Tea Scum

28 July 2003

We bought a new teapot on Saturday. It works a bit like a cafetiere but with tea leaves. Anyway after making several damn fine cups of tea we noticed that the pot produced rather a lot of "tea scum". This got me thinking and wondering what tea scum was and whether it can be eliminated from the tea brewing process. The internet being what it is, surely the answer was only a few clicks away, so armed with a cup of tea (complete with scum) I set off on a voyage of discovery.

The general concensus is that tea scum is 15% calcium carbonate and 85% complicated organic chemicals. The calcium carbonate is formed by the combination of calcium and bicarbonate ions. The "complicated organic chemicals" are a family of polyphenols and are anti-oxidants that are generally regarded as being good for you by removing oxidising chemicals from your body. This work came from a study by chemists Michael Spiro and Deogratius Jaganyl from Imperial College of Science, Technology and Medicine, London.

The other main theory put forward by Ralph A. Lewin from the Scripps Institution of Oceanography, California is that tea leaves are covered with a waxy waterproof fat that dissolves in the hot water forming the scum.

So how do we stop scum? As most of the tea scum is to do with the calcium - it can be reduced by brewing with soft or distilled water and by not adding milk. Acid also reverses the calcium carbonate reaction, and so the addition of lemon juice should make a scum-free cuppa.

Hello. My name is Roy. I live in rural Oxfordshire.

This is my blog. I write about things that interest me, make me laugh or that I want to remember.