After you swallow your coffee, see how long the flavor stays with you. Does the coffee flavor drop off immediately, or does it stay for 10 seconds or more?
A long finish is preferable. It is related to:
- The quality of the coffee; higher quality = longer finish. This is because higher quality coffees have more flavor compounds in the bean as a result of the care taken on its behalf (managed shade, soil, fertility, proper pruning, good variety for region, and a host of other cares that are needed after the beans are harvested). The amount of coffee solids that can enter the water during brewing is related to how many flavor compounds are in the bean to begin with.
- The body of the brew: brew strength is just as important. If the brew is weak (too much water and not enough grinds), the effect is bitter with an immediate flavor drop-off. Good aftertaste comes from brewing coffee to the strength needed to extract enough solids to thicken the mouth-feel. Coffee is about 20% oils and fat by weight. We know what butter does for the flavor of vegetables and how its buttery-ness improves and lengthens the finish of foods. Coffee oils and fats do the same, but you need to be bold in your coffee to water ratio.