Scientists are often accused of being far too wrapped up in quarks and genes to be of much help in the kitchen. So, could they tell us how to make the most out of tomorrow's meal? Roger Highfield and Aisling Irwin report
TOMORROW will see one of the largest home scientific experiments of the year as millions of people tackle a fiendish problem in applied chemistry: how to cook the perfect Christmas lunch.
In previous years, this page has tackled the muscle biochemistry of turkeys, how to hunt a sixpence with a body scanner, the molecular structure of brandy sauce and the thermodynamics of Christmas puddings.
Today, we decided to show how you can make the most of the traditional feast by asking physicists and chemists from a number of laboratories to provide some seasonal scientific insights and advice.
Let the turkey "rest" after roasting. Allowing the bird to cool a little offers several advantages, according to Dr Peter Barham, a physicist at Bristol University who has spent many years investigating the science of cooking.
First, it makes the meat easier to handle. Cooking the bird at high temperatures means the molecular structure of the collagen connective protein shakes apart and its three component strands unwind to form gelatin.
This gelatin will remain in a liquid state at temperatures above about 35C. On cooling, however, it will gel to form a semi-solid which will hold the meat together, making it very much easier to carve.
Dr Barham says the change in texture will also improve the "mouth feel" of the turkey. Also, the extra time that the turkey spends at elevated temperatures during the cooling allows further chemistry to go on, breaking down the large proteins and so on into smaller flavour molecules.
. . . but don't let it get too cold. Keeping the turkey warm enhances the release of its flavours. Although we think that our sensing of flavour is done by the taste buds in the mouth, in fact they only respond to sweet, sour, bitter and salt. The complexities of flavour are detected by our sense of smell. The turkey will release aromas in the mouth during chewing which travel up through the back of the throat and into the nasal passage.
These aromas - or volatiles - are more readily released into the air in the mouth and in turn wafted up the nose, if the festive bird remains relatively warm.
Add salt. Turkey is such a bland and uninteresting meat that it cries out for a sprinkle of salt to enhance its flavour. Salts have been used this way for thousands of years in the cuisine's of many cultures but their effects are subtle and some remain mysterious.
The best known salt is sodium chloride - ordinary table salt. But despite its ubiquity, and its simplicity, it has caused scientists headaches.
There is more to sodium chloride than its salty taste: in the Eighties experimenters demonstrated that it has no enhancing effect on flavours, leaving scientists, if not chefs, perplexed as to how it does improve flavour.
Then Dr Paul Breslin and Dr Gary Beauchamp, of the Monell Chemical Senses Center in Philadelphia, found that salt filters flavours so that unpleasant tastes such as bitterness are suppressed more than palatable tastes, such as sweetness.
This occurs due to the blocking properties of charged sodium atoms on the bitter-taste receptors in the mouth. And once these taste signals reach the brain, the flavour of the food is very much enhanced.
This is due to the fact that in the brain, bitter and sweet tastes have a tendency to partially cancel each other out. But when bitter or bad tastes are knocked out as a result of the chemical action of salt on taste buds, the more desirable, sweet tastes are intensified, as they are no longer being so suppressed by the bitter tastes. (This occurs even with salts, such as sodium acetate, that do not taste all that salty because it is the sodium that is the key ingredient rather than the chloride or acetate.)
"Salt is a really fascinating and complex substance to add to food," said Dr Breslin. "It impacts flavour in ways we have yet to understand."
Moisten the mouthful of turkey with gravy. Moisture is important for the release of flavour and also necessary for creating a wet bolus of food ready to travel down to the stomach. "Dry food like turkey is sucking out your saliva as you chew," says Dr Wendy Brown of the Institute of Food Research in Reading, an expert in chewing and flavour perception. "You have to keep oozing more and more saliva on to it until it is lubricated enough to swallow." Some people produce much less saliva than others and the addition of other liquids helps improve their perception of both texture and flavour.
Microwave the chestnuts. Dr Peter Barham has a simple suggestion on how to avoid burning your fingers when peeling the chestnuts to make the stuffing. "Pierce the nuts with a sharp knife and then cook about 10 at a time on full power for about 80 seconds in a 650 watt microwave."
The dry skins contain very little water and so are not significantly heated by the microwaves (which are absorbed by water molecules) but the nut inside is heated and some of the water is turned to steam which in turn "blows off" the inner paper-like membrane. "So when the nuts are taken out of the microwave you can simply squeeze them between thumb and forefinger to eject whole, peeled chestnuts."
Artificial pudding maturation. The maturation process that occurs when you store your Christmas pudding for several years are more or less the same as those that occur in wine. They both involve the slow chemical changes in chemicals called tannins. Dr Peter Barham suggests that if you have a good old claret with your meal you should "keep the dregs left after decanting the wine and pour them over the pudding before you start to reheat it. Further, if you can afford the luxury, when the pudding is ready, pour over a good well-aged brandy and leave to soak for five minutes before lighting".
Taste versus waistline. When you are looking for something to put on your pudding, drop the low-fat substitutes for custard and cream if you want to ensure a good flavour.
This is because flavour chemicals are carried predominantly in the fat. When manufacturers replace the fat with something else they disrupt this complex and need to work very hard to restore the balance. "There's a big commercial interest in how to retain the flavour balance," says Dr Brown.
Savouring chocolates. The pleasure from the chocolates eaten after the feast comes from keeping them in the mouth for a long time, says Dr Brown. "Quite often you don't get much flavour while chewing them," she says. "Only as the fat melts and is smeared round the inside of your mouth, giving that lovely smooth feeling, does the flavour emerge. This is because you have increased the surface area from which flavour can be released." Since there are 120 different flavour volatiles in chocolate, all being released at different rates and in different concentrations, it is worth giving them time to work their magic.
Nuts. Finally, as you chew on your almonds, consider Dr Brown's research which shows that within 10 chews you will have broken them into 350 to 600 fragments, depending on your mastication power, giving a huge surface area from which the flavour is released.
