inside? 
A: Because charring the inside of a cask reduces it to a kind of charcoal; and charcoal (by absorbing animal and vegetable impurities) keeps the liquor [liquid] sweet and good.”

So water and wine casks were already undergoing charring at the time this was written, and was common enough that his information was thought vital enough to be included in what seems to be a general almanac. No proof exists, then, that any one producer was exclusively using charred oak prior to it becoming the norm and then a legal requirement, but as to why they were charring oak and how and where it originated these facts are lost to the mist of time.

So while there is no definitive answer to the question of who started charring barrels, the processes of heat treatment via charring and toasting have different effects and produce different flavors. For example toasting helps converts complex insoluble sugars (hemicellulose) in simpler sugars, which is turn break down into caramelization products like fufural and maltol amongst a host of others, which will in term develop into the structures that will give color, as well as notes of cooked and burnt sugar and of course 'toasty notes' which primarily come from the fufural. 

Different temperatures of toasting will break down the hemicellulose to different levels, which will in turn produce different simple solubles and therefore different flavor profiles as a result of maturation from the finished barrel. 

Graph from World Cooperage

Charring on the other hand not only creates a whole different range of flavor compounds (vanillin, eugenol, syringaldehyde), but also has creates a larger contact surface area as the wood cracks and converts to charcoal. A larger surface area means a much faster interplay between wood and the now developed sugars and solubles, providing an easy passage for spirit to enter the wood and absorb the sugars and solubles that create the flavor of a matured spirit. 

The charcoal also acts as a filter, absorbing sulfurs and esters from the spirit, smoothing out your spirit from the rough white spirit to the aged final product.


Relative Atmosphere: Temperature & Humidity

Once the barrel is treated is filled with spirit to be aged and stored in a warehouse for the length of it's maturation. The vast majority of these storage houses will not be climate controlled; indeed it is the natural climate and relative atmosphere that characterizes regional liquors, imbuing them with the spirit of their land of origin.

For example, take two spirits, a Scotch whiskey and a Caribbean rum, both aged at seven years, both matured in an ex-bourbon barrel of comparable size. Both of these spirits will go into the barrel from the distillery crystal clear, and only develop their color from time spent in oak. In the vast majority of cases the rum will be much darker than the Scotch. 

This is because of the two factors of relative atmosphere as it affects maturation of spirits: temperature and humidity. 

For quick reference, the average annual temperature in Havana, Cuba varies from 16c(60.8f) to 32c(89.6f), and humidity from 50% to 97%. Islay Airport, conversely, records an average annual temperature range of 2c(35.6f)to 17c(62.6f) and a humidity range of 59% to 99%.

So while they have a similar humidity, Scotland is far colder annually than Cuba (look out for our future blog post, Grass is Green and the Sky is Blue). 

Obvious conclusions aside, what does the temperature have to do with the maturation process? Higher temperatures affect the oxidization reactions of the wood solubles, increasing the levels of fufural, tannins and aromatic compounds. 

However, high temperatures also accelerate the oxidization of ethanol, which will convert into ethyl acetate, the strong, sweet nail-polish remover note that is often present in rums produced in high-temperature regions, which can be either stripped via charcoal filtering, extended aging, or masked with added sugars.

Low temperatures avoid this issue of rapid oxidization, but as a result the aging process takes a lot longer to achieve comparable results. While it may be advantageous to age spirits at high temperature to cut down on aging time and increase turn around between distillery and market, you risk adding harsh esters and acetones to your spirit which then have to be masked with additives.

At high humidity ethanol evaporates faster in your barrel, whereas at a low humidity it is the water that evaporates at a quicker rate. 

Beyond just altering the final proof of your products, the portion that evaporates will change the character of what remains in the barrel. Both water and ethanol are solvents but for different compounds; water contains the caramel coloring and the wood sugars, whereas ethanol contains the lignins, vanillin and tannins.
 
So at an extreme high or low of humidity would it be possible to evaporate the entirety of the ethanol or water content of the spirit? Well no, as we covered earlier when we were looking at freeze distillation thermodynamic law dictates that there shall never be an absolute separation of ethanol and water in a solution. As you would never be able to truly freeze 100% ethanol off of water, also it is impossible to separate the two components via evaporation.

Therefore, high-humidity maturation will result in a sweet, dark spirit, but without the nuance of character that comes from the complex soluble compounds in the oak. It will take a lot longer to draw these flavors from the oak, but if aging in a high-temperature region, rapid oxidization will starts to produce unpleasant esters and acids that can ruin a barrel of spirits. 

This is not to say all esters created during maturation. are unpleasant and unpalatable, as some aromatic esters are highly prized in spirit production.


In Kentucky there is the greatest fluctuation in both temperature and humidity; from -4c(24.8f) to 31c (87.8f) and 41% to 94% annually. This, coupled with a high diurnal temperature variation (the difference between daytime and nighttime temperatures) means that bourbons aged in non-climate controlled warehouses have a huge amount of temperature fluctuation inflicted upon them. 

This means both the oak and the spirit inside will expand and contract on a daily basis, the oak becoming more porous as the day heats up while the spirit pushes itself deeper into the wood, dissolving solubles in the deep grain of the charred barrel. Capillary motion, similar to how a pair of lungs works, pulls the liquid into the staves, diffusing the whiskey throughout the cell structure of the wood.  As night falls and temperature drops, the oak will contract, forcing the absorbed spirit back into the mix, bringing with it extracted flavors from deep in the porous, loose grained American oak. The elastic expansion and contraction drives the interplay between spirit and wood, the humid afternoons drawing out the angel's share as it dissipates into the air, further driving rich, toasty notes into the bourbon.

I've just realized that description sounds vaguely erotic. 

Nonetheless, the temperature & humidity in Kentucky creates an ideal atmosphere for quick maturation while maintaining an environment that discourages oxidization and the development of unpleasant flavors.

Another potential atmospheric factor is the mineral content of the air - more specifically, the salt content of atmosphere in locations where spirit is aged adjacent to the ocean, particularly whiskeys from the Islay region of Scotland. 

'Salty' is a tasting note popular with tasters and distillers alike for describing their product, but there is little information on the science behind the evident salty taste. Indeed 'salt' as a descriptive is a relatively recent development; "Salty" as a descriptive wasn't used until 1978.

The commonly accepted theory is that the briny sea air of Islay leaches sodium chloride and other saline metals into the wood, which is then absorbed into the final spirit, giving the final product a salty note, with most distilleries going so far as to suggest that, without confirming it as actual fact. That is probably for the best, as some Islay distilleries age their whiskeys on the sea front with the salt waves washing against their warehouses, where some age their whiskey in a warehouse far inland where you can maybe see the ocean if you stand on the roof on a clear day and squint real hard, yet they both claim it is the relative atmosphere that cause salty notes in their whiskey

Others have opined that it is the water used by distillers that imparts these briny notes, that is mostly disregarded as distillation removes the vast majority of sodium solids from the spirit, as the brine waste is denser than water or ethanol and can be separated in a still with ease. Others claim it is the peat used to smoke the malt, claiming you can taste the difference between peat harvested on Islay and on the mainland (most famously between Bruichladdich's Octamore 1 & 2), but this is all subjective evidence. 

As to whether or not there is any scientific evidence behind the perceived 'salty'-ness of Islay whiskeys due to the relative atmosphere, it is not publicly available as far as I can find. I'm sure Suntory, Beam Global or Diageo has researched this but they are keeping their findings close to their chest.

As always, if you know anything to the contrary on this, please feel free to send me a message and I will be happy to publish a correction. But that still begs the question, what changed since 1978 to make everyone start recognizing salty notes in Islay whiskey? Was there a conscious choice amongst whiskey makers to change something to introduce this flavor? Or was is simply a trend followed by whiskey enthusiasts & profilers, disseminated by Michael Jackson (not that one) and accepted as fact as the popularity of Islay whiskey has increased over the last few decade?

Without proof I'm still inclined to tend towards the latter, and while there have been various studies published on phenol content, gas chromatography and esters present in Islay whiskey, there is nothing so far that has covered saline or similar heavy metal content in whiskeys that are described as having such a flavor.

Alcohol Proof, Thieving Angels and Time

We've already covered how different fields of humidity cause a dominant portion of either water or ethanol to evaporate in a cask, which strip certain flavors and introduce others. This loss of volume can either raise or lower the final proof of an aged spirit, but it is a hard constant to graph, as the many variables of changing atmosphere, constantly changing ratios of ethanol to water and other solids, trade between oak and spirit, potential of oak density change due to temperature, and lack of universal oak grain as a constant, all of which is taking place in a barrel over the course of years, make for a incredibly complicated set of variable to try and track.

What we know for sure is that a higher alcohol percentage will have a faster extraction rate, it will also draw a higher amount of tannins from the wood, which can cause bitterness and astringency in high levels. Higher abv also means in most cases more water will have to be added to dilute the final product for general consumption (believe it or not, not everyone loves Smith & Cross and overproof whiskey), which dilutes the effects and flavor of the barrel aging in the first place, defeating the purpose of trying to speed up aging with a higher abv product. 

Therefore, most distillers accept that 55-65% alcohol is optimum for maturation, dissolving a higher ratio of wood sugars and caramel coloring from the oak then the tannins it will pull. Furthermore, studies have confirmed that this ABV is the best for maintaining the porous nature of the oak, facilitating a better passage for water to evaporate, meaning in most cases the final spirit will have a higher ABV then the spirit that went into the barrel pre-maturation, with a higher concentration of lignins, vanillins and oak lactones, all good things for creating a complex and nuanced spirit.

It also is worth noting that that the combination of high annual temperature and humidity is a reason many rum producers in tropical climates prefer ex-bourbon 'refill' barrels to mature their spirits in. As a general rule of thumb each time a barrel is refilled it will take twice as long as the previous aging period to extract flavor compounds from the wood, as the spirit has to diffuse deeper into the cells of the oak. New make barrels with high level of lignin & tannins will extract too heavily in high-proof spirits, so the abundance of ex-bourbon barrels allows for a more controlled aging in tropical climates, so the spirit can pull color and sugar from the wood without becoming too bitter and astringent.

The loss of volume by evaporation is called the angel's share, born of the old belief that angels were taking a certain percentage of distilled spirits as some sort of holy tax. As adorable as this is as a story, and as many bars and cocktail menus around the world have profited from this superstition, the fact is that for most cases, you can expect around 7-10% loss from the volume of a standard oak barrel annually. This is even higher in tropical climates, around 10-15%.

From the position of a major supplier, this mean you are potentially 'losing' hundreds of liters of delicious whiskey to freeloading angels every year, which can equate to hundreds of thousands of dollars. This realizations have led to some attempts at arresting this loss, ranging from the slightly ingenious (the case of a certain rum house installing a cooled corrugated iron roof above its barrels to collect evaporation and funnel it back into other barrels) to the bizarre (Diageo's experiments in cling-filming their barrels to try and decrease evaporation).

While this may amuse some and raise hackles in others, it does call to light the pedestal upon which we have placed barrel aging, and the common misnomer that older is automatically better. While better aging can indicate a spirit with more complex character, often the price of a bottle or a nip is directly related to the amount of time a spirit has spent in a barrel.

To clarify I'm not saying all super-aged whiskeys are inherently bad, I've had some stunning 27, 30, 35 year old whiskeys. But I've also tasted bottle with a retail price north of $500 that taste like chewing wood with a chaser of old sugar syrup and sherry.

Excessive aging can cause high levels of astringent and drying tannins, unpleasant esters and the development of cask spoilage in the form of brettanomyces, a yeast strain that can develop during oxidation (not necessarily a bad thing, if you like the funky horse-must and saddlery aroma it creates). These factors are often compounded by the fact that after a whiskey spends a certain amount of time in wood, it stops tasting like whiskey and starts to just taste like smooth, woody chocolate. 



So if we can decrease maturation times through the use of barrel sizes, wood surface area to spirit ratio, char and toast, temperature and atmosphere, surely we can recreate a facsimile of an aged spirit by exploiting these factors? 

What other woods can we use to age spirits, and what flavors and characteristics can we extract from them? How are other, global brands speeding up the maturation process to get an aged product into the hands of consumers who increasingly believe that age=quality? How can you achieve their results in your home or bar? And is artificial aging unethical, or a necessary evil? Or if you can match the quality of an aged product in a fraction of the time, is it evil at all?

Find out next time, as usual, right here on Bottlestore Galactica