MECHANISTIC STUDY OF EQUILIBRIUM AND KINETIC-BEHAVIOR OF TEA CREAM FORMATION

We report on the formation of tea cream of black tea infusions using t urbidimetry and time-resolved (static and dynamic) light scattering. I n all cases, the 'equilibrium' phase diagrams (which are to some exten t kinetically determined) display similar trends to those of simple mi xtures with solubility at high temperatures but separation into immisc ible phases below an 'upper critical solution temperature'. Especially in the more concentrated region of the miscibility gap (>2% w/w), dem ixing (spinodal decomposition) is the predominant mechanism of cream f ormation, reflecting the substantial insolubility of polyphenols. Time -resolved light scattering results demonstrate that the (narrow) metas table region of the miscibility gap is in general difficult to access even at low concentrations of tea and small temperature quench depths. Only in the case of a more water-soluble decaffeinated tea material d id it prove possible to access such a region, with nucleation and grow th then having been demonstrated as the important mechanism. (C) 1998 Elsevier Science Ltd All rights reserved.