??Well, they're not dyed for St. Patrick’s Day. These are just from potatoes in which chlorophyll had started to form. This can happen when potatoes, which grow underground, are exposed to too much light in the field or factory, in storage, on the store shelf, or in your home.
The USDA’s “Standards for Grades of Potatoes” consider a potato that’s more than 5 percent green to be damaged, and potato lots that contain them will be graded below US Grade #1. That means most green potatoes never even make it to market.
You’ll still see some every now and again, either in whole or chip form, if conditions in the potato chip plant, the grocery store, or your kitchen are right. Fluorescent lighting and a room temperature of at least 68°F can get the greening process going in a raw potato in just three to five days, and some varieties of potato will start turning in as little as 12 hours even under low incandescent lighting.
By itself, chlorophyll is nothing to be worried about; it’s tasteless and nontoxic. In the process of a potato going green, though, conditions are also right for it to synthesize more of a glycoalkaloid (alkaloid + sugar) poison called solanine, which potato plants produce in their leaves, stems, sprouts and flesh as a defense against insects and other predators. Ingesting solanine can cause nausea, diarrhea, vomiting, stomach cramps, burning sensations in the throat, dysrhythmia, headaches, fever, hallucinations, jaundice, paralysis and death. Toxic levels for people are around one one-hundredth of an ounce for a 200-pound person, who would have to eat about 20 pounds of normal whole potatoes in one day to get sick. With very green potatoes, where the solanine level can increase ten-fold, only two pounds of spuds could leave you ill.
As for potato chips, solanine formation is localized near the potato's skin, usually no deeper than 3 mm. As they're peeled for processing, most of the flesh making up those three millimeters is typically removed. Whatever flecks of green are left are not going to be enough to do anything to you. So, go ahead - finish the whole bag if you want.
What About Dark Brown Potato Chips?
A different matter altogether. Brown potato chips are the result of potatoes being stored too long at low temperatures and accumulating excess sugar. When a potato chip is baked or fried, the sugar reacts with amino acids to produce that beautiful golden-brown color, but too much sugar leads to a very dark brown, almost burnt-looking, color and a slightly different, off flavor.