What you see: A red potato with dark patches on its skin; below the skin the potato has turned green.
What it is: In response to light exposure, the potato is producing harmless chlorophyll, but also defensive toxins that could make you sick if you ingest enough of them.
Eat or toss: If you peel a red potato and see a lot of vivid, bright green, toss. If the green areas are lighter and isolated, trim them off.
Why do red potatoes turn green?
Previously, we’ve written about the perils of green potatoes. The color change happens when, due to light exposure, either from the sun or overhead lights, potatoes produce chlorophyll, which is green and harmless. But when the potato gears up for photosynthesis by making chlorophyll, it also produces toxins, specifically some types of glycoalkaloids, which can be harmful if you ingest too much.
But you may be wondering if greening on a red potato is any different from greening on a russet or white potato.
Not really. You still want to store red potatoes away from light and not eat any red potatoes that have developed lots of greening. But, keep in mind that a red potato’s skin won’t have the same obvious green color as a russet potato might.
Telltale green warning won’t be as obvious on the skin of a red potato
When mixed with green chlorophyll, a red potato’s skin can darken to purplish brown patches, as you see in the potato pictured here.
You might not see the green until you peel the potato.
But, how green is too green?
It’s always a judgment call. The glycoalkaloids (namely solanine and chaconine), which can cause headache, nausea, vomiting, diarrhea and, in very large amounts, even death, will be elevated, not just in the green area, but throughout the potato.
Still, concentrations will be highest in the green area around the peel. So, while it’s a good idea to trim away the green areas, if there’s a lot of green, even the white parts of the potatoes could contain problematic amounts of glycoalkaloids.
When I shared the potato image above with Nora Olsen, a professor and potato specialist at the University of Idaho, she said it appeared to be “field green,” meaning it was likely exposed to sunlight in the field, resulting in a more intense greening. Potatoes that turn green under lights at the supermarket or in your kitchen may not get quite this green. (Storage tip: store potatoes in a dark place.)
From looking at a green potato, it’s always hard to tell whether it has dangerous levels of glycoalkaloids. In fact, they’re actually present in small amounts in all potatoes and contribute to flavor. As with many substances, the dose makes the poison. But different potato varieties produce different amounts, so an intense patch of green alone doesn’t guarentee the rest of the potato could sicken you.
Also good to keep in mind: Documented instances of poisoning from excessively green potatoes are rare and potato breeds sold in the United States are selected for low levels of glycoalkaloid production.
And, glyocoalkaloids have a “tell”: they’re bitter. Enough of them can even burn your throat.
Potatoes with dangerous toxins taste bitter
So, was the potato above too green to eat? I decided to experiment. On my husband.
I cut off the green areas, with wide margins. Then I boiled the rest of this potato separately from a batch of potatoes with no evidence of greening.
I tasted both types and couldn’t taste much of a difference. My husband’s taste test was entirely blind and he also couldn’t detect any extra bitter flavors from the green potato. At even a hint of a bitter taste, we would have dumped the tubers and deemed them not fit for eating. But they were fine.
Olsen said our approach was entirely reasonable. Though, she said, she would have probably skipped a potato like this altogether, given how intense the greening was and that it covered maybe 20 percent of the potato. To be fair, I handled these very carefully and made sure to do a taste test, something that might not be practical for most people whipping up a quick dinner.
“I would have been like, ‘Oh, that’s pretty dark and I would have set it aside,’” Olsen said.
- Nora Olsen. Potato specialist and professor. University of Idaho.
- Can you eat green potatoes? EatOrToss.com. Sept. 27, 2017.
- Colorado woman ends up in ER after eating poisonous green potatoes. Feb. 20, 2020. Fox6 Milwaukee.
- A Review of Occurrence of Glycoalkaloids in Potato and Potato Products. Duke Gekonge Omayio, George Ooko Abong* and Michael Wandayi Okoth (Department of Food Science, Nutrition and Technology, University of Nairobi). Current Research in Nutrition and Food Science. 2016.
This post was originally published on Nov. 23, 2021, and was updated Jan. 18, 2023.