Coffee acidity is a highly valued quality, especially in Central American and East African coffees. However, excess acid may lead to sourness in the coffee.
Coffee with acidity has been the result of coffees that are grown at a high altitude in mineral rich volcanic soils. Washed coffees will also have a higher acid taste that processed (dry) coffee. The amount of acid that is in a cup of coffee is also dependent upon the coffee roasting degree, the type of roaster, and the method of brewing the coffee.
There are three groups of acids that are found in roasted coffee, as follows: aliphatic, chlorogenic, and alicyclic carboxylic and phenolic acids. For each of these acid levels, it was found that the typical medium roast coffee had levels of 0.30%, 0.22%, 0.13%, 0.07%, and 0.27%, respectively. For light roasts, the levels of each of these acids were around 1.58%, and for dark roasts, the levels of these acids can be as low as 0.71%. Chlorogenic acids can make up around seven percent of the dry weight of Arabica coffee. These acids are mostly degraded during the brewing process into quinic acid.