What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (28 page)

Then there are the sugar alcohols (
polyols
), which chemically speaking are not sugars, although they taste sweet. Glycerol (glycerin) is one. Their molecules have the characteristics of both sugars and alcohols. They contribute only about one-half to two-thirds as many calories as sugar, because they are converted only very slowly into glucose and may escape from the southern end of the alimentary canal before being fully metabolized. As a result, they can have a slight laxative effect if consumed in excessive quantities.

Because sugar alcohols don’t cause tooth decay or a sudden increase in blood sugar, they are used mainly in sugar-free candies and chewing gums. You’ll see them listed separately by name in the ingredient lists: sorbitol, xylitol, lactitol, mannitol, or maltitol. (Look for the suffix -
itol
.)

The sweet leaf of a South American shrub called stevia has been used for centuries by South Americans to sweeten their
yerba maté
. But the United States, Canada, and the European Union will not permit it to be added to foods, because although it is surely “natural,” its safety has not been proved. (Ironically, however, it may be sold in “health-food” stores as a nutritional supplement.) While South America clearly hasn’t been depopulated by stevia-sweetened drinks, the health authorities’ reasoning goes that if stevia were permitted as a food additive in the United States and Canada, North Americans, addicted as they are to sweet soft drinks, might consume enormous quantities of it. And the effects of quaffing huge Slurpees and Big Gulps full of stevia have not been investigated.

Another sweetener used to some extent in the Middle Ages, but most enthusiastically by the Romans, was sugar of lead, a sweet-tasting but highly poisonous chemical known to chemists as lead acetate. The Romans used lead-lined cooking vessels to boil down crushed grapes and old wine that had partially soured. Soured (
oxidized
) wine contains acetic acid, and any freshman chemistry student will tell you that acetic acid plus lead metal will make lead acetate. All lead compounds are poisonous, but lead acetate is one of the few that are soluble in water—and wine. Thus, not only could over-the-hill wine be made sweet again, but sugar of lead could be produced for sweetening other beverages and foods. The oldest existing cookbook,
De Re Coquinaria
(On Cooking) by the first-century Roman gourmet Marcus Gavius Apicius, contains scores of recipes that include sugar of lead among the ingredients.

Lead poisoning is cumulative and causes a variety of maladies from gout to sterility and insanity. It was primarily the Roman patricians who could avail themselves of lead-sweetened wines and foods, and as a result they were the prime victims. For no lack of trying (he was quite a man with the ladies), Julius Caesar was able to sire only one (illegitimate) child. His successor, Caesar Augustus, was reportedly completely sterile, whether with spouse or concubine.

Today, good old-fashioned sugar—pure sucrose, whether from sugar cane or sugar beets—plays many roles in foods besides making them sweet. It makes breads, cookies, and other doughs more moist and tender; it stabilizes foams such as beaten egg whites; it acts as a carrier of other flavors, and it caramelizes when heated, making foods brown and giving them that unique sweet-sour-bitter caramel flavor. And it preserves foods—notably, when used in jams and other fruit preserves.

According to W. C. Fields, anyone who hates dogs and children can’t be all bad. Sugar’s not all bad either.

So many health foodies tout honey as the most natural, healthful, and nutritious of all sweeteners, certainly when compared with refined sugar. But I understand that babies must not eat it. Kind of contradictory, wouldn’t you say?

....

I
don’t know what “most natural” means, unless somebody can give me a good reason why sugar cane and sugar beets are somehow less natural than honey. Perhaps because they are not produced by hairy insects?

But chemically, there is quite a difference. Sugar cane and sugar beets are loaded with sucrose, whereas honey’s sugars are primarily fructose (39 percent), glucose, (31 percent), and maltose (7 percent), with only 1.5 percent sucrose. (See Table 4 on p. 206.) In addition, 4 percent of honey consists of other carbohydrates and small amounts of minerals, vitamins, and enzymes. Most of the rest (17 percent) is water, making honey a supersaturated solution of sugars. That is, there is more sugar dissolved in the water than the water should ordinarily hold. That’s why the excess sugar will “undissolve” slowly and fall out as crystals (the honey becomes
granulated
) when stored for long periods of time. It’s mainly the glucose that initiates the crystallization process.

Actually, I love the crunchiness of granulated honey. Storing it between 50 and 70ºF (10 and 21ºC) will hasten crystallization; higher and lower temperatures discourage it. Take your choice.

Among its enzymes, honey contains
invertase
, which converts sucrose to a mixture of glucose and fructose, or
invert sugar
. (See “A nano-course on carbohydrates,” p. 203.)

Another enzyme in honey is
amylase
, which breaks starch down into smaller units. Honey also contains small amounts of all the B vitamins and vitamin C, plus the minerals potassium, calcium, phosphorus, sodium, and traces of others.

The healthful reputation of honey is undoubtedly attributable to these minor constituents plus its content of flavonoid antioxidants. Medical history has credited honey with a variety of therapeutic and antibacterial qualities. Moreover, honey is much more interesting than ordinary sugar because it has an intriguing variety of flavors, depending on which local nectar bars the bees are in the habit of frequenting.

Unfortunately, as an anaerobic (oxygen-free) environment, honey is a good breeding ground for
Clostridium botulinum
, the bacterium that manufactures botulin toxin, a deadly poison. Bees may pick up
C. botulinum
spores while foraging (they are found in soil) and incorporate them into their honey. Human adults, with their fully developed immune systems and intestinal bacteria that destroy such spores, can handle a reasonable number of them, but babies under one year of age can’t and may contract infantile botulism. It’s a rare occurrence, but why take the chance? Feeding honey to your little Honey is just not worth it. And as one source put it, chances are your baby is already sweet enough.

Chapter Six

From Sea to
Shining Sea

....

W
ITH A FEW
minor exceptions, there are only two environments in which life can thrive on our planet: in air and in water. We
Homo sapiens
are one of millions of plant and animal species that thrive in our sea of air, the atmosphere, and there may be a similar or even greater number of still undiscovered species that thrive in the seas of water. And yet, few air-living species can live without water, and few water-living species (that we know of) can live without air, especially its oxygen and carbon dioxide.

But in the context of human food, that’s where the symmetry ends. As an air-living species, we have exploited our environment, first by simply collecting the plants and animals that Nature provided, and later by growing our own preferred plants and breeding our own preferred animals. In the seas, however, we are still in the hunter-gatherer stage, venturing out onto the ocean’s surface to collect what we can find. Only very recently have we begun to raise a few of our preferred species by aquaculture.

Among our preferred aquatic food species are many dozens of vertebrate fish and a variety of invertebrates, including mollusks (clams, oysters, mussels, scallops, squid, octopus) and crustaceans (lobsters, crabs, shrimp, crayfish).

This chapter is, in effect, a fishing expedition, in which we can hook or net and examine only a very small sampling of our favorite finfish, mollusks, and crustaceans.

As a chef with an avid interest in nutrition, I’ve been wondering: In light of all the controversy surrounding the dyes used in the feed of farm-raised salmon to give them their pink hues, has anyone thought about using lycopene, the red phytochemical in tomatoes with alleged antioxidant benefits, instead?

....

I
must duck your question for two reasons: (1) I don’t know the answer, and (2) you’re not going to drag me into the raging battle among salmon farmers, wild-salmon fishermen, and environmentalists. However, to muddle a few metaphors, I will walk a tightrope through the minefield and drop what pearls I can.

From decades-long experience, we consumers have expected our salmon to be a nice, orange-pink color. The muscle tissue of wild salmon ranges from deep red in the sockeye to pale pink in Chinook or king salmon. The colors come from the fish’s diet of tiny shrimplike crustaceans called krill that contain a pink carotenoid compound called
astaxanthin
. Wild (not lawn-dwelling) flamingoes are pink for the same reason.

Carotenoids are the chemical pigments largely responsible for the variety of beautiful colors in nature, both in plants and, via feeding, in many animals as well. There are over six hundred known carotenoids in flowers, fruits, vegetables, and birds.

Salmon raised in aquaculture pens do not have much access to the carotenoid pigments in krill, and are fed an artificial diet containing an added colorant: either astaxanthin itself or another FDA-approved carotenoid, canthaxanthin. (The latter, oddly enough, is also sold as a human skin-tanning drug.) Astaxanthin produces a somewhat redder hue (in salmon) than canthaxanthin, and salmon farmers can actually choose the shade they want in their fish by selecting their feed mixture from a color wheel.

On April 23, 2003, a Seattle law firm filed three class-action suits against the supermarket chains Kroger, Safeway, and Albertson’s, claiming that all consumers who purchased farm-raised salmon over the preceding four years—not to mention the lawyers themselves—should be showered with literally millions of dollars because the stores failed to disclose the shocking fact that their salmon had been artificially colored. The families of those consumers who, we must presume, died of humiliation upon learning that they had eaten colored salmon certainly deserve to be compensated most generously, don’t you think? Fortunately, the court didn’t think so, and the suit was thrown out.

(Insert your favorite lawyer joke here.)

Less frivolous concerns about salmon farming are based upon such issues as whether the wild salmon population is endangered; whether fugitive farm fish will interbreed with wild stock, to the detriment of genetic diversity; whether crowded, net-caged salmon pollute their environment with parasites and disease; and whether their pens are contaminated with PCB’s (
polychlorinated biphenyls
), any of about two hundred probably carcinogenic synthetic industrial chemicals that have not been manufactured since 1997 but that still show up in the environment.

And by the way, your suggestion of feeding salmon lycopene instead of astaxanthin is probably impractical unless we could get salmon to eat tomatoes, in which lycopene is the predominant pigment. Might be worth a try.

I love sushi, especially the yellowfin
nigiri
. The raw tuna sometimes has different colors, however, ranging from pink to dark red. I never thought much about it, but I just saw a story in the newspaper saying that raw tuna is being treated with carbon monoxide to give it a bright red color, even if it isn’t fresh. Isn’t carbon monoxide lethal?

....

Y
es it is, under the right—that is, the wrong—circumstances. But not in the case of monoxide-treated tuna.

First, for the uninitiated, yellowfin tuna, which may be listed on the menu as
maguro
, the generic Japanese word for tuna, is not to be confused with yellowtail, a kind of amberjack, or with
toro
, the prized fatty belly of the bluefin tuna.
Nigiri
sushi is a filet of the raw fish on a pillow of vinegared rice.

Every year in the United States, several thousand people are treated in hospital emergency rooms for carbon monoxide poisoning. Some two hundred per year die from carbon monoxide given off by improperly vented gas-burning appliances such as furnaces, ranges, water heaters, and room heaters, while many others are killed by automobile engines running in enclosed spaces.

Carbon monoxide gas is particularly toxic because it goes from the lungs into the bloodstream, where it replaces the oxygen in the blood’s oxyhemoglobin, destroying its ability to deliver oxygen to the body’s cells. And the organs most likely to crash from oxygen starvation are the heart and brain.

All devices that burn carbon-based fuels, including gasoline-burning automobiles, gas-burning furnaces, kerosene-burning heaters, and even charcoal-burning hibachis, emit carbon monoxide because their fuels don’t burn completely; the combustion process is inevitably inefficient. Instead of burning all the way to carbon dioxide, CO
2
(two oxygen atoms for every carbon atom),
some of the carbon atoms in the fuel can’t find that second oxygen atom and end up as carbon monoxide, CO. That’s why these devices should never be operated in an enclosed space: the inevitable CO can build up to a lethal concentration.

Eating raw tuna that has been exposed to carbon monoxide gas is another matter entirely. In this case you’re not breathing the gas, and for that matter you’re not even eating it. Gases, of course, are ephemeral, and the carbon monoxide doesn’t hang around on the fish after it has done its job of brightening its color. The FDA has declared carbon-monoxide-treated tuna to be GRAS—generally regarded as safe—because residual carbon monoxide on the fish is virtually absent.

But why should a food processor do such an outlandish thing as exposing fish to a poisonous gas? Well, follow the money. The red color of freshly cut tuna can change within a few days to an unappetizing brown. Consumers don’t like brown fish and are willing to pay more for “fresher-looking” red. Hence, the cosmetic application of carbon monoxide “rouge.”

Tuna flesh, like the flesh of many land animals, contains myoglobin, a pigmented protein that stores oxygen in the muscle tissue. Myoglobin changes color, however, depending among other things on how much oxygen is available to it. The dark, purplish-red color of freshly cut tuna is due to
deoxymyoglobin
, which in air changes first to bright red
oxymyoglobin
and then to brown
metmyoglobin
. Tuna purveyors must therefore rush their tuna from the boat to the sushi bar while it is still in the red
oxymyoglobin
stage.

Carbon monoxide thwarts these color changes by replacing the oxygen in the
oxymyoglobin
molecules (as it does in our blood’s oxyhemoglobin molecules), converting them into a very stable complex: the watermelon-red
carboxymyoglobin
. The
oxymyoglobin
is thus derailed from being oxidized to brown
metmyoglobin
.

Tuna cosmetologists can of course buy their carbon monoxide gas in steel tanks, like many other gases. But there’s a cheaper way to get it: by burning wood. Because of the incomplete combustion process described above, wood smoke contains carbon monoxide. The tiny particles that make smoke smoky can be filtered out along with the tarry chemicals that give smoke its flavor, leaving a mixture of gases—carbon dioxide, carbon monoxide, nitrogen, oxygen, and methane—called filtered smoke or tasteless smoke. It can be used instead of pure carbon monoxide to brighten the fish’s color. The justification is made that tasteless smoke can be no more harmful than “whole smoke,” traditionally used to make smoked fish and other meats. According to the FDA, however, foods treated with filtered smoke may not be labeled “smoked,” because the expected smoked flavor isn’t there.

The irony in all this is that the color of untreated tuna is
not
an indicator of its wholesomeness. Myoglobin’s color changes take place long before the fish has begun to deteriorate. The association of bright color with freshness is all in the consumer’s mind.

So is there anything wrong with carbon-monoxide-treated tuna? Not because of any presumed health hazard. But there will always be a few rascals who try to conceal over-the-hill fish by touching up its color, and that is an actionable offense according to the FDA. Moreover, research by the Food Science and Human Nutrition Department of the University of Florida has shown that dangerous time-induced spoilage can continue in monoxide-treated fish even though the color remains bright, perhaps luring unsuspecting diners to disaster like a gussied-up siren.

Because of the possibility of abuse by tuna suppliers, several countries prohibit carbon-monoxide-treated fish. Sushi-conscious Japan has outlawed it since 1997, while the European Union has begun to enforce its ban only since early 2004.

Your best resource as a consumer is, as usual, your confidence in your source. You shouldn’t eat raw fish in any but the most trustworthy sushi establishments anyway, for reasons unrelated to carbon monoxide. If a given restaurant would never sell contaminated or spoiled fish under other circumstances, it would certainly never sell contaminated or spoiled fish that has been cosmetically enhanced. Fresh tuna has a clean flavor, relatively firm texture, and of course, no odor, no matter what its color. So if in doubt, just shut your eyes and let your mouth and nose be your guides.

And remember that yellowfin tuna varies in color from pink in smaller fish to deeper red in larger fish, so once again the color itself is no indication of freshness.

If your fish is a bright, unnatural-looking watermelon red, it has probably been treated with carbon monoxide or filtered smoke. But there is no known health hazard if the fish itself is fresh and clean.

All my life, I’ve heard rumors that some scallops sold in fish markets aren’t scallops at all, but have been punched out of skate wings or other kinds of fish. Any truth to that?

....

I
can’t say that it’s never been done, but I doubt that it has been done very often. And surely few of us would continue to patronize a fishmonger or restaurateur who had been found to try such a trick. At one time, skate was a low-priced fish caught accidentally (in the “by-catch”) by fishermen in pursuit of more lucrative quarry. But no more. Skate isn’t as cheap as it used to be, and the crime wouldn’t pay as well as it used to.

An even better reason to doubt this urban legend is the fact that running through the middle of a skate wing is a thin sheet of plastic-like cartilage. A “scallop” with a layer of plastic in the middle wouldn’t be very convincing. It’s true that if the skate is big enough (the common skate can run up to 200 pounds), it can be filleted into two slabs, one above and one below the sheet of cartilage, and convincingly thick “scallops” could be punched out of each. But there are easier ways to make a dishonest buck.