Basic aromas? Researchers define ten categories of smell

Writing in PLoS One​​, the US-based research team noted that while it is established that we can taste at least five basic tastes (salty, sweet, bitter, sour and umami), there is no definition of how many odours we can smell.

"It's an open question how many fundamental types of odour qualities there are," ​explained lead author Jason Castro from Bates College. "This is in striking contrast to olfaction's 'sister sense,' taste, where we know that five basic qualities seem to organize sensations."​

The researchers explained that while senses such as hearing and vision can be discussed in terms that most people understand, and that are tied to measurable physical phenomena, the sense of smell has so far not lent itself to such a systematic understanding of what smells we perceive and how those perceptions relate to physical phenomena.

Using advanced statistical techniques, the researchers developed an approach that systematically described smells in a way that was able to characterise and group them - finding that there are likely to be ten basic categories of odour.

"This study supports the idea that the world of smells is tightly structured, and organized by a handful of basic categories,"​ explained Castro.

Indeed, based on their current findings, the Castro and his team believe they may be able to help industry to better predict the smells produced by compounds that hold potential for use as food flavourings or aromas for cosmetic applications. This ongoing work will involve the team reversing their current approach to the problem by applying their current research findings to a bank of chemical structures - in an attempt to predict how any given chemical is going to smell.
"That's something that nobody's really done with any kind of compelling accuracy," ​said Castro. "And obviously perfume companies, flavour and fragrance companies, are really interested in doing that well." ​

Study details​

The team used a standard set of data - Andrew Dravniek's 1985 Atlas of Odor Character Profiles - in the investigation. Using this data they applied a mathematical method to simplify the olfactory information into coherent categories - similar to the way compressing a digital audio or image file reduces the file's size without, ideally, compromising its usefulness.
In doing this, Castro and this colleagues identified 10 basic odour qualities: fragrant, woody/resinous, fruity (non-citrus), chemical, minty/peppermint, sweet, popcorn, lemon and two kinds of sickening odours: pungent and decayed.