Issue 31, 2023

Tea film formation in artificial tap water


On the surface of tea infusions, the formation of a transparent, shiny film which cracks upon disturbance can often be observed. This study aims to determine how water composition, tea varieties, and tea additives impact the formation and properties of tea film, often also called tea scum. The strength of the surface film, composed of polyphenols complexed with various ions from tap water, was investigated by interfacial rheology. Microscopy and ellipsometry were used to investigate structure and thickness of the adsorption layer, respectively. We find that green tea forms more visible layers than black tea in soft and moderate artificial tap water, but in these same waters, black tea demonstrated greater surface strength. In hard artificial tap water, green tea demonstrated greater surface strength than black. No visible layer nor surface strengthening was observed on rooibos tea. Brews in hard artificial tap water formed brittle films for green tea, fracturing at strains one order of magnitude lower than in soft or moderate. Despite large variations in film strength, black tea at all water hardness levels tested formed a film with 20 nm thickness. In black tea an increased resilience to deformation was found when adding β-casein, a protein found in milk.

Graphical abstract: Tea film formation in artificial tap water

Article information

Article type
10 Feb 2023
19 Jul 2023
First published
19 Jul 2023
This article is Open Access
Creative Commons BY license

Soft Matter, 2023,19, 5967-5977

Tea film formation in artificial tap water

C. E. Giacomin, R. Y. Chen, E. Hack and P. Fischer, Soft Matter, 2023, 19, 5967 DOI: 10.1039/D3SM00169E

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