Acidity

The perceived acidity of coffee results from the proton donation of acids to receptors on the human tongue. Acidity is typically a highly valued quality especially in Central American and some East African coffees. Sourness, however, is an extreme of acidity and can be considered a defect. Acidity has been correlated with coffees grown at very high altitudes and in mineral rich volcanic soils. The perceived acidity of washed coffees is also significantly higher than the acidity found in naturally (dry) processed coffees. This is likely due to an increase in the body of naturally processed coffees relative to wet processed coffees since body masks a coffee's acidity. The acid content in a brew is also greatly dependent upon the roast degree, type of roaster, and brewing method.

The pH of a coffee has been found to correlate with the perceived acidity of a coffee by Pangborn, Sivetz and Desrosier, and Griffin and Blauch; whereas Voilley et al. suggests that titratable acidity produces a better correlation to perceived acidity.

The acids found in roasted coffee may be classified into three groups: aliphatic, chlorogenic, and alicyclic carboxylic and phenolic acids

Aroma

The aroma of a coffee is responsible for all flavor attributes other than the mouthfeel and sweet, salt, bitter, and sour taste attributes that are perceived by the tongue. Therefore, it might be said that the aroma is the most important attribute to specialty coffee, as it constitutes the biggest factor affecting taste. Even instant coffee has the components responsible for stimulation of our taste buds. The difference, however, is that instant coffee lacks most of the aromatic volatile compounds causing a dramatic decrease in the overall flavor.

Aroma is perceived by two different mechanisms. It can either be sensed nasally via smelling the coffee through the nose or retronasally. Retronasal perception occurs when the coffee is either present in the mouth or has been swallowed and aromatic volatile compounds drift upward into the nasal passage.

The number of aromatic compounds found in coffee increases every year. Today, the number is well over 800 and as our analytical methods become more precise more will be uncovered. Yet, the perception of aroma is dependent upon both the concentration of the compound and its odor threshold. With that said, understanding coffee aroma is not as difficult as understanding how over 800 compounds interact with the olfactory epithelium. It is probable that a relatively small group of compounds that share both a high concentration and a low odor threshold make up the fragrance we know as coffee aroma. This article will discuss the recent research that has narrowed in on these aroma impact compounds.

Body

Body is the weight of the coffee that can best be sensed by allowing the coffee to rest on the tongue and by rubbing the tongue against the roof of the mouth.  Body ranges from thin, to light, to heavy and is a result of the fat content.  The viscosity, however, results from proteins and fibers in the brew.  Medium and dark roast styles will have a heavier body than lighter roasted coffees, but conversely will have less acidity.