Spinning One's Wheels

Given my recent work on cannabis aroma for Headspace Sensory, LLC, I’ve been thinking a lot about sensory description. A short post at the Scent Culture Institute on “smell wheels” caught my eye. In it, Claus Noppeny (and/or one or more of his sidekicks at the SCI) looks at visual representations of smell, such as Michael Edwards’ Fragrance Wheel and Mandy Aftel’s Natural Perfume Wheel. (Both of these, I should note, were preceded by Ann Noble’s 1987 Wine Aroma Wheel, which really launched the modern enthusiasm for wheels.)

SCI asserts that the wheel format for displaying fragrance families (or aromatic notes in wine) has limitations, the primary one being that the circle implies completeness while allowing for no further additions (e.g., new fragrance notes). SCI immediately undercuts its latter charge by noting that Mandy is currently revising her wheel. However, the observation that wheels project an all-you-need-to-know—nothing else matters!—completeness is, I think, correct. Self-enclosed circles are a poor way to encourage new ways of thinking and perceiving.

But epistemological isolation is the least of the aroma wheel’s problems. For me, more serious problems arise from the format’s practical implications. Let’s consider three such problems.

Problem 1: Size of Slice

In a typical wheel layout, one moves radially outward from categories (“fruity”) through subcategories (“citrus”) to specifics (“grapefruit”). This creates a pizza-slice shape for each category. Some slices are a lot wider than others. Why? Because they have a lot of specifics (the Wine Aroma Wheel “fruity” category has 19), while others have a few (“woody” has just 7). Assigning a large fraction of the wheel to “fruity” implies that it is a dominant odor category, and that “woody” is relatively subordinate.

But from a sensory evaluation perspective, this is not necessarily true: a given wine may display several fruity notes, but it’s extremely unlikely that any wine will display all 19 fruity notes. Furthermore, even when several fruity notes are present, it doesn’t mean that they dominant that wine’s aroma. A Chardonnay’s fruit notes may be overpowered by oakiness.

Problem 2: Arrangement of Slices

My impression is that categories on most, if not all, aroma wheels are arranged based on intuition. That is to say, their ordering around the wheel is not based on data regarding relative similarity. More likely, it is based on the subjective impression that floral and fruity are more closely related smellwise than floral and woody.

Problem 3: Making Ends Meet

Even if there are data confirming the similarity sequence floral : fruity : woody, what justifies us linking floral to woody in order to make a circle? Would it not be more honest to portray the relationship as a linear smell spectrum? Or maybe a triangle? (But it wouldn’t look as cool.—Ed.)

These intellectual objections cannot offset the appealing simplicity and visual allure of the wheel format. But in an age of innovative data visualization, there are surely better ways to display sensory descriptors and their interrelationships.