Why do cooked foods taste different after they have cooled from the way they tasted when they were hot?
鈥� Cooked, solid foods are not static substances. Chemically and physically they are complex dynamic systems, continuously changing without stopping to suit anybody, so there are penalties for eating them too early or when they are past their best.
Cooking or cooling changes various substances in foods, affecting composition and flavour. Yesterday鈥檚 leftovers have undergone reactions, including oxidation and the evaporation of aromas and flavour components. Food also changes physically on cooling, by congealing, crisping or crystallising, for example. These changes may prevent some substances from reaching the nose or the tongue, or expel or redistribute fluids. Few such changes reverse precisely on reheating, just as one cannot uncook food by chilling it.
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Some changes are desirable, such as the setting of jelly or ice cream, but it is not for nothing that various foods are prepared at a particular temperature. Fresh hot food presents copious aromas in particular balances that reheating can never recapture.
Jon Richfield, Somerset West, South Africa
鈥� Only a small amount of the taste of food is detected by the tongue, where taste buds recognise just five flavours: bitter, salt, sour, sweet and umami (or savoury). The majority of what we call 鈥渢aste鈥� is more specifically described as 鈥渇lavour鈥� and it comes from odour identified by nasal olfactory cells. That requires the flavour molecules to be wafted up from the mouth. This is more readily achieved when food is hot, creating convection currents and making odour molecules, as well as water molecules, volatile and mobile.
Water from food and saliva can dissolve flavour molecules so those more readily reach the taste buds while flavour vapours hit the nose. Having a cold that blocks the nose is even more effective in reducing flavour than eating food cold, and can make apples and onions indistinguishable.
Elisabeth Gemmell, Bearsden, Strathclyde, UK