PinCha’s Ceylon Ruhuna Black Tea would become turbid and orange-yellow, the phenomenon of “cream down”, aka ”tea cream”. The cream is made of theaflavins, thearubigins, and flavonol glycosides, the ratio around 12:86:2 (Powell, 1993). The theaflavins group is the key to make black tea appear “bright” and show the “golden circle”. When the temperature of the tea decreases, the thearubigins and caffeine will stick together and gradually stack, making the tea look turbid.
Powell, C., Clifford, M. N., Opie, S. C., Ford, M. A., Robertson, A., & Gibson, C. L. (1993). Tea cream formation: The contribution of black tea phenolic pigments determined by HPLC. Journal of the Science of Food and Agriculture, 63(1), 77-86.