Spouting or Greening Potatoes . . . Keep or Toss?

“Should a potato with sprouts be used or tossed?” There is a great deal of conflicting advice on the question of use or toss. It comes down to the condition of the potato.

Sprouted potatoes in bag
Photo: MGeiger

As the warmer months approach, potatoes in storage may be showing signs of sprouting or even vigorously sprouting; shriveling may also accompany sprouting as the starch in the potato is converted to sugar to feed the new plants. Potatoes have an inherent natural dormancy maintained by endemic plant hormones. The concentration of the hormones in the tubers decreases over time resulting in sprouts forming at the eyes. When sprouting starts to occurs, this is a sign that the dormant period is over and nature is telling them it is time to reproduce. Even under ideal well ventilated, cool, dry, and dark storage conditions, this natural phenomenon occurs. Potatoes that are improperly stored in the home may exhibit the same sprouting and shriveling regardless of time of year as conditions may trick them into “thinking spring.”

Why the Concern?

Potatoes contain two kinds of glycoalkaloids called solanine and chaconine. Both are naturally occurring chemical compounds. Glycoalkaloids are found throughout potato tubers, but are in highest concentration in the leaves, flowers, sprouts, green skin and the area around the potato ‘eyes’. The lowest concentration is found in the flesh of the tuber.

In normal tubers, glycoalkaloids concentrations are small with a slightly higher concentration in a thin layer immediately under the skin and around the eyes. Peeling potatoes and removing the eyes reduces the presence of the compound. The concentration of glycoalkaloids in sprouts is much higher and can be high enough to be toxic to humans. The more potatoes sprout, the greater the presence of glycoalkaloids in both the sprout and potato itself. High concentrations of glycoalkaloid compounds give potatoes an unpleasant, bitter taste and can lead to headaches, vomiting and other digestive issues.

According to articles by Michigan State and North Carolina Extensions, removing the sprouts will allow safe consumption of the rest of the potato as long as the potatoes are firm, not soft or shriveled, and the sprouts are small. Further, most of the nutrients are still intact. But if the sprouts are long (1 inch or more) and the potato has shriveled, it should be tossed.

The same is nearly true for potatoes exhibiting greening. Green skinned potatoes have been exposed to too much light. Light causes the potato to produce chlorophyll and activate the skin cells to produce solanine which has a bitter taste and is an irritant to the digestive system. Because of the bitter taste, most people do not eat enough to get sick. Despite that, always use caution when greening is found on the tubers as this indicates elevated levels of solanine. Peeling the potato and removing the green portions by simply cutting them out will eliminate most of the toxin. However, if more extensive greening occurs into the tuber, throw the tuber away. Never eat tubers that are green beneath the skin. 

Cooking does not destroy glycoalkaloid compounds; therefore, potatoes exhibiting sprouts and shriveling or deep green parts should not used. Potatoes that are firm and exhibiting only small sprouts at the eye and/or skin-deep greening can be eaten if the entire sprout and any green-tinged parts of the potato are cut away.

Storing Potatoes to Prevent Sprouting and Greening

Storing potatoes the right way will prevent sprouting and greening. As mentioned earlier, potatoes should be stored in a cool (45-50 degrees), dark, dry, and well ventilated location for maximum freshness.  Kept in these conditions, potatoes will likely last up to three months or longer. At room temperature, potatoes will usually last about 2 weeks. Storing potatoes in a cellar or cool basement is ideal. Storage areas should always be away from appliances that give off heat or any area that allows light. If potato tubers will be consumed soon, they can be stored in a cupboard/pantry in a paper bag.

Don’t store potatoes in the fridge. Cold temperatures turn the starches in potatoes into sugars. This makes potatoes sweeter and cook dark. Also, potatoes should not be stored with onions. Storing them together shortens their shelf life. Onions produce ethylene gas which causes potatoes to spoil prematurely. The high moisture content of potatoes can cause onions to turn brown and rot.

In conclusion, sprouted or green potatoes are not necessarily destined for the landfill or compost pile.  With certain precautions, the potato may be safe to eat as long as sprouts and green spots can be cut away. If there is extensive sprout growth, shriveling, and deep green within the tuber, potatoes should be tossed to prevent risk of potential toxicity from solanine and chaconine, the two natural glycoalkaloid compounds found in potatoes.

For other questions about food safety and storage advice that will help keep food safe after purchase or harvest, The Food Keeper is an excellent resource. This handy reference tool was produced by the Food Marketing Institute at Cornell University in conjunction with the United States Department of Agriculture (USDA). It contains useful guidelines for storing food safely. The app is just a finger touch away for IOS and Android smartphones users by visiting the App Store or Google Play and searching for “FoodKeeper Mobile App.” The same app is also available for computer or pads at FoodSafety.gov.

Sources:
Toxic Glycoalkaloids in Potatoes, Centre for Food Safety
Glycoalkaloids in Potato Tubers, Oregon State University Extension
Food Safety of Potatoes, Michigan State University Extension 
Is It Safe to Eat a Potato That Has Sprouted?, North Carolina Extension
Is It Safe to Eat Sprouted Potatoes? Here’s What the Experts Say, EatingWell
Are Sprouted Potatoes Safe to Eat?, Poison Control

Reviewed and updated 3-2024, mg.

Marlene Geiger

I am a graduate of the University of Nebraska-Lincoln with a BS in Home Economics Education and Extension and from Colorado State University with a MS in Textiles and Clothing. I enjoy spending time with family and friends, gardening, quilting, cooking, sewing, and sharing knowledge and experience with others.

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