WE'VE been eating them for hundreds of years, but the secret of a perfect sandwich can now be revealed - bubbles.

Manchester University's Dr Grant Campbell says air bubbles in bread are just as important as the filling.

Dr Campbell, a chemical engineer, said: "Bread is special because of its bubbles. It's got these bubbles because wheat, when mixed with water, salt and yeast is the only cereal that can trap the carbon dioxide and give us raised bread.

"That raised bread makes for soft bread and it's soft because of the bubbles.

"It's one of the reasons why brown or wholemeal bread is less suitable for making tasty sandwiches - the bran pops the bubbles."

At a time when experts are encouraging people to choose the healthier option of wholemeal, Dr Campbell - who says his personal perfect sandwich would be `smoked salmon on malted granary bread' - believes that chemical engineers may hold the key to persuade the public, in particular white-bread loving children, to make the switch.

He said: "Nutritionists have been telling us to eat more wholemeal bread for decades but we still prefer white bread because it tastes better.

"Chemical engineers are working to find a way of getting bran into bread recipes without popping the bubbles. By doing this we will create a healthier bread without sacrificing the tastiness."

Dr Campbell, who has taught in Manchester for 13 years, was presented with an award at a meeting of the Institution of Chemical Engineers in Birmingham in recognition of his outstanding service to chemical engineering education.

He is the editor of the book Bubbles in Food which explains the key role bubbles play in chocolate, champagne and meringues, among other things.

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