This is the second post in a series that looks at the number of aromas we can detect in a wine. My first post explained that many tasters claim to be able to identify several aromas in the same wine, while scientific research has shown that we are incapable of identifying more than four. Here I will explain more precisely how the research was carried out, and what it found.
The research was carried out by David G Laing and co-workers in the 1980s and 90s. As far as I know it has not been replicated in other laboratories, but as will become clear the experiments were effectively repeated in the same laboratory, and as far as I know the results are not controversial. They are, for example, described in Avery Gilbert’s book What the Nose Knows without being questioned.
In Laing’s first published work on this subject, mixtures of odourants were delivered to the noses of the subjects in vapour form through a duct 150cm long and 55cm in diameter, and the subjects were asked to identify the odours present. Each of the 7 odourants was a single chemical compound with a distinctive smell, and introduced to the subjects under its everyday name: vinegar, almond, spearmint, fruity, cloves, orange or camphor. Odourant concentrations were chosen to be moderately strong perceptually, and roughly equally strong for all odours individually. The odourants and were also known to be identifiable in binary mixtures in the chosen concentrations. The mixtures were created in vapour form for delivery to the subjects’ noses. Vapour, rather than liquid, mixing was chosen to reduce the possibility that the odourants would react chemically. It seems to me that all reasonable steps were taken to give subjects the best possible chance of identifying the odours.
The subjects were first allowed to familiarise themselves with the individual odours for several minutes. Then they were given mixtures that varied in terms of the odourants used and the number present, and asked to identify the odours in the mixture. The results are summarized in the figure below, which is the basis for the assertion that no more than 4 odours can be identified.A few possible reasons for the low number of identifiable odours spring to mind: maybe the subjects were not skilled enough, or maybe the odours chosen were particularly difficult to identify. The investigation of those two possibilities was the subject of two further studies [2, 3], which were based on the same experimental setup.
To determine the effect of training and experience, two different sets of subjects were used: experts, and trained non-experts. The non-experts were trained over the course of 5 days, and on day 5 they were tested to ensure they could reliably identify all 7 odours when presented individually. The other group were expert perfumers and flavourists; they were “highly familiar with the test odourants, had daily experience with odour discrimination, and had a prerequisite before entering their respective professions of an excellent ability to discriminate and identify odours”. The experts and trained non-experts performed slightly better than the subjects in the initial study, with the experts being the most competent, but nevertheless the number of correct judgements still dropped to negligible levels when more than 4 odourants were presented.
The next study looked at the importance of the type of odours used in the mixtures. A panel of 10 perfumers and flavourists selected two sets of 8 single compound odourants: good and poor blenders. The poor blenders were judged to be perceptually very different, and thus easier to identify in mixtures than good blenders. The common names of the good blenders were rose, musky, cinnamon, coconut, fruity, orange, burnt caramel and almond, while the poor blenders were bad breath, mushroom, cut grass, Dencorub, garlic, antiseptic, aeroplane glue and mandarin. The results were as suspected in the sense that the poor blenders were easier to identify. However, the differences were not large, and for 5 or more poor-blender odourants the number of correct identifications was still very low indeed.
The fourth study brought the experiments one step closer to the reality of wine. Here, none of the odourants were single chemical compounds, but complex mixes of chemicals usually identified as a single odour: smoky, strawberry, lavender, kerosene, rose, honey, cheese and chocolate. Again, the results were similar to those of earlier studies, suggesting that we identify the smell of familiar objects as a single gestalt odour, even if multiple chemical compounds are involved in creating it.
In the last article of Laing’s I will discuss here, subjects were trained to identify the test odours, and then required to detect a single highly familiar odorant in stimuli consisting of one, four, eight, twelve, and sixteen odorants by using a selective-attention procedure. Identification fell to chance level when sixteen odorants were present. Unfortunately I only have access to the abstract of this article, but I presume that the important distinction between this and earlier studies is that the subjects were attending only to one odour, and that the odour was highly familiar. It seems that it was those factors that enabled some people to identify an individual odour in blends of twelve, which is a big improvement on the limit of 4 found in earlier studies.
For now, I shall let you draw your own conclusion on the applicability of these results to wine tasting notes. I will return to that subject eventually, but in my next post I should like to take a closer look at how wine tasters arrive at long lists of aromas that seemingly break Laing’s four odour limit. In the meantime, if you found this blog post interesting you might also like to take a look at this one on the subject of olfactory white.
 Laing, D. G., and Francis, G. W. (1989). The capacity of humans to identify odors in mixtures. Physiology & Behavior, 46(5), 809–814.
 Livermore, A., and Laing, D. G. (1996). Influence of training and experience on the perception of multicomponent odor mixtures. Journal of Experimental Psychology Human Perception and Performance, 22(2), 267–277.
 Livermore, A. and Laing, D. G. (1998). The influence of odor type on the discrimination and identification of odorants in multicomponent odor mixtures. Physiology and Behavior 65 (2): 311– 320.
 Livermore, A. and Laing, D. G. (1998). The influence of chemical complexity on the perception of multicomponent odor mixtures. Perception and Psychophysics, 60 (4): 650– 661.
 Jinks, A., and Laing, D. G. (1999). A limit in the processing of components in odour mixtures. Perception, 28(3), 395–404.