Not so! The greenish tint is actually a sign that the potatoes have been exposed to too much light—the green is our good friend chlorophyll, which is nontoxic and potentially beneficial for human health. But that friendly greenness signals the arrival of solanine and chaconine, which tend to develop in conjunction with chlorophyll if the potato is exposed to environmental stress, including improper storage conditions or injury. The skin and eyes (and sprouts, if the potatoes are old enough) contain the highest concentration of the alkaloids, although the investigators in the schoolboys’ case also found significant levels of solanine and chaconine in the flesh just beneath the skin as well.
Harold McGee writes in On Food and Cooking: “Most commercial varieties contain 2 to 15 milligrams of solanine and chaconine per quarter-pound (100 grams) of potato.” For comparison, investigators at the London day school found that the potatoes in question contained 47.7 milligrams of alkaloid in their peels alone—plenty to make the boys sick.
Chaconine is more toxic than solanine, but researchers believe that it works synergistically with solanine to produce what is often referred to as solanine poisoning: Symptoms include hypothermia, headache, slow pulse, abdominal pain, vomiting, blurred vision, shock, and, in extreme cases, even death. The onset of symptoms is typically around 2 to 24 hours—which is why some of the schoolboys didn’t feel sick from their lunch until later that evening. (If you suspect solanine poisoning, Mount Sinai warns against attempts to treat symptoms at home. Instead, it advises people to call a poison control hotline or head to the emergency room immediately.)
Current statistics for solanine poisoning are hard to come by, but bad potatoes have certainly been responsible for large outbreaks in the not-so-distant past. As food processing and handling practices have improved, however, and as consumers have become aware of the potential for poisoned potatoes, those large outbreaks have become more rare. But individual poisonings still pop up regularly, such as the case of a Colorado woman who ended up in the ER after eating a bad batch of mashed potatoes in 2020.
Hmm, so what do I do with all these little green guys?
The USDA says that you don’t need to discard green potatoes, but you should prepare them properly: “Peel the skins, shoots, and any green color; that is where the solanines concentrate.” Be a little aggressive if the flesh is still green beneath the peel and remove all traces of it.
Keep in mind that, unlike bacteria such as E. coli and salmonella, solanine and chaconine are not destroyed by baking, frying, or boiling. (UC Davis’s Postharvest Technology Center notes: “Glycoalkaloids are heat stable and minimally impacted by cooking.”) Boiling toxic potatoes might cause them to lose some of their alkaloids to diffusion in the pot of water, but it’s wise not to take chances here.
Incidentally, solanine is quite bitter, so even if you don’t see any outward signs of solanine buildup in your potatoes, you will almost certainly taste it if it’s present in significant quantities. McGee notes that the subclinical levels of these alkaloids in normal potatoes “is part of their true flavor” but “strongly bitter potatoes should not be eaten.”
How should I store potatoes, then?
Potatoes are a root cellar vegetable: That means they’re best stored in a cool, dark environment. McGee adds that potatoes “can be stored in the dark for months, during which their flavor intensifies; slow enzyme action generates fatty, fruity, and flowery notes from cell-membrane lipids.”
Temperature-wise, aim for 45º to 50º Fahrenheit. At that temperature, UC Davis advises, “potatoes should have good quality after storage of 3 to 5 weeks,” though “new” or immature potatoes should typically be eaten within 3 weeks. Storing them in colder environments could lead to a buildup of sugars that make them brown excessively during frying.
Of course, it’s always hard to know exactly how long the potatoes you buy in a grocery store have been off the vine; you might have better luck buying directly from a farmer at a local market. And unless you feel like hallucinating while hacking up your insides, keep an eye out for that dreaded greenish tint—and when in doubt, toss ’em out.
