There are more than 400 organic and inorganic chemical compounds present in coffee, and not one can be regarded as the principle flavoring agent. This makes coffee rather intriguing and complex. Interestingly, many of the chemical components, when separated and concentrated, have highly objectionable flavors.
Many of the natural components of coffee’s flavor are unstable at room temperature, either rapidly evaporating or recombining with other components to form new flavor compounds. Further complicating things is the intricate method in which the human palate responds to multiple sensations. Our ability to perceive flavor comes from the simultaneous sensations of aroma and taste.
Coffee aroma is created by the gaseous natural chemical components of roasted coffee, which are released after the coffee beans are ground, and as vapors after the coffee grounds are brewed. This aroma sense is recorded through olfactory cells located on the nasal membrane. The process of sensing odors is called olfaction. We have the ability to interpret the combination of thousands of compounds present, and also their intensity. This information is recorded as a unique aromatic pattern.
On the other hand, the palate records sensation of taste through buds located on the tongue. The process of taste is called gustation, the simultaneous sensation of four basic tastes: sweet, salt, sour and bitter.These basic tastes interact with one another in a process called taste modulation.
Residues remaining in the palate that have not vaporized or dissolved create a sense of body, or mouthfeel. Thus, the sensory evaluation of coffee’s flavor falls into these three stages: olfaction, gustation and mouthfeel.
Olfaction
The chemical compounds in coffee change from a liquid to a gas at different temperatures, which divides coffee aromas into four categories:
- Dry aroma – or “fragrance” is the chemical compounds that are normally gases at room temperature or slightly warmer.
- Cup aroma – usually what we refer to as “aroma” when it is derived from the gases leaving the surface of the brew.
- Nose-derived – these are vapors that are trapped by adhesion to liquids or solids in the brew. They are released as the coffee is taken into the mouth.
- Aftertaste – vapors developing from the coffee residue left on the palate after the coffee has been swallowed.
These three latter categories relate to gases that come about as a result of the brewing process. Dry aroma is the basic aroma of roasted, but unbrewed coffee. All four are distinct points at which we evaluate the aromatic properties of coffee. The unique pattern of aromatic properties is known as the bouquet.
The bouquet of a particular coffee is unique. When combined with coffee’s particular taste modulation, it creates the specific flavor profile of an individual coffee. Therefore, olfaction is the primary sensory means of differentiating coffees of similar origins from one another.
Gustation
Gustation is the sensory evaluation of the water soluble matter extracted from the coffee grounds during the brewing process. The primary taste sensations in the gustation of coffee are sweet, sour and salt. The function of the bitter sensation serves to modify or enhance the impression of the other three, and should not be a dominant taste.
Taste modulation is known as the process by which our perception of one basic taste is altered by the relative strength of one or more of the other basic tastes. As an example, when we add salt to tomato juice it increases the juice’s perceptible sweetness. The modulation of the three basic tastes in coffee – again, sweet, sour and salt – lead us to six primary coffee tastes.
Mouthfeel
We sense things through nerve endings that are located on the tongue, gums and hard and soft palates. For coffee, our nerve endings sense the beverage’s viscosity and oiliness, which we know as body.
The amount of perceived viscosity is simply the amount of solid material suspended in the brew (mostly just microscopic bean particles that snuck through the filter during the brew process).
The oiliness is the amount of lipids (fat, oils and waxes) in coffee. These oils are extracted from the being during the brewing process, but remain undissolved. They separate from the brew and can form an oily residue on the surface of the beverage.
