Acid: A normal characteristic of arabica coffees, particularly of high-growth varieties. Some strains are sought for this particular taste (Kenya), which is influenced by the degree of roasting and does not seem to be objectively expressed by pH measurement. Experts recognize three types of acidity: 1) natural desirable: acid, 2) natural undesirable: sour, and 3) undesirable: process acidity (sometimes sought as a substitute for natural acidity but generally has a biting, puckery flavor.