Veggie Color & pH

Besides the wonderful nutrition they give us, vegetables also add great color and texture to our meals. If you are planning on cooking these veggies, you need to be aware that how you cook them will determine how they will look and taste on the plate. That is the subject of this Cooking Tip.

Green veggies

What gives veggies a green color is chlorophyll. This chemical, though, is destroyed by acids, such as lemon juice and vinegar. To maintain the color, cook them quickly in minimal water. Leave off the lid so any acidic elements can escape.

Chlorophyll also has a tendency to turn dull and brown during extended cooking and storage.

Have you ever noticed that canned green beans tend to be a dull olive-brown color, whereas frozen green beans are intensely green? When green beans are canned, the acids that are naturally in the beans are released into the cooking water. Due to the canning process the acids stay in the can, which means they are cooked and stored under slightly acidic conditions. Thus, the darker color.

Frozen green beans, on the other hand, are blanched in water with a neutral pH, which is less detrimental to the color. They are then frozen to preserve their color and freshness.

Cooking in an alkaline environment causes different chemical changes that result in a greener color. As opposed to regular chlorophyll, the compound that results from these changes is water soluble. Therefore, you may see the cooking water turn very green as well. The downside of cooking in an alkaline environment is that the veggies can turn mushy.

White veggies

Potatoes, onions, cauliflower, and the white parts of celery, cucumbers, and zucchini get their white color from flavones. They may turn a brownish-yellow when cooked with alkaline ingredients. 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. Overcooking can give these veggies a very unappetizing gray color.

Yellow and orange veggies

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 generally retain their color unless they are overcooked. In that case, the color may fade.

Red/purple produce

Anthocyanins impart the red & purple color found in red cabbage, beets, cherries, red and purple grapes. Under neutral conditions, anthocyanins are usually purple. Under acidic conditions, they can become a brighter red. When they’re exposed to alkaline conditions, they will appear more blue or green.

This reaction is reversible in that if your food has changed color due to the addition of too much of an acidic or alkaline ingredient, you may add more acid/alkali to balance the pH, which will reverse the color change. To see a visual of these changes, see this article by Decoding Delicious.

Another point about anthocyanins is that they tend to lose color rapidly during cooking. So, just like green vegetables with chlorophyll, fruits and vegetables with anthocyanins should be quickly cooked with little exposure to water or other fluids.

What does this all mean in practical terms as you are in your kitchen? First, if any these color changes occur, look at the ingredients to see if you can pinpoint the culprit. If you are unsure whether a food is acidic or alkaline, see this chart, which is free of health claims and cautions.

It can also help you improve the color of your veggies. For example, just a small amount of acid will give red beets and red cabbage a bright red color. Have you ever noticed how often cabbage is cooked with tart apples? The acid from the apples will brighten the color.

You do need to be careful about adding acid as it can toughen vegetables and prolong the cooking time. Therefore, if your recipe calls for an acid (lemon juice, tomatoes, vinegar), add just a bit at the beginning of cooking and put in the rest toward the end, after the vegetables have become tender.

If you have ever had your red cabbage lose its red color and turn green, there may be a chemical reaction going on producing both a blue and yellow pigment. When combined, blue and yellow make green. You can prevent this by adding a small amount of acid such as lemon juice or vinegar. If you are making a dish with baked cherries or walnuts, adding just a bit of buttermilk or yogurt may help prevent the discoloration.

There is much more to properly cooking veggies but we will have to leave that to another Tip!