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Researchers at Leeds University have discovered eggs-actly how to tell whether or not an egg is fresh. Food scientist Malcolm Povey uses waves of ultrasound to detect the thickness of the egg white. The thinner the white, the older the egg is.

Dr Povey said: "Sound is absorbed much more by thick than by thin egg white. By measuring how much ultrasound goes through an egg we can get a good idea of how much white there is inside."

Dr Povey also hopes that shoppers will be able to use the technique to choose really fresh cream, while banana farmers will be able to tell when their crop is ripe.