Black tea interfacial rheology and calcium carbonate ...

• Main Authors: Giacomin, Caroline, Fischer, Peter
• Format: Article in Journal/Newspaper
• Language: English
• Published: ETH Zurich 2021
• Subjects: Sea ice
• Online Access: https://dx.doi.org/10.3929/ethz-b-000505412; http://hdl.handle.net/20.500.11850/505412

An interfacial phenomenon can be observed in the kitchen in a cup of black tea. When tea is left to cool after steeping, a thin film at the air-water interface can form. In certain conditions, this film is observable by naked eye and, when disturbed, cracks visibly like sea ice. The mechanical properties of this interfacial film are assessed using bicone interfacial rheometry. Water hardness, acidity, the presence of sugar or milk, tea concentration, and brewing temperature all affect the formation of this film. Interfaces formed in hard water (200 mg CaCO3/L) exhibit increased elastic modulus vs those in moderately hard water (100 mg CaCO3/L), soft water (50 mg CaCO3/L), and Milli-Q water. All films formed in chemically hardened water exhibit yielding point behavior in the interfacial oscillatory shear. Film physical thickness shows no correlation with measured physical strength. Conditions forming the strongest film, chemically hardened water, may be industrially useful in packaged tea beverages for ... : Physics of Fluids, 33 (9) ...