What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (50 page)

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Cocoa butter
or cacao butter: The fat from the cacao bean.
Butter
is a more appealing word than
fat
, but don’t let it fool you into thinking it comes from a cow. Not even a brown cow.

•
 Cocoa
, cocoa solids, or cacao solids: The brown, solid parts of the cacao beans, ground to a powder.

That’s it. Just three main players in the cast of characters: whole chocolate, its fatty part, and its solid part. If the cocoa butter and the cocoa solids are separated, they can be combined with sugar in various proportions to make a variety of different “chocolates.”

“Unsweetened chocolate” or “baking chocolate” is simply chocolate liquor that has been poured into molds and solidified by cooling. The FDA requires that it contain between 50 percent and 58 percent fat, a leeway of 4 percent on either side of natural cacao beans’ fat content of 54 percent.

In addition to its 54 percent content of fat, chocolate liquor contains about 17 percent carbohydrates, 11 percent protein, 6 percent tannins, and 1.5 percent theobromine, an alkaloid similar to caffeine and a mild stimulant. It also contains less than 1 percent of phenylethylamine, a somewhat stronger stimulant similar to amphetamine, known in certain quarters as “speed” or “uppers.” Other minor ingredients of chocolate are polyphenols, antioxidants that counteract harmful free radicals; and anandamide, a close relative of tetrahydrocannabinol (THC), the active ingredient in marijuana. But note that the amounts of all these physiologically active and psychoactive chemicals are minuscule. Moreover, the “highs” they produce are short-lived and not very lofty.

Before a batch of molten chocolate is ready to be poured into bar molds, it is usually
conched
: kneaded and massaged in heated tanks for anywhere from two to six days while chemical changes take place, flavors develop, moisture and bad flavors such as acetic acid evaporate, and the sugar is reduced to smaller particles, leading to a smoother texture. (The word
conch
comes from the shell-shaped blades of the early conching machines.)

Chocolate factories can squeeze the fat out of whole cacao, thus separating the fat from the solids. The fat-free solids are commonly and quite properly called cocoa and are sold as such. The manufacturer often adds some of the separated fat to a chocolate-bar mix in order to adjust the smoothness and melting properties of the ultimate bar. Because this added cocoa butter changes the cacao’s natural 54-to-46 ratio of fat to solids, it is listed separately as an additive in the list of ingredients. The percentage number on the wrapper includes this added fat.

Note that I have not included milk, milk solids, or nonfat milk among the ingredients because (and I know I’ll get flak for this) I don’t consider milk chocolate to be chocolate. It’s just candy. Milk chocolate contains so much milk and sugar that its percentage of true cacao may be as low as 10 percent, the minimum required by the FDA for calling it “chocolate” on the label. Hershey’s milk chocolate contains about 11 percent cacao. By contrast, a serious dark chocolate bar will contain anywhere from 65 to 85 percent cacao.

The smoothness of a chocolate bar—one result of how much fat it contains—is a matter of national preference. In continental Europe, people like their chocolate very smooth, containing sugar particles no bigger than 80 millionths of an inch (2 microns), while the British prefer slightly gritty chocolate containing 400-millionths-of-an-inch (10 micron) sugar particles. Almost nobody likes the grittiness of chocolate containing solid particles bigger than 600 millionths of an inch (15 microns).

In 2003, as a result of squabbling among Belgium, England, France, and Germany with anxious input from Switzerland, the European Union ruled that up to 5% of the cocoa butter in chocolate may be replaced with other vegetable fats. That’s why many of the best European dark chocolate bars brag about their high cacao content by printing their percentage numbers in huge type on their wrappers.

If you’re truly interested in upping your snob quotient, taste as many serious dark chocolate bars as you can find (or afford; they’re not cheap). Use the percentage of chocolate liquor only as an initial indicator of how sweet or bitter you like your chocolate. Then try a variety of bars in that range to find your favorites in brittleness or “snap,” flavor, and mouth feel. Learn the cacao percentages and countries of origin of a few bars, and at every opportunity, talk about them in terms taken from a wine magazine (bouquet, fruit, finish, and so on). Use the word
cacao
(not cocoa) as often as possible, and you can be as good a chocolate snob as any of your friends.

As a pastry chef, I know all the techniques for working with chocolate to prevent disasters such as my chocolate’s seizing or losing its temper, or being too hard or too soft for molding or piping, etc. From training and experience, I know all the exact temperatures and so on, but I would like to know more about how and why they work.

....

C
hocolate is indeed a difficult material to work with, owing to its complex composition, mostly its content of several different fats.

As it arrives in the kitchen from your purveyor in the form of slabs or pastilles, it consists of microscopic particles of cocoa and sugar distributed throughout a sea of solidified fat or cocoa butter. It’s the fat that’s the main problem, because it consists of at least six different chemical compounds—different fats that have different crystallization temperatures—and you have to keep all but one of them from crystallizing. It’s a temperature juggling act called tempering. Table 7 shows what chocolatiers have to deal with.

In the table, the six different fats are listed, from bottom up, in order of increasing crystallization temperatures. What is a crystallization temperature? Consider the liquid called water. When we cool it down to 32°F (0°C), it crystallizes into what we call ice. But when we heat it above 32°F (0°C), the crystals melt into liquid. That magic temperature is both the
crystallization temperature
and the
melting temperature
of H
2
O.

Similarly, the crystallization temperatures in the table are the approximate temperatures below which the fats crystallize into their own unique kinds of crystals and above which they melt into liquid. Of the six crystal forms (
polymorphs
), it is only number V that has exactly the properties we want in our chocolate: it’s glossy and, when solid, crisp and snappy when bitten into. But it will still melt in our mouths because our body temperature of 98.6°F (37°C) is a few degrees higher than its crystallization (or melting) temperature of 94°F (34°C).

The problem is, how do we get rid of the other, less desirable crystal forms? First (see the graph on p. 438), we heat the chocolate to about 120°F (50°C), which melts all six forms. Then we cool it down to about 80°F (27°C), where forms IV and above will crystallize. And then we slowly raise the temperature to 90°F (32°C), which melts the crystals of form IV, leaving us with only forms V and VI in crystallized form. But since form VI requires days or weeks to crystallize, it doesn’t. The result is that the only crystals remaining are those of the desirable form V. We have tempered our chocolate to achieve the ideal working characteristics for the pastry chef.

If, while you are working with the tempered chocolate, it loses its temper (along with you losing yours) by being heated or cooled too much, there is nothing to do but repeat the entire tempering cycle.

In cooking, rather than in decorating, with chocolate, there are a number of pitfalls, the most exasperating of which is seizing: the chocolate’s suddenly turning from a smooth, viscous liquid into a mess of grainy, muddy clumps. This can happen for several reasons, the most common of which is the effect of a small amount of water. But paradoxically, a large amount of water or watery liquid such as cream will not make the chocolate seize; the chocolate and the watery liquid will blend together like a dream.

Here’s why.

Think of well-tempered chocolate as zillions of microscopic cocoa (and sugar, if it’s semisweet) particles suspended in a sea of fat. Cocoa and sugar particles are not fat-loving (lipophilic); on the contrary, they are water-loving (hydrophilic). If even a few drops of water are added, the water will be attracted to and will wet the particles, making them clump together into something like a mud ball. And a little bit of water can wet an awful lot of tiny particles, creeping between them in a thin film and holding them together by capillary attraction.

If stirred, virtually the entire pot of melted chocolate will then freeze into a thick mud—useless for making into smooth, glossy frostings and confections. That’s why melted chocolate must be protected from contact with the tiniest amount of water, such as condensed steam from a double boiler. Many of today’s pastry chefs melt their chocolate in a microwave oven to sidestep this danger.

But oddly enough, a
large amount
of watery liquid will not make the chocolate seize. If you have ever made a sand castle at the beach, you know that a little bit of water will cement the sand grains together into a mass that will hold its shape. But when a wave washes in, the
large
amount of water disintegrates the mass by separating the grains from one another.

That’s why, in the recipe for ganache on page 443, you can add a whole cup of cream to the melted chocolate and it won’t seize. The fact that heavy whipping cream is about 38 percent fat doesn’t hurt.

Tempering chocolate. The chocolate is first heated to 120ºF (50ºC) to melt all crystal forms, then slowly cooled to 80ºF (27ºC) and reheated to 90ºF (32ºC), so that all crystal forms are melted except the desired form V. (See Table 7.) (Temperatures are approximate.)

In a box of assorted chocolates I noticed that only the candies covered with dark chocolate acquired a white film after several months, while the milk chocolates did not. I have wondered what in the chemical composition of the dark chocolate causes this.

....

A
fter several months, you say? In my house, a box of chocolates is lucky to last a week.

The white film is called “bloom” and is caused by excessive or varying temperatures. You have committed the crime of chocolate abuse by not storing it properly.

The white film is not mold and is perfectly harmless, affecting only the chocolate’s appearance and to some extent its texture. Milk chocolate typically consists of about 70 percent powdered milk and sugar, with only about 12 percent chocolate liquor, so it isn’t as prone to bloom as is dark chocolate, which may contain as much as 75 percent.

There are three kinds of chocolate bloom: fat bloom, sugar bloom, and age bloom.

Fat bloom happens when under conditions of excessive warmth some of the liquid fat constituents migrate to the surface, where they form relatively large, light-reflecting crystals. Chocolate should never be stored at a temperature higher than 80°F (27°C); 63°F (17°C) is ideal.

Sugar bloom happens when the chocolate is wet or stored in high humidity, which dissolves some of the sugar out of the surface, where it remains as solid crystals when the water evaporates.

Age bloom happens to old chocolate, when the slow-forming fat crystals of form VI (see p. 437) have had a chance to develop. They form big, coarse crystals that disrupt the smooth texture of the chocolate to the extent that it may actually crumble. For example, if you drop a bar of chocolate behind the seat of your car and forget about it, discovering it only two years later when you’re cleaning out the car before selling it, you will notice—oh, I can’t go on! It’s just too horrible to contemplate.