How to Prevent Discoloration in Vegetables When Cooking

Vegetables Color Problems When Cooking

Vegetables are such a vital part of our diet, it is important to know how to prepare it correctly and as many varieties as possible. After all, you need to keep eating your greens to keep you healthy. Most people don't get nearly the recommended amount of vegetables each day, but now lack of knowledge can't be your excuse!

Cooking changes a vegetable's texture, flavor, color, and nutrient content. High temperatures make vegetables tender and enhance flavor. In addition, cooking usually makes vegetables safer to eat by killing microbes. Overcooking, however, will cause texture, flavor, color, and nutrient content to deteriorate.

1) The key to cooking vegetables is to make the tissue tender without making it too soft. You can determine whether a vegetable is done by testing a piece during cooking. Most vegetables should be tender but still firm. Color can also indicate whether a vegetable is done. Green vegetables are overcooked if they turn an olive green. Delicate leafy vegetables require only a few minutes to cook, while stem and root vegetables may require more time.

2) Quick cooking and the least exposure to water or other fluids are recommended.

3) Acidic ingredients, such as citrus juice, tomatoes and vinegar, should be withheld during the very last minutes to help avert color loss.

4) The firm cellular structures of some vegetables are vulnerable to both heat and acids. Raw green vegetables are less affected than cooked vegetables because their protective cell walls have not been exposed to heat. If green vegetables are cut into small pieces to facilitate faster cooking, this may help retain the phytochemical chlorophyll.

5) Chlorophyll is the source of their bright green color pigment present in all green vegetables such as asparagus, green beans, broccoli, peas, and spinach. Chlorophyll is destroyed by acids, such as lemon juice and vinegar, and by baking soda. Prolonged cooking or overcooking causes bright green vegetables to turn a drab olive green. Steaming is the most preferred method for cooking because steam cooks food rapidly, lessens the loss of nutrients and flavor, and does not break up delicate vegetables.

6) Potatoes and onions may turn a brownish-yellow when cooked with alkaline ingredients, such as egg whites, or in certain metal pots, such as aluminum or iron. This reaction may be due to the flavonoids in potatoes and onions, plant substances with antioxidant properties. An acidic ingredient, such as cream of tartar, lemon juice or vinegar, may be added to help neutralize the alkaline environment in which these vegetables are cooked and prevent discoloration.

Flavones are the white pigments found in potatoes, onions, cauliflower, and the white parts of celery, cucumbers, and zucchini. Cook these vegetables for a short time to avoid loss of nutrients, flavor, and color. Overcooking and hard water turn white vegetables a dull yellow or gray.

7) Acidic tomatoes, chili peppers and/or onions may also help to prevent avocadoes from turning brown in guacamole. Other colorful photochemicals, or plant compounds that undergo the effects of cooking, include anthocyanins, betalains and carotenoids:

8) Carotenoids are the yellow and orange pigments found in carrots, corn, sweet potatoes, tomatoes, and winter squash. These pigments are very stable to acids and heat, but loss of color, nutrients, and flavor occurs with overcooking.

9) Anthocyanins, found in ruddy cherries, red and purple grapes, red cabbage, walnuts and wine, tend to lose their color rapidly during cooking. Like bright green vegetables with chlorophyll, fruits and vegetables with anthocyanins should be quickly cooked with little exposure to water or other fluids.

Anthocyanins are the red pigments found only in a few vegetables, such as beets and red cabbage. These red pigments react very strongly to acids and alkalis. Acids make anthocyanins brighter red, and alkalis turn them a blue or blue-green color. So a small amount of acid gives red beets and red cabbage a bright red color. This is why red cabbage is often cooked with tart apples. Because acids toughen vegetables and prolong cooking time, in recipes that call for lemon juice, tomatoes, or other acids, add only a small amount at the beginning of cooking and the remaining toward the end after the vegetables have become tender. Since anthocyanins dissolve easily in water, cook these vegetables quickly in as little water as needed.

10) Red cabbage loses its color and turns green in some sauces because of two chemical reactions: one that produces a blue pigment and one that produces a yellow pigment. When these two pigments combine, they produce a blue-green color. To prevent this reaction, a little acidic lemon juice or vinegar may be added to the cabbage. Likewise, a little acidic buttermilk or yogurt may be added to cherries or walnuts during baking to help prevent their discoloration.

11) Betalains, found in purple-red beets, rapidly stain other ingredients. To prevent staining, once beets are cooked, they should be carefully dried and added last to other ingredients. If beets are marinated in an acidic ingredient, such as lemon juice or vinegar, it may darken their color.

The reverse is true with grapes: the longer grapes are immersed in a sauce or dressing, the greater the chance that they will lose their color.

12) Carotenoids, found in brightly colored orange and red fruits and vegetables, such as carrots, tomatoes, pumpkins and sweet potatoes, generally retain their color unless they are overcooked.

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Basic Cooking Methods to Prevent Color Changes in Vegetables

General Procedures:

1) Use as little water as possible, with the exception of strong-flavored vegetables like cabbage.

2) Cover yellow, orange, and red vegetables. Do not cover green and white vegetables.

3) Cook vegetables as quickly as possible to soften fibers and retain nutrients, color, and flavor.

4) Drain vegetables, but save the cooking water because it contains nutrients and flavor. Use the water in soups, sauces, and gravies.

5) Season vegetables before serving. Use salt and high-fat sauces and butter sparingly.

6) You should stop cooking vegetables when they become tender. Desired tenderness varies depending on the vegetable. Winter squash, eggplant, and similar vegetables are properly cooked when they turn soft, but most vegetables are best when cooked very briefly or until they are crisp tender. At this stage vegetables maintain their maximum flavor, color, and nutrients.

Using Microwave Oven to Cook Vegetables

1) Vegetables cook quickly and easily in the microwave oven. Only a few tablespoons of water are needed and microwaving preserves the nutrients, color, and texture of most vegetables. Always cover vegetables in the microwave. To microwave vegetables:

2) Place evenly cut vegetables in a ceramic dish. Add 2 tablespoons of water to fresh vegetables. Frozen vegetables usually require no extra water.

3) Cover the vegetables and cook on high until fork tender. Halfway through the cooking cycle, stir the vegetables.

Steaming is a Good and Healthy Option

1) This method can be used for both pressurized steam cookers and range-top steamers which contain a perforated basket over a pot of boiling water. Pressurized steamers are not recommended because it is too easy to overcook the vegetables.

2) If you use a pressurized steam cooker, follow the manufacturer's instructions. For range-top cooking, bring 1 to 2 inches of water to a boil in a saucepan.

3) Arrange vegetables in shallow, even layers in a perforated pan or basket for cooking.

4) Insert pan or basket into steamer or saucepan and cook until fork tender for most vegetables. Follow guidelines for preserving color, texture, and nutrients.

5) Use 2-Tiered 6-quart capacity steamer that creates instant steam for preparing all kinds of food like Oster Food Steamer.

In summary, heat may cause bright green vegetables to lose their color during cooking. In order to preserve the color of vegetables, it is better to shorten the cooking time; use tap water, which is a little alkaline; plunge the vegetables into ice water to halt the cooking process and then reheat briefly; or add a little protective seal of fat or oil right after cooking. This may be a bit of olive oil or butter. The use of an acidic ingredient in a sauce or dressing should be withheld until the very last minute, since the acid may further break down the cell walls. To make your cooking easier use the recommended cooking times below:

Recommended Cooking Times for Common Vegetables

Vegetable	Steam	Microwave	Blanch	Boil	Other
Artichoke, whole	30 to 60	4 to 5 each	not recommended	25 to 40	not recommended
Artichoke, hearts	10 to 15	6 to 7	8 to 12	10 to 15	Stir-fry 10
Asparagus	8 to 10	4 to 6	2 to 3	5 to 12	Stir-fry pieces 5
Beans, green	5 to 15	6 to 12	4 to 5	10 to 20	Stir-fry 3 to 4
Beans, lima	10 to 20	8 to 12	5 to 10	20 to 30	not recommended
Beets	40 to 60	14 to 18	not recommended	30 to 60	Bake 60 at 350°F
Broccoli, spears	8 to 15	6 to 7	3 to 4	5 to 10	Blanch, then bake
Broccoli, flowerets	5 to 6	4 to 5	2 to 3	4 to 5	Stir-fry 3 to 4
Brussels sprouts	6 to 12	7 to 8	4 to 5	5 to 10	Halve; stir-fry 3 to 4
Cabbage, wedges	6 to 9	10 to 12	not recommended	10 to 15	Blanch leaves, stuff and bake
Cabbage, shredded	5 to 8	8 to 10	not recommended	5 to 10	Stir-fry 3 to 4
Carrots, whole	10 to 15	8 to 10	4 to 5	15 to 20	Bake 30 to 40 at 350°F
Carrots, sliced	4 to 5	4 to 7	3 to 4	5 to 10	Stir-fry 3 to 4
Cauliflower, whole	15 to 20	6 to 7	4 to 5	10 to 15	Blanch, then back 20 at 350°F
Cauliflower, florets	6 to 10	3 to 4	3 to 4	5 to 8	Stir-fry 3 to 4
Corn, on cob	6 to 10	3 to 4	3 to 4	4 to 7	Soak 10; bake at 375°F
Corn, cut	4 to 6	2 per cup	2 1/2 to 4	3 to 4	Stir-fry 3 to 4
Eggplant, whole	15 to 30	7 to 10	10 to 15	10 to 15	Bake 30 at 400
Eggplant, diced	5 to 6	5 to 6	3 to 4	5 to 10	Bake 10 to 15 425°F
Greens, collard/mustard/turnip	not recommended	18 to 20	8 to 15	30 to 60	Stir-fry mustard greens 4 to 6
Greens, kale/beet	4 to 6	8 to 10	4 to 5	5 to 8	Stir-fry 2 to 3
Kohlrabi	30 to 35	8 to 12	not recommended	15 to 30	Bake 50 to 60 at 350°F
Mushrooms	4 to 5	3 to 4	not recommended	3 to 4 in broth or wine	Stir-fry or broil 4 to 5
Onions, whole	20 to 25	6 to 10	not recommended	20 to 30	Bake 60 at 400°F
Onions, pearl	15 to 20	5 to 7	2 to 3	10 to 20	Braise in broth 15 to 25
Parsnips	8 to 10	4 to 6	3 to 4	5 to 10	Bake 30 at 325°F
Peas	3 to 5	5 to 7	1 to 2	8 to 12	Stir-fry 2 to 3
Peppers, bell	2 to 4	2 to 4	2 to 3	4 to 5	Stir-fry 2 to 3
Potatoes, whole	12 to 30	6 to 8	not recommended	20 to 30	Bake 40 to 60 at 400°F
Potatoes, cut	10 to 12	8 to 10	not recommended	15 to 20	Bake 25 to 30 at 400°F
Spinach	5 to 6	3 to 4	2 to 3	2 to 5	Stir-fry 3
Squash, sliced	5 to 10	3 to 6	2 to 3	5 to 10	not recommended
Squash, halves	15 to 40	6 to 10	not recommended	5 to 10	Bake 40 to 60 at 375°F
Squash, whole	not recommended	5 to 6	not recommended	20 to 30	Bake 40 to 90 at 350°F
Tomatoes	2 to 3	3 to 4	1 to 2	not recommended	Bake halves 8 to 15 at 400
Turnips, whole	20 to 25	9 to 12	not recommended	15 to 20	Bake 30 to 45 at 350°F
Turnips, cubed	12 to 15	6 to 8	2 to 3	5 to 8	Stir-fry 2 to 3
Zucchini	5 to 10	3 to 6	2 to 3	5 to 10	Broil halves 5

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Keep yourself healthy and happy cooking! :-)