The Chemistry of Whiskey

"Understanding the delicate interplay between chemistry and aroma could be a huge help to distillers looking to tweak their whiskey to encapsulate that perfect blend of smoky and spicy….It’s research that means that the perfect whiskey–smoky, spicy, or however you want it–might not be so elusive after all."(2)

Inside the Jack Daniels Distillery

This Thanksgiving, as per usual, I'll be making the long overland journey to Nashville to see my brother. Although the visits are, of course, enjoyable the question always arises among my  family: what on earth are we going to do for four days while we're not stuffing our faces? This year, it looks like we're taking a tour of the Jack Daniel's Distillery in Lynchburg, TN.

My immediate reaction to this was, I bet they have a lab. Then, I wonder if they're hiring? Well, like most companies which produce alcoholic beverages, they do indeed have a lab and a fairly extensive one at that.

According to an article in the New York Times the use of high-tech analytical chemistry equipment and techniques wasn't fully implemented at the company until 2002, 136 years after it's founding. Sensory scientists were concerned that not all the key aroma compounds of their whiskey had been identified and that therefore there could be room to improve its taste (if not by changing the formulation then through ensuring the balance of compounds is perfect for each and every batch). This new research into their own product went as far as analyzing the effects of the type of oak used for aging barrels (1).

Whiskey Lactone: β-methyl-γ-octalactone

The basic process for making whiskey starts with fermentation of a blend of corn, rye, malt and barely. That product runs through several feet of sugar maple wood charcoal, is distilled, and allowed to age in an oak barrel (usually for years). Interestingly - well, there's two really interesting things here - the charcoal removes the esters from the whiskey making it less fruity and pungent, and the distillate leaves behind a material with upwards of 500 unknown compounds, some of which might be aroma or flavor chemicals. When this chemical mass was sifted through for potential whiskey additives, scientist's at Jack Daniels "identified 28 critical compounds that seemed to give the most flavor to the bourbon, including beta-damascenone, which give the taste of cooked apples; lactones, which provide coconut flavors and eugenol from the oak barrels, which give clove like flavors" and "when the 28 compounds were added to the alcohol and other compounds, the result was a pretty good bourbon" (1).   

Similarly, a Smithsonian Magazine article divulges the chemical complexity of whiskies in general. A University of California, Davis researcher (Tom Collins) and his team analyzed 60 American whiskies and found over 4,000 different non-volatile compounds in total, many of which overlapped among the brands and types. Because whiskey is made from a variety of grains and because yeast is involved there is an overwhelming number of potential chemicals that can be produced during the process (2). 

The purpose of the research was to answer on a fundamental level the question: why are all bourbons whiskey but not the other way around? The team found a more technical answer than production regulations can supply, "there are 50 to 100 chemical compounds such as fatty acids and tannins that can be used to distinguish a Tennessee whiskey from a bourbon" (2). 

An article from the Royal Society of Chemistry gets into the fine details and complexities of Scotch Whiskey production. The Scotch Whiskey Research Institute in Edinburgh, Scotland delves into the chemistry behind Scotch whiskey as its own class of liquor with its unique flavor and aroma compounds. 

Like most liquors scotch whiskey contains many of the major classes of flavor chemicals: fatty acids, aldehydes, esters, and more. Unlike Tennessee whiskey, the only raw material involved is barely (becomes malt upon fermentation, hence "malt whiskey") so the flavor combinations from starting materials is relatively limited. However, traditional scotch production has some interesting conventions: smoking the aging barrels over a peat-fire, the use of copper stills, and aging in oak barrels for 12 to 16 years. 

The complexities of peat-smoke is practically a field on its own: one study found that peat in different locations around Scotland produced a different chemical profile (4). Like dripping the undistilled brew through sugar maple wood charcoal in Tennessee whiskey production, the firing of the casks produces a layer of active carbon which removes undesirable chemicals. Additionally, lignin from the wood breaks down during ethanolysis which produced aromatic aldehydes and whiskey lactones which are often fruity and even coconut-like (3). 

Peat Site in the Shetland Islands

Like the charcoal, the use of a copper still reduces the amount of sulfur compounds that end up in the final product. Although these chemicals are important to produce meaty flavor, as noted in last week's post, no whiskey purist wants their drink to taste like turkey (3). 

The type of barrel used for aging also has effects on the product. Bourbon producers and some Tennessee whiskey producers like Jack Daniels only use their oak casks once before selling them to other companies (which seems incredibly wasteful to me…). Casks from different alcohol production processes effects the Scotch whiskey. For example, if rum or sherry casks are re-used, the whiskey will be darker and sweeter. More important than the type of cask used, however, are the reactions that occur when the liquor in is contact with the wood. These include the absorption of dimethyl sulfide into the wood, reducing the pungency of the final product and the oxidation of alcohols and aldehydes to form characteristic esters (3). 

Based on the articles I read it seems that the chemistry and complexity of whiskey is something that has only recently been deeply explored. It's left me wondering how much research has been done on other liquors and the various processes that go along with them. Wine, of course, has been extensively studied for some time but the in-depth analysis of flavor and aroma compounds of other alcohols are potentially just as intricate yet not fully understood or even appreciated. 

If you want to know everything ever about Scotch Whiskey production, here's a documentary narrated with an excellent accent. 

And for kicks, here's your holiday guide for whiskey tasting. 

Ashley 

1. Chang, Kenneth. "What's in that Bottle of Jack Daniel's? A Chemistry Mystery." The New York Times (Archives), Nov. 5, 2002. Web. Accessed Nov. 23, 2014.

2. Geiling, Natasha. "How Chemistry Can Explain the Difference Between Bourbon and a Tennessee Whiskey." Smithsonian Magazine Online. Sept. 9, 2013. Web. Accessed Nov. 23, 2014.

3. Gills, Victoria. "A Whiskey Tour." The Royal Society of Chemistry "Chemistry World." December 2008. Web. Accessed Nov. 23, 2014.

4. B Harrison et al, J. Inst. Brew.,  2006, 112, 333