What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (25 page)

Your solidified soup phenomenon is not unique to peas; it is caused by the peas’ abundance of starch, and exactly the same thing will happen in any starchy soup or sauce, such as a gravy that has been thickened with cornstarch or flour and subsequently refrigerated. They, too, will be unyieldingly thick and gelatinous after having been refrigerated.

Here’s a simplified version of what’s going on.

Under a low-power microscope, starch looks like a collection of translucent round or ovoid capsules of various sizes, called granules. Inside each granule are millions of invisibly small starch molecules, arranged in a relatively organized pattern.

As we heat a starch-bearing food in water, the starch granules become dispersed throughout the liquid, where they gradually absorb water and swell. The swollen granules then rub up against one another like too many overfed fish in too small a pond, and the entire mixture becomes more viscous, or thicker. Some of the granules may even burst and spill their contents, further thickening the soup or sauce into a sort of paste. This entire process is generally called gelatinization.

A dish containing gelatinized starch is just fine if you eat it while it’s hot. The smooth, silky texture of a properly made flour- or starch-thickened white sauce, for example, is one of gastronomy’s great pleasures.

But when the starchy leftovers are cooled in the refrigerator, two processes take place in succession: first,
gelation
(not gelatinization), and then
retrogradation.
(Note that gelatinization—becoming gelatin-like—took place upon heating, while gelation—formation of a gel—takes place upon subsequent cooling.)

In the first cooling stage, gelation, starch molecules inside the swollen granules slow down because of the falling temperature. (All molecular motion is slower at lower temperatures.) The starch molecules can then begin to mesh with one another and tangle together, forming a weblike structure that traps a lot of water. That kind of structure, a semisolid mass containing a large amount of locked-in liquid, is called a
gel
. As the gel continues to cool and more starch-to-starch bonds form and tighten the net, some previously trapped water may even be squeezed out, a phenomenon known as
syneresis
. The soup or sauce “weeps,” and little beads of water can be seen on the surface.

After several hours of cooling and aging, the starch molecules are so tightly tangled with one another that they are no longer dispersible in water. If you add water to try to thin it out, the thick, gummy mass refuses to break up and return to its earlier consistency, because in their tangled gel form the starch molecules cannot unbond from one another to make room for the water and then swim freely into it. In short, the starch has
retrograded
—gone back—to an insoluble form. You can then try beating it into submission by adding water and whisking vigorously while heating, but it may never be as smooth as it was just after being cooked.

Don’t despair. I’m told that the traditional Dutch pea soup (
erwtensoep
), also called
snert
(that’s right,
snert
), is deliberately made a day ahead and refrigerated, so that when reheated, it will be thick enough to support a spoon standing straight up. When much of your country is below sea level, I guess you have to do
something
for fun.

Servings in Chinese restaurants are often too large to finish, so I end up taking “doggie bags” home for the refrigerator. But the rice always hardens into tough, separated grains, a far cry from the soft, sticky consistency it had in the restaurant. I thought it might have been dehydrated, but adding water just makes it mushy. How can I restore its soft texture?

....

I
know what you mean. The waiter asks, “Do you want me to pack the rice also?” And you say, “Yes, please,” while thinking, “Not really, but I paid for it, and I don’t want him to think I lack respect for the soul food of his homeland.” So there you are, two or three days later, wondering whether your conscience will allow you to throw it out.

Some dehydration does indeed take place in the fridge, as you can see from the fact that the top layer of rice is drier than the rest. But the main effect is that the starch in the rice has undergone a partial reversion (retrogradation) to the hard, water-insoluble state it was in before it was cooked. The same two processes—gelation and retrogradation—take place in the rice’s starch as take place in pea soup and all starch-thickened gravies and sauces when the cooked foods are refrigerated. (See “In a fog about pea soup,” p. 209.)

Replacing the water that was trapped during retrogradation isn’t easy, but heating the rice in a very small amount of water may partially restore its soft texture. Personally, I don’t try to restore leftover rice to softness. I make fried rice out of it.

I understand that Chinese rice is sticky, rather than in separate grains the way we Americans like it, so that it can be picked up with chopsticks (though not by me). Is it a special rice, or a special way of cooking it?

....

I
t’s the type of rice. Bear with me and I’ll reveal an ancient Chinese secret—okay, a modern American one—for using chopsticks.

There are tens of thousands of varieties of rice known today, but in the interests of sanity we can divide them into three categories: short-grain (less than 5 millimeters long), medium-grain (from 5 to 6 millimeters long), and long-grain (6 to 7 millimeters long).

In recent years, several specialty rices have become popular in the United States. One is the traditional Italian arborio rice, a particularly absorptive medium-grain variety. It is rich in amylopectin starch (see the illustration on p. 205), the branched, bushy molecules of which trap and absorb water quite readily. Arborio rice will easily absorb three times its own volume of stock or broth, making it ideal for risotto. The choice rices for paella, which needn’t be as sticky, are the medium-short, less-amylopectin-containing Valencia or
bomba
varieties.

Other exotic rice strains that have caught the American fancy are jasmine and basmati rice from Thailand and India, respectively. Jasmine rice is a long-grain white rice with a fragrant aroma. Basmati rice is also aromatic (the Hindi word
basmati
means fragrant), with a nutty flavor and aroma. Close genetic relatives of both these Asian varieties have been appropriated by growers in the United States, however, and the word
jasmine
or
basmati
on a package can no longer be depended upon to mean the genuine, imported product. (A Texas company named RiceTec even attempted to patent the name
basmati
in 1997, although most of its claims were disallowed when the Indian government made waves.) In the United Kingdom, however, the term “basmati rice” may be applied only to the long-grain aromatic rice grown in India and Pakistan.

Chinese and Japanese rice is short-grained and rich in the branched molecules of amylopectin starch, which make it sticky when cooked. American long-grain rice, on the other hand, is richer in the straight-chain molecules of amylose starches that don’t trap as much water. It cooks up into fluffy, separate grains that after retrogradation (see p. 210) are easier than the Chinese variety to resoften with moist heat.

Now to your dexterity perplexity.

While East Asians are incredibly adept in using chopsticks to pick up their sticky rice, Westerners are often bamboozled when finding themselves forkless. To most of us, chopsticks are the
real
Chinese torture. Bamboo slivers under the fingernails are painful, yes, but at least you don’t starve to death.

I’m one of those insufferable Western snobs who always use chopsticks in Chinese and Japanese restaurants, claiming that the food “tastes better” that way. Even more insufferably, I bring along my own pair of ivory sticks. The simple truth, however, is that I just happen to possess the manual dexterity for handling chopsticks, and I like to show off.

Well, help is at hand, so to speak, for the rest of you. Never mind those how-to-hold-your-chopsticks instructions that are printed on the place mats but which might as well be in Chinese for all the help they give. There really is an easy way to eat Chinese and Japanese food with aplomb, or even without the plum.

The secret to chopstick
savoir faire
is a simple little rubber band. With it, you can transform those infernal wooden shafts into a tool that can be used efficiently by even the most digitally challenged klutz.

I would love to say that I discovered this secret while traveling through the Far East several years ago, but I didn’t. On that trip I could only watch with amusement as my fellow Americans attempted more maneuvers than in Sun Tzu’s
The Art of War
in an effort to convey perhaps every fifth morsel of food to the general vicinity of their oral cavities.

In China and Taiwan, I observed some of my desperate companions holding the sticks about an inch from the bottom, in the mistaken belief that less leverage would make them more controllable. (It doesn’t.) In Japan, the chopsticks were often pointed, so stabbing quickly became the method of choice. And watching my fork-facile friends deal with wet noodles was more fun than SeaWorld.

I’ll never know why the rubber-band trick didn’t occur to me on that trip. I had to wait until a server in a Samurai Japanese Steak House, right here in the USA, showed me how to do it. (See “How to use chopsticks, though American,” on the following page.)

A recipe tells me to add parboiled rice to a casserole. How does one make parboiled rice?

....

P
arboil it.

Okay, seriously: Parboiling is boiling a food just enough to cook it partially but not completely. Quixotically, the word comes from the Latin
per
bullire
, meaning to boil thoroughly, but in Middle English
per
became
par
and was confused with
part
or
partial
. Thus, “thorough boiling” came to mean its opposite, “partial boiling.”

When you’re cooking a casserole that contains rice along with faster-cooking ingredients, the recipe may tell you to parboil the rice first so that everything will be done at the same time.

As rice comes from the field, its grains are encased in an inedible, protective hull or husk, which is removed at the mill. Beneath the husk is a thin layer of bran, which is left on for brown rice or removed by abrasion to make white rice. The bran layer gives brown rice its characteristic tan color and nutty flavor. Brown rice is chewier than white rice and takes longer to cook.

Before the hulls are removed, rice is often treated with high-pressure steam, a treatment that rice millers call parboiling. Besides softening the hull, the steam forces nutrients from the bran into the starchy white grains or endosperm, but it doesn’t qualify as parboiling in the timesaving kitchen sense; the rice is still “raw” and may even take more time to cook than non-parboiled rice.

By the way, in case you’ve also wondered what “converted” rice is, it’s Uncle Ben’s trademark for factory-parboiled rice. “Quick” or “instant” rice is rice that has been fully cooked and then dried, for people who are
really
in a hurry.