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It is not safe to eat potato sprouts on soft potatoes, though firm potatoes with sprouts are typically safe and can be used once the sprouts have been cut away. Soft, mature tubers that have grown sprouts produce the chemicals solanine and alpha-chaconine. These chemicals act as a natural fungicide and pesticide for the plant, but are toxic for humans. Solanine and alpha-chaconine concentrations are highest in the stems, leaves and in the potato sprouts and green-colored skin of over-ripe and soft potatoes. Poisoning by potato sprouts can be avoided by properly storing potatoes, consuming them soon after purchase and, when present, cutting away the potato sprouts and green skin before consuming.
Soft potatoes with sprouts and green skin should be a signal to the consumer that a potato has undergone an internal change and that the potato flesh is now toxic. When potato sprouts form and a potato is soft, it means the meat of the potato has changed from a starch to a sugar and some of those sugars have been further converted to the glycolalkaloids solanine and alpha-chaconine. The amount of glycolalkaloids depends on the storage condition and age of the potato.
The best way to avoid this poison is to select smooth firm potatoes without sprouts and consume potatoes soon after they are purchased. Sprout formation is accelerated by warmth, moisture and light. If the potatoes cannot be consumed right away, then the potatoes should be stored, unwashed, in a cool, dark, dry area. The storage container should allow for proper air flow and prevent the buildup of moisture.
If potato sprouts form regardless of storage and the potato is firm, then the conversion from starch to glycoalkaloid has not yet occurred and the potatoes are safe to eat once the poor-tasting sprouts have been removed. Potatoes that are soft with spouts and green skin should be discarded. If the potatoes must be eaten in this condition, then the green areas and sprouts should be completely cut away before consuming.
Cooking conditions can also impact the concentration of the solanine and alpha-chaconine. The best way to reduce the toxicity is to fry the potatoes at 338 degrees Fahrenheit (170 degrees Celsius). During the frying, the solanine and alpha-chaconine will leach into the oil. Boiling potatoes suspected of containing solanine and alpha-chaconine does not reduce the toxic concentration. Microwaving suspect potatoes will slightly reduce the toxicity.
When consumed, solanine and alpha-chaconine typically only produce mild gastrointestinal problems such as abdominal cramping, vomiting and diarrhea. A more severe poisoning will produce, along with severe gastrointestinal problems, neurological problems such as headache, a decrease in body temperature, slow pulse and breathing rate, numbness, hallucinations and paralysis. The poisoning is dose-dependent, with the higher doses producing more severe neurological problems and lower doses producing gastrointestinal problems.