Potatoes can keep producing sprouts long after they are brought home, but food experts say whether they should be thrown away depends on how green, soft, shriveled, or heavily sprouted they have become

That bag of potatoes sitting in your pantry might look fine from the outside, but a few sprouts poking out of the eyes can make anyone pause before cooking dinner. According to Oregon State University Extension Service’s ‘Glycoalkaloids in Potato Tubers,’ the average level of glycoalkaloids in market potatoes should be less than 200 milligrams per kilogram. These naturally occurring compounds increase dramatically after a potato is exposed to light or begins to sprout. The good news is that a sprouting potato doesn’t have to go in the trash. The real question is how far things have gone.

Why do potatoes sprout in the first place
Potatoes are not just dead vegetables in your kitchen. They are living tubers, and they will try to grow with the heat and time. Potatoes belong to the Solanaceae plant family, which also includes tomatoes, eggplants and peppers, and naturally produce glycoalkaloids as a defense against fungi, insects and other pests, as noted in this Oregon State bulletin.

The compounds behind the caution
The two glycoalkaloids of primary interest here are solanine and chaconine. According to the Iowa State University Extension and Outreach AnswerLine article, these compounds are found throughout the potato but are most concentrated in the leaves, flowers, sprouts, green skin, and the area just around the eyes, and least in the flesh. That is why it makes a difference to cut away and peel off sprouts and green spots.

A 2019 peer-reviewed study by Zhang et al. , published in the journal Genes, supports that point. In this research on light-exposed potato tubers, it was found that glycoalkaloid levels could pose a danger to human health. The paper also explains that alpha-solanine and alpha-chaconine account for more than 95% of the glycoalkaloid content in cultivated potatoes, and that chaconine is the more toxic of the two. It notes that levels above 140 milligrams per kilogram make potatoes bitter, while concentrations over 200 milligrams per kilogram can cause burning in the throat and mouth, with severe cases leading to neurological symptoms or even death.

So, keep it or toss it?
The AnswerLine team has a simple rule of thumb: The Iowa State University Extension article cites guidance from Michigan State University and North Carolina State Extension that firm potatoes with only small sprouts can be eaten safely after the sprouts are cut away, and most of the nutrients remain intact.

The guidance changes when sprouts grow long, generally an inch or more, and the potato itself becomes soft or shriveled. That same Iowa State source also says the combination indicates real quality loss, and the potato should be thrown away, not trimmed.

Green means proceed with caution
Greening is a visible warning sign and deserves its own attention, not just as a cosmetic problem. This Oregon State research found that a normal, non-illuminated potato tuber contains about 12 to 20 milligrams of glycoalkaloids per kilogram, while a green tuber can contain 250 to 280 milligrams per kilogram and green skin can contain 1,500 to 2,200 milligrams per kilogram. That’s a big leap.

The bulletin adds that glycoalkaloids rise not only in the green tissue but also in the peel, eyes, injured spots, and sprouts, and that light is the strongest driver of this increase after harvest. It also notes that most tubers mature in about 118 days, and that smaller potatoes tend to have higher concentrations because they carry proportionally more skin.

If the green is only skin deep, it is usually enough to cut it away with a generous margin of flesh. But the Iowa State article says that if the green penetrates deeply into the skin, the tuber should be thrown away entirely because cooking does not destroy glycoalkaloid compounds in any meaningful way.

What actually happens if you eat too much
If you see a single sprouted potato, don’t panic. The Iowa State source explains that the high concentrations of glycoalkaloids make potatoes taste bitter and unpleasant, which is typically enough to dissuade people from eating a dangerous amount. But the same article points out that these compounds can cause headaches, vomiting and other digestive problems in higher concentrations, so if a potato tastes unusually bitter after cooking, it shouldn’t be eaten.

The easiest fix is better storage
Prevention beats sorting through a sprouting bag every week. Potatoes should be stored in a cool, dark, dry, and well-ventilated place, preferably between 45 and 50 degrees Fahrenheit, according to the Iowa State article. This method of storing potatoes can extend their shelf life to three months or more, compared to only about two weeks at room temperature.

The bottom line
A sprouting potato is not an automatic write-off, nor is a potato that is a little green. Firm texture, small sprouts, and surface greening can be worked with a little trimming. But food safety experts draw the line at softness, shriveling, long sprouts, or deep green flesh under the skin. If you’re in doubt, trust your hands and your nose before deciding whether that potato is still dinner or destined for the compost bin.