What Einstein Kept Under His Hat: Secrets of Science in the Kitchen (24 page)
Read What Einstein Kept Under His Hat: Secrets of Science in the Kitchen Online
Authors: Robert L. Wolke
Chapter Five
For Amber Waves
of Grain
....
I
T MAY
seem strange that after two chapters on agricultural crops that supply us with our vegetables and fruits, I now turn to the cultivation of grass. And I don’t mean what some readers might think.
Nor am I referring to the hundreds of square miles of home-encircling green carpet that we plant, water, fertilize, spray, manicure and trim, only to harvest the top inch time and time again and throw it away. (Futility, thy name is lawn.) And don’t get me started on the wastefulness of golf courses, especially in the water-starved desert regions of our country.
No, by “grass” I’m referring to cereal grasses, the family of plants that, more than any other, feeds the world. Also called grains, cereal grasses supply us with the starchy, edible seeds we treasure: wheat, rice, rye, oats, barley, and corn. Not only do these six plants sustain most of the world’s human population, but they feed the cattle and poultry who turn them into meat. Grains are the most ancient and still the most important of all food crops.
Wheat is probably the oldest. It is still a widely cultivated grain, with a worldwide annual production (in 2003) of 556 million metric tons. It is surpassed by rice, at 589 million metric tons, 90 percent of which is grown in Asia. But the world’s champion is corn (maize), with 638 million tons being produced in 2003. All other grains (barley, rye, oats, and sorghum), known as coarse grains, total another 242 million metric tons worldwide. (Source: United Nations Food and Agriculture Organization, FAOSTAT.)
The most important nutritional feature of all grains is their starchiness. Starch is, of course, a carbohydrate, as are its building blocks, the sugars. So speaking chemically rather than agriculturally, this chapter might more broadly, if also more textbookily, be titled “Carbohydrates,” whether from grains, legumes, or, in the case of honey, insects.
In that vein, allow me to set the stage with a Sidebar Science on carbohydrate chemistry which, as with all sidebars, may be scanned, skimmed, or skipped.
Sidebar Science:
A nano-course on carbohydrates
THE MOLECULES
of all carbohydrates—sugars and starches—are made up of anywhere from two to hundreds or even thousands of molecules of glucose, all joined together. As the number of glucose units per molecule increases from a few to dozens or hundreds, we cross the rather fuzzy borderline between sugars and starches.
•
Monosaccharides:
Its name derived from the Greek
mono
, meaning one or single, and
sakcharon
, meaning sugar, a monosaccharide is a basic “sugar unit” whose molecules cannot be broken down (by
hydrolysis
) into any simpler sugars. Monosaccharides are the smallest of carbohydrate molecules. The most common ones are glucose, fructose, and galactose. (See Table 4 on p. 206.)
Glucose is the ultimate, energy-giving breakdown product of all the carbohydrates we eat. It can go directly into the bloodstream.
•
Disaccharides:
Table sugar, sucrose, is a disaccharide (“two sugars”); its molecules are made up of one molecule each of glucose and fructose, the very sweet simple sugar found in fruits. When treated either with an acid or with the enzyme
invertase
, the sucrose molecule breaks down into a mixture of equal amounts of its glucose and fructose parts. The resulting mixture is called
invert sugar
and is, surprisingly, sweeter than sucrose itself because fructose is sweeter than sucrose.
This illustrates a fundamental principle of chemistry: A chemical compound (sucrose, for example) can have very different properties from a simple mixture of its components (a mixture of glucose and fructose, for example). The obligatory chemistry-textbook example is sodium chloride (table salt), which we eat with impunity despite its being composed of a metal that explodes in water (sodium) and a poisonous gas (chlorine).
Other disaccharides are lactose, found only in the milk of mammals, and maltose, formed when grains are malted—soaked in water until they sprout, such as in making beer and Scotch whisky from barley.
•
Oligosaccharides
:
Oligosaccharides—the name comes from the Greek
oligos
, meaning few—are carbohydrate molecules made up of fewer than ten monosaccharide units, and are still generally referred to as sugars rather than starches. The three- and four-unit oligosaccharides raffinose and stachyose (note that the names of all sugars end in -ose) are present in beans but are not digestible by humans. Instead, bacteria in our intestines feed on them, showing their ingratitude by producing those gaseous consequences we associate with beans.
•
Polysaccharides:
Finally, there are polysaccharides (“many sugars”), also called complex carbohydrates or starches, whose molecules are made up of anywhere from about forty to thousands of glucose units. If the units are joined in long, rather straight chains, they are called amylose starches; if they are joined in a branching, bushy configuration, they are called amylopectin starches. Because of their different molecular shapes, they impart different properties to our starch-containing foods. Most plant starches are mixtures of both amylose and amylopectin.
Other polysaccharides whose names you may have seen on food ingredient labels are dextrins, which are rather large molecular chunks that break off from bigger polysaccharide molecules like dead branches from a tree, when the polysaccharides break down in water.
Too lazy to articulate a four-syllable word, many people today are talking about—and counting—the number of grams of “carbs” in their foods. Carbohydrates—uh, carbs—range upward in molecular size and complexity to thousands of glucose units. If the molecules are big enough, we can’t digest them and they pass right through our alimentary canals without giving us any calories or nutrition. The smaller, digestible carbohydrate molecules—sugars and starches—are loosely referred to as “net carbs” in the proliferating literature of weight-loss dieting, because they’re the ones that are metabolized to yield calories at the rate of 4 calories per gram.
The two forms of starch molecules. Top: the linear structure of amylose. Bottom: the branched structure of amylopectin. Each hexagon represents one glucose unit.
THE FOODIE’S FICTIONARY:
Invert sugar—Whoops! I knocked over the sugar bowl
| | M*A*S*H | |
Every time I make mashed potatoes I get different results. Worst of all is when they turn out sticky and gluey. What am I doing wrong?
....
M
ashed potatoes would seem to be the easiest thing in the world to make: just boil ’em and mash ’em, right? But potatoes are mostly starch, and a lot depends on how the starch behaves.
Potato flesh is made up of plant cells. Inside the cells are thousands of starch granules, little round packages in which the plant has stored the molecules of starch that it manufactured during photosynthesis. The starch inside the granules has a gelatinous consistency, so that the granules may be thought of as tiny sacks of glue.
The OXO potato masher. When used with a straight up-and-down motion, it extrudes the potato through its rectangular holes, producing a coarse, non-gluey texture.
When heated in a moist environment, the granules take on water and swell until some of the sacks disintegrate, spilling their gummy contents. The granules lose their grainy structure and become
gelatinized
. (See “In a fog about pea soup” on the following page.)
But the game isn’t lost yet. If the spilled gelatinous starch remains trapped within the potato’s cells, your spuds are still okay because the potato’s cell structure keeps them firm. But if you then smash the cells open, the gooey starch runs out and gums up the works.
The best masher, in my opinion, is the type that has square or rectangular holes in a flat plate. It extrudes the potato through the holes as a ricer does, rather than crushing it. When mashing, use an up-and-down motion; don’t slide the masher sideways, which would squash open more starch grains. That’s the trouble with those zigzag rod mashers; their round rods squish the potato sideways. And never use a food processor. It is notorious for making gluey potatoes because its sharp blades slash through the swollen starch grains, liberating lots of gluey gel.
Beyond all that, some potatoes are better for mashing than others. Small redskins are waxy and make a waxy mash. Best are the russets, or “Idaho baking potatoes,” and Yukon Golds, whose cell structures give a nice, mealy texture. And the color of the Yukon Golds (see p. 117) makes your guests think there’s more butter in the mashed potatoes than there is.
How to make mashed potatoes
Cut the potatoes into 1-inch pieces and precook for about 10 minutes at a simmer, not a full boil. That gives the starch grains a chance to swell without rupturing. Then drain the potatoes and let them cool. That allows the swollen starch granules to firm up. When you’re almost ready to mash, simmer the potatoes the rest of the way until they’re barely tender, not mushy. Drain them very well and mash them with a potato masher or ricer. The firmed-up starch granules won’t release their goo as easily as they would have without the precooking and cooling steps.
| | IN A FOG ABOUT PEA SOUP | |
Why is it that when I make split pea soup and put the leftovers in the refrigerator, they set up like cement? I then have to add a lot of water and beat it into submission to make it thin enough to eat with a spoon.
....
B
efore I answer your question, have you ever wondered why split pea soup has to be made from split peas, rather than whole ones? I know I have. After all, once they’ve been reduced to pottage, who cares whether they were originally intact spheres or, one must presume, had been carefully split in two at the factory by a tribe of elves wielding tiny machetes?
In truth, the split pea is a specific variety of pea whose proper name is field pea, originally native to southwestern Asia and one of the earliest crops cultivated by humans. They have a weak plane or layer that splits apart when the peas are dried. That easy-splitting phenomenon, also found in some minerals, is what mineralogists call cleavage. (Now get your mind back on what I’m talking about!)
All peas are varieties of
Pisum sativum
. The field pea is to be distinguished from the common garden pea, a.k.a. green pea or English pea, which is usually sold fresh and still in its pod, to be shelled by grandmothers seated at the hearth or, when fresh and young (the peas, not the grandmothers), to be eaten whole, pod and all. The French are particularly fond of their tiny young peas, which they have imaginatively named
petits pois,
or “little peas.”
