Just like our underarm odor, we're all a bit different in the make-up of our sexual secretions. Cleanliness is fine, but during cunnilingus, there is a flow of lubricating fluid from a woman's Bartholin's gland-analogous to the "pre-come" produced by the Cowper's gland in the men. Some people produce more than others. No matter how much you've washed, this fluid, like a fine wine, will exhibit the "terroir" of the owner.
Personally, this reminds me of why I liked wearing a mustache so much; The lovely, tangy fragrance in the morning was a reminder of the incredible coitus we had and I become aroused all over again.