An “old potato” is a tuber showing visible signs of deterioration from prolonged storage or improper conditions, such as greening, sprouting, shriveling, or softening. Consumers are concerned about their safety before consumption. The primary risk is not simple spoilage, but the potential buildup of naturally occurring toxic compounds. This article guides you through the specific dangers and provides advice on how to manage your potato supply.
The Primary Danger: Glycoalkaloid Buildup
Potatoes, members of the nightshade family, naturally produce steroidal alkaloids called glycoalkaloids as a defense mechanism against insects and diseases. The two main compounds are alpha-solanine and alpha-chaconine, accounting for over 95% of the total glycoalkaloid content. These compounds act as the plant’s natural pesticide and fungicide, concentrating in vulnerable areas like the sprouts, skin, and “eyes.”
The concentration of these glycoalkaloids increases when a potato is exposed to light, physical damage, or high temperatures, which triggers the plant’s stress response. A normal, healthy potato typically contains well under the safety threshold of 200 milligrams of glycoalkaloids per kilogram. A green tuber can easily exceed this level. Once ingested, these toxins disrupt cell membranes in the digestive system and interfere with the nervous system by inhibiting the enzyme acetylcholinesterase.
The toxic dose for humans is 1 to 2 milligrams of total glycoalkaloids per kilogram of body weight. For a 150-pound adult, consuming a single meal’s worth of potatoes with an extremely high toxin concentration could lead to adverse effects. The bitter taste that often accompanies old or green potatoes is a warning, as the compounds are detectable when concentrations reach about 14 milligrams per 100 grams of potato.
Signs and Symptoms of Potato Poisoning
Ingesting elevated levels of glycoalkaloids primarily affects the gastrointestinal tract and the nervous system. Mild cases, which are the most common, manifest as gastrointestinal distress, including nausea, vomiting, stomach cramps, and diarrhea. These symptoms usually occur within a few hours of consumption and often resolve within a day.
Consuming a toxic dose can lead to more severe reactions. These symptoms include headaches, fever, and neurological issues such as apathy, drowsiness, confusion, or shaking. In rare instances involving massive consumption of highly toxic potatoes, serious effects like paralysis, respiratory failure, or coma have been reported. If you experience persistent vomiting, diarrhea, or any neurological symptoms after eating potatoes, seek medical attention immediately.
Safety Guidelines for Consumption and Disposal
When a potato shows signs of age, discarding the entire tuber is not always necessary, but preparation steps are required to mitigate risk. Since glycoalkaloids are heavily concentrated in the outer layers and sprouts, peeling the potato removes a substantial amount of the toxin. You should also use a knife to generously trim away any sprouts and any area that appears green beneath the skin.
If a potato exhibits extensive greening, is soft or mushy, or has a noticeable, strong bitter taste after cooking, it must be discarded completely. The bitter flavor reliably indicates that the glycoalkaloid concentration is dangerously high and cannot be safely reduced through simple trimming. Peeling, cutting, and boiling only reduce the toxin content by a small amount, as the compounds are not destroyed by cooking at normal temperatures.
Preventing Premature Aging of Potatoes
The best way to manage the risk from old potatoes is to prevent the conditions that cause toxin levels to rise. Potatoes should be stored in a cool, dark, and dry environment to maximize shelf life and minimize glycoalkaloid production. The ideal storage temperature range is between 45 and 55 degrees Fahrenheit, which is cooler than most pantries but warmer than a refrigerator.
Light exposure accelerates greening and toxicity, as the conditions causing chlorophyll production also stimulate glycoalkaloid synthesis. Therefore, potatoes must be kept away from direct sunlight or bright artificial light. Also, never store potatoes next to fruits and vegetables that emit ethylene gas, such as onions, bananas, or apples, as this hormone speeds up the sprouting process and premature aging.