Descaling is essentially cleaning out the coffeemaker from that white lime build up that comes with making lots of cups of coffee. In the old days people used to make a pot of coffee with vinegar to "clean it out." Now you buy the single cup coffee maker cleaner - a descaling solution. It comes in a small bottle. You add an ounce to a tank of water and run a few brew cycles (without the coffee). Then you run about 2 clean water tanks and your coffee maker should be descaled. Your brewer should come with instructions.