Q. When I harvested my potatoes, I noticed that some of the potato skins had areas with a green discoloration. I’ve been told they’re poisonous. Should I discard the green potatoes or the entire crop?
A. Potatoes are an edible tuber that forms underground. It’s important to keep the tubers covered during the growing season so that the maturing potatoes are not exposed to sunlight. The potato skin turns a green or a greenish blue color when exposed to light. The damaged area could be large or small depending on the exposure. The green portion of the skin contains toxins and should not be eaten but that isn’t the issue. The greenish coloration is merely a sign that a potato has been exposed to light, prompting it to produce more chlorophyll, and chlorophyll is not toxic to humans. What creates the problem is that the light exposure also produces a substance called solanine, a glycoalkaloid, which has been shown to be toxic when consumed in great quantities. Solanine is a natural defense mechanism of a potato to ward off fungus and pests. It can also be triggered when a potato is bruised, so you should discard these potatoes. Since solanine collects only under the skin and not throughout the potato, it is safe to peel away the skin and a thin layer of white flesh before cooking; however, I would discard any potato that is entirely green. Again, this is an individual problem that doesn’t affect the other potatoes you harvested, so enjoy them. Potatoes should be stored in a cool dark location. I’d used brown paper bags or a cardboard box and then covered them with newspaper. Dark plastic bags can be used, however you’ll need to punch holes in the bag for air circulation. This keeps the potatoes dry and prevents mold from forming. The kitchen counter is not an ideal location except for a short-term use. Next year when you plant, you can avoid the problem by adding potting soil or other types of organic matter to the potatoes for a couple of months after planting. This is sometimes referred to as ‘Hilling’ and it’s not unusual to add a foot or more of material. Scientists have determined that an adult would have to eat about four and half pounds of light-exposed potatoes to reach toxic levels of solanine. Potatoes are, to a certain degree poisonous, though not in a deadly manner, and usually not enough to make anyone sick. The leaves of the potato plant contain high levels of a toxin, and are direct relatives of the deadly nightshade plant, as are tomatoes. In the US, it has been over fifty-years since any one has succumbed to potato poisoning, so the risk is very low. And finally, according to Wikipedia, deep-frying green potatoes at high temperature at three hundred an sixty degrees effectively lowers the level of toxins but boiling them at two hundred twelve degrees has no effect.
Buzz Bertolero is Executive Vice President of Navlet’s Garden Centers and a California Certified Nursery Professional. His web address is www.dirtgardener.com and you can send questions by email at dirtgarden@aol.com or to 360 Civic Drive Ste. ‘D’, Pleasant Hill, Calif. 94523 and on Facebook at Facebook/.com/Buzz-Bertolero
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