Think about taste: there are countless variations but just five basic categories (sweet, salty, sour, bitter and umami) that can be detected by the taste receptors on the tongue. Touch is categorized as heat and cold, pressure and pain. Sight and sound are easy because we’re perceiving the light and sound waves, which are measurable physical phenomena.
For too long, scents were divvied up into good smells and stinky ones.
Smells are tricky.
There are more than 100,000 smells floating around the globe, but most of us can perceive just a few hundred. They’re processed in the limbic region, the emotional center of the brain, where the sensory data gets all tangled up in memories, especially those of childhood. That’s why a whiff of roasting turkey can flood you with warm and fuzzy memories of family Thanksgivings, or a fragrant bouquet of flowers will have you thinking of your beloved grandmother, even if you never knew that her hand cream was lily-scented. But you could also be allergic to poultry, or those same lilies could have perfumed the air of a friend’s funeral, and to you the odors are detestable. This subjectivity, in the absence of empirical measures, has forever stymied scientists.
Until now. A group of researchers has finally come up with a statistical approach that allows them to systematically measure various dimensions of a smell in a way that allows it to be characterized and grouped. The newly published study, using a methodology known as non-negative matrix factorization, claims that the vast world of smells is actually very tightly structured, and that every smell in the universe can be assigned to one of 10 basic categories: woody/resinous, fruity (non-citrus), chemical, minty, sweet, popcorn, fragrant, citrus, pungent, and decayed.
Before you start arguing the inadequacy of the 10 categories (and doesn’t naming one of them ‘fragrant’ sound like a copout?) remember that they’re classifying a single, discrete scent. A smell can be sensed by just a handful of molecules reaching your nose, and an object can have hundreds or even thousands of different volatile compounds all throwing off their own molecules. A wine enthusiast might swirl a single glass and detect notes of canned asparagus, burnt toast, mango, and pickle brine. A complex odor like wet dog or new baby might even combine elements of all 10 scent categories.
Smell and taste are the sister senses, basically playing off of the same molecules.
While we don’t know where this research will lead, it’s considered a major breakthrough, and one that’s got the food world buzzing.
Fun olfactory fact: Most of what you smell is coming through the left nostril. The reason you never noticed this is because 80% of noses are not in the middle of the face but pitched slightly to the right, so it seems like the smell is coming right up the middle.