Milk proteins, particularly caseins, bind strongly to tea tannins (polyphenols), forming insoluble complexes. This precipitates the tannins out of solution, which is exactly why milk reduces astringency so effectively. However, this binding also reduces the bioavailability of polyphenol antioxidants. The 'milk first' vs 'tea first' debate has scientific merit at the margins — adding cold milk to a hot cup may cause localised denaturing of milk proteins, theoretically affecting flavour.
For a deeper dive into related topics, explore our full Tea Learning Hub with over 500 expert articles.