Single-cup coffeemakers using sealed cups such as the Keurig or Tassimo are very popular for their ease of use and uniformity of brew but since they have more components than a standard automatic-drip coffeemaker cleaning is more involved. Fortunately you can thoroughly clean your single-cup coffeemaker using an old toothbrush and vinegar.
Housecare weblog Clean My Space offers a helpful video tutorial displayed above. The standard Keurig coffeemaker has some dishwasher safe parts such as the water reservoir, but other parts must be cleaned by hand. While those parts are in the dishwasher take your old toothbrush and clear any coffee grinds left in the K-cup holder. Take this opportunity to wipe down the surface of the machine with a paper towel or dishrag and a little all-purpose cleaner. Clean any white crusty buildup (mineral deposits) with a touch of white vinegar. When the dishwasher is finished, reassemble your Keurig.
Now you're going to run vinegar through the machine to create a descaling brew to remove mineral deposits in the internal workings of the coffee maker. Fill your water reservoir halfway with white vinegar and run several brewing cycles with no K-cups to get rid of the vinegar and then rinse out the reservoir, fill with water, and run enough brewing cycles to empty the water reservoir again. This will get rid of the vinegar—you don't want any leftover vinegar ruining your cuppa.
This routine will take around 15-20 minutes but you don't have to do it very often. I'd say maybe once a season if you use the machine everyday; less so if it's only used occasionally.
Clean a Keurig Coffee Maker | Clean My Space via 366 Days of Pinterest