We all know that vegetables, whether edible or not, are part of plants-potatoes are enlarged parts of the roots, carrots are the roots themselves, celery is the main stalk, spinach is the leaf, artichoke is the flower and eggplant is the fruit. Mushrooms are exceptions. They don’t belong in the Plant Kingdom but are fungi.
Several parts of certain plant may be edible, such as the root and leaves of turnips and beets, while in some plants a certain part is edible, others may be poisonous. The enlarged root of the potato plant is perfectly healthy to eat but the poisonous leaves you want to eat only if you are contemplating suicide. Rhubarb has a wonderful edible stalk but the leaves can kill you.
All vegetables have fibers, a substance essential to human health, but some have more, others have less. Fibers give rigidity and shape to the living plant. We cannot digest fibers, which are organic substance called cellulose, so they have no nutritive values to the body. But we cannot digest our foods without them.
The vegetables that cook quickly, e.g. cabbage, have relatively low amounts of fiber, those that are slow-cooking, such as artichoke, are often high in fiber. Age also determines how much fiber a vegetable has. The older it is, the more fibrous. A young kohlrabi is soft and tender like a fresh radish, while an old one is hard to cut through with a knife, it is so full of tough fibers.
The root-end parts of plants have higher fiber content than the blossom-end part. The bottom portion of an asparagus is full of coarse, tough fibers while the young top velvety-tender tips have very little.
Cooking for best appearance
There are pigments that Nature uses to dye vegetables. Intensely colored vegetables on the plate give a great impact to our visual senses that translates to heightening appetites. Our early American heritage from English and northern European immigrants favored overcooked vegetables, a tradition that continued until relatively recently.
Overcooking kills flavor because the volatile flavor components escape with the steam, but it also kills color pigments. Compare the favor and color of overcooked green beans to crisp quick-cooked beans. Today’s tendency of vegetable cookery among the new foodies is crisp, but tender-brief cooking to the point of al dente. But such tendency is regional. People in the southern U.S., for instance, still tend to cook vegetables longer than their compatriots on the East and West coasts.
Green is the most common vegetable color. The pigment chlorophyll gives the green coloration and this pigment is sensitive to length of cooking and acidity of the cooking liquid. Both destroy the pigment and change it to another pigment that has a drab, unappetizing army olive-green color.
Never cook green vegetables in acidic liquid. Yet, all vegetables contain some acid and long cooking leaches those into the cooking liquid. As a result, the water becomes more and more acidic and the chlorophyll pigment disappears. Cooking green vegetables in uncovered pot is helpful because in covered pot water concentrates the acid, but without the lid much of it evaporates with the steam.
Older cookbooks suggest adding baking soda to the cooking water to make it alkaline and retain bright colors. More recently nutritionists found, on the other hand, that vegetables they cook in alkaline water lose much more nutrients than those they cook in neutral and acidic water. Hence, never add baking soda to the vegetable cooking water.
Yellow and orange vegetables owe their colors to pigments called carotenoids. Carrots, corn, tomato, winter squashes and red peppers carry these pigments. They are very stable in either long cooking or acids, but if you cook these vegetables very long, even these pigments transform and the vegetables’ color turn dull.
Red and purple color pigments are called anthocyanins. Beets and red cabbage carry these. They are very stable on long cooking but prolonged overcooking still destroys them, and your beet or cabbage turns colorless. But these pigments are extremely sensitive to acidity. Acid brightens the pigments, alkali changes them to blue or blue-green as you may have noticed when cooking red cabbage.
The change is not permanent-add a little acid (vinegar, lemon juice or cream of tartar) to the cooking water for your red cabbage that had turned blue, and it changes back to red.
White color pigments are the anthoxanthins. Potatoes, white cabbage, onion and cauliflower carry these pigments but also the white parts of leeks, celery, cucumber and zucchini. White pigments are stable on long cooking and remain stable in acidic cooking water.
Alkalic water changes them to yellow pigments. So if you want your cauliflower to turn dingy yellow for your dinner guests you don’t like, add baking soda to the cooking water. Otherwise a little lemon juice or other acid keeps white vegetables snow white. But prolonged overcooking or holding vegetables over heat too long also changes colors to dull yellow, grayish pink or any unappetizing shades.