Coarse Tea

On Saturday, somebody at the clinic asked what we all we do to avoid catching cold. One person said he gargled "bancha". 番茶 is simply put coarse tea. However, when I looked it up in my dictionary I came upon this curious expression:

鬼も十八番茶も出花 = おにもじゅうはちばんちゃもでばな

鬼　＝　devil
出花　＝　the fragrance of freshly drawn tea.

Now according to my dictionary this translates as "At eighteen one is in the bloom of one's beauty" but at first glance it's hard to see why. Translated literally it seems to say "Even the devil, even coarse tea, has a freshly drawn fragrance" which doesn't make sense at all. Look it up on Jim Breen's dictionary though and things become a little bit clearer: "just as even coarse tea tastes good when fresh, even homely girls look beautiful at the peak of their youth". Not sure where the devil comes into it though, or even how common this expression might be...