Acidity: 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 is what coffee people call acidity. It should be distinguished from sour, which in coffee terminology means an unpleasant sharpness. The acidy notes should be very clear and bright in the Mexican, a little softer and richer in the Sumatran, and overwhelming in the Yemen Mocha. Aged coffees, and some old crop, low-grown coffees, have little acidity and taste almost sweet. 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, vibrant, etc. An acidy coffee is somewhat analogous to a dry wine. In some coffees the acidy taste actually becomes distinctively winey: the winey aftertaste should be very clear in the Yemen Mocha. In brochures you may find the aftertaste that I call winey described with other terms: fruity is a favorite. Fruit connotes sweetness, however: I find the better analogy is to the sharpness of a dry wine, hence my preference for the term winey. The main challenge is to recognize the sensation, however: once you do that, you can call it anything you like.