It is a question that has long preoccupied connoisseurs of the take-away: why does cold pizza taste great the day after while burgers and fish and chips turn the stomach? The answer lies in the topping, says a chemistry lecturer who has analysed the ingredients of Italy's tantric convenience food
"The answer to the mystery lay in the tomato purÃ©e used in pizzas," said Dr Maureen Cooper, a chemistry lecturer at Stirling University. "Cheese on toast has a base like pizza, but turns soggy and tastes terrible the next day." The purÃ©e has tomato fibres that trap a layer of water, like capillary matting. And because fat and water do not mix, the melted cheese topping is trapped above the tomato fibres and the doughbase. Dr Cooper said: "The fat molecules are repelled by the water molecules, so the pizza doesn't turn soggy" - a phenomenon called "immiscibility".
But she warned that some unauthentic pizzas were not good next day because thepuree was inexpertly applied.
To achieve longer-lasting cheese-on-toast, she recommended spreading a thin layer of tomato sauce under the cheese. Dr Cooper is also studying the chemistry of baked Alaska, an ice-cream dessert coated with baked meringue.