smell, the sense of , is the detection of diverse volatile compounds to which humans are sensitive and is an essential tool for analyzing and enjoying spirits. Understanding how humans collect and register various odorants (the volatile compounds that create olfactory sensations) can help lead to greater appreciation of the nearly limitless variety of descriptors inherent in a spirit, as well as better comprehension of those specific odorants that are crucial to specific spirit categories, although it is important to bear in mind that people differ in their abilities to sense, smell, and identify many compounds, with some of that difference being physical and some experiential. A key, even essential, part of identifying aromas is having a personal library of smells to which one can compare them.
Within the sinus cavity are two olfactory epithelia, each six to twelve square centimeters, one at the top of each nasal passage. They include about twenty million cilia-laden olfactory sensory neurons (a tenth of the number dogs have) that constantly regenerate themselves, although the rate decreases with age. The cilia contain odorant-bonding olfactory receptors, and the information they collect is sent from these olfactory bulbs to the brain.
Fascinatingly, the once prevalent theory that each cilium receives one odorant (the old “lock and key” method) is long discredited. Instead, we have found no fixed code for odorant perception; the manner in which glomeruli in the olfactory bulbs respond to aroma seems more experiential than physiologically predetermined. For the purposes of spirits analysis and description, this means that until you’ve experienced a particular smell, it’s virtually impossible to describe that smell. Though that may seem to be circular logic, imagine trying to describe “artichoke” to someone; all would be best served by simply smelling and tasting artichoke.
Olfactory sensations belong to the limbic system, which directly or indirectly encompasses the olfactory cortex, the amygdala, the hippocampus, and other primordial brain structures involved in the formation of memory and emotion. This unmediated and direct linkage is part of the reason why many drugs are designed to be inhaled. But just as interestingly, smells take longer to notice and identify than other sensations (taste, touch, sight, hearing). The words are usually hard to find; the sense of smell doesn’t travel through the thalamus like other senses, and the thalamus works with language.
For most tasters and all professionals, the greatest challenge is the disparity between what is often referred to as “detection threshold” and “identification threshold.” A smell is constructed in the brain: it is a report generated after the brain has compared a detected volatile compound or set of compounds to its database of identified, half-identified, and even unidentified but retained smells. As Harold McGee puts it, smells are “shaped and presented as simplified conscious perceptions by the actively editing, synthesizing brain.” It’s frustrating to smell something but to be unable to determine exactly what it is—to get an inconclusive report. While there is debate whether the detection threshold is fixed (it’s not), there is general agreement that the identification threshold responds to experience—that tasters can to some degree train themselves to identify a smell they detect. Members of the wine industry, for example, have trained themselves to smell TCA (2,4,6-trichloroanisole), that moldy newspaper-cork smell, as well as volatile acidity or ethyl acetate. See TCA (2, 4, 6-trichloroanisole).
If you struggle finding words to apply to the aromas in spirits and beverages, however, you are normal. Anthropologists maintain that among the world’s languages there are fewer words exclusive to the sense of smell than to any other sense. A large part of olfactory training for spirits tasting is cultivating a vocabulary of descriptors that are both consistent and communicable—so that ideally whenever you’re presented with a spirit that has been aged in a new American oak barrel, for instance, you have a unique olfactory identifier for that fact on which you can rely, and which you can communicate to others so that they too can identify that fact.
This is not easy. Furthermore, there are barriers for even trained nosers. Some are long-term: as humans age, we lose sensitivity to smell; partly this is because the epithelial pads lose their ability to regenerate olfactory receptors. Most people’s sense of taste will not lessen, fascinatingly; but some scientists believe that perhaps half of the population aged 85 or older is anosmic, or unable to detect most smells.
Others are temporary, or at least reversible, but frustrating. For instance, olfactory receptors become unresponsive after continued exposure to certain smells; adaptation (some call it olfactory habituation) explains why a smelly room stops being so smelly, but when pet owners return home from a vacation (for instance), they are first struck by how smelly that room “has become.” Yet the same phenomenon can happen in only a minute or two of nosing a particular beverage, so tasters find that smelling the same spirit repeatedly provides fewer and fewer descriptors. It’s best to switch to something else for at least a few seconds. The brain, as it were, resets quickly and provides a wealth of aromas as if the spirit was poured anew. It can also help to switch nostrils: for some reason, we continuously favor one nostril over the other. No pattern in that preferential use of only one nostril for oxygen as well as aroma detection can be found; and the brain seems to switch from nostril to nostril throughout the day.
Equally, a barrier to the communication of aromas can be posed by generational or geographical differences: people grow up with different smells around them, and the common benchmarks from which we construct our vocabulary of smells can be obscure to people who grew up in another time or place.
aroma and tasting spirits.Beauchamp, Gary, and Linda Bartoshuk. Tasting and Smelling. Cambridge: Academic Press, 1997.
Classen, Constance, David Howes, and Anthony Synnott. Aroma: the Cultural History of Smell. London: Routledge, 1994.
McGee, Harold. Nose Dive: A Field Guide to the World’s Smells. New York: Penguin, 2020.
Wolfe, Jeremy, Keith Kluender, and Dennis Levi. Sensation and Perception. Sunderland, MA: Sinauer Associates, 2011.
By: Doug Frost