What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (17 page)

In high school biology, I learned that legumes are plants like alfalfa and beans that “fix” nitrogen gas by taking it out of the air and putting it into the soil so that plants can use it. But from experience I also know that legumes like beans are responsible for another kind of gas: what happens to us after we eat them. Is there any “fix” for avoiding these unpleasant consequences?

....

W
ell, one thing you can do is to cut down on the amount of alfalfa in your diet. But giving up all those other legumes, including peas, peanuts, lentils, and the dozens of kinds of beans, would be too much to ask. It’s just one of those many times in life when we have to balance the benefits against the risks.

Leguminous plants are those that produce their seeds in pods. Nutritionally, legumes (as the seeds are called) are high in protein and contain many, but not all, of the essential amino acids. The problem is that they also contain certain complex carbohydrates (raffinose oligosaccharides, among others) that humans unfortunately lack the enzyme to digest. I say “unfortunately” because those carbohydrates pass straight through the stomach and small intestine to the lower bowel, where bacteria feed on them, producing various gases—odorless carbon dioxide, hydrogen, and methane, seasoned with highly odorous hydrogen sulfide and other sulfur-containing compounds called mercaptans. These gases, finding themselves already in our nether regions, depart the body via the nearest exit.

Unfortunately (again), none of several recommendations for circumventing these ventings has been proven to be dependably effective, including rinsing the beans several times before cooking, or cooking them along with any one of a variety of herbs, such as epazote, that supposedly reduce the gas. And perhaps on the theory that the best defense is a good offense, some people say that the more beans you eat on a regular basis, as is done in countries where beans are a staple, the less your social reputation will be sullied.

Because both beans and people vary so much, it would be difficult to carry out the controlled scientific experiments that would be necessary to determine the efficacy of these strategies. One would have to measure the bean inputs of a large number of people under various conditions and measure the volumes of their gaseous outputs. I, as one scientist, shall not volunteer to do that experiment. Nevertheless, as is the case with many folk practices that lack scientific substantiation, people believe what they want to believe. And who’s to say no?

One defense against your chemical weapons of mass eruption is Beano or one of the other commercial products that supply the digestive enzyme (alpha-galactosidase) our systems lack.

Another measure that apparently works in many people is swallowing capsules of charcoal, which adsorbs gas in the intestine. (Yes, that’s
adsorb
with a
d
, not
absorb
with a
b
. The gas molecules diffuse into the extensive interior surfaces of the highly porous charcoal grains and adhere there. That adherence phenomenon is called adsorption.)

Both Beano and charcoal capsules are available without prescription. They’re worth a try in an emergency, such as when you’ve had bean burritos for breakfast before church.

In the end (if you’ll pardon the metaphor), there’s really not much you can do beyond letting nature take its course and saying, “Who, me?”

My grandmother told my mother and my mother told me: Always add a pinch of baking soda to the water you soak your dried garbanzos in. Of course, mothers never tell us why. So, why?

....

A
lways do what your mother says. When I was a kid my mother told me (really!) that if I wore my rubber rain boots in the movies it would ruin my eyes. I forgot to take them off once, and today I have to wear glasses.

But seriously, your mother’s dictum is somewhat more rational. Garbanzos, the Spanish name for what Italians call
ceci
and we call chickpeas, are often sold in dried form—hard, tough-skinned beans that are notoriously difficult to soften. In many South Asian, Middle Eastern, and Mediterranean countries, one of which your grandmother may have come from, it has long been the custom to soak dried garbanzos at least overnight before cooking them. It was also found that a bit of baking soda shortened the soaking and cooking time.

We now know that alkalis such as bicarbonate of soda attack the fibrous cellulose skins and make them more permeable to water. Various alkalis (lye, potassium carbonate, lime) are used in other cultures to remove the cellulosic hulls from corn kernels in order to make such foods as hominy and
masa harina
, the dough used to make tortillas. (See “Tortilla tips,” p. 230.) We also know that a pinch of baking soda is particularly helpful if the beans are being soaked or cooked in hard water, because bicarbonate removes the calcium and magnesium in the water, which otherwise could form hard, insoluble compounds in and between the beans’ cell walls and make the beans less susceptible to hydration. Too much baking soda, however, will soften the beans too much and spoil their texture, not to mention contributing a soapy, salty flavor.

But is it really necessary to soak dried garbanzos or other dried legumes in water before cooking them? Drying, which obviously predates canning by many centuries, is simply a way of preserving beans and other legumes for storage. It is still used for convenience in packaging and ensures a long shelf life. These days, however, you can buy many types of beans in cans, already cooked and soft.

Almost as much has been written—and argued—about soaking dried beans as about the 2000 presidential election, and in my opinion just as futilely. To soak or not to soak just doesn’t have a simple answer.

The original reason for soaking was undoubtedly that it reduced the cooking time and therefore conserved valuable fuel. Today, most of us don’t have to chop wood for cooking, and the small amount of gas or electricity saved by soaking matters little in our prodigal society. Inasmuch as soaking dried legumes has the same major objective as cooking them—making them soft and chewable—it’s mostly a matter of how you want to split that chore between a preliminary soak and a hot-water simmer. The three relevant factors are size, temperature, and time.

•
 
Size:
Tiny lentils and small peas, especially split peas, have large surface areas compared with their weights or volumes (that is, they have a high surface-to-volume ratio), so water is offered abundant entryways into their interior. Since they hydrate quickly during cooking, there is little reason to give them a cold-water head start.

Relatively bowling-ball-sized garbanzos, on the other hand, have a smaller surface-to-volume ratio, and the water has farther to go to penetrate into their centers. For these virtually impregnable seeds, a preliminary soak in cold water may well cut the cooking time down to a finite number of hours.

•
 
Temperature:
The diffusion of water into dried seeds occurs more rapidly at an elevated temperature. Thus, an hour of simmering at the boiling point is much more productive than an hour of soaking in cold water. By comparing likely diffusion rates, I estimate that an hour of simmering accomplishes as much hydration as 3 hours of cold soaking. So if it would take 5 hours of simmering to bring dried garbanzos to a toothsome texture, you could do it in only 4 hours of simmering if you first soaked them for 3 hours.

•
 
Time:
How much time you have available is a consideration, as is what
kind
of time—attended (simmering) or unattended (soaking). It’s tempting to do a lot of soaking because you can do it while you sleep, but trading off too much simmering for soaking can adversely affect the flavor of the finished dish. You want enough cooking time to allow the softened beans to absorb and release flavors from and to whatever other ingredients are keeping them company in the pot.

Oceans of ink and tons of hot air have been spilled over such questions as whether soaking affects the ultimate texture of the beans; whether to salt the beans (if at all) before or after simmering; whether soaking beans removes nutrients and flavors or removes gas-forming oligosaccharides. In the former case you would want to retain the soaking water, while in the latter case you would want to discard it. Research appears to show that small amounts of both oligosaccharides and thiamine (vitamin B
1
) are extracted into the soaking water, reducing both nutrition and emission. You can’t win.

But cooking beans is neither rocket surgery nor brain science (or something like that). Over the centuries, many different traditional means of dealing with beans have evolved in different cultures, without much scientific justification. So just do ’em the way your own ethnic background decrees.

And if it makes you feel righteous to “honor thy mother,” by all means go ahead and soak ’em just because she told you to.

Chapter Four

Above the
Fruited Plain

....

O
N THE PAGES
of his published works, William Shakespeare used the words
fruit
or
fruits
122 times. On the pages of the King James Bible, the words
fruit
or
fruits
appear 361 times. On the ethereal pages of today’s World Wide Web, the words pop up more than 20 million times.

In metaphor, we speak of an action that produces positive or profitable results as being “fruitful” or “bearing fruit,” while an unsuccessful endeavor is said to be “fruitless.”

What is it that so fascinates us about fruits?

The word itself comes from the Latin
fructus
, meaning enjoyment, an apparent allusion to the sweetness of a ripe fruit. Besides honey, no other source of sweetness was known outside of Asia and the South Pacific islands, where sugar cane originated, until post-biblical times.

There may be a deeper reason for the allure of fruits. Botany defines a fruit as the mature ovary of a flowering plant, its purpose being to contain, to nurture, and ultimately to disperse the plant’s seeds. The fruit is thus the ultimate goal of the plant’s existence, a tangible expression of its intent to procreate. A fruit is a symbol of life, hope, and aspiration.

But what, really, is a fruit? That’s not an easy question to answer. Classifying the structural parts of the 270,000 known plant species into a small number of categories is a daunting task. But with their penchant for classifying things according to subtleties of form and function, most botanists divide fruits into three basic types, depending on how the flower’s ovary develops into the fruit:
simple
fruits,
aggregate
fruits, and
multiple
fruits. Other classifications do exist. If you ask any two botanists, you may well hear three different classification schemes. However, we’ll stick to triaging our fruits into
simple
,
aggregate,
and
multiple
. And don’t be surprised at seeing some foods that you never thought of as fruits at all, or even some whose classification as fruits might seem a bit nutty. (All nuts are fruits, and so are peanuts, although they’re not nuts.)

•
 A
simple fruit
develops from a single ovary of a single flower, and may be either fleshy or dry.

Among the
fleshy
simple fruits
are the so-called berries and the drupes. The berries include the avocado, bell pepper, blueberry, grape, grapefruit, orange, and even the tomato and banana. (Yes, according to botanists, bananas are berries. Bananaberry pie, anyone?) The drupes, in which the inner layer (the
endocarp
) of the ovary’s wall (the
pericarp
) has hardened into a pit or stone, are also known as stone fruits. They include the apricot, cherry, coconut, olive, peach, plum, and even the cacao pods from which we remove the seeds to make chocolate.

Among the
dry
simple fruits
are the legumes (beans, peas, peanuts), the nuts (acorns, hazelnuts, walnuts), and the grains (corn, rice, wheat). Yes, grains are fruits. But they play such a central role in the human diet that I devote a separate chapter (Chapter 5) to them.

•
 An
aggregate fruit
, such as the blackberry or the raspberry, develops from a single flower with many ovaries, making a mass of small drupes resembling a tight bunch of tiny grapes. (Botanically speaking, blackberries and raspberries are not berries like, for example, bananas. Sheesh!)

•
 A
multiple fruit
,
such as the pineapple, develops from the ovaries of many flowers growing in a cluster.

But where, oh where, is your favorite and mine, the strawberry? And where is that doctor-deterring apple? By now you will accept calmly the statement that strawberries are not berries. Nor are they simple, aggregate, or multiple fruits. They, along with the so-called pomes (apples and pears), are
accessory
fruits
, fruits that develop from parts of the plant other than the ovary. Happily, I shall not attempt to describe their botanical configurations.

Enough botany! On to gastronomy!

When I read in my newspaper’s food section what’s new and abundant in the produce markets, I buy these things but often don’t know what to do with them after I get them home. How do I know which fruits are ripe and may quickly deteriorate, and which ones will improve if I keep them a while before eating?

....

I
t’s not easy. The chemical changes that take place in ripening fruits are quite complex, with different fruits differing mainly in the timing of those reactions.

For every type of fruit, there comes a time when the ripening reactions reach their peak, after which senescence (deterioration) sets in, ultimately leading to decay. That’s Nature’s dust-to-dust plan, and the bell tolls as well for thee and me.

Your problem is to know exactly when that peak of ripeness occurs. That’s when the fruit will have a good color (green will have changed to yellow-orange or red-blue), a soft texture, and the best flavor, because acids will have decreased, sugars will have increased (except in lemons and limes), and various flavorful and aromatic substances will have been produced.

But hitting that moment of maximum ripeness can be like timing the stock market. For one thing, you don’t get to make your selection in the store until some time after the fruit has been picked, and you don’t really know how ripe it was at that time or what has happened to it since. It’s like buying a stock based on last week’s price.

Avocados don’t begin to ripen until after they’re picked, so don’t be afraid to buy them rock-hard. But most other fruits reach their best eating qualities when fully ripened on the plant and ready to fall. That’s Nature’s get-’em-while-they’re-hot plan to entice animals into eating them and spreading their indigestible seeds.

Many fruits, such as commercial tomatoes, strawberries, and especially bananas, are deliberately picked unripe so as to better withstand the rigors of shipping. Others (peaches, plums, melons) can be picked, shipped, and sold in an almost ripe condition, with a firm flesh that will slowly soften.

The most useful distinction to be aware of is that some fruits can continue to ripen after being picked, and some can’t. If they can’t, there’s nothing you can do about it after you get them home; you have to buy them in an already perfectly ripe condition (good luck, if there’s not a farmers’ market handy) and refrigerate them to keep them that way, because low temperatures slow down the senescence reactions.

Fruits that continue to ripen after picking are another story. If they’re bought in an unripe condition, there is something you can do at home to move them along: You expose them to a gaseous plant hormone called ethylene, a.k.a. ethene, H
2
C
5
CH
2
, that speeds up the ripening process. We don’t usually think of a gas as being a hormone, but ethylene qualifies because, like other hormones, it is effective in tiny amounts of less than one part per million.

Where do you get the ethylene? The fruits themselves provide it. Many fruits undergo a burst of ethylene gas at just about the time they reach optimum ripeness and before senescence sets in. These fruits are called
climacteric
fruits, because their rates of ethylene production climax and then decline. (If you think you see a parallel with the decrease in female hormones at menopause, also referred to as climacteric, you’re right on target.)

If a climacteric fruit is not yet ripe, it can be egged on toward ripeness by ethylene from another ethylene-emitting fruit, or even by its own emitted ethylene (if prevented from drifting away), which will stimulate it to make even more ethylene. In chemical lingo, this kind of self-stimulated reaction is said to be
autocatalytic
.

Fruits that don’t exhibit a rise and fall in ethylene production during ripening, the so-called
nonclimacteric
fruits, are less affected by exposure to the gas. So all you have to know is which fruits are climacteric, and then you can gas them with ethylene to hasten their ripening. You get the ethylene from climacteric fruits that are still in the ethylene-producing stage.

Here’s what you do. First, check Table 2 on page 153 to see which category your fruit belongs to. If it’s in the nonclimacteric list, it may soften a little and lose its green color, but it won’t get any riper before it starts heading downhill. Refrigerate it to preserve what ripeness there is.

But if it’s in the climacteric list, leave it at room temperature; refrigerating it would slow down its ripening. If you want to speed things up, place a couple of the fruits without crowding into a paper bag with a few holes punched in it. That will trap some, but not all, of the ethylene that the fruits are emitting and hasten their ripening. Ethylene is slightly lighter than air, so some of it will escape through the holes in the bag. That’s fine, because all it takes is as little as one part of ethylene per million parts of air to do the job. Don’t use a plastic bag; the ethylene concentration and moisture may build up inside and nudge the fruit over the hill from ripe to spoiled. Remember that increased ripeness doesn’t necessarily mean increased sweetness. Fruits will soften and perhaps intensify in fragrance, but among the most common climacteric fruits only apples, bananas, mangos, and pears will become sweeter as they continue to ripen off the plant.

If you’re really in a hurry, put a world-class ethylene producer—an apple, banana, or passion fruit (the champ)—in the bag along with your climacteric fruit. Be sure to check the bag’s contents every 10 to 12 hours or so, or you may be surprised to find rotted fruit inside.

“One rotten apple can spoil the whole barrel” may be a bit of an exaggeration, but if the baddie is still in its stage of copious ethylene emission it can certainly speed its brethren toward their ultimate demise. Especially if the bad apple is at the bottom of the barrel, its lighter-than-air ethylene may wash over all the other apples as it rises.

How, then, do apple growers prevent tens of thousands of boxes of apples harvested in September from overripening before they are shipped to market in January or later? For one thing, they refrigerate the apples at 31 to 36°F (-0.6 to 2.2°C) to slow down the ripening reactions. (Do the same at home to keep your apples at their peak.) But more important, the growers control the amounts of oxygen and carbon dioxide in the refrigerated rooms, because in addition to giving off ethylene, apples “breathe in” oxygen and “breathe out” carbon dioxide. This “breathing,” more properly called respiration, continues in all fruits and vegetables after they are picked. It can be inhibited by low temperatures and also by reducing the amount of oxygen and increasing the amount of carbon dioxide in the storage room (which you are quick to recognize would also inhibit human respiration). In the apple industry, this is called controlled atmosphere (or CA) storage.