We can see millions of variations in color but we split up the rainbow into just six main colors when trying to describe what we see--red, orange, yellow, green, blue, purple. For the thousands of odors that we can smell we have barely any words at all, usually resorting to simile--smells like fresh cut grass, lemon, wet dog, stinky cheese. Chemists, sensory psychologists, and snobs of all types have been trying to define and categorize smells for decades, settling on seven main categories: musky, putrid, pungent, campohoraceous, ethereal, floral, pepperminty.
These categories do a good job for most things, but every kind of smelly thing can have its own connoisseurs and its own categories, none more so than wine. While most people (over the age of 21) can tell the difference between red and white wine, the words that sommeliers and wine critics use to describe wine can seem wacky at best. Scientists and wine makers wanted a way to standardize and categorize wine smells, to know how different soils and winemaking methods affected the taste of the final wine. Ann C. Noble is just one such scientist, a sensory chemist working in the UC Davis Department of Viticulture and Enology. She separated wine aroma into twelve categories--fruity, vegetative, nutty, caramel, woody, earthy, chemical, pungent, oxidized, microbiological, floral, and spicy. Her true innovation, however, came in the way that she presented these categories in a way that made identifying wine aromas accessible to everyone. Her wine aroma wheel connects the different wine smells to the smells of everyday things that are almost all available at a grocery store year round.
Armed with the aroma wheel and the reference smells you can train your nose to identify all the subtle flavors and aromas of wine:
For your very own wine tasting experience you can buy a wheel for just a few dollars online, as well as find a variety of knockoffs and images of various levels of copyright infringement. Add words about mouthfeel, throw in some creative metaphors and you're well on your way to true wine snobbery. Today there are also aroma wheels available online for all your smell-related snobbery needs, for perfumes, beer, cheese, chocolate, coffee, whisky, olive oil, and even body odor.
For a lot more about smells (including a short section on how scientists study the chemical composition of farts that alone makes the price of the book worth it) I heartily recommend What the Nose Knows: The Science of Scent in Everyday Life.