Skin deep Chun pei is one of the few flavourings that gets more expensive as it ages. This "old skin" is made by leaving tangerine peel out to dry in a breezy, sunny place until it's completely desiccated, then putting it in an airtight jar. Rather than losing flavour as it ages, as with many spices, chun pei becomes more complex and potent. When used in restaurants, the description of the dish will often state how old the chun pei is, especially if it's aged peel. Shops that carry a range of chun pei usually have some peel that's aged for 10 years or more, and a small box can sell for hundreds of dollars.
Chun pei is sold at shops specialising in dried ingredients, as well as by traditional Chinese medicine herbalists. In TCM, it's prescribed for a wide variety of complaints, including coughs, stomach ailments and inflammations.
Its use in Chinese cuisine is just as varied. It's often one of the ingredients used to smoke meats (along with star anise and cinnamon), and is added to braising liquids for beef and mutton. The popular dish usually called "orange chicken" is traditionally made with chun pei, although (in inexpensive overseas restaurants, anyway) it's turned into a sickeningly sweet and sticky concoction that incorporates orange marmalade. Noodle shops sell beef balls flavoured with fine slivers of chun pei, and the peel is also delicious when mixed with minced pork and water chestnuts to make steamed pork patty. It's an essential ingredient in the tong sui (sweet soup) made with red beans and rock sugar.