The Blue Flowers

• Purple cabbages, beets, blue potatoes and many other foods in vivid shades of red, blue and purple owe their color to molecules called anthocyanins. The name derives from the Greek words for "blue flower," not at all inappropriate considering cabbage's resemblance to a flower bud. Anthocyanins are part of the large family of phenolic compounds that give plant-based foods much of their flavor, aroma and appearance. Unfortunately, unlike many other plant pigments, anthocyanins are both water-soluble and very sensitive to pH. That can cause problems when you cook a purple cabbage.

Washing Away

• Adding a handful of finely shredded purple cabbage to your favorite vegetable soup, or using it to give a different look to your St. Patrick's Day meal of corned beef and cabbage, can be a very bad idea. The purple hue of your cabbage dissolves readily in water or broth, and quickly spreads throughout the liquid. It will tint your soup broth and pale vegetables with a pale lavender hue, and will turn your cheerfully pink corned beef to a ghastly gray-blue. It's much better to cook the purple cabbage separately in its own pot, then add it to each bowl or plate at the last minute before serving.

Sweet and Sour

• Anthocyanins also respond poorly to alkalinity. If your tap water is even slightly hard, or if you've added a pinch of baking soda to the water to keep your green vegetables greener, the cabbage will fade to an unhappy blue almost immediately. You can counter that tendency by adding acidity to the recipe, usually in the form of wine, fruit juice or vinegar. Many dishes call for braising the purple cabbage slowly until tender, relying on this acidity to help preserve its attractive color. They usually add some sweetness to offset the acidic tang, and savory ingredients such as bacon or smoked ham to pull all the flavors together.

Fast Cooking

• If you love the crunch of cabbage but don't always want to eat it raw, there's another alternative. Stir-frying your purple cabbage doesn't compromise its color, because it's cooked quickly without any water being present. Shred your cabbage finely enough to cook in the same length of time as your other ingredients, and add it to your wok in small handfuls. The cabbage will wilt and shrink as it cooks, so you'll be able to add more than you think.