title_body: How long can I keep my carafe on the warmer?
upvoted_answer: It would depend on a number or factors including temperature of the warmer and humidity in the room.  However, personally, I can begin to taste a difference after as little as 45 minutes on the warmer.  I tend to drink two cups of coffee pretty quickly to avoid this.  
  
  Coffee is a product always best fresh, but how long before your palate can detect that it isn't fresh any longer is a matter that varies by individual.  My wife will drink coffee from a pot that has been sitting for four hours plus; after about an hour and a half I'll throw the pot away and make another.  Your own mileage may vary.