Reporter 446, 7 February 2000
The freshness of unbroken eggs can now be deduced for the first time thanks to a simple technique developed by University food scientist Malcolm Povey. Waves of ultrasound can pick out eggs laid the same day from those placed in cold storage months before. As well as determining the age of ‘fresh’ supermarket eggs, the technique can predict the shelf-life of cream and even tell banana growers when their crop is ready to harvest.
Eggs-actly: Malcolm Povey can tell the freshness of eggs without breaking them
Meringue makers and fried egg fans will already know the thick egg whites found in fresh eggs give the best results. The longer eggs are kept before use, the thinner the egg white becomes. This is bad news for cooks but good news for Dr Povey.
"Sound is adsorbed much more by thick than by thin egg white," he said. "So by measuring how much ultrasound goes through an egg we can get a good idea of how much thick and thin white there is inside." Large amounts of thin white are a tell-tale sign the egg was laid some time ago.
Ultrasound is more usually associated with pregnancy scans, which use reflected sound waves to build up an image. Cracking eggs proved somewhat tougher. "Human tissue is far better suited to ultrasound probing than most food materials," said Dr Povey.
Dr Povey’s discovery could give consumers the chance to choose eggs that are truly ‘fresh’, but industry has yet to take up the challenge. "They told us they have enough methods of rejecting eggs already," he said.
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