Oily residue from brewing, along with hard-water deposits and other impurities, build up in coffeemakers over time. Your coffee can end up with an unpleasant flavor. A monthly cleaning will help ensure a great-tasting cup of coffee.
To Clean: once a month, fill the water reservoir with a mixture that's half distilled white vinegar and half water. Turn on the coffeemaker. Let several cups run through, then turn it off and let sit for an hour. Start the machine again to complete the cycle, discarding the vinegar mixture afterward. Run plain water through the coffeemaker a few times until the vinegar odor disappears. To clean the carafe and filter basket, place in the top rack of the dishwasher.
Everyday Food Martha Stewart October 2006