Taste those high, thin notes, the dryness the coffee leaves at the back of your palate and under the edges of your tongue? This pleasant tartness, snap, or twist, combined with an underlying sweetness, is what coffee people call acidity. It should be distinguished from sour or astringent, which in coffee terminology means an unpleasant sharpness. The acidy notes should be very clear, powerful and transparent in the Costa Rica, rich and wine- or berry-toned in the Kenya, and deeper-toned and muted in the Sumatra. They should be drier in the Costa Rica and perhaps a bit sweeter in the Kenya. Robustas and some lower-grown arabica coffees may display virtually no acidity whatsoever and consequently taste flat.
You may not run into the terms acidity or acidy in your local coffee seller’s signs and brochures. Many retailers avoid describing a coffee as acidy for fear consumers will confuse a positive acidy brightness with an unpleasant sourness. Instead you will find a variety of creative euphemisms: bright, dry, sharp, brisk, vibrant, etc.
An acidy coffee is somewhat analogous to a dry wine. In some coffees the acidy taste actually becomes distinctly winy; the winy taste should be relatively clear in the Kenya. In promotional tags you may find the tones that I call winy described with other terms: fruity, dry fruit, and various specific fruit names, particularly berry and black current. The main challenge is to recognize the fundamental complex of fruit and wine-like sensations; once you do that, you can call them anything you like.