THAT’S THE WAY THE COOKIE CRUMBLES (6 page)

I sprinkled a little lysine into the gently boiling corn syrup. Within minutes, the kitchen was filled with the aroma of freshly toasted bread. Then I added a little of this brew to a cup of hot water and tasted it. Sure enough, it tasted like toast. Actually, it tasted almost exactly like another potion I sometimes prepared by soaking toasted bread in water. By now you’re probably thinking that I must lead a pretty dull life if I have to resort to investigating the properties of toast water, but such is not the case. When the public demands answers to important questions — such as whether white or whole wheat bread toasts more quickly — a responsible scientist must set other work aside and carry out the pertinent experiments.

I was certainly not the first to study the chemistry of toast. That honor goes to Louis-Camille Maillard, who actually had a more ambitious project in mind: he wanted to unravel the secret of life. In 1912, Maillard developed an interest in how amino acids combined to form proteins in the body. He tried heating mixtures of amino acids, but without much luck. Then he decided to mix in some other chemicals that could reasonably be found in cells, such as fats and sugars, to see if these would somehow enhance the reaction. As soon as he added glucose, the most common sugar found in the body, the solution turned brown. This was due to a mixture of compounds, many of which contained nitrogen furnished by the amino acids. Since amino acids and sugars are present in the body, Maillard suggested that this reaction could have consequences for human health. But the greatest practical importance of his discovery, he thought, would pertain to the gingerbread and beer industries, because he was now convinced that the colors of these products were due to the “Maillard reaction.”

As it turned out, not only did the high-temperature reaction between amino acids and sugars cause the gingerbread and beer to turn brown, but it also explained the brown hues of baked bread, coffee, soy sauce, and roasted meats. Even more important, the products of the Maillard reaction produced flavors; in fact, they produced a large variety of flavors because food contains a diversity of amino acids and sugars. By the middle of the 1900s, chemists at General Foods had investigated the Maillard reaction in such detail that they were able to produce specific flavors by manipulating the appropriate sugars and amino acids. When they added serine to hot glucose, they created the smell and taste of maple syrup. Cysteine produced the characteristic taste of roasted meat. Indeed, the secret to making a tasty stew is to brown floured meat (the flour is a sugar source) in hot oil before diluting the mixture with liquid. The Maillard reaction requires a temperature higher than the boiling point of water — if water is present, then the temperature cannot rise above its boiling point.

Artificial flavors had great commercial appeal, so chemists remained busy investigating numerous combinations of amino acids and sugars. One of these combinations, lysine and glucose, emitted the characteristic smell and flavor of toast — the very reaction I reproduced in my kitchen. The more lysine I added, the more the house smelled of toast. Now I was ready to tackle the problem I had set myself. My prediction was that whole wheat bread, which contains more lysine, a common amino acid in wheat gluten, would toast more quickly. Alas, how often do we see a beautiful theory ruined by one simple experiment! I observed no significant difference in the toasting rates. I perused the labels of the two breads. The white bread did indeed contain less protein, but it had ten percent more sugar. And there was another factor I hadn’t considered: moisture content. If the whole wheat bread had a higher water content, its browning rate would be reduced. So I placed both breads in a vacuum chamber (this time in a real laboratory) and pumped out the water. The whole wheat bread did contain somewhat more than the white. Apparently, these factors conspired to prevent my whole wheat bread from demonstrating its championship toasting potential. I think that the extra sugar in the white bread compensated for its lower protein content.

Sugar not only contributes to the Maillard reaction, but it also caramelizes, thereby deepening the brown color. I confirmed this by toasting raisin bread — not just any raisin bread, but one made with “soluble raisin syrup,” which boosted the loaf’s sugar content to about six times that of white bread. I had hardly popped a slice into the toaster before the smoke alarm started blaring away. Raisin bread was clearly the toasting champ.

By now I’d had my fill of toast, but I was stuck with a pile of leftover experimental products. Wondering how to dispose of the stuff, I remembered reading that in the 1700s the English would steep toasted bread in water to make a “restorative” beverage. It cured all kinds of ailments. Or so they claimed. (Today we tend to worry about consuming too many burned foods, because they contain carcinogens.) I felt that after eating all that toast, a restorative was in order. Gathering up my remaining toast pieces, I tossed them into a glass of wine — just like they did in Shakespearean days to improve the wine’s flavor; they would then raise their glasses and offer a “toast” to celebrate important moments. I can tell you that it tasted a lot better than either the natural toast water or my synthetic analogue. Its restorative properties remain to be tested, but maybe one day we’ll be drinking a toast to toast wine.

If you have a headache, just take a banana and split it. Then tape half the peel to your forehead and the other half to the back of your neck. I learned about this high-tech therapy from none other than Ann Landers. One of the advice columnist’s correspondents suggested that it was a practically foolproof method of getting rid of headaches. Doesn’t sound foolproof to me. In fact, I think that a person who walked around with banana peel duct-taped to his head would look like a fool. But apparently that doesn’t deter people who are convinced that the therapy works. And such people do exist. I know. I’ve spoken to one. A desperate one.

A lady who often resorted to the banana headache therapy called me one day in a panic. She had received an e-mail about the risk to Americans posed by Costa Rican bananas. These fruits, the letter asserted, harbored the strep A bacterium, which is responsible for necrotizing fasciitis, better known as flesh-eating disease. All are advised, the writer said, to stay away from bananas, unless they want to end up as a heap of festering flesh. Needless to say, this is total nonsense. Flesh-eating disease is not transmitted through food. This is not the only myth I’ve heard spun about the safety of bananas. A gentleman once informed me that bananas that had turned black were poisonous. Another insisted to me that this wasn’t so, but that green bananas made you sick. Actually, the only thing these colors do is provide us with some interesting chemistry.

The banana, believe it or not, is the most popular fruit in North America. And it isn’t even a fruit; botanically speaking, it’s a herb. But never mind. Fruit or herb, bananas are picked green, because if they weren’t they would never make their way into our mouths, or onto our foreheads. They would be overripe. The green color is chlorophyll, the plant pigment that is the key to photosynthesis. As a banana ripens, its need for photosynthesis decreases, and the membranes around the chloroplasts, the cells that produce chlorophyll, begin to break down. This allows the enzymes that metabolize chlorophyll to enter, and the green color gives way to the yellow of various anthocyanins. This cascade of events is triggered by the release of the plant hormone ethylene, a process that banana producers mimick by ripening their green produce with ethylene gas after transport. Indeed, you can make use of this bit of chemistry at home. Place green bananas in a bag with a yellow one, and the green will quickly turn yellow.

As a banana ripens, it goes through other changes as well. Its starch converts to sugar. A ripe banana has the equivalent of about five teaspoons of sugar, almost double that of a chocolate bar. To most people, a brown or black banana peel and the bruised fruit inside it are decidedly unappetizing. If a banana is bruised, it will quickly turn brown, but all the poor fruit is trying to do is protect itself. As far as the banana is concerned, a bruise is an attack on its integrity. It cannot tell the difference between an attack by fungi, insects, or humans — who may attempt to duct-tape its peel to their heads.

Any sort of injury causes chemicals called polyphenols to leak out of cells and come into contact with an enzyme known as polyphenoloxidase, or phenolase. The polyphenols are converted to quinones, which apparently have antifungal and insecticidal properties. Quinones can also react with each other to form giant molecules, or polymers, which are brown. This, in fact, is similar to the chemistry that occurs in our skin upon exposure to the sun. Damage to bananas can also result from cold temperatures — like those found in refrigerators or freezers. So much phenolic polymer forms that the banana skin turns black. It may look terrible, but it’s still perfectly safe to eat.

In the early 1980s, quite a stir was created at McGill University by researchers examining the claims made by a healer named George Ille. The man had said that he could demonstrate his power by waving his hands over bananas and causing their color to change. He even had photographs to prove that the bananas subjected to his hovering hands ripened more quickly than a bunch of controls. I don’t know how good a healer Ille was, but he could have made a fortune in the fruit business.

We should eat plenty of bananas, discolored or not. They are a great source of potassium, which can lower blood pressure. One study has even indicated that low levels of potassium in the blood may correlate with the risk of stroke. Bananas are effective against diarrhea as well. They absorb bile acids, which are linked with loose stools. You can even make use of the peel of a banana after you’ve finished eating the fruit. The peel contains amyl acetate, a good solvent. I’ve used banana peel to clean my shoes.

There’s another interesting aspect to the banana peel. Surprisingly, perhaps, some of the polyphenols that are ultimately responsible for its dark discoloration have some effect upon the central nervous system. Serotonin, dopamine, and norepinephrine are all recognized neurotransmitters in the human nervous system. Banana peels do not contain much of these substances, but their presence perhaps explains why hippies in the 1960s tried to smoke banana peels to get high. But all those adventurous hippies got was indigestion. And maybe a headache.

So, we are back to that. Can there possibly be anything to the idea of treating headaches with banana peel? A chemistry teacher actually responded to the question in Ann Landers’s column, suggesting that potassium absorbed through the skin could cure headaches if these were caused by hypertension. Makes about as much sense as the Costa Rican flesh-eating bananas. But I wouldn’t rule out the possibility that tying anything to the head will help. Maybe binding the head collapses painfully distended blood vessels in the scalp, relieving a vascular headache. Put that in your pipe and smoke it.

What would summer be like without sizzling steaks, charcoal-broiled hamburgers, or grilled hot dogs? Well, for one thing, it would probably be a little healthier. Let’s find out why. The word
barbecue
derives from the ancient Caribbean tradition of cooking food over a fire on a scaffold made from green wood, a device that the Spanish named ��barbacoa.” They referred to the technique itself as “boucan.” Shipwrecked sailors and runaway servants who found themselves on Caribbean islands picked up the method, and these people came to be called “boucaniers” — or, in English, “buccaneers.” Many of us still turn into summertime buccaneers, brandishing our long forks and spatulas as we grill, roast, broil, and, of course, burn food to our stomach’s content. But are we being a little too cavalier with our health?

As the saying goes, if you play with fire, occasionally you’ll get burned. Especially if you try to rekindle smoldering charcoal with a squirt of lighter fluid. The fluid stream can catch fire and ignite the whole container, as well as its startled holder. There’s more. Lighter fluid’s volatile hydrocarbons can escape into the air, with about half the fluid evaporating before you ever strike a match. These vapors are unhealthy, and they contribute to smog formation. Self-igniting charcoal is not a useful alternative; it comes saturated with flammable hydrocarbons. The pollution effect is not trivial. During an average day in southern California, barbecues emit three to four tons of hydrocarbons, nitrogen oxides, and carbon monoxide — about the same daily emission rate as a petroleum refinery.

The best way to light a charcoal fire is with an electric starter or a newspaper tinder chimney. Real charcoal, made by heating wood in the absence of oxygen, is easier to light than briquets; it burns hotter, produces fewer noxious vapors, and leaves less residue. Briquets are made from crushed, charred wood scraps to which fillers such as starch or coal have been added. When we use these, we should only begin to cook after a uniform covering of gray ash has formed, indicating that the fillers have all burned away.

Gas barbecues burn much cleaner and hotter than charcoal ones. As long as it receives sufficient oxygen, propane will convert primarily to carbon dioxide and water vapor. The gas flame should be mostly blue, with some yellow at the tip. Too much yellow in the flame means that there is incomplete combustion. The yellow color is caused by the glowing pieces of soot that form when a partially blocked gas pipe prevents proper mixing of the propane with oxygen. Soot is an intricate network of carbon atoms with a very large absorbent surface area. It can absorb some of the unhealthy components of incomplete combustion and deposit them on the food. We must therefore thoroughly clean the cobwebs and soot from gas pipes at the beginning of each barbecuing season.

No matter what precautions we take, burning wood, coal, or meat will always produce some carcinogens. One of these compounds, benzopyrene — a polyaromatic hydrocarbon, or PAH — is so carcinogenic that researchers routinely employ it to induce cancer in the animals they use to evaluate new cancer treatments. There are several factors governing the amount of PAHs produced during barbecuing. These are the temperature at which we cook the food, the fuel we use, and the fat content of the food. Basically, the higher the temperature, the more carcinogens form.

Some outdoor chefs favor mesquite wood, because it imparts a unique flavor to the food. It does, however, exact a price. The major component of mesquite is lignin, which burns much hotter than the cellulose that makes up the bulk of most other woods. As a consequence, the smoke produced by mesquite contains more than twice as many polyaromatics as other wood smokes.

How can we minimize our exposure to these nasty polyaromatics? By precooking our meat in a microwave oven, we can minimize the time required on the grill. Barbecuing only low-fat foods, such as skinless chicken or fish, also helps. Barbecue sauce, due to its high sugar content, burns very easily, and we should therefore apply it to the food only near the end of the cooking process. The farther we position the food from the fire, the less likely it is to be contaminated with carcinogens. If we place the food too close to the fire, the outside will char quickly, but the inside will remain cool. The scientific explanation for this is that the outside cooks by heat radiation, and the inside cooks by conduction of heat via water. So our aim should be to place the food far enough from the heat source to permit the browning rate to match the conduction rate.

In most gas barbecues, the grill is at a fixed distance from the flame and cannot be adjusted. Lowering the flame, however, accomplishes the same effect as moving the food farther away. Skewering the meat on a metal rod — as we would do with a shish kebab — can also speed up the internal cooking. This is because the metal readily conducts heat into the food. Many backyard cooks barbecue with the lid down, as they’ve noticed that this makes the food more flavorful. Unfortunately, this is because the lid-down method involves more flaring up and more smoke, neither of which is desirable in terms of health. Finally, it is important that we clean the grill after each use to eliminate deposits of those nasty compounds. Oven cleaner works well — but let’s face it, working with concentrated sodium hydroxide is not a particularly attractive prospect.

Given all of these concerns, why shouldn’t we just forget the whole business? Because barbecued food tastes good. Specifically, it tastes good because high temperatures and smoke combine to produce very flavorful compounds. And, unfortunately, carcinogens. So does all of this mean that science is raining on our barbecues? No, but there may be a few sprinkles. The greatest risk involved is probably the fact that when we barbecue, we tend to eat too much fatty food. But the occasional barbecue — featuring low-fat foods grilled high above a source of low heat on a clean grill — is one of life’s acceptable little pleasures. Just make sure that you don’t put cooked food onto a plate that has held raw meat. This can result in food poisoning severe enough to make the most ardent backyard barbecuer leap for broccoli. Actually, eating broccoli along with barbecued food is a great idea. It contains sulphoraphane, one of the most potent anticarcinogens we’ve discovered so far. I wouldn’t barbecue it, though.