Scientists' acid test for cup that cheers

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The Independent Online
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IT MAY be the cup that cheers without inebriating, but the average cuppa comes with unslightly scum on the top.

Now, however, British science has shown that if the British want to drink their tea without scum on top, then they will have to copy the Russians and drink it with lemon.

Professor Michael Spiro, of Imperial College, London, and Dr Deogratius Jaganyi report in today's Nature, the scientific journal, that scum-formation seems to be associated entirely with the presence of dissolved calcium and biocarbonate in the water - characteristic of the South-east's hard water. But when the researchers scooped the film off the top and put it under the scanning electron microscope and subjected it to chemical microanalysis, they discovered that calcium carbonate accounted for only about 15 per cent of the material; the rest appeared to be complex organic compounds from the tea itself.

Professor Spiro's research was funded by some of the tea companies anxious to find objective measures of tea quality and of how different blends perform. The scientists found that 'addition of milk greatly increased the amount of scum formed'. The secret appears to be that acidic tea forms less scum - lemon juice is acidic - and strong tea has little scum because the stronger a brew the more acidic it becomes.

But Professor Spiro's research has not changed his habits. 'I still take milk in my tea,' he said.

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