Why Scum Forms on Tea

We all have our own views about what makes a cup of tea perfect, but scientists from Switzerland – a nation not known for its tea-drinking habits – have one over us. The scientists have discovered how to get rid of the layer of film that often forms on top of a cup of tea. It was believed the film forms when the waxy coating on tea leaves rises to the top of the water, but apparently this is not the case. Instead, experts in rheology, the study of how liquids and gases flow, found the film is created when polyphenols, the organic compounds in tea leaves and other plants, bond with the calcium carbonate in tap water. Using soft water, which has a lower mineral content, will stop a thick layer of scum forming, but the Swiss scientists warn that pure forms of water can make the tea taste bitter. Drinking the tea while hot and adding lemon juice can also stop the layer of scum. Anyone fancy a cuppa?