Q: What causes the greening of potatoes? Is it really toxic?

A: The green color that occurs on potatoes is a result of inadequate soil coverage during the growth stage and subsequent exposure to sunlight. Or it may be due to exposure to artificial light during storage or while on the retail store shelf.

Greening is affected by more than light exposure. It’s affected by the intensity and quality of light, the duration of light, temperature, as well as the potato variety, maturity and age. White-skinned varieties often green more readily than the red or russet varieties. The latter can green also, but it may be masked and not as easily detected. Immature potatoes and those recently harvested green more readily due to lack of a thick outer skin. Potatoes also develop more greening under light exposure, when temperatures are higher, e.g., 68 degrees versus 41 degrees.

Retail packaging can also contribute to increased greening. Consumers want to be able to view produce prior to purchase. Packaging materials have changed over time from burlap and other opaque materials to transparent bags, which allow exposure to light during retail storage and display.

The green is nothing more than chlorophyll, a harmless and tasteless compound found in all green plants. However, when potatoes turn green there is usually an increase in a glycoalkaloid compound called solanine. The bitter taste associated with green potatoes is caused by the solanine, not chlorophyll. In addition, because glycoalkaloids are slightly toxic, the green portion of the potato can be harmful if eaten in large quantities.

Since the concentration of solanine is greatest in or directly beneath the skin, peeling is effective in removing most of the affected tissue. Also, cooking in steam or water reduces solanine to 60 to 70 percent of the value in raw material.

To be safe, it is best to peel or cut away the green area prior to cooking. Plus, the bitterness can affect the flavor of the cooked potato. Also, certain people may be allergic to the greening.

In addition, as a consumer, it is important to store potatoes in the dark to prevent greening at home.

Q: Are potatoes healthy?

A: Potatoes are a rich source of potassium, vitamin C and fiber. Like other fruits and vegetables, potatoes are a low-calorie food and are free of fat, cholesterol and sodium.

Try roasted potatoes — they are so easy and so good!

Basic roasted potatoes to serve four: Leave the skin on three medium (5- to 6-ounce) red or yellow potatoes. Cut each potato into at least eight chunks. Arrange potato pieces in a single layer on a nonstick baking sheet. Drizzle with 1-2 tablespoons olive oil; toss to coat. If desired, season with your favorite herb or seasoning. (My favorite is Tone’s Canadian Steak Seasoning, which I can find only at Sam’s Club.) Roast, uncovered, in a preheated 425-degree oven for 25 to 30 minutes (or until golden brown and tender), stirring at least once halfway through roasting.

Parmesan potato wedges: Cut three medium (5- to 6-ounce) yellow potatoes into 1-inch wedges; coat with olive oil. Sprinkle with 1/4 cup-grated Parmesan cheese; toss and place on nonstick baking sheet. In a preheated 425-degree oven, roast 15 minutes. Meanwhile, seed and cut one each medium red and green bell pepper into 1-inch strips. Toss in bowl with 1 teaspoon olive oil; place among potato wedges on baking sheet. Roast an additional 10 to 15 minutes, or until potatoes and peppers are tender.

Cajun fries: Cut two russet potatoes (about 8 ounces each) into french fry shapes; coat with olive oil. Sprinkle with 2 to 3 teaspoons Cajun or Creole seasoning; toss and place on nonstick baking sheet. Roast 15 to 25 minutes in a preheated 425-degree oven, or until golden brown and tender.

Pesto-scented potatoes: Quarter eight small red potatoes, uniform in size (about 1 pound). Omit the olive oil (above) and substitute 2 tablespoons prepared basil pesto and 2 minced garlic cloves; toss to coat. Place on a nonstick baking sheet. Roast 15 to 25 minutes in a preheated 425-degree oven, or until golden brown and tender.

Q: Which potatoes are best for what recipes?

A: Potatoes that are high in starch, like russets, have a light, mealy texture. They are best for baked potatoes, french fries, mashed potatoes or potato pancakes.

Yukon golds are medium-starch potatoes. They contain more moisture than those high in starch, so they don’t fall apart as easily. Therefore, they are considered an all-purpose potato — good for roasting, scalloped or mashed.

Most round red, round white and new potatoes are low-starch potatoes, often called waxy. They are dense and hold their shape. They are ideal for boiling (to use in salads) and roasting. Because they are dense, they do not absorb as much salad dressing when making potato salad.

— Susan Krumm is an Extension agent in family and consumer sciences with K-State Research and Extension-Douglas County, 2110 Harper St. She can be reached at 843-7058.