What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (13 page)
Read What Einstein Kept Under His Hat: Secrets of Science in the Kitchen Online
Authors: Robert L. Wolke
When you cook an egg, heat expands the air in the pocket and its pressure increases. As long as the white is still liquid, it can’t flow into that air space because of the pressure. As the white cooks, it solidifies around the shape of the air pocket. Hence the dimple.
And by the way, those ropes of thick albumen that extend from the yolk to the membranes at both ends of the egg (see p. 86) and that hang on to the yolk when you’re separating an egg are not the beginnings of an embryo. They’re called
chalazae
(kuh-LAYZ-eye), a word inexplicably derived from the Greek meaning “hail.” They serve to keep the yolk centered in the white. Chalazae are more prominent in very fresh eggs. There’s no need to remove them, except perhaps if you are making a soufflé or a custard and want it to be as lump-free as possible.
Some hard-boiled advice
The American Egg Board recommends the following method for making hard-cooked eggs: “Place eggs in single layer in saucepan. Add enough tap water to come at least 1 inch above eggs. Cover. Quickly bring just to boiling. Turn off heat. If necessary, remove pan from burner to prevent further boiling. Let eggs stand, covered, in the hot water about 15 minutes for Large eggs (12 minutes for Medium, 18 for Extra Large).”
But take it with a grain of salt. As the nation’s self-proclaimed eggsperts, the AEB must disseminate instructions that will work for the
average
cook. But one can drown in water that
averages
only six inches in depth.
Eggs may vary not only in size and freshness but also in their temperatures when placed in the saucepan, so they may not all reach boiling temperature as soon as the water boils. Also, different stoves and different pans will require different amounts of time to boil the water. And after the burner is turned off a heavy, porcelain-lined iron saucepan will keep its water hot longer and at a higher temperature than a thin aluminum one.
For these reasons, Marlene has not found the AEB’s recommendations to be reliable. So what does she advise? Follow the AEB’s instructions up until the water boils. But don’t turn off the heat; turn it down to a bare simmer and begin your timing. Using the AEB values as a guide, base your timing on your own experience with your own stove and saucepan, your own usual-sized eggs, your own refrigerator, and the degree of hardness you prefer in your yolks.
It’s worth sacrificing a few eggs to the gods of experimentation to find your “personal best.” Jot down your chosen simmering time on a piece of paper and tape it to the inside of a kitchen cabinet door.
And may your eggs be forever perfect—for you.
| | THE QUEST FOR DIVINITY | |
Are pasteurized egg whites okay to use for making Divinity? I tried them once, but not being a great baker did not get a good result. I ended up with little patches of sticky goo. I was wondering if the pasteurization changed the egg whites enough to make Divinity impossible.
....
I
t may be difficult for any mortal to achieve divinity, but with patience you can do it.
Pasteurized-in-the-shell eggs are intended to eliminate the hazards of the food-poisoning bacteria
Salmonella enteritidis
and other salmonella species that can be found in poultry, meat and meat products, raw milk, and the yolks (usually not the whites) of raw eggs, among other places. Temperatures of 160°F (71°C) or above will kill the bacteria, but using raw egg yolks in such preparations as mayonnaise and Caesar salad can be risky.
If you had been able to get past the egg-white whipping stage, your Divinity would have been safe even with unpasteurized eggs, because for one thing you’re using only the whites, and for another you’re cooking them. The sticky goo was egg white that wasn’t beaten enough, and that’s the trouble with pasteurized eggs: the whites don’t whip as well because the mild heating during the pasteurizing process partially denatures*
†
or “cooks” the protein.
Eggs are pasteurized in the shell by being heated in warm water. A combination of time and water temperature heats them just enough to kill any salmonella without cooking the eggs. Nevertheless, pasteurized eggs will have a slightly thickened yolk and a slightly opaque white. They will cook in the same way as un-pasteurized eggs, but the whites won’t whip as well because the proteins have been slightly denatured or reconfigured and won’t form a good, stable foam as easily. While regular egg whites usually whip to the stiff peak stage in 1 to 3 minutes, pasteurized egg whites may take as long as 10 minutes.
So with one additional ingredient—more elbow grease—your Divinity will be truly divine. (Elbow grease adds no calories. In fact, it
uses up
calories.)
| | A SLIGHT EGGSAGGERATION | |
I always thought that thousand-year-old eggs were a myth until I saw some for sale in a Chinese market. How did people in the eleventh century know we’d want them in the twenty-first? And where have they been kept all that time?
....
O
kay, you’re putting me on.
Touché
!
Thousand-year-old eggs, called
pidans
in Chinese, are a tongue-in-cheek eggsaggeration. Less lyrical Chinese may call them hundred-year-old eggs. Truth be told, however, they’re only about a hundred
days
old, which may strike you as bad enough.
Here’s how they’re made.
Take a fresh duck egg in the shell, plaster it all over with a thick coating of a paste made of salt, lime (from a garden-supply store), pine ashes from your fireplace (or charcoal-grill ashes, if that’s all you have), and strong brewed black tea, all thatched together with rice straw or even grass clippings. Now bury the thing in your garden for about three months. Dig it up, wash it off, remove the shell, and enjoy it with soy sauce and chopped ginger as an appetizer—despite the fact that it looks like a de-appetizer, with its dark green yolk and its blackish-amber “white.”
I know whereof I speak. Several years ago, when I was sailing around the world on a Taiwanese ship, I was invited to the captain’s quarters for dinner. He had his own private chef, who prepared a dazzling variety of unusual (to me) Chinese delicacies, including shark’s-fin soup, sea cucumber (also known as sea slug), pigs’ stomach linings and ovaries, and one of those eggs of uncertain age. It had a pungent, cheeselike flavor, the creamy texture of an avocado, a greenish-black yolk and a mottled blue, black, and amber-colored “white.” It wasn’t half bad, although I don’t think I’d want one every day for breakfast.
Note that I have written this entire section with only one pun on the word
egg
, even though you may have eggspected me to take an eggstraordinarily eggcessive eggscursion into the realm of eggsotic and eggstremely eggsaggerated puns until you were completely eggsasperated and eggshausted.
But I hope you can take a yolk.
Sidebar Science:
Improving (?) with age
THE CHANGES
that take place in a “thousand-year-old egg” are caused primarily by the lime and the wood ashes, which are both rather strongly alkaline. (Lime is calcium oxide, CaO, and wood ashes contain potassium carbonate, K
2
CO
3
.) Over time, these alkaline substances infuse the tea, which seeps through the shell and acts on the proteins in the egg white, reconfiguring their molecules similarly to what cooking them would do. In the meantime, some of the normal chemical changes that take place in a, shall we say, “mature” egg yolk are also taking place, producing chemical products such as aldehydes and ketones, which are responsible for the sharpest of the flavors.
Chapter Three
Whatsoever a
Man Soweth . . .
....
. . .
that shall he also reap.
Not to wax excessively biblical, but permit me to begin this chapter with a modernized version of Genesis.
In the beginning, there was one helluva Big Bang.
Exactly nine billion years later (I think it was on a Tuesday), God created the Earth. And the Earth was without form, and void.
And God said, Let the waters under the heaven be gathered together unto one place, and let the dry land appear; and it was so. And God called the dry land Earth.
But the dry land was not what we call dry land today. It was not soil. It was molten rock (magma), which after a couple of billion years more cooled and became solid rock. And not that there was anybody around to complain, but you can’t grow crops in rock.
So when did soil appear on the surface of our planet, so that our ancestors could begin to sow, reap, and eat plants?
As the eons of seasons came and went, the rocks weathered and broke down from both physical and chemical causes. Physically, the rocks expanded in warm seasons and contracted in cold, causing cracks and fissures. Water that seeped into the cracks froze during the ensuing cold seasons and rended the rocks asunder by the powerful pressure of expansion when it froze. Moving glaciers scraped away at the surface rock, making rock dust, while the wind and running water contributed to the physical degradation of rocks into smaller and smaller fragments, from boulders to very fine grains.
Meanwhile, chemical reactions with groundwater and atmospheric carbon dioxide transformed the original rock minerals into new minerals, softer rocks, and soluble compounds that were transported by rivers and streams to other locations.
Eventually, God’s “dry land” became small particles of mixed gravel, sand, silt, and clay, distributed wherever they could lodge over the face of the Earth. They were now soil.
When plants began to grow and die in this mineral-rich bedding, their decaying organic matter enriched the soil, making it even more fertile for humans to cultivate. And so was agriculture made possible in the most recent two-millionths of our planet’s history.
The variety of foods we now raise in Earth’s soil is limited only by climate and opportunity. In the preceding chapter we sampled the products of one kind of farm: the dairy farm. In subsequent chapters we focus individually on fruits and grains, which hold special places in the pantheon of human sustenance. But for now, we’ll browse through the green fields, stopping here and there to examine a few of the hundreds of miscellaneous plant foods that we throw into the catchall category of “vegetables.”
| | A PALETTE FOR THE PALATE | |
Every time I pass the produce department of my supermarket I’m impressed by the number of vivid colors, especially greens, reds, oranges, and yellows, among the fruits and vegetables. If it’s not too complex, what are all the chemicals that make these colors, and what is their purpose?
....
T
he kaleidoscope of brightly colored fruits and vegetables—the red tomatoes, watermelons, strawberries, and beets; the orange carrots, sweet potatoes, pumpkins, apricots, and mangoes; the yellow lemons and squashes; the bluish-purple grapes, plums, and cabbages; and all the green beans and leafy vegetables—are due to a variety of phytochemicals that can be classified into three main groups, chlorophylls, carotenoids, and flavonoids, the last of which includes anthocyanins and anthoxanthins.
A
phytochemical
, from the Greek
phyton
, meaning “plant,” is any chemical compound produced by plants. But lately the term has been appropriated by health-foodists to mean any plant chemical—beyond the nutritious proteins, carbohydrates, fats, minerals, and vitamins—that may be deemed “good for you.” That includes many of the red, orange, yellow, green, and blue pigments in fruits and vegetables, which do indeed have known health benefits. But nicotine and cocaine are also phytochemicals, are they not?
Chlorophyll
needs no introduction. It is a green compound, each of whose molecules contains a magnesium atom. But chlorophyll has taught us that it’s not easy
staying
green. When chlorophyll molecules are reconfigured (
denatured
) by heat, their magnesium atoms are released, converting the chlorophyll into pheophytin and pyropheophytin, the dishearteningly olive-drab colors of overcooked green vegetables. (See p. 111.)
Carotenoids
range in color from yellow to orange and red. Orange beta carotene is converted into vitamin A in the body. Carotenoids beautify everything from carrots to corn, peaches, citrus fruits, squash, paprika, saffron, tomatoes, watermelons, and pink grapefruit. The last three, especially tomatoes, contain the fat-soluble carotenoid lycopene, an antioxidant that has been touted as a possible preventive of prostate cancer.
Anthocyanins
are water-soluble pigments found in grapes, berries, plums, eggplant, cabbage, cherries, and autumn leaves. Purple or blue in alkaline environments, they turn red in acidic media.
With not too many exceptions, you can think of the carotenoids as the yellow, orange, and bright red colors in vegetables and the anthocyanins as the blue, purple, and dark red colors.
Among the less common food colors are
betalains
, the intensely red, water-soluble pigments in beets. When beets are sliced before cooking, much of their color dissolves out into the water. But when unpeeled and cooked whole, they remain as defiantly red as Fidel Castro.
And what is Nature’s purpose in painting all these vegetables such pretty colors? It’s not just for still-life painters. The bright colors attract animals, who eat the plants, to their mutual benefit. The animals benefit from the healthful antioxidant properties that Nature has built into many of the colored chemical compounds, while the plants benefit by the animals’ pollinating their flowers and spreading their seeds.
THE FOODIE’S FICTIONARY:
Harvard beets—part of an unlikely sports headline
Sidebar Science:
Tomatoes are red, violets are blue
THE CHARACTERISTIC
red color of tomatoes, often attributed to lycopene, actually results from a combination of carotenoid pigments, of which lycopene is only the most abundant. The color of the fruit doesn’t always correlate with the amount of carotenoids, much less with the amount of lycopene. So one can’t draw valid conclusions about lycopene content from the redness of a tomato. Nevertheless, all tomatoes are pretty good sources of lycopene.
(To justify my heading, I am obliged to explain that the blue color of violets and the red color of roses are both due to an anthocyanin that is an acid-base indicator [see “A litmus quest,” p. 14]. It is red in the slightly acidic rose petals and blue in the slightly alkaline violet petals.)
| | WHEN GREEN GROWS GRIM | |
Why do my green vegetables turn a drab color when I cook them?
....
T
he green color in plants and algae is a miraculous molecule called chlorophyll that can absorb the energy of sunlight and use it to convert carbon dioxide and water into glucose and oxygen gas. The plants then either use the glucose directly for their own growth energy or polymerize it (connect thousands of glucose molecules together) to form starches, which they store for future use. And because animals derive their vitality from eating those sugar and starch carbohydrates in plants, the chlorophyll molecule can be thought of as the source of most life on Earth.
But chlorophyll is a fickle friend to humans, the only species that cooks its plant foods to tenderize them. For when we do, the green color can become a dreary, unappetizing khaki. What happens is that the chlorophyll turns into chemicals called pheophytins.
A chlorophyll molecule consists of a conglomeration of carbon, hydrogen, oxygen, and nitrogen atoms called a
porphyrin
(POR-fer-in), with a magnesium atom buried in the center. But chlorophyll isn’t a single chemical compound. There are two main types, which chemists, always eager to demonstrate their literacy, have named
chlorophyll a
and
chlorophyll b
. Chlorophyll a is blue-green, while chlorophyll b is a yellowish-green. Different ratios of
a
’s to
b
’s (most often two or three
a
’s to each
b
) determine the exact hues of various green plants.
When we cook our green beans, peas, Brussels sprouts, broccoli, or spinach, the heat first changes the shapes of the chlorophyll molecules (they
isomerize
), and if the vegetable is slightly acidic, as most vegetables are, the magnesium atoms may be ousted and replaced by a couple of the acid’s many hydrogen atoms. This transforms the chlorophylls into chemicals called
pheophytins
. Chlorophyll a turns into a grayish-green pheophytin and chlorophyll b turns into an olive-green one. Because chlorophyll a is usually more prevalent and undergoes this change more rapidly than chlorophyll b, the grayish-green color is what we get.
The fact that acids initiate the chlorophyll-conversion reactions has on occasion tempted people to add a pinch of baking soda (sodium bicarbonate) to the cooking water to make it alkaline. But alkalinity attacks the complex carbohydrates that cement the vegetables’ cells together, so one is merely trading ugliness for mushiness—with the dubious bonus of a soapy flavor from the bicarbonate.
Another chemical oddity in cooking green vegetables is that sodium, magnesium, and calcium salts inhibit the chlorophyll-conversion reactions, presumably by making it more difficult for the hydrogen atoms to get through the cell membranes and oust the magnesium atoms. Thus, salted cooking water (containing sodium chloride) and hard water (containing magnesium and calcium salts) help to retain the green color.
The practical message in all this is that the quicker a green vegetable is cooked, the less of its chlorophyll can change to muddy-colored pheophytins. In one study, broccoli lost 17.5 percent of its chlorophyll after being cooked for five minutes and 41.1 percent after ten minutes.
| | GERM WARFARE | |
What’s the best way to wash my fruits, vegetables, and produce to make sure there aren’t any germs, pesticides, and insecticides on them?
....
N
othing personal, but haven’t we become a bit of a paranoid society? Our drugstores and supermarkets cater to our fears (or do they encourage them?) by displaying dozens of antibacterial soaps, sprays, gels, lotions, hand washes, body washes, wipes, deodorants, and mouthwashes. Television commercials strike terror in our hearts by suggesting that there might be a germ or two lurking in our toilet bowls. (Well, for crying out loud, where are those poor little germs
supposed
to live?) I call it “bacteria hysteria.”
What does this have to do with food? A search of my unanswered reader mail (forgive me; I try) reveals 130 communications bearing the words
germs
or
bacteria
and 195 bearing some form of the word
danger
, referring to food contamination. It sometimes seems as if there are more people who are afraid of their food today than people who are enjoying it. Are we becoming a nation of verminophobes, mysophobes, toxiphobes, and sitophobes? (See definitions below.)
I generally avoid writing about health issues because I’m not a microbiologist, nutritionist, or physician. But I will say a few words about possible pathogens and toxins in or on our foods—in particular, on our fruits and vegetables. After all, they have inevitably been in contact with microorganism-harboring soil, and have possibly been subjected to agricultural chemicals such as weed killers and insecticides, not to mention manure and other “natural” fertilizers used to raise organic foods.
There have been several products on the market intended for washing our lettuce, scallions, tomatoes, apples, and such, presumably to remove both bacteria and toxic chemicals. In the fall of 2000, Procter & Gamble introduced a product called Fit Produce Wash, but they soon discontinued it and sold the formula to HealthPro Brands. At $5 for an 8.5-ounce bottle (no wonder it didn’t sell), it was a mixture of water, oleic acid, glycerol, ethyl alcohol, grapefruit oil, potassium hydroxide, baking soda, and citric acid.
Why these particular ingredients? The glycerol, alcohol, and oleic acid were presumably intended to dissolve and remove chemicals such as pesticides, which are generally insoluble in water. The potassium hydroxide attacked waxes, which are in any event approved by the FDA as harmless coatings for fruits such as cucumbers. As far as I can tell, the baking soda and citric acid were there only to react with each other to emit carbon dioxide gas, producing an Alka-Seltzer-like fizz to give the impression that the product was working hard.
Still on the market at this writing is Bi-O-Kleen Produce Wash, which “contains no animal ingredients” (should we have expected any?) and is “PETA approved” (but does it kill those poor little microorganisms?). It is made of “lime and lemon extracts, grapefruit seed extract, coconut surfactants, cold-pressed orange oil, and pure filtered water.” I don’t know if all those tutti-frutti ingredients do anything besides making the stuff sound yummy, but the “coconut surfactants” happen to be a synthetic (very unnatural) chemical called sodium cocoyl isethionate, a high-sudsing detergent used in soaps and shampoos.
Bi-O-Kleen has a couple of sister products. Veggie Wash claims to be “non-toxic, non-fuming, non-hazardous, non-caustic, and hypoallergenic” (and non-radioactive and non-explosive?). Organiclean contains “an anionic surfactant derived from coconuts”—very likely that same sodium cocoyl isethionate. All three products claim that they are more effective than plain water in cleaning fruits and vegetables.