Tea film formation in artificial tap water

Area of Science:

• Food science
• Colloid and surface science
• Materials science

Background:

• Tea infusions form a surface film, commonly known as tea scum, composed of polyphenols complexed with water ions.
• Understanding the factors influencing this film's formation and properties is crucial for beverage science and quality control.

Purpose of the Study:

• To investigate the impact of water composition, tea varieties (green, black, rooibos), and additives (β-casein) on tea film formation and properties.
• To quantify the strength and structural characteristics of the tea surface film.

Main Methods:

• Interfacial rheology was employed to measure the surface film's strength.
• Microscopy and ellipsometry were utilized to analyze the film's structure and adsorption layer thickness.

Main Results:

• Green tea formed more visible films than black tea in soft/moderate water, but black tea exhibited greater surface strength.
• In hard water, green tea showed greater surface strength than black tea; rooibos tea did not form a visible layer or strengthen the surface.
• Green tea films in hard water were brittle, fracturing at significantly lower strains. Black tea films maintained a consistent 20 nm thickness across water hardness levels.
• Adding β-casein to black tea increased the film's resilience to deformation.

Conclusions:

• Water hardness and tea variety significantly influence the formation, visibility, strength, and brittleness of tea surface films.
• Black tea forms a stable and resilient film, with properties enhanced by milk protein (β-casein).
• The findings provide insights into the physical chemistry of tea beverages and potential strategies for controlling tea film properties.