Letter: Letters: Milk in tea

From ALISON WARD and STEPHEN BECK

We offer the following explanation to Colin McCoy’s question about how
adding milk first or last affects the taste of tea (Letters, 20 June).

Strong black tea is a nasty brew which is rendered innocuous by the
addition of milk. The tea contains polyphenols which have a highly astringent
taste. When milk is added, the milk protein (casein) forms a complex with
some of the polyphenols which reduces the astringency.

When milk is added to a steaming mug of black tea, the temperature falls
to the equilibrium value. During this time, the milk gets hot enough to
denature some of the casein before it has formed a complex with the polyphenols.

On the other hand, if tea is poured onto the milk, the temperature
gradually rises to the equilibrium. The polyphenol-casein complex thus
has time to form before the milk protein is denatured, and remains stable
at this temperature.

Alison Ward and Stephen Beck Sheffield