Aroma. Some neuroscientists feel that among our five senses, aroma is perhaps the most powerful. The sense of aroma ties directly into the most primitive parts of the brain, evoking pleasure, disgust, recognition, and memory. A strong aroma can transport the human mind directly into the past, over years or even decades, to a particular place or moment. Most of what we think of as our sense of “taste” is actually based on aroma.

The tongue senses sweetness, sourness, saltiness, bitterness, and perhaps umami, but the nose perceives everything else. After the visual appeal, aroma is usually at the forefront of a beer experience but can also be a large part of the lingering finish as residual volatiles feed back into your nose and stimulate your olfactory sense. In beer, especially full-flavored beer, aroma is exceedingly important.

We are all aware of aroma as a major sense, although we aren’t always conscious of it moment to moment. In fact, many of aroma’s effects are subtle and subliminal. It is, of course, a well-recognized animal sense providing essential information about the environment, food, and other animals. In humans it is particularly important in assessing, and appreciating, the character of food and beverages and, of course, beer.

Aroma detection involves specific sensory receptors in the nose being stimulated by volatile chemicals in the air we breathe. Aroma appreciation involves not just the receptors but interlinking neurons, the brain pathways, and psychology, particularly learned experiences of attraction and aversion. As a result it is much more than a “smell it and like it” effect and involves numerous inputs that will modify our responses.

Taking these parts in turn, however, we should look first at the physiology of the nasal cavity and the sensory organs that detect aroma.

Two of these sensory organs can be identified in the nasal cavity—the sensory receptors themselves and the trigeminal nerves. These occur in different parts of the nose with the trigeminal receptors being located at the entrance and the sensory receptors at the top of the cavity.

These two groups of receptors also respond to different stimuli: the trigeminal to physical stimuli such as cold air and high concentrations of carbon dioxide, the sensory receptors to specific aroma molecules. Beer contains elements from both of these groups and it is important to look for their balance to judge a beer’s character. Low temperature and carbonation in beer will stimulate the trigeminal receptors while hop, fruit, and alcohol aromas among others will stimulate the sensory receptors.

Analysis of beer aromatics has identified major and minor groupings. Major beer aromas are those present at levels greater than twice their threshold level, the level at which most humans can detect them. These would include fruit aromas, floral elements, sulfur-based compounds, volatile hop aromatics, and fusel alcohols. Other aromas will be less distinct, but low levels of two or more aromas can act synergistically to create a combination aroma. This is particularly evident with fruit aroma produced from a number of esters or stale aroma produced from a range of oxidized compounds. See fruity.

Detecting aroma requires more than just breathing while you drink. To accentuate the aroma, it is important to coat the surface of the glass with beer—this requires a swirl before smelling. Coating the glass surface allows a thin film of beer to evaporate into the air, making the aromatic molecules available to your olfactory receptors. Breathe deeply and bring the air up into the top of your nose; a few sharp sniffs gives a better assessment than one long snort. In addition, note the aroma generated as you swallow. This arises retro-nasally from the back of the nose and can provide a more sensitive detection where less concentrated aromas become more evident in the aerosol generated by swallowing.

It is possible to simply appreciate the aroma from smelling without specific analysis—a great beer would be far less pleasant if we were forced to consider it analytically at every sip. Unconsciously, however, we do respond with pleasure or displeasure and judge the beer appropriately. More consciously we can use recognition skills to identify specific aromas and assess their suitability and balance in the context of a beer.

Knowing beer aromas requires both practice and a mental flavor directory. Specific aromas arise from specific organic chemicals and having exposure to these provides the reference for identification. For the professional brewer or taster, training is required so that an aroma is correctly associated with the corresponding chemical. It also requires standardization of language. This is easy with specific aromas such as diacetyl, which smells of butter or butterscotch, or the ester iso-amyl acetate, which smells rather like bananas. See diacetyl and isoamyl acetate. However, less distinct smells may lead to personal impressions that may not correlate. Saying that a beer has the smell of an attic is too imprecise as attics have a wide range of aromas to different people.

Individually we respond differently to aromas, both from our genetic makeup and from experience. Taste training allows us to identify aromas and profile a beer, but our inherent abilities of aroma detection may vary widely. Typically we are more sensitive to some aromas than others, and one person may vary considerably in their specific sensitivities than another. This is one reason why we have different beer preferences. Interestingly, for example, it’s recently been discovered that many people are genetically unable to smell a major hop aromatic component called linalool, which has a floral aroma. This has implications for the brewer, since some hop varieties (Saaz, for example) are heavy in linalool, which can make up the majority of that hop’s aroma. It is therefore possible to add to a beer an aromatic element that many people cannot smell at all. It is also interesting to note that recent studies show that some aromatics can intensify the perception of a trigeminal flavor. Therefore, an intensified hop aroma can make a beer seem more bitter to the tongue and to the mind, even when actually bittering compounds are not intensified. Our senses are complex and not always easily separated or explained.

Aroma detection is also affected by hormones and emotion. We also respond differently to a beer if we are in company and according to our impression of the environment. We eat food faster in brightly lit conditions and many aromas are now recognized as enhancing the sales potential of shops. Studies are yet to identify the specific effects of beer aroma on consumption, but there is evidence that most people consider a fresh hop aroma to be desirable in a beer, even if they cannot identify the aroma. Undoubtedly a large range of aroma components come together and influence our unconscious individual selections.