What you see: Greenish skin on a potato.
What it is: Chlorophyll buildup that signals higher levels of specific types of glycoalkaloids, which can be toxic if you consume them at high concentrations.
Eat or toss? Is it just a little green? If so, cut or peel away the green area, and eat! But if your potato is starting to look like an emerald, then it’s time to toss.
So, are green potatoes edible?
A slightly green potato is still edible. The toxin associated with green potatoes tends to concentrate in the peel, so if you peel it, or simply peel off the green area in a slightly green potato, you’ll reduce the toxin load. However, if your potato is very green, the toxin level could be particularly high throughout the potato so you won’t want to eat it.
Why potatoes turn green
The “green” in green potatoes is harmless chlorophyll, which the potato happily created when it was exposed to natural or artificial light.
It’s the kind of thing that might happen in the farmer’s field if there was a crack in the soil, in the grocery store under those bright florescent lights or even in your kitchen if you’ve left them on the counter uncovered. (Rule: keep your potatoes in the dark as much as possible).
A toxin lurks in green potatoes
The chlorophyll won’t hurt you, but it does indicate that something more sinister is happening inside the tuber. When chlorophyll builds up, so do specific types of glycoalkaloids, which can be toxic if you consume large quantities of them.
Those glycoalkaloids don’t need light to develop, but they form faster and in greater volumes in a bright environment.
Glycoalkaloids also accumulate in those sprouting potato “eyes” and can cause some nasty things, including severe gastrointestinal distress, along with vomiting and diarrhea, and even death. Potato glycoalkaloids affect the nervous system and can mess with the body’s ability to regulate a chemical involved in nerve impulses.
But a small amount of potato glycoalkaloids won’t make you sick. In fact, any time you’re eating potatoes you ingest small amounts of them—they even contribute to the potato’s taste. Like many things, it’s the dose that makes the difference and very green potatoes carry a large dose.
You need to eat a lot of glycoalkaloids to get sick
While glycoalkaloids are present in trace amounts in normal-looking potatoes, a 200-pound person would need to eat 20 pounds of not-green potatoes in a single day to reach toxic levels, according a report published by the University of Nebraska – Lincoln Extension.
If, writes author Alexander Pavlista, those potatoes had been exposed to light, which can easily increase glycoalkaloid concentrations by 10, that same person could suffer to some degree after eating two pounds of potatoes. For perspective, a large baked potato can weigh about a pound.
Reports of people getting sickened by eating green potatoes are rare. Though it’s also possible that people who only suffer mild symptoms never connect their illness to having eaten green potatoes.
You’ll probably taste bitterness in a green potato before it harms you
Here’s a bit of good news — high concentrations of glycoalkaloids taste so bad that you’ll likely notice the bitter flavor before you’ve consumed enough to make you sick.
Nora Olsen, potato specialist for the University of Idaho, has studied glycoalkaloid concentration in potatoes, but when she encounters a potato with a bit of green in her kitchen, her first worry is flavor, not sickening people.
“They’d have to be really green to get at levels that are going to cause you issues,” she said.
Olsen said that if a potato is slightly green in one area, she’ll just cut that part off. If it’s a deep, vivid green, or green all over, however, she’ll toss it.
Worth keeping in mind—glycoalkaloids tend to concentrate in the peel, so that’s an area where you should be especially cautious. Also important: while cooked potatoes will stop producing glycoalkaloids, cooking will not eliminate existing glycoalkaloids.
Potatoes sold in the US are typically low in glycoalkaloids
One more bit of good news: When it comes to glycoalkaloids, Olsen says that the potato industry has your back. The potatoes that are bred and distributed are selected for their tendency to produce low amounts of glycoalkaloids.
“There’s work in the background going on,” she said.
For more on green potatoes, including what happens when red potatoes turn “green” and a taste test I conducted on a partially green potato, check out the post, “Red potato with dark patches and green under the peel.”
SOURCES:
- Nora Olsen – Potato Specialist for the University of Idaho
- A Review of Important Facts about Potato Glycoalkaloids by Marita Cantwell. Perishables Handling Newsletter.
- G1437 Green Potatoes: The Problem and the Solution. Alexander D. Pavlista. University of Nebraska at Lincoln. Jan. 1, 2001.
- Idaho Potato Commission. FAQ
- Tater Taught: Are Green Potatoes Poisonous? Snopes.com
- Healthy Foods that Can Kill You. Cooking Light.
- Horrific Tales of Potatoes that Caused Mass Sickness and Even Death. Smithsonian.com
- FDA Poisonous Plant Database (Now decommissioned)