High temperatures and minimal cooking times usually produce the best results. Vegetable tissues soften slowly at around 190°F/85°C, and faster at the boil. Overcooking turns most vegetables mushy and unpleasantly aromatic. Thin leaves are done in just a minute or two.
Some vegetables are slow to soften or never get completely soft when cooked. Beets, water chestnuts, bamboo shoots, lotus root, and many mushrooms remain firm naturally. Potatoes and some other vegetables can be usefully made to do so by holding them at around 140°F/60°C before boiling them. Acid cooking liquids will also slow the softening of most vegetables.
To cook vegetables well, taste them frequently, and stop the cooking as soon as they reach the desired texture.
Cut vegetables to roughly the same size so that pieces will cook through at the same time.
To slow discoloration of cut or peeled vegetables prone to browning, including potatoes and artichokes, drop the pieces into ice water containing dissolved antioxidant vitamin C (250 milligrams per cup/250 milliliters), or acidulated with lemon juice or citric acid (1 tablespoon/15 grams juice or 1 gram acid per cup/250 milliliters). Or toss with powdered vitamin C, lemon juice, or citric acid.
Cut green vegetables into pieces that will cook through in 5 minutes or less. The chlorophyll pigments turn dull if cooked much longer. Cut mature leaves from their thick stalks and midribs so that they can be cooked separately and more briefly.
"Shocking" green vegetables in cold water right after cooking isn't necessary to "set the color." It's a restaurant method that prevents the continued cooking and color dulling that can occur when hot vegetables are simply piled in a colander after boiling or steaming. Shocked vegetables have to be reheated to serve them hot, and reheating can dull color too.
At home, cool just-cooked vegetables to non-dulling serving temperature by transferring them to the serving dish and tossing them with any other ingredients.
Acids of any kind dull green chlorophyll. Dress green vegetables with acidic ingredients (vinegar, tomatoes, or lemon or other fruit juices) at the last minute.
To prevent a wrinkled surface on many cooked vegetables, including asparagus, green beans, carrots, and corn, coat them right after cooking with a little oil or butter. This prevents the hot vegetable from losing evaporated moisture and shrinking.
Cook most frozen vegetables without thawing. For spinach and other delicate leaves that cook very quickly, thaw just enough to break the block apart into small pieces.
Herbs are seldom cooked on their own, either because their flavors are too strong or they're too easily lost in cooking.
Purees of parsley retain their colors and flavor well, while cilantro loses its aroma and basil darkens. Blanching for a few seconds in boiling water helps retain green colors, and cilantro aroma, but diminishes basil aroma.
Brief frying crisps most herb leaves and leaves them translucent while taming the pungency of sage and oregano and retaining some native aroma in basil and parsley. A few seconds in oil at 350°F/175°C is enough for most leaves. Avoid pressing the leaves against the pan bottom, which browns them.
KEYS TO GOOD COOKING provides simple statements of fact and advice, along with brief explanations that help cooks understand why, and apply that understanding to other situations. Not a cookbook, Keys to Good Cooking is, simply put, a book about how to cook well.
Excerpted from Keys to Good Cooking by Harold McGee Copyright © 2010 by Harold McGee. Excerpted by permission of Doubleday Canada, a division of Random House of Canada Limited. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.