Chemistry of a guilty treat

Many people find chocolate hard to resist, but is it actually addictive? Research suggests that it is a mood-enhancing drug and bingeing may well be a healthy response to stress. Sanjida O'Connell reports

WHEN it was introduced to London in the mid-17th century, a pound of chocolate cost the equivalent of pounds 500. So a cup of chocolate (which was how it was consumed then) could be enjoyed only by the very rich. Chocolate houses were set up to purvey this treat, and by 1707 it was the most fashionable drink in Britain. Made from milk, ground beans and sugar, it was remarkably like cocoa; the only difference was that in the 18th century our quintessentially blameless bedtime drink was seen as the height of decadence.

Exactly what it is about chocolate that has taken it from decadent luxury to near-universal treat has been the subject of research carried out by Dr Peter Barham of the physics department at the University of Bristol. He has analysed the physics and chemistry of chocolate from pod to bar, and discovered what it is that makes it so appealing. And according to recent research conducted by Professor David Warbuton, head of the psycho- pharmacology department at Reading University, chocolate is a mood-enhancing drug that increases our feelings of well-being; indeed, chocolate bingeing may be a form of self-medication.

Chocolate is the single most craved food. In Britain we spend pounds 3 billion a year to ward off our desire, but Switzerland consumes more chocolate than any other country in the world; every Swiss munches their way through 21 pounds or nine and a half kilos a year. Why? The reasons for cravings for chocolate lie in its chemical composition. It contains over 300 different chemicals, which are responsible for giving chocolate its distinctive flavour and texture. Some of these chemicals are mood-altering drugs. Most of them form during the roasting process. When the beans are laid out in the sun, the larger molecules are broken down into smaller ones and they provide the essential flavour and smell of chocolate.

One of these chemicals is responsible for the stimulating effects of chocolate. The English Jesuit Thomas Gage wrote in 1648 in Mexico, "and when I was purposed to sit up late to study, I would take another cup about seven or eight at night, which would keep me waking till about midnight." There is caffeine in chocolate, but according to Dr Barham the main stimulant is a very similar chemical known as theobromine. Its name comes from the Latin for the cocoa tree. In 1728 the famous Swedish botanist Carolus Linnaeus christened the tree Theobroma cacao, meaning "food of the gods" - inspired, perhaps, by the way that chocolate literally melts in the mouth.

The special nature of chocolate fat (chocolate contains more than 50 per cent fat) is responsible for this "melt in the mouth" sensation. The fat is stored in small pockets within a rigid framework of carbohydrates in the cocoa beans. Grinding the roasted beans releases the fat. Most foods that have a high fat content contain different kinds of fat, each with its own melting point. Cocoa butter has a uniform melting point and remains brittle right up to 34C - just below body temperature. Melting requires energy; because the melting point is so sudden and absorbs energy in the form of heat, when chocolate melts in the mouth, it gives a feeling of coolness. The fat in chocolate is not water-soluble, so for the water- based acids in our stomach to start digesting it, it has to be broken up into tiny droplets. This takes time, and as a result chocolate spends a relatively long time in our stomachs, which is why it is so satisfying.

Part of the reason why chocolate feels so good when we eat it is because of its particle size, Dr Barham says. Particle size, apparently, is very important: it imparts that rich, creamy texture. During the manufacture of chocolate, the liquid mixture is crunched through heavy-duty rollers up to four times. This reduces the particles of sugar and the tough carbohydrate in the chocolate to microscopic size. On the Continent they are fussier than in Britain about particle size: each one must be less than a hundredth of a millimetre. The reason is that the smaller the particles, the better the emulsion (liquid with a tiny solid particles suspended in it). The solid particles would naturally clump together, but they're prevented from doing so by using emulsifiers - molecules with two ends; one attaches to the solid particle and the other end dangles in the liquid. Lecithin is the emulsifier normally added to chocolate. The thickness of the emulsion is determined by the viscosity of the liquid, and also by the number and the size of the solid particles in it. Smaller particles give a thicker emulsion, which is important if you like chocolate to linger in the mouth and leave a strong after-taste. British chocolate flows more quickly round the mouth so we taste it quicker - but the flavour goes sooner.

Making a good bar of chocolate is tricky. The chocolate should form crystals hard enough to hold it together but not so tough it's impossible to take bites out of the bar. The melting point of the crystals needs to be above room temperature, but below the temperature inside the mouth, and the crystals should be small: when they're not, the chocolate tastes gritty and it's impossible to get a smooth glossy finish. The white bloom you sometimes get on a bar is where it has been allowed to heat up to 20C; the cocoa butter has migrated from the crystals to the surface and recrystallised in a different form.

Gritty crystals and chewy texture definitely detract from the chocolate- eating experience, but it is 300-odd chemicals that are chiefly responsible for its appeal. According to Professor David Warbuton of Reading University, more than 50 per cent of people who eat four squares of chocolate feel in a better mood afterwards. This is thought to be because chocolate contains phenyl-ethyalamine. Chemically, this molecule is closely related to amphetamines, which raise blood pressure and blood glucose levels, making us feel more alert and giving us a sense of well-being. Phenyl-ethyalamine probably has the same effect. It's a chemical that we produce naturally in our bodies, especially during times of stress. Bingeing on chocolate may, in fact, be an attempt to balance the chemicals that control mood after an emotionally upsetting incident.

Cadbury's argue that you cannot become physiologically addicted to chocolate in the same way as you can to substances such as nicotine in cigarettes. Ms Corine Sweet, a counsellor with the Eating Disorders Association and author of a book about addiction, Off the Hook, disagrees. She sees people who, she believes, are addicted to chocolate. They eat nothing but chocolate, and once they start eating they find it difficult to stop until they have consumed 10 Mars bars or 10 tubs of chocolate ice-cream at one sitting. "I have to say, it is physiologically and psychologically addictive. It is a mood-altering substance. People get hooked on the chemicals in chocolate and the trash energy, that rush of blood sugar."

Drs Marion Heatherington and Jennifer Macdiarmid from the University of Dundee have studied chocolate addiction. They found that although eating chocolate made people feel better, in genuine addicts the pleasure was short-lived. Most felt incredibly guilty after a chocolate binge. This guilt may do them even more harm, says Dr Warburton. Guilt creates stress hormones, which mobilise fatty acids such as cholesterol and cholesterol clogs up the arteries, which can lead to a heart attack.

We can also get emotionally addicted to chocolate. "We have a treat mentality," says Ms Sweet, "Our culture is hooked on treats that are given for good behaviour, but these treats are forbidden." In later life, people may snack on chocolate because it is naughty. Women are supposed to binge on it more than men, but this is a myth says Ms Deborah Risby, the media relations manager for Cadbury's. Women buy chocolate, but this is because they tend to do most of the shopping. In the study by Drs Heatherington and Macdiarmid, more than half of the women reported an increase in their craving for chocolate just before a period. Ms Sweet says that this is because many women feel low in energy then and need to boost their sugar levels. Chocolate also contains a lot of zinc, which women need at this time.

Why did Dr Barham become interested in the subject? "Because my wife eats so much of the stuff," he says. Every year for her birthday, he bakes a chocolate cake and every year he tries to make the cake inedible by adding yet more chocolate. He has never succeeded. !