“You’ve gotta give it a taste to know!” answered the long-haired, cowboy shirt-wearing distiller dude at Madison, Wisconsin’s Old Sugar Distillery. He was responding to my incessant questions about how long their liquors take to age. His answer was interesting, but I wanted numbers! After some more pointed questions, he told me that most of their liquors take around 5 months to age properly in their smaller-than-usual 5-gallon barrels—”about a month per gallon,” the distiller/bartender informed me. With those numbers in hand, I knew I had the key to connecting my occasional nighttime interest, liquor, to my constant daytime interest, nanotechnology.  Stay with me…

In order for Kentucky Whiskey to be called “straight bourbon,” it must be aged for a minimum of two years. This is way longer than the five months of aging that happens on the corner of Main and Brearly in Madison. According to lots of new startup craft distilleries like the Old Sugar Distillery, their small barrels are the key reason they can churn out their liquors so much more quickly than the big distilleries, who typically use large 53-gallon barrels.

Smaller barrels = quicker liquor?

As a liquor sits in its barrel, the flavor changes through two slow processes. One change is the result of flavorful and colorful chemicals slowly migrating from the wood into the liquor. The other change occurs as the chemicals in the liquor slowly change their atomic structure by reacting with chemicals in the wood as well as with oxygen from the air—creating brand new chemicals and brand new flavors. Barrel size primarily affects the rate of the first process. The smaller size allows for more contact between the inner barrel surface and the liquor, which allows the flavor chemicals to hop into the liquor much more quickly. There is more liquor/barrel intermingling because as objects get smaller, they have more surface area than they do volume. This is shown below for external surface area of cubes, but the same applies for internal surface area of hollow objects like barrels.

So even though the 53-gallon and 5-gallon barrels are made of the same stuff, their interactions with other things change as a function of their size. The smaller barrel is unique because it allows for more rapid aging of liquors (though some argue the liquors aren’t quite as nice as those aged traditionally).

Size Matters in Liquor and Energy Production

Much next generation solar technology takes advantage of a similar phenomenon. Most solar cells currently on the market are made of silicon. Dark crystals of this substance absorb energy from sunlight and inject electrons into an electric circuit—thus creating the  electricity we know so well.

A new type of solar cell in development is made of much cheaper chemicals, like titanium dioxide. The only problem with titanium dioxide is it is white, so doesn’t absorb any visible light. White paint and other white things you buy likely contain titanium dioxide, because it’s so good at making things white!

A solar cell that doesn’t absorb light would be useless. To get around this, researchers put a thin coating of a vibrantly colored chemical on the titanium dioxide surface. This colored “dye” then absorbs the light, which causes an electron to be injected into the titanium dioxide and on into the electrical circuit. This is known as a “dye-sensitized solar cell.”

However, just like large barrels take a long time to “inject” their delicious chemicals into liquor, a large chunk of titanium dioxide coated with a dye would generate electricity really slowly in part because only the dye-coated surface of the titanium dioxide chunk can absorb energy from the sun.¹ The answer to this problems is to create more surface area for the titanium dioxide and dye to intermingle. Just like the distillers use smaller barrels, scientists just use smaller chunks of titanium dioxide to create more surface area.

Thus enter our good nanoparticle friends! They can be made in such small sizes (1 billionth of a meter!) that they are almost all surface! Coat the surface of titanium dioxide nanoparticles with dye molecules and you have the key ingredients for a reasonably efficient solar cell. There is so much dye-coated surface that they collect way more light energy from the sun than they would if they weren’t nano-structured.

Nano-liquor?

It works well for solar technology, so what about nanotechnology in liquor aging? Instead of a big 53-gallon or smaller 5-gallon barrel, what if distilleries used a nano-sized barrel? How quickly could you age the liquor inside a barrel that is 10 nanometers tall and 10 nanometers in diameter? What I’m about to do is a dramatic oversimplification that might upset many distillers and scientists alike. With that warning aside, I can say that a barrel that size would age the liquor inside it in approximately one half of a femtosecond.

That is SUPER fast! In 3000 femtoseconds, light travels just one meter! But, as I said before, it’s definitely not that simple. When you get down into nano-sizes, things just get weird, and I’ll leave the weirdness for another post.

All crazy speculation aside, there is way more science at work in both liquor aging and solar cell technology than just surface area. For that reason and because I need to get to the Old Sugar Distillery to pester the distiller with more questions while he’s there, I’m calling this post complete.

References and Further Reading:
Science of the Silicon Solar Cell (lots of cool animations!)
Craft of Whiskey Distilling (especially Chapter 4)
Whiskey Startups are Rolling Out a Small Barrel Sooner
Development of Titanium Dioxide Nanoparticle Solar Cells
Nanocrystalline Titanium Oxide Electrodes for Photovoltaic Applications (subscription required)

Footnote:
1 – A solar cell made of a big chunk of titanium dioxide would work poorly for a number of other reasons too, not just the surface area reason discussed here.