Pu-erh (or Puer) tea is in a category all its own. Though it could simply be classified as a type of Chinese black tea, it is differentiated from other black teas by the fact that it is fermented not once, but twice. The double oxidation process is followed by a period of maturation, which is often used to develop a thin layer of mold on the leaves. Pu-erh tea is often consumed for medicinal purposes rather than for pleasure ? aside from being known for its strong earthy quality, it is recognized as a powerful digestive aid.