The Heavy Ninth

Nine coins are indistinguishable in size and appearance. Eight have exactly the same weight, while the remaining coin is slightly heavier. You have a balance scale with two pans, but no standard weights. Each use of the scale can produce one of three results: the left pan is heavier, the right pan is heavier, or the pans balance. You must devise a method that is guaranteed to identify the heavier coin, regardless of which coin it is. What is the fewest number of times you need to use the balance scale?