Where Does Coffee's Rich Aroma Come From, and Why Does Specialty Coffee Smell More Aromatic Than It Tastes

Often when brewing coffee and cupping at FrontStreet Coffee, you can smell the fragrant floral and fruity aromas, or caramel, sugarcane, and honey notes wafting through the air. However, when you take a sip of the hot coffee, that wonderful sensation you smelled doesn't quite translate—perhaps to put it directly, it's not as aromatic as it smelled.

To unravel this mystery, we must first understand coffee flavors and our sense of smell. Some acidic and sweet flavors are both water-soluble and volatile, meaning they can be detected both by smell and taste.

Coffee Flavor

Coffee flavor is composed of volatile aromas (gases), water-soluble tastes, and mouthfeel.

Volatile aromas include dry fragrance and wet aroma, perceived through both orthonasal and retronasal olfaction.

Water-soluble tastes encompass sour, sweet, bitter, salty, and umami, detected by oral taste receptors.

Mouthfeel, comprising smoothness and astringency, results from the interaction between different proportions of sour, sweet, bitter, salty, and umami tastes.

Why Coffee Smells More Aromatic Than It Tastes

The reason coffee smells more aromatic than it tastes is actually due to the "Maillard reaction" during the roasting process, which combines various volatile compounds such as esters and aldehydes with the coffee beans' organic acids.

Coffee uniquely possesses an enormous variety of complex chemical compounds. Besides those mentioned above, it also contains other organic acids, inorganic acids, alkaloids, and more.

When grinding or brewing, these volatile compounds or organic acids vaporize, allowing us to perceive the pleasant coffee aroma.

Of the 850+ aromatic compounds in coffee, most are only volatile and can only be identified through our sense of smell. A portion of these compounds possess both volatile and water-soluble properties, allowing them to be perceived by both smell and taste. The purely water-soluble aromatic compounds in coffee are the fewest and must be detected by taste buds.

Since most of coffee's aromatic compounds are volatile, many people find smelling coffee more satisfying than drinking it.

Orthonasal and Retronasal Olfaction

Generally, our sensory perception of flavor follows this hierarchy: smell > taste > mouthfeel.

The breadth and accuracy of smell perception surpass those of taste and mouthfeel because smell is the only sense with dual functionality. The nose can detect odors from the external world—known as "orthonasal olfaction"—but it can also "smell" aromas from food and drink in our mouths, known as "retronasal olfaction."

Coffee's volatile components—including caramel, cream, acidity, floral, fruity, herbal, nutty, grainy, resinous, wine-like, spicy, smoky, earthy, woody, and medicinal notes—are all perceived through both orthonasal and retronasal olfaction.

Some flavor molecules with sour and sweet characteristics are both volatile and water-soluble, allowing them to be enjoyed by both smell and taste. However, unpleasant bitter and salty flavors are water-soluble but not volatile, meaning they can only be detected by taste, which is why many people find coffee more pleasant to smell than to taste.

Research also indicates that another reason for the change in coffee taste is that out of the 631 chemical compounds that compose coffee flavor, 300 are destroyed by saliva, causing the flavor to change even before we swallow.

In his book "Coffee Science," Mr. Han Huaizong explained that coffee smells more aromatic than it tastes because of the combined action of orthonasal and retronasal olfaction, which can distinguish thousands of different aromas, while taste can only perceive five water-soluble flavors: sour, sweet, bitter, salty, and umami.

Studies have also shown that chocolate and lavender are currently two known flavors that produce the same sensation whether entering the nasal cavity or emanating from it.

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