ODOR MIXTURES & HOW WE EXPERIENCE THEM

One of the goals of wine education, and of tea and coffee education, too, is to enable you to detect and identify the different flavor elements in a sample of the beverage. One way to learn is to identify the different odors individually, and then figure out which odors are present in your glass or cup. This concept underlies Le Nez du Vin kit and its congeners, and is one of the ideas behind the creation of innumerable flavor wheels, including the latest coffee wheel from the Specialty Coffee Association of America. The mark of a connoisseur is said to be the ability to individually recognize the many odorants in a wine, coffee, or tea.

Here's a tea flavor wheel from the International Tea Masters Association.

(Don't worry, you're not going blind, this version is too small to read! Go to the link above for a readable version.)

Before I discuss a recent paper on the subject of odor recognition,* a couple of definitions: 

• elemental perception is the process of recognizing individual components in a mixture;
• configural perception is the process of recognizing mixtures as a single odor.

Another important point: some mixtures of odors yield a configural perception that is different from the elemental perceptions of the individual components. These odors are said to "blend well." One example, used in this study, is the odor of Furaneol® (= strawberry furanone—see my previous post), which smells like strawberry, and ethyl maltol, which has a caramel odor. Mixed together, they smell like pineapple.

By contrast, some odors still retain their distinctive characteristics after mixing. In the experiments described in the paper, the authors used guaiacol, which has a smoky odor, and isoamyl acetate, the typical odor of bananas. The two odors could be distinguished in the mixture, and were said to be "poorly blending."

In the experiments described here, Charlotte Sinding and her colleagues asked the question: when it comes to experiencing odors individually and in mixtures, is there a difference between odor mixtures that blend well and mixtures that don't blend well?

Participants in the study were divided into four groups, two each for each odor combination. For each odor combination, one group was exposed repeatedly to the smell of the individual components and then was asked to describe the odor as they smelled the mixture, and the other group first was exposed repeatedly to the odor of the mixture and then was asked to describe the odor as they smelled the individual components.**

Even after multiple exposures, participants who were preconditioned to smell strawberry and caramel separately smelled "pineapple" when the two compounds were mixed together, though slightly less strongly so than did those who had not been preconditioned. In other words, for mixtures that blended well, configurable perception dominated elemental perception.

By contrast, those who were first exposed to the elements of the poorly blending odors were able to identify them individually in the mixture. Strangely, the smoky odor intensity decreased while the banana odor increased in the mixture for those who were first exposed to the individual components. Elemental perception persisted, but somewhat altered.

Participants who were exposed to the "poorly blending" mixture first, then smelled the individual odors after, the smoky odor developed a slight banana-y quality! In other words preexposure to this mixture led to a phantom configural perception of the individual guaiacol odor.

Finally—this is my observation—there was a wide spread in people's responses. What I discussed above are the generalities, but clearly there were very important individual differences in how these experiments played out perceptually. Part of these differences are going to be genetic: there are huge differences among people in their genes for perceiving odorants. Part of these differences may be due to experience: we live in a world of odors, but each of us has a different experience of these odors—which came first in our experiences? which was blended with which when we first encountered it?

This study confirms and builds upon previous studies of mixtures of odorants. So far these studies are severely limited in the number and type of odorants, odorant mixtures, and number of odorants in a mixture. Furthermore, we don't have a table listing elements that blend well or poorly.  

Which raises a question in my mind about connoisseurship, namely how do we develop it? Do we use kits like Le Nez du Vin, and accept that the odors we perceive in a given wine may be different from what we perceive when we sniff individual odors? If we study with the kit, will our perception of an individual odor carry over to some other quite different odor, as was the case with guaiacol in the experiments presented here? And if so, how will we know that has happened when we sniff or sip an actual beverage?

And perhaps more importantly, should connoisseurship be based on a consensus of what one should smell? If so, what about the person who perceives odors differently?***

* 

Charlotte Sinding et al.

Experience shapes our odor perception but depends on the initial perceptual processing of the stimulus. Attention, Perception, & Psychophysics. July 2015, Volume 77, Issue 5, pp 1794-1806.

** The protocol was in fact more complicated than this, with numerous appropriate controls, but this is the gist.

*** An anecdote: was invited with one of my students to sit in at a senior wine and food pairing class, when the professor broke out a superb bottle of Burgundy wine from 1949 that had been well stored, so in perfect condition. Professor went around the class asking what flavors people experienced. Out gushed a symphony of red fruits and deep thoughts, until they came to me and my student. We said it tasted like mushrooms. Dead silence. Disapproving stares. Professor said: how could that be? We weren't invited back.

By the way, my student and I both love mushrooms, so we enjoyed the wine immensely. And I think that's what matters.