Marlene Parrish - What Einstein Told His Cook 2

“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

Rhubarb 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(chapter 2). In shopping, look for the deepest pink stalks.

1 pound rhubarb (about 6 stalks, each 12 inches long)

1 cup sugar

¼ cup water

1.Cut the rhubarb into ½-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?

First 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 GENERALare 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.

THE TEAR FACTOR

I’ve read so many hints about how to cut onions without crying, but none of them seems to work. Is there some trick that I can use, short of always buying sweet or “no tears” onions, which don’t have the same pizzazz as ordinary ones?

What makes me cry is all the misinformation going around about onions, primarily about what causes the eye irritation and how sweet onions differ from ordinary ones.

The tear-producing chemical (the lachrymator ) in onions is not pyruvic acid, as has too often been stated in print. Nor does pyruvic acid “come from sulfur in the soil,” as has also been frequently asserted, because pyruvic acid contains no sulfur. Nor does the lachrymator consist of sulfonic or sulfurous acid or any of the other often-blamed chemicals. Indeed, it is not an acid at all. It is a sulfur-containing compound called thiopropanal sulfoxide, a.k.a. thiopropionaldehyde-s-oxide, which I shall henceforth refer to as compound T , for tear gas.

While knowledge of that fact isn’t going to change your life, the record has long been in need of being set straight. So there.

Many people apparently think that there is a single chemical in onions that both irritates our eyes and gives us the flavor effect of pungency, a hot, sharp, and stinging sensation in the mouth. But these two effects are largely due to different compounds. Compound T is not primarily responsible for the onion’s pungency, as is commonly stated in the popular food literature. Nor are the most pungent onions necessarily the most notorious tearjerkers.