Chocolate Explained

This is the second edition of "The Science of Chocolate," by Stephen P. Beckett, and it is an excellent, well-written text, useful for the layman or the serious scientist who wants to learn more about this sweet subject. Some sections will require a scientific background, but most of the book can be understood by any interested reader. Beckett was trained as a physicist, but he performed research on chocolate for decades before his retirement from Nestlé in the U.K.

The book is a basic source for anyone who wants both an overview and a specific detailed discussion of chocolate—a highly processed food. In everyday terms, Beckett skillfully takes the reader through the facts about Theobroma cacao, the plant that bears cacao beans from which chocolate is made. He covers such details as the plant's growth in a narrow range around the equator under rain forest conditions, hand harvesting the football-sized bean pods, separating the beans and pulp, fermenting the beans with removal of the pulp; drying, sorting, and roasting the beans; winnowing out the shells; grinding the separated cocoa (nibs), separating the cocoa butter from the cocoa, and final formulation of the cocoa using various processes to produce the finished chocolate that we enjoy. A reference to the unique role of the tiny insects, the midges, which are absolutely necessary to pollinate the small blossoms of T. cacao, would have been helpful.

The reader should not be misled by the fact that the table of contents for editions one and two of the book are almost identical. The second edition includes the best features of edition one with significant improvements: The text throughout has been tightened, chapters 10 and 11 are new, and where possible the photographs are now in color for better contrast.

Beckett traces chocolate history from the use of cocoa as a drink for priests and tribal leaders in ancient Central America to its present worldwide use as a solid food and drink. How did Native Americans, more than 1,000 years ago, discover the complex process to produce chocolate as a drink? The answer is lost in time. Don Cortez in the 1520s took the first cacao beans from Central America to Spain, where the processed drink, having reported medicinal and other useful properties, was kept as an expensive trade secret within the Catholic Church and Spanish aristocracy for more than 100 years. Slowly, over another 200 years, chocolate as a drink spread to Italy, France, other European countries, and then to North America. A controversy arose about 1900 as to the true inventor of milk chocolate. Beckett has included a copy of the 1875 laboratory notebook page of Nestlé Swiss chemist Daniel Peter as evidence that he was indeed the inventor of milk chocolate.

Beckett moves on to modern-day chocolate and how it is made. Most people are familiar with the ingredients found in chocolate food products: cocoa; added natural sugars and sugar substitutes; vanilla flavors; fillers, such as air, fruits, and nuts; and milk and milk products. The book describes in detail the complex processing of the cacao bean: Cacao beans are fermented together with generation of heat for seven to 10 days to kill the bean and convert the exterior pulp to acetic acid derivatives—otherwise there is no flavor of chocolate in the final product. Next comes drying, usually in ambient air; roasting, often in conventional coffee roasters; shell removal from the cocoa (nibs) using pressure; winnowing the cacao nibs from the shell using moving air; and various types of grinding to reduce and create a more uniformly sized cocoa powder.

Cocoa is ground or milled to obtain particle sizes of about 30 μm or smaller to produce a chocolate product that does not taste gritty. Conching—so named because the shape of the early machines resembled a sea conch—is a mixing, finishing, and grinding process to change cocoa flavors and to obtain a more uniform particle size. Cocoa powder may be pressed to remove cocoa butter and then reformulated to control the flow properties of liquid chocolate with special attention to particle size and fat additives.

The proper crystallization of the fat particles in chocolate is important to taste and smoothness in melting. This crystallization is controlled by tempering—that is, precrystallization and seeding of liquid chocolate to obtain desired crystal structure—and by the selection and proper mixing of different edible fats. The book explains chocolate "bloom" as fat component migration to the surface of solid chocolate, which causes discoloration but usually has little effect on the overall quality of the chocolate.

The author discusses how the final food products of chocolate are created, including tempering (creating desired crystal formation), molding (the simplest method of forming familiar chocolate shapes), enrobing (mechanically coating sweet centers by pouring warm liquid chocolate over them), and coating (by hand or mechanically). Different chocolate products for different uses have specific formulations—for example, for ice cream coatings, for shape retaining chocolate, air-filled chocolate shapes, and chocolate-covered fruits or nuts.

The book describes many old and new analytical techniques for determining chocolate particle size, moisture content, fat level, viscosity, flavor, crystallization, and so on, the control of which is critical to the properties of the final chocolate product. Old techniques include wet chemistry and use of micrometers and viscometers. New techniques include nuclear magnetic resonance and differential scanning calorimetry.

In a new chapter, Beckett describes in general the legislation and official standards for chocolate ingredients, shelf life, packaging, and the like for countries in the European Union. The U.S. has similar standards and regulations enforced by the Food Drug Administration.

The nutritional and health aspects of chocolate are popular in the current media, particularly the benefits of the antioxidants, primarily the polyphenols. In the book, Beckett has compiled a table showing that, among foods rich in these antioxidants, dark chocolate has the highest unit content, with milk chocolate second. For healthy eating of chocolate, a rule of thumb is the darker, the better—in moderation.

General, physical, and analytical chemists will enjoy the book's approach, especially chapter 12, which has 14 experiments that deal with the physical properties of chocolate and their determination in the laboratory. Some college chemistry courses use the book as a lab guide. For example, experiment 10 on page 220 covers the measurement of the change in hardness of chocolate with change in temperature. It describes an experiment using familiar equipment, such as a temperature-controlled cabinet, weights, and a countersink with the measurements performed with a ruler and a hand magnifier.

Nearly all of the references cited throughout the book cover the European scientific literature, some of which can be found on the Internet. Other original sources may not be readily available for a U.S. reader.

Beckett does mention some aspects of what is known in the trade as the "dark side of chocolate." That is, most cacao beans are produced by hand in underdeveloped countries by unskilled labor and then exported. However, most of the workers on the cocoa plantations, which often include children, have never tasted finished chocolate products. Additionally, these countries usually have few, if any, enforced environmental regulations, and trace contaminants such as pesticides, lead, and other heavy metals may bioaccumulate and become a concern regarding the quality and safety of chocolate in the future.

Organic chemists, biochemists, and biologists will find some familiar chemical structures in the book. For example, the structures of some antioxidants—the polyphenolic catechins—found in chocolate are shown in chapter 3. Indeed, the literature reports the identification of more than 300 different compounds, primarily organic compounds, in chocolate (J. Chem. Ed. 2004, 81, 1131).

The present reviewers, biased as organic chemists, would suggest that the book include more discussion of the substituted xanthines, fused six- and five-member rings each containing two nitrogen atoms. They are found in nature and in medicine. Theobromine in cocoa (theobroma translates from the Greek as "food of the gods") and caffeine in coffee and tea differ in chemical structure by only one methyl group.

Theophylline, an oral asthma drug having a narrow effective range, is different from these two structures by a methyl group. And minor changes at the molecular level to the fused xanthine structure produce guanine, a component of DNA. The human body easily differentiates between these similar organic ring structures and responds accordingly.

The book has a few shortcomings. In this electronic age, we would have found a page or two of recommended Internet sites useful for further reading. An Internet search for "chocolate," for instance, turns up more than 183 million sites. Which are useful? We would also include a longer list of terms in the glossary to aid the reader.

Overall, if the subject of chocolate doesn't grab you or the title of the book doesn't bring a smile to your face, then the cover alone should pique your interest. It shows a tempting pile of various chocolates. This book, as well as the well-worn first edition, is in our library and it should be in yours. And plan to meet Beckett at the Royal Society of Chemistry booth at the ACS national meeting in Philadelphia in August. He will be there signing copies of the book.