At it's most basic, aroma is the smell of coffee. It's responsible for many of the flavor attributes not directly perceived by the tongue (which are sweet, salt, bitter, sour and umami). There are over 800 known aromatics in coffee with new ones being discovered regularly thanks to advances in testing equipment.
Because aroma is the release of flavorful compounds from coffee through the air, fresh coffee will have a much stronger aroma than older, stale coffee (also why it tastes better!) Generally, as a roast gets darker, more of the compounds in coffee are changed and become detectable, meaning the aroma becomes stronger. The process of roasting (especially to darker levels) destroys the compounds that give high end coffee their unique characteristics and eliminating some of the benefits of paying more for coffee.
Depending on the roast of the coffee, it can range anywhere from light and fruity to burnt. Most coffee will smell lightly caramelized and almost nutty.
A stale coffee will smell musty and cardboard-like.
The Best Smelling Coffee
The best smelling coffee will be one that's fresh roasted - the roasting process makes coffee rapidly lose flavor, which can be sensed by smell. Less smell = less flavor. If you want the best smell you'll need to buy it from a coffee roaster directly, rather than from a store shelf. Ordering coffee with a 1-way valve seal bag will keep coffee as fresh as possible for as long as possible. If possible, order whole beans and grind at home.
It's your call at the end of the day whether you prefer a strong "coffee" smell over the subtleties of each origin - an inexpensive Colombian or Brazilian coffee can have a great aroma without high cost.
Primary Coffee Qualities
Aroma is one of the primary coffee qualities denoting a coffee's flavor along with body, acidity, sweetness, bitterness, and aftertaste. A coffee's aroma is one of the main categories used by professional coffee tasters (cuppers) to judge the quality of a coffee.
Coffee Aroma Descriptions
The aroma may be described as, for example, complex, smoky, nutty, herbal, or fruity. Many fine coffees reveal subtle floral notes in the aroma - the notes are often best experienced at the moment the crust of grounds is broken during a proper coffee cupping.
For example, Yemen Mocha coffee is known for its fresh floral aroma.
Also known for nice floral notes are the finer Kona coffees and the best Colombian coffees. A coffee's freshness and its roast are important factors in preserving and enhancing the coffee's desirable floral aroma.
Coffee Aroma and its Relation to Coffee Taste and Acidity
A coffee's aroma is also related to the coffee's flavor and acidity. For example, if a coffee is very rich-flavored, then the aroma will also reflect that richness, and if a coffee is acidic it will smell acidy.
Some of the more subtle flavor notes (e.g., high, fleeting notes) of a coffee appear most clearly in the aroma. Since human senses tend to work in concert, the aroma may also affect the coffee flavor characteristics/taste sensations, which may be very subtle.
Coffee's Volatile Components and their Effect on Aroma
A coffee's aroma, which may range from herbal to fruity, is created by the coffee's volatile components - vapors and gases - which are released from the brewed coffee and then inhaled through the nose where they come in contact with the olfactory (nasal) membranes.
Retronasal is also important in coffee - this is detected when coffee is swallowed and the aromatic compounds drift up the nasal passage internally.
The Nose, or Bouquet of Coffee
A coffee's aroma is also referred to as its Bouquet or Nose, and is distinguished from a coffee's fragrance, which in coffee terms refers to the smell created by the coffee's vapors and gases - the volatile organic compounds - which are released from the coffee beans during grinding and then inhaled as aromatic compounds through the nose, contacting the nasal membrane. Also see Aromatic Profile.
You can also read about the world's top gourmet coffee and learn about coffee's rich past in the World's Best History of Coffee.
Coffee terminology, coffee tasting terms, and lots more coffee and espresso information can also be found in the Espresso Coffee Guide's Coffee and Espresso Glossary.
Aroma Espresso Bar is also the name of a coffee brand based out of Israel and present in the Toronto, Canada as well is the North-East United States.