Pu-Erh Cakes

The original purpose of pressing flat, round cakes of tea leaves was for ease of transportation. Later, cakes offered another advantage: with less leaf surface exposed to air, the fermentation process happened more slowly and allowed more flavor complexity to develop, with less risk for dangerous mold.
Pu-erh tea is a fermented product that continues to improve in quality as it ages, so — if properly stored — it lasts nearly indefinitely.