Legumes are all edible when young in the pod, although we only eat beans, peas and fava beans at that stage of growth. We are more familiar with legumes after they fully mature and dry.
In fact, a major contributing factor to their historical popularity, besides their nutritional value, is that they store so well in dried form-almost indefinitely without deteriorating. A third way we eat legumes is freshly sprouted.
Dry legumes, like most seeds, quickly sprout in moist, warm conditions, providing flavorful and crisp sprouts, but only modest nutrition. It is in the dried form that most legumes find their ways to our dining tables.
Once legumes reach their mature stage, the pods become dry and brittle, they crumble and release the seeds. Before the farmers can be harvest legumes, the pods must dry thoroughly on the vine. Though they originally contain a lot of water (about 80 percent), by the time they are fully dried, their moisture content is less than 20 percent.
If we look at a seed under the microscope, we find three parts. The central mass of substance is the main storage area for the new plant, called the cotyledon. Inside this mass is the embryo of the new plant complete with two tiny leaves, roots and stems. A tube attaches this embryo to the mass of cotyledon, and once the plant emerges, the embryo receives its food supply through this tube, like human embryo through an umbilical cord.
The third part is the seed coat, which acts like our skin. It keeps the whole thing together and protects it from external threats. To serve this purpose, it needs to be tough-a significant fact for cooks, because it is the last thing to soften on cooking. If we cook legumes too long, the skin bursts, spilling out the soft, mushy insides.
The seed coat is tough but it doesn’t protect the seed from hungry insects and animals with sharp teeth and strong jaws. The bean needs other defenses to combat them. Its first defense is two proteins (protease inhibitor and lectin) that interfere with digestion of an animal that is foolish enough to eat the seeds raw. Scientists have shown in experiments that animals fed only raw soybeans actually lose weight because it takes more energy to digest them than they provide.
Rather than learn how to cook them, as we did, animals learned to avoid the raw legumes-those that didn’t died of starvation. One of these two proteins (lectin) provides another protective mechanism-agglutination. It actually causes cells in the eater’s body to clump together. When scientists feed rats only raw beans, they die within a few days because of this.
There’s still another line of defense, this is more straightforward. Many legumes contain the toxin cyanide, that kills any hungry creature that attempts a meal from them. Don’t worry much about this one, though. Only lima beans contain enough to cause a problem in the human body. Older varieties of lima beans had to be cooked thoroughly to eliminate cyanide.
Newer varieties people grow in most parts of the world have had most of the cyanide bred out of them. However, even if it contains cyanide, properly cooked lima beans is not poisonous. Cooked in an uncovered pot the cyanide evaporates. A covered pot traps it, and it falls back into whatever is cooking in the pot. While heat can deactivate the cyanogenic compound in lima beans, cooking old varieties in a covered pot could deactivate you.
Don’t take beans out of your diet because of what you’ve just read. Heat gets rid of the two proteins that interfere with digestion and the cyanide as well.
Legume varieties
Of the 20 major species of legumes we find 7 that are reasonably well known in North
America:
1. Common beans with about a dozen varieties
2. Lentils-the most common variety is brown lentil
3. Peas-yellow, green and black-eyed
4. Chickpeas-we also know it as garbanzo beans by its Italian name
5. Fava beans
6. Soybeans-we use very little directly for food, but for its oil and in innumerable
7. Peanuts-always popular in many forms; we use them as nuts
We cook beans, lentils, peas and chickpeas in many different dishes, fava beans much less frequently, and usually as fresh young vegetables. We use soybeans in a variety of forms but rarely by themselves-we combine them with other ingredients.
The seventh popular legume, the peanut, we actually use as a nut, so I included it in the chapter on nuts. Here is a list of the 13 best known common beans among the hundreds of varieties:
Adzuki (or Chinese)
Black (or turtle)
Cranberry
Great Northern
Lima (both baby and large)
Mung (both green and black)
Navy
Pinto
Red kidney (both light and dark)
Pink
Small red
Small white (or California small white)
White kidney (or cannellini)
While most of the common beans look different, they have very similar flavor. You probably could not tell one from another unless you were taste-testing them side by side.
Tradition, however, demands a specific bean for a specific dish. For a chili con carne, for instance, we prefer pinto beans, for Boston baked beans, navy beans and for the Southern hopping john, black-eyed peas. But don’t be afraid to substitute with whichever you happen to have on hand. It is what you add to them that gives the flavor definition.