What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (14 page)
Read What Einstein Kept Under His Hat: Secrets of Science in the Kitchen Online
Authors: Robert L. Wolke
Most experts, however, say that washing vigorously in running water is still the best bet. Running water will wash soil particles out of leafy greens, and that’s where the harmful bacteria, if any, are most likely to be hiding. Water won’t actually kill them, but neither will the produce-wash products, for that matter. If they did, they might leave residues of toxic (to humans) materials on the food. Moreover, if they claimed that they killed microorganisms, they would have to be tested for human safety and registered with the EPA as pesticides. (What irony!) So the produce washes sold to retail consumers are merely washes, not disinfectants. They’re especially good at washing money out of your pocket.
For skin-enclosed fruits, such as apples, tomatoes, pears, peaches, cucumbers, lemons, and oranges, a few drops of liquid dishwashing detergent applied vigorously with a brush and rinsed off well will do a good job of removing any contaminants. That’s an especially good idea for lemons and oranges if you intend to use their zest or peels in cooking.
One of the best defenses against bacteria on produce, which I employed when living in South America, is to wash the produce in a solution of about a teaspoon of chlorine bleach (a solution of sodium hypochlorite in water) per quart of water. Because the tapwater itself was suspect, I let the bleach solution stand for several hours before using it on the food, an unnecessary precaution here in the States.
Another safe and simple antibacterial treatment was devised in 1996 by food scientists at the University of Nebraska–Lincoln. It consists of spraying the produce with hydrogen peroxide solution (the 3 percent strength sold in drugstores as a disinfectant) and then with white vinegar, or vice versa. The two liquids mix on the food and react to release germ-killing oxygen gas. Any residual hydrogen peroxide on your lettuce will decompose quickly and is, in any event, tasteless, while any residual vinegar will give you a head start on the salad dressing.
Both the chlorine bleach method and the vinegar-and-peroxide method will also disinfect cutting boards and other food-preparation surfaces, especially after a scrub with detergent and a brush. If your cutting board reeks of chlorine after you use the bleach, a vinegar rinse will kill the smell.
While we’re on that subject, there are many commercial sprays in the supermarket for disinfecting everything from kitchen counters to entire bathrooms—but they are
not
meant to end up on our food. They contain alkyl dimethylbenzy ammonium chloride, a powerful catalyst that greatly accelerates the decomposition of esters and amides, which are major components of all living organisms from microbes to people. In high enough doses this chemical will kill us, but it is present in commercial disinfecting sprays at a concentration of only 0.2 percent. Nevertheless, disinfecting sprays and wipes should not be used on surfaces such as cutting boards that will come in contact with foods.
Oh, yes, the definitions. A verminophobe is a person who is excessively afraid of germs; a mysophobe is a person who is afraid of dirt or contamination; a toxiphobe is a person who is afraid of being poisoned; and a sitophobe is a person who is afraid of food or eating, probably because he or she is already a mysophobe or toxiphobe.
For a list of other phobias, go to
www.phobialist.com
, unless you’re a logizomechanophobe, in which case you will probably never know what logizomechanophobia is.
THE FOODIE’S FICTIONARY:
Swiss chard—burnt cheese
| | A YUKON GOLD RUST | |
Yukon Gold potatoes are my favorites, but it seems impossible to buy any that don’t have rusty-looking grayish-purplish marks in the flesh. After I cut out these dark marks, the potatoes are only fit for mashing. I have yet to find potatoes that don’t require major surgery. What is the purple-gray mark, and why does this seem to occur in Yukon Gold and not in other potatoes?
....
Y
ukon Golds, along with cabbage, onions, and yellow rice, get their yellow color from chemicals called anthoxanthins. Anthoxanthins react with traces of metals such as iron and aluminum, which turn them blue-gray. A carbon steel knife can have that effect, so it’s best to cut and slice these vegetables with stainless-steel knives. Other varieties of potatoes contain smaller amounts of anthoxanthins and don’t stain as easily.
Storage at high temperatures can also turn anthoxanthins dark. So if some of the potatoes are already stained upon purchase, seek out a market that stores its supply at cooler temperatures.
Speaking of anthoxanthins (now there’s a segue you won’t see every day), carrots contain small amounts of anthoxanthins, the colors of which can depend on the presence or absence of metal ions (charged metal atoms) such as iron and aluminum. People who bake carrot cakes in cast-iron or aluminum pans are sometimes startled to find that the carrots have turned green.
As in the case of the Yukon Golds, the reaction product of a carrot anthoxanthin with iron or aluminum can well be blue. And guess what blue plus the carrot’s yellow makes? Green!
| | Spanish Mashed Potatoes | |
W
hen garlic is sizzled in olive oil, the intensity of the garlic is toned down while the oil is flavored. To make this recipe for a crowd, use this formula: For each 2 cups mashed potatoes, add 2 to 4 tablespoons extra-virgin olive oil, 2 sauteed cloves garlic,
1
/
2
teaspoon coarse salt,
1
/
2
teaspoon smoked sweet Spanish paprika (pimentón),
1
/
4
teaspoon ground cumin,
1
/
8
teaspoon cayenne pepper, 2 slices bacon, and 1 scallion. Leftover mashed potatoes are wonderful warmed up the next day as potato pancakes with a fried egg on the side. Serve with Sherry-Browned Chicken with Garlic (p. 32).
4 large russet baking potatoes or 4 Yukon Gold or all-purpose
potatoes, enough to make about 4 cups mashed potatoes
1
/
4
cup extra-virgin olive oil, or more to taste
4 cloves garlic
4 slices bacon
1 teaspoon coarse salt
1 teaspoon smoked sweet Spanish paprika (
pimentón
)
1
/
2
teaspoon ground cumin
1
/
4
teaspoon cayenne pepper
2 scallions, both white and green parts, thinly sliced
1.
Make the mashed potatoes: If using russet potatoes, place a rack in the middle of the oven. Preheat the oven to 400°F. Prick the potatoes with a fork, place on the rack, and bake for 1 hour, or until tender when poked with a knife. If using Yukon Gold or all-purpose potatoes, peel them, cut into 1-inch chunks, and simmer in salted water for 12 to 15 minutes, or until barely fork-tender. When the baked potatoes are done, remove from the oven, cut them in half lengthwise, and scoop the flesh out into a pot. When the simmered potatoes are done, drain and leave in the pot.
2.
While the potatoes are cooking, pour the olive oil into a small skillet and add the chopped garlic. Cook over medium-low heat until the garlic sizzles and begins to take on faint color. Remove from the heat before it browns.
3.
In a medium skillet, fry the bacon over low heat until done and crisp. Chop the slices into 1/4-inch bits.
4.
Add the olive oil and garlic, salt, paprika, cumin, and cayenne pepper to the hot potatoes. Mash the potatoes coarsely using a potato masher (see p. 207). Taste for seasoning.
5.
Pile the mashed potatoes into a warmed serving dish. (Or scoop the mashed potatoes back into the potato shells.) Top with the bacon and scallions.
MAKES 4 SERVINGS
| | A RHUBARB OVER RHUBARB | |
A biologist friend tells me that rhubarb is poisonous. But I argue that that can’t be true because I’ve been eating rhubarb pie for years and am still kicking. Who’s right?
....
B
oth of you.
All parts of the rhubarb plant (
Rheum rhaponticum
) contain various amounts of oxalic acid and its chemical progeny, oxalate salts, ranging from 0.1 to 1.4 percent. That’s largely what gives rhubarb its prodigious pucker power, which must be tamed with sugar in the pie. Oxalic acid and oxalates are indeed poisonous.
During World War I, when fresh vegetables were in short supply in Britain, there were reported cases of people suffering oxalic acid poisoning from eating rhubarb leaves, which contain the largest concentration of oxalic acid anywhere in the plant. But inasmuch as you are still capable of arguing with your biologist friend, it should be obvious that the stalks, which are what you’ve been eating in your pies, contain much less oxalic acid than the leaves. Moreover, while there is no doubt that oxalic acid is poisonous, there is some doubt that it’s the oxalic acid alone that poisons rhubarb-leaf eaters.
“Poisonous” is a relative notion, of course; it’s purely a matter of amount. Cabbage, spinach, beet tops, potatoes, and peas also contain small amounts of oxalic acid, and the amounts in rhubarb stalks, although higher, are likewise considered harmless. As for rhubarb leaves with their much higher concentration of oxalic acid, you’d still have to eat about 10 pounds of them to reach the so-called LD
50
: the lethal dose for 50 percent of human subjects.
So keep eating rhubarb stalks. And thank you! The more you eat, the less there will be for me. I hate it.
THE FOODIE’S FICTIONARY:
Pie—3.1415927 . . .
| | Rhubarb Coulis | |
R
hubarb is not a fruit, although some people think of it that way because they make fruitlike pies out of it. It comes into season early and is often paired “half and half” with strawberries in pies and other desserts. Used here as a sauce, its tartness is a good foil for sweet desserts such as cheesecake (p. 71). In shopping, look for the deepest pink stalks.
1 pound rhubarb (about 6 stalks, each 12 inches long)
1 cup sugar
1
/
4
cup water
1.
Cut the rhubarb into
1
/
2
-inch pieces. You will have about 4 cups.
2.
Place the rhubarb, sugar, and water in a medium saucepan over medium-low heat. Cover and cook gently for about 20 minutes, or until just tender and juicy. The mixture will get very watery as it cooks.
3.
Let the mixture cool, and transfer 1 cup of it to a blender or food processor, purée it, and then pour it into a jar. Repeat with the remainder, 1 cup at a time. When all of the rhubarb has been puréed, store the jar in the refrigerator until ready to use. The coulis keeps for about 1 week.
MAKES ABOUT 2 CUPS
| | WHAT BLUTO NEVER KNEW | |
I often read that a particular fruit or vegetable contains certain minerals—iron, potassium, etc. Since many of these fruits and vegetables can be grown almost anywhere, that must mean that all soils, including my back yard, must contain at least trace amounts of these minerals. Is that really true? What would happen if I planted spinach (“rich in iron”) in soil that contained no iron? Would the spinach refuse to grow? Or would it grow but be deficient in iron, contradicting what the nutrition tables say?
....
F
irst of all, if you check the “USDA National Nutrient Database for Standard Reference” (
www.nal.usda.gov/fnic/foodcomp/Data/SR17/sr17.html
), you may be surprised to find that spinach does not contain an unusual amount of iron: it has less than most breakfast cereals, about a quarter as much as raw clams, and about the same as canned pork and beans (not counting the can).
Here’s how the spinach–iron connection got started.
Near the end of the nineteenth century, German scientists correctly found that the amount of iron in spinach is comparable to that in meat: some 3 milligrams per 100 grams, or 30 parts per million. But in the report of their findings somebody put the decimal point (actually, in Europe, a comma) in the wrong place, making the yield of iron appear to be ten times as great. The error was corrected some forty years later, but not before Popeye decided to adopt spinach as his power food. After all, iron is strong, right? If Bluto only knew that Popeye’s cans of spinach were a bluff!
The final irony (pun intended) in all this is that whatever iron spinach does contain is not readily absorbed by the body because spinach also contains a small amount (1 percent) of oxalic acid, which ties up the iron into an insoluble form, ferrous oxalate. So only a fraction of spinach’s modest amount of iron is available for our metabolism.
What if you did plant spinach in your back yard and there wasn’t enough iron in the soil? That’s really very unlikely, because iron is needed by plants in only trace amounts and iron is a widely distributed element, constituting about 5 percent of Earth’s crust. Hypothetically, though, without any iron at all your spinach would grow, but it would show symptoms of a nutritional deficiency, just as you would if you were deficient in a vitamin. The leaves would be a sickly yellow instead of green, because plants use iron in synthesizing chlorophyll.
Sidebar Science:
What plants eat for breakfast
PLANTS IN GENERAL
are made up almost entirely of compounds of carbon, hydrogen, and oxygen—compounds that chemists refer to as organic, with no relation to the word used to designate foods that conform to the USDA’s National Organic [Foods] Program. Minerals, on the other hand, are the seventeen inorganic chemical elements that are essential nutrients for plants. Agricultural soils must contain all of them, either inherently or added as fertilizer.
Six of these seventeen elements, the so-called
macronutrients
—potassium, nitrogen, phosphorus, sulfur, magnesium, and calcium—are required by plants in rather large amounts. Without any one of them, plants would grow abnormally or not at all. The other eleven essential elements—iron, manganese, zinc, copper, molybdenum, cobalt, nickel, sodium, boron, chlorine, and silicon—are called
micronutrients
because they are needed by plants in only trace amounts. The distribution of these elements around the Earth is more spotty, and that’s one way in which dissimilarities might arise among otherwise identical crops.
When we say that a certain element is present in the soil for a plant to absorb and utilize, that doesn’t mean that the element is present in its elemental form—that is, as free atoms, not combined into compounds with other elements. They are indeed present as compounds. The iron, for example, isn’t present as metal; it is present as compounds with oxygen and other elements (that is, in an
oxidized
form).
Nevertheless, and quite surprisingly, when you see “reduced iron” among the ingredients of a breakfast cereal, it is actually present as tiny particles of metallic iron! (
Reduced
is the chemical opposite of
oxidized
.) You won’t have to stay away from magnets after breakfast, however, because the finely divided particles dissolve promptly in the hydrochloric acid in your stomach.
