Why Doesn't Coffee Taste as Good as It Smells? The Nature of Coffee Aroma and Fragrance Compounds

When we walk into a coffee shop, it's easy to be captivated by the aroma of coffee permeating the air. Especially when coffee beans are being ground, the fragrance fills the space, making our hearts race, compelling us to order a pot immediately to experience the splendid aroma of coffee.

The Discrepancy Between Smell and Taste

However!!! The moment the coffee enters your mouth???????? What is this? Were all the floral and fruity aromas I smelled just an illusion?!?!?

This brings us to our senses of smell and taste! Olfaction is divided into orthonasal and retronasal smell. Orthonasal smell refers to the external odors we detect, while retronasal smell is the aroma we perceive when food and drink pass through our mouth and travel outward through our nasal cavity.

Taste involves signals from our five senses (sight, hearing, smell, taste, and touch) transmitted to the cerebral cortex and processed by the central nervous system. Therefore, all five senses serve as mediums for taste perception.

They often lead us to the illusion of "what you smell is what you get." The reason why the aroma we smell differs from what we taste when drinking is because the properties of the aromas we inhale through smelling versus drinking are not the same.

Different Properties of Coffee Aromas

1. Volatile Aromas

The aromas we smelled at the beginning actually belong to coffee's aromatic compounds. Because most have volatility, we can perceive them through our sense of smell.

When we grind coffee beans, the floral and fruity acidic aromas, with their lighter molecular weight and high volatility, are released first. Even from a distance during grinding, we can smell these types of aromas.

Next are the medium molecular weight aromas like nuts, almonds, caramel, and chocolate. They disperse over shorter distances, requiring us to get closer to detect them.

Finally, we're left with high molecular weight aromas like resin, spices, and roasted notes. Due to their heavy molecular weight, we need to press our nose close to the coffee grounds to detect them.

All of the above belong to coffee's dry fragrance. Since some volatile aromatic compounds cannot vaporize at room temperature, they require hot water during brewing to release their aromas, which is what we call coffee's wet fragrance.

2. Water-Soluble Flavors

Another group of aromatic compounds has both volatility and water solubility, so we can both smell and taste them. Aromas gradually vaporize and dissipate. As the brewing process concludes, the detectable smells decrease, which is when our retronasal olfaction and tongue come into play.

What we perceive when coffee enters our mouth—whether this coffee tends toward sour or sweet—are messages conveyed to us by water-soluble flavor compounds.

Incidentally, a small number of substances that only have water solubility can only be perceived through our sense of taste. For example, bitter and salty flavors, which we call the dreaded over-extraction flavors, are only water-soluble, so we cannot smell them. This is why we can only determine the quality of a cup of coffee by drinking it.

3. Different Experiences from Flavor Combinations

Sour, sweet, bitter, salty, and umami are the five tastes we can perceive. Among coffee's aromatic compounds, the most common are sour, sweet, bitter, and salty. These four tastes can blend and balance each other. When one taste becomes too prominent, it can suppress or enhance the expression of other tastes, ultimately affecting the tasting experience.

Let's use the sour and sweet flavors in Guodingding as an example: When the brewed sour components are lower than the sweet components, you might taste a refreshing lemon green tea. However, when the sourness exceeds the sweetness, it will evolve into a full-bodied juice sensation.

Coffee begins with over 300 aromatic compounds from the green beans. Through chemical reactions during roasting, it can ultimately develop more than 1,000 aromatic compounds. Experiencing these delicious aromas through orthonasal and retronasal olfaction as they combine with each other is one of the great pleasures of drinking coffee.

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