Abstract
The unsightly film on the surface of black tea infusion is called "scum". We concluded that the 'oily film'developed on the surface of oolong tea infusion is scum. The scum was formed when tea catechins were incubated at around 80°C in water containing calcium under a weak alkaline condition. The scum is usually observed much less frequent in green or black teas than in oolong tea in Japan. The reason is considered to be the difference of the manners of serving among these teas.
