The dimensions of mind are beyond anything the discriminations of intellective thought can possibly know: they are beyond anything that the non-discriminations of not thinking can possibly fathom. Because this is the way the dimensions of body and mind are, it is also the way the dimensions of cleansing are.
-Shobogenzo
Poor cleanliness is yet another avenue for unwanted flavours to make their way into your brew. This applies to your whole system; from your water through to your cup. Keep your kit scrupulously clean. One of the more fundamental ways to do that of course is to keep your entire system as simple as possible. A friend of mine was using my cheap little grinder one day, and wondered if it had ever been used before. He couldn’t find a single speck of coffee anywhere on the thing. Then I showed him the toothbrush I use. A more serious culprit however is the actual device that you brew your beverage in. Residual coffee and scale can impart tastes that you don’t want. So keep it clean, but remember the simpler your system is the easier it is to keep spotless.