Vegetables should be cooked as quickly as possible, as they loses their color and mushy if overcooked, and worst of all loses vitamins and minerals. Cut vegetables into similar sized pieces so they cook evenly. If vegetables are to be reheated or served cold, use a cold bath to halt the cooking process, but this will also leads to loss of vitamins and minerals.
I do not suggest covering your cut vegetables during cooking as that would make them bland way quicker. Try to add salt or other seasonings at the end of cooking, as salt would quickly discolor the vegetables also can leave dark spots on vegetables. While herbs and spices loses their flavor or can become overly intense. Only use a small amount of water to cook fibrous vegetables. Usually no water are needed for fresh vegetables, as they have plenty of water in their fiber. Besides, too much water increases cooking time and leads to nutrient loss. It is not necessary to add water to frozen vegetables. Eggplant, cassava, potato, squash and tomato should be pricked before being baked in the oven. This would allows steam to escape and prevents them from bursting.
Boiling is vegetables are cooked in boiling water. Place vegetables in a pot large enough to cook them evenly. Only add vegetables when the water is at full boil and keep the heat on high so that the water return to boiling point quickly. If you are cooking hard vegetables, lower the heat so that the vegetables are cooked at simmer preventing the outer layer to soften before the inner are cooked. You can keep covered when cooking hard vegetables, reducing cooking time and the evaporation of volatile substances. Never ever cook green vegetables covered, otherwise, the acids they contain become concentrated and destroy their chlorophyll – make them loses their color.
Adding alkaline substance， such as baking soda, to the cooking water of green vegetables, better preserves their color. However, the downside is they become soft, affects their taste, destroy their thiamine content and accelerates the loss of vitamins.
Adding acidic substance, such as vinegar, dry wine, citrus juice, cider, do preserves the color and firmness of red and white vegetables.
Salt draws out water from vegetables, also tenderizes them. Adding salt at the beginning makes the vegetables juice leak, also leads to nutrients loss. Hence salt are usually added at the end of the cooking process.
Use the least amount of water to boil the vegetables to prevent the reduction of flavor and nutritional value.
Steaming is where vegetables are cooked from the heat released boiling water. Only add the vegetables to the steamer when the water is boiling. Keep covered during steaming. Steaming vegetables results is lesser loss of nutrients and flavor.
Pressure cooking is where cooking in an airtight pressurized container. In a pressure cooker, temperature rises above cooking point, so cooking time are rapidly reduce. Take extra care with the cooking time, even 30 seconds do make a different.
Quick-braising is where vegetables are cooked in their own juice after sauteeing in a small amount of fat or oil. A small amount of liquid can be added if desired at the beginning to get the process started. Cover and cook over a medium heat to blend flavors well. Recommended for squash, mushrooms and hard vegetables.
Braising is slowly cooking the food, covered over a low heat. Cook vegetables whole or cut. Braising suits hard vegetables. Can either braise by vegetables themselves or with a piece of meat for a tasty combinations.
Alternatively know as oven baked or barbecue. Cook in whole with their skin or cut. Cooking with dry heat makes the vegetables tender, juicy and tasty, as well as limit nutrients loss, especially if the skin is left on.
Stir-frying is a quick frying over high heat or steaming process, or a combination of the two. Fry them quickly over high heat, beginning with those that require the longest cooking time. Stir frying vegetables seal in nutrients and preserve color, texture and flavor. Usually garlic or ginger are added as aromatic at the beginning of stir frying. Small amount of liquid are added and then keep covered to initiate the steaming process. Finish off with seasoning.
Deep-drying, as the name has told, cooking at high temperature by immersing vegetables in liquid fats. Peanut oil, flower oil or soybean oil can be used. Heat up the oil temperate to between 300° F – 350° F (oil will catch fire at 425° F). Dry off vegetables or coat them with batter or flour. Cooked vegetables will rise to the surface. Deep frying tend to add large amount of fats to the vegetables without improving their nutritional value.
Microwaving vegetables works best in preserving the color and flavor of the vegetables better than any other cooking method. Keep the vegetables covered to prevent water loss. Cooking time depends on the setting of the microwave oven. Check whether the vegetables is done to avoid overcooking, and return for further cooking if necessary.