What's Inside Scotch Whisky
science beverage


Single malt scotch whisky is a magical potion; a nectar from the gods. I first became aware of how good this stuff could be when I was a student at Dartmouth and a member of The Glen Tuck Society. I still have no idea why imbibing a substance that is equal parts jet fuel, cough medicine, and essence of bonfire tastes so good.

Simplicity is what I admire most about single malt whisky. It is unassuming and minimal, but complex; consisting of only water, barley, and yeast. Focused through distillation and developed with age, whisky absorbs the smells and substances of it’s surroundings to impart powerful flavors of the sea, highlands, and other regions. When you mix the end product in your mouth and the vapors rise to envelope your nasal cavity you can taste and smell the principle ingredients transformed by age and environment into something truly spectacular.

Whisky is like all great things that humans create - part science and part art. This post will focus on the science of whisky. Specifically, on a few key compounds inside great malts. If you need a primer or a refresh on whisky basics, head over to Malt Madness. If you looking for whisky buying advise, check out my Objective Analysis of Single Malt Whisky blog post.

A Note On Complexity

Single malt scotch whisky may only have a handful of ingredients, but it is extremely complex. Microorganisms create massively diverse flavor profiles during fermentation through production of secondary metabolites. In addition to yeast, Simpson et al found greater than 60 different bacterial species in the fermentation of whisky from a number of samples in Scotland. Here are the main mechanisms for generating flavor diversity in whisky.

  • Thousands of pre-existing chemical compounds within barley, yeast, and bacteria
  • Secondary metabolites generated by yeast, bacteria, and other fungus during fermentation
  • Chemical reactions during barley germination, drying, peating, and fermentation
  • Chemical reactions that occur from heating the wash and reactions that occur between the metal of the stills and the wash
  • Chemical reactions between individual compounds in the finished spirit
  • Chemical reactions between the spirit and the wood cask

Here is a brief look at five interesting compounds commonly found in some of your favorite single malts.

Whisky Lactone

3-Methyl-4-octanolide or as it is commonly called “whisky lactone” is a chiral compound that comes in two forms, cis or trans. trans-3-Methyl-4-octanolide is a natural insect repellent, while cis-3-Methyl-4-octanolide is extremely fragrant and is the most important form for flavoring whisky. Whisky lactone is primarily found in American Oak wood and the compound becomes infused in whisky after years of storage within oak casks. The high alcohol content of whisky functions to extract whisky lactone from the cask and into the spirit. This process infuses whisky with a wonderfully sweet flavor that is often described as coconut with subtle roasted and/or woody qualities. Unsurprisingly, the compound is used as a flavor additive for candies and other sweets. To me, whisky lactone is probably most noticeable in tasting single malts from Glenrothes and some malts from anCnoc.

Ellagic acid

Ellagic acid is a phenolic compound derived from tannins in barley. Tannins are hydrolyzed during barley germination to generate ellagic acid. In recent years, considerable interest in ellagic acid has surfaced in the scientific community. It is speculated to have potent anti-cancer properties related to it’s ability to inhibit cell growth and trigger cell death (Heber et al.). Based on a number of scientific studies, ellagic acid is now being marketed as a health supplement. Who says drinking is unhealthy? Ellagic acid imparts a pungent and astringent quality into whisky. Balvenie malts are especially known for their high ellagic acid content.


No talk of the composition of scotch whisky would be complete without highlighting peat. One interesting compound particularly abundant in peat infused whisky from Islay and Orkney is acetovanillone (Harrison et al). Acetovanillone has numerous useful pharmacological properties. Acetovanillone is a potent anti-inflammatory used to treat arthritis and atherosclerosis. The compound has even been shown to be effective in treating Lou Gehrig’s disease in mice ([Harraz] et al). In whisky, acetovanillone adds a strong vanilla flavor that I think is most noticeable in Bunnahabhain malts.


Furfural is a ubiquitous organic compound found in many single malts. It is generated from a barley sugar polysaccharide precursor called hemicellulose. When barley is germinated, enzymes inside the barley become activated and convert hemicellulose to another sugar called xylose though a hydrolysis reaction. During the distillation process, xylose then undergoes a dehydration reaction to make furfural. Furfural is toxic and even lethal at high concentrations. Furfural is characterized as having an almond or caramel taste and is common component of many single malts, but I find it most apparent is beer; especially Belgian beer like the St. Bernardus Tripel.


ortho-Cresol is a phenolic compound that is toxic and corrosive with disinfectant and antiseptic activity. It is used as a disinfectant and/or solvent in many industrial applications. It is found in LYSOL disinfectant spray and a number of commonly used industrial cleaning products! ortho-Cresol has a musty, coal-tar, and phenolic taste and is frequently found in relatively high concentrations in whisky for the Islay Region. I find ortho-Cresol taste to be especially pronounced in Talisker malts.

Interested in Whisky? See my An Objective Analysis of Single Malt Whisky.