WHAT'S THAT STUFF?
December 4, 2000
Volume 78, Number 49
C&EN EAR 78 49 p.82
Can you imagine life without chocolate? Possibly not. Can you imagine chocolate without science? Probably yes. Well, think again the next time you snap a bar of that delicious brown or white stuff and allow a piece to melt in your mouth.
Chocolate's varied flavors, colors, shapes, and textures result from different recipe traditions that have evolved in different parts of the world. However, although the preparation of top-quality chocolate products may be regarded as an art form, modern processes for manufacturing the most popular brands rely heavily on science and technology.
The essential ingredient in all chocolate is cocoa, which is made from the cream-colored beans that grow in pods on a tree with the botanical name Theobroma cacao. The cocoa or cacao tree, as it is commonly known, is a native of the tropical regions of South and Central America. Nowadays, it is also cultivated in West African and Southeast Asian countries that have humid tropical climates and lie within 20 degrees of the equator.
After harvesting, the beans are removed from the pods and piled in heaps. The growers allow the beans to ferment for several days in order to develop the chemical precursors of the chocolate flavor. The beans are then dried and transported to chocolate factories.
At the factory, the cured beans are sorted and impurities such as sand and plant materials are removed. The beans are then roasted. This process makes the bean shells brittle, darkens the color of the beans, and converts the beans' flavor precursors into the aldehydes, esters, lactones, pyrazines, and other groups of compounds that give chocolate its distinctive flavor and aroma.
The next step is to break up the roasted beans into pieces called nibs and remove the thin shells by blowing air through the beans in a process known as winnowing. The nibs are then ground into chocolate liquor--a thick brown liquid that solidifies at about room temperature.
Approximately 55% of the liquor is cocoa butter, a fat consisting of various triglycerides. Each triglyceride has three fatty acids attached to a glycerol backbone. Oleic acid, stearic acid, and palmitic acid account for more than 95% of the fatty acids in cocoa butter.
The concentration of fat in the liquor is too high for making cocoa powder and too low for making so-called eating chocolate. The trick is to remove about half of the cocoa butter from the liquor using heavy-duty presses and use the butter for making eating chocolate. The solid block of cocoa that remains is pulverized. The powder is used to manufacture drinking chocolate and cocoa. Dairies, bakeries, and confectionery manufacturers also use the powder as a flavoring ingredient.
"If you made a chocolate drink from ground-up cocoa, a lot of the fat would rise to the top of the drink and it would look ghastly," explains Stephen T. Beckett, departmental head at Nestlé Product Technology Centre, York, England, and author of "The Science of Chocolate" (Cambridge, U.K.: Royal Society of Chemistry , 2000).
Dark chocolate is made by mixing the separated cocoa butter with chocolate liquor and sugar. The same ingredients plus dried milk are used to make milk chocolate. White chocolate contains cocoa butter, sugar, milk, but no chocolate liquor. Eating chocolate typically contains between 25 and 35% fat and 50% sugar. Flavorings such as vanilla may also be added, depending on the product. Sugar substitutes are used for low-calorie products.
During processing, chocolate spends much of its time as a liquid. Viscosity, flow properties, and particle size are therefore important factors in chocolate manufacture. Fat content is a key consideration in determining these properties and, according to Beckett, can have a dramatic impact on viscosity. For example, increasing fat content of chocolate from 27% to 28% can halve its viscosity. Chocolate viscosity can also be reduced by adding a small amount of an emulsifier, such as lecithin, a naturally occurring surface-active agent.
The next stage in chocolate manufacture involves cooling the liquid under controlled conditions to allow the fat, which holds all the solid sugar and cocoa particles together, to set in a crystalline form that has a smooth texture and appealing appearance. For molded products, the fat must also contract on cooling so that the solid chocolate can be removed from the mold. The rate at which chocolate sets, the texture and color of the product, and its melting properties depend on the percentage of cocoa butter and milk fats in the mixture.
Finally, the product is packaged or wrapped to protect it from dirt, external odors, moisture, and insect infestation.
Migration of fat and moisture from caramel, peanuts, wafers, or other ingredients at the center of a confection through chocolate leads to deterioration of the product quality, Beckett points out. The rate of migration is largely determined by the temperature and humidity of the air around the chocolate and also by the moisture content of the chocolate and the type of fat present in the other components.
Chocolate is a food that contains a range of nutrients--including not only fats and sugar, but also other carbohydrates and proteins. In addition, chocolate contains small quantities of salts of metals such as magnesium, potassium, calcium, and iron; the vitamin riboflavin; the stimulant caffeine; and water.
Beckett tells C&EN that cocoa contains around 800 chemical compounds. They include a group of polyphenolic compounds known as flavanols or catechins. A 40-g (about 1 oz.) milk chocolate bar contains around 300 mg of these compounds, a relatively high amount compared with most other polyphenol-containing foods. Polyphenols exhibit antioxidant activity. They have, for example, been shown to inhibit oxidation of low-density lipoprotein cholesterol and may therefore help to protect against cardiovascular disease.
Chocolate, regardless of its nutritional benefits, is a pleasure to eat. I'm even tempted, at this moment, to reward myself with a bar of the luscious stuff. Can I tempt you to join me?
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Copyright © 2000 American Chemical Society