Tea is categorized according to its level of fermentation. The type of Oolong determined to have weight-reducing properties has a fermentation level of 60 to 70 percent. Tunting Oolong has a level of 30 to 40 percent.
茶的分類一般以醱酵程度區分，所謂的烏龍茶，醱酵程度在百分之六十到七十之間，日本人宣稱具有減肥功效的，就是這種「烏龍茶」；而南投縣盛產的「凍頂烏龍」，醱酵程度介於百分之卅到四十，其實是「包種茶」的一種。