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October 21, 2002
Volume 80, Number 42
CENEAR 80 42 pp. 47-48
ISSN 0009-2347


CHEMISTRY LESSONS FROM THE KITCHEN

REVIEWED BY SARA J. RISCH

Have you ever wondered why crackers have holes in them? Or wondered about the best way to open a bottle of champagne, or why there are special spoons for caviar? These and many other questions are explored in "What Einstein Told His Cook: Kitchen Science Explained," by Robert L. Wolke.

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Even though we eat on a regular basis, most people seldom contemplate the complexity and chemistry that enter into growing, processing, manufacturing, packaging, storing, and finally preparing food for consumption. Wolke, professor emeritus of chemistry at the University of Pittsburgh, has been addressing the questions of consumers regarding foods in a weekly newspaper column, "Food 101," syndicated by the Washington Post. In "What Einstein Told His Cook," Wolke has taken more than 100 questions he has been asked and used them as the basis for explaining the science of what happens in the kitchen.

Consumers are often confused by conflicting messages about foods and their ingredients and processing. Some of this confusion arises because new research disproves previous theories, some comes from general dissemination of misinformation, and some is the result of interest groups using bits of information taken out of context to prove a particular point. Wolke tries to dispel this confusion with a book that is designed to be a ready reference for those common-- and sometimes not so common--questions. He uses easily understandable terms interspersed with, as he calls it, "techspeak"--scientific terms that help explain the concepts he is describing. He defines "hygroscopic," for example, in his discussion of the fact that sugar picks up moisture and uses "volatile" to describe molecules that easily fly off into the air.

In nine chapters, Wolke leads the reader through specific ingredients, such as salt and sugar, as well as general categories of food, like turf and surf and liquid refreshment. The first chapter, "Sweet Talk," seems a little disjointed, almost as if it's an area that does not hold the author's interest. As a result, the chapter doesn't hold the reader's interest either. But the chapter contains interesting information if you can stay with it.

He begins with a good discussion on the five basic taste sensations (sweet, salty, sour, bitter, and umami) and then works his way through a number of questions about sweeteners. I applaud his addressing the issue of the supposed evil of white sugar by explaining that refining is simply a process of three successive crystallizations to separate sucrose from other components of sugarcane syrup. Brown sugar and molasses contain the same sucrose; they just have a few additional components.

The chapter titled "Fire and Ice" provides an interesting discussion of the effects of two of the most used items in the kitchen--the refrigerator and the stove. Wolke answers questions about why cooking time changes with altitude, whether all of the alcohol is boiled off in cooking (it is not), and what freezer burn is (dehydration of the surface of foods).

He also presents some interesting research that he himself has conducted trying to determine, for example, whether sidewalks really get hot enough to fry eggs. Although he wasn't able to coagulate egg proteins using only the heat from a sidewalk, he writes that his newspaper article drew one letter from a woman in Tempe, Ariz., who claimed to have done so on a sidewalk there when the temperature was 122 °F. An interesting addition to this discussion is that the woman commented that after less than 10 minutes on the sidewalk, the yolk broke. Wolke concluded that dehydration caused the surface of the yolk to become brittle and crack.


Even though we eat on a regular basis, most people seldom contemplate the complexity and chemistry that enters into preparing food.


In another experiment, Wolke wanted to determine if rolling a lime (or lemon) or microwaving it prior to juicing would yield more juice than just squeezing it. In the first part of the experiment, he compares the amount of juice that you get from limes that have either been rolled or microwaved with limes that receive no treatment. He uses a mechanical juicer and finds that the treatment doesn't yield any more juice. However, when he squeezes the juice by hand, he finds that rolling followed by microwaving will yield 26% more juice than not doing anything to the fruit before squeezing it.

In another experiment, he confirms a conclusion that Harold McGee came to in one of his books that mushrooms do not soak up water when they are washed. Some people think that mushrooms should not be washed because it will make them watery. In Wolke's tests, button mushrooms absorbed only 2.7% by weight water after soaking, not enough to have an impact on cooking performance. He speculates that most of the water that is picked up is actually trapped in the underside of the cap and not absorbed at all.

The chapter on liquid refreshment covers a wide variety of questions about various beverages. Wolke presents information on carbon dioxide in bottles and addresses the issue of why soda in unopened bottles goes flat--yes, the carbon dioxide does permeate through the bottle. He dispenses with the myth that pumping air into soda bottles will help the carbonation last longer, as it really doesn't do anything to help keep the dissolved CO2 in the soda.

As you read this book, you realize that Wolke must get some very odd questions sent in by his readers. Someone wanted to know, for example, if burping would contribute to global warming. His answer is no, this is not a significant factor.

One very nice addition to the book is recipes supplied by Wolke's wife, Marlene Parrish. These recipes are interspersed throughout the text, where they highlight what Wolke is discussing. It would have been helpful to have some direct comments about the chemistry involved in the recipes, as they demonstrate some of the questions that Wolke answers. A recipe for chocolate velvet mousse, for example, follows the discussion on the differences between unsweetened, semisweet, and sweet chocolate. A recipe for butter cookie stars shows that it is best to use unsalted butter in some applications so as to know exactly how much salt will be in the final product. An unusual recipe for Portuguese poached meringue follows the discussion of cream of tartar. Other interesting recipes include oven-"grilled" vegetables and champagne jelly. The recipes offer insight into the ingredients, and they made me want to head straight for the kitchen and try them.

WHAT EINSTEIN TOLD HIS COOK: KITCHEN SCIENCE EXPLAINED, by Robert L. Wolke, W. W. Norton, 2002, 350 pages, $25.95 (ISBN 0-393-01183-6)

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Sometimes Wolke seems to use a question as a starting point for something he wants to discuss. The reader may spend several pages reading interesting tales, wondering if the question is ever going to be answered.

In most cases, he does eventually answer the question, although it may be somewhat indirect. The truly curious will occasionally be left wondering what the answer really is, because some items are simply dismissed with the comment "don't ask" (what all the yellow-green stuff is inside crabs) or "you don't want to know" (concerning the "evil chemicals" that smoke for smoking meats contains). He includes a statement about "depositing horrible chemicals" when flare-ups occur when too much fat drips onto hot charcoal on a grill. This does not do much to reassure the reader about the safety of our food.

There are also a couple of specific technical issues that are not exactly correct. Wolke says that bread stored in the refrigerator becomes stale because it dries out, when actually staleness is caused by starch molecules packing together and becoming more difficult to bite through. Wolke also comments that any paper is safe in the microwave oven, when, in fact, it's possible that some recycled paper contains enough microscopic pieces of metal to cause burning. His general discussion of microwave ovens is quite good and includes how these ovens work. Although this is one of the most widely used pieces of equipment in the kitchen, it is definitely the least understood.

Several questions concern nutrient loss and chemical changes during cooking. One of these arises in a discussion about microwave ovens. Wolke tends to dismiss the question by saying that all cooking changes food without giving much detail. A little more information would definitely be useful so readers can better understand the changes that do occur, particularly with regard to nutrient content and how different types of cooking impact different nutrients.

In the final chapter, Wolke addresses a variety of different questions. This includes an insightful discussion on different types of cookware and their heating properties. In an informative section on nonstick cookware, he offers a good chemistry lesson as he explains how it is possible for one side of the surface polymer coating to stick to the pan while food does not stick to the other side. He also tackles some of the newest technologies in cooking, such as induction heating and the use of high-intensity light to heat foods.

"What Einstein Told His Cook" covers a wide variety of very interesting questions about the foods we eat and the ingredients they contain. Wolke provides insight into many processes that occur in the kitchen as he addresses many common questions people have. His attempts at humor are not exactly to my taste, but they do add a little fun to the book. For example, after explaining that the impact of very salty water on bacteria is to inhibit their reproduction by dehydrating them, he quips: "Not tonight dear, I'm dehydrated."

Wolke addresses many myths about our foods and answers the questions in not too technical terms. His engaging book will help readers better understand the chemistry behind the foods we enjoy every day.


Food chemist Sara J.Risch is a consultant to food, flavor, and packaging companies.



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