Use a sharp knife to cut vegetables, and try not to bruise them. The destruction of vitamin C is hastened by an enzyme that is present in raw fruits and vegetables. This enzyme becomes active when leaves or fruit are damaged by drying, bruising, or ragged cutting.
Cut vegetables in fairly large pieces for cooking. This reduces the amount of surface area exposed to water and oxygen, and will cut down on vitamin C and folacin losses. Never soak vegetables in water for long periods of time.
Prepare vegetables just before serving. If they are not going to be eaten right away, cool them, put them in the refrigerator, and reheat just before serving. Never keep vegetables at high temperatures for any lenght of time.
Adding the vegetables to boiling water shortens the cooking time and prevents the oxidative destruction of vitamin C by removing some of the oxygen dissolved in the water. Once the water has come to a second boil, turn down the heat so the vegetables boil gently. Avoid overcooking. Overcooked vegetables will not be very nutritious.
Cook vegetables in as little water as possible. There should be little or no water left by the time the vegetables are through cooking.
Cover cooking vegetables. This shortens cooking time, and cuts down on the loss of vitamin C and folacin from oxidation.
Cook vegetables until just fork tender. Make them crunchy rather than soft and mushy.
Drain leftover cooking water into a covered container. Use it within two or three days in soup, stew, or gravy. This water contains vitamin C and folacin from the vegetables.