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What's with all the Green on my Potatoes

Q:

I know you have covered this before, but what is with all the green on my potatoes when I get them home from the store?

A:

Controlled temperature, humidity and light contribute to maintaining the high quality of Idaho® potatoes. Variations in one of these important factors can cause significant changes in appearance and taste. Greening is the result of one such change.

The “greenish” hue sometimes seen on potato skin occurs when the tubers have been exposed to either natural, artificial or fluorescent lights in storerooms or in supermarket displays.

The color is actually chlorophyll developing in the skin. In some varieties it is green; in others, purple. Along with this change, an increased quantity of solanin is also formed. Solanin, a glycoalkaloid present in all potatoes, is actually part of the flavoring complex that gives the potato its taste.

More of this naturally occurring substance is found in some varieties than in others. In the Russet Burbank, the level is very low. But in all varieties, green potato skin is an indication that excessive solanin is present. The brighter the color is, the higher the level or solanin and the more bitter the taste.

Solanin is generally concentrated close to the potato’s surface and is easily removed when peeled. Only if the potato has had prolonged exposure to light will the bitter taste and color penetrate into the tuber. The green portions can easily be discarded in preparation.

There is little concern about solanin being harmful. At levels that could cause adverse reaction, the solanin level would have to be so high that the potato would be inedible. Furthermore, solanin, if accidentally eaten, does not accumulate in the body. Animal research shows that it is poorly absorbed and rapidly excreted.

Careful measures are taken by the potato industry to keep greening at a minimum. During storage, the tubers are held in darkened cellars and are carefully inspected before shipping. The polyfilm, burlap and cardboard containers used are designed to filter or block out light. Even the dirt left on the potato can have a protective effect in blocking light.

Similarly, in your foodservice operation, fresh potatoes should be stored in a cool, dry, dark, well-ventilated place to maintain quality. When potatoes are on display, they should be rotated regularly and covered whenever possible to reduce overexposure to light.

The Idaho® Potato Commission wishes to thank Robert Dwell, Ph.D., Associate Professor of Plant Physiology, Idaho Research & Extension Center and Stan Osman, Ph.D., Research Leader, USDA-ARS Research Center for the expertise and assistance with the preceding information.