Identifying Problem Potatoes

• "Greening" of potatoes typically affects the skin, though the green color can extend a half-inch into the potato's flesh. It may be hard to spot this greening when harvesting potatoes, because of the soil clinging to the outside, but it is easily spotted during food preparation. Because the greening can be missed during industrial processing, you may see potato chips with green edges or fries with green ends.
  
  

The Science behind the Color

• As members of the nightshade family (Solanaceae), potatoes naturally contain a small amount of toxic solanine, a glycoalkaloid, which is concentrated near the skin. Green spots on potatoes contain a much higher concentration of solanine. The green color actually results from chlorophyll, which is not dangerous itself, but it serves to signal the presence of the accompanying solanine.
  
  

Toxic Effects of Green Potatoes

• Alexander D. Pavlista, of the University of Nebraska, reports that "potentially high" levels of toxic solanine for a person weighing 100 pounds could result from eating about 16 oz. -- the sizes of a large baked potato. He estimates that a healthy adult of 200 pounds could safely eat much more, making green potatoes a particular danger for children. The National Library of Medicine lists toxic effects including fever, diarrhea, headache, low pulse, stomach pain, hallucinations, delirium and shock.
  
  

Preventing Potato Greening

• Potatoes turn green when exposed to sunlight. Because potatoes are not really roots -- but specialized stems -- they develop the green color in the sunlight, just like the stems of other vines and herbaceous plants. The same chemical process that develops the chlorophyll, turning the potatoes green, also concentrates the solanine. Preventing this greening is easy: Keep potatoes covered both in the field and in the pantry.
  
  

Safely Handling Green Potatoes

• Solanine is only toxic when eaten, so have no fear of handling green potatoes. Simply cut away the green portions -- including the skin and flesh -- and discard. Pavlista recommends that people with food sensitivities or allergies should avoid eating the whole potato. Because clinging soil can make it hard to spot the greening, wash potatoes thoroughly before cutting or cooking them.