title_body: Coffee cup patina; is there any logic in not washing the cup
upvoted_answer: It may be superstition but many people, myself included, don't wash out their coffee cups. I rinse out my cup but don't wash it - I don't want soap going into my favorite coffee cup. I like the way it smells of coffee. I don't have to see or touch my favorite coffee or tea cup to know which one is which. 
  
  In addition I never use soap on either my coffee or tea filters.
  
  Would I notice the difference if I had two identical mugs - one with the "patina" and one without? Maybe not. But I prefer it that way.