Potatoes begin to sprout as a natural sign of breaking dormancy, a process triggered by environmental cues that signal it is time for the plant to reproduce. This common occurrence in home storage means the potato is converting its stored starches into sugars to fuel the growth of new shoots. The appearance of sprouts, often called “eyes,” signals the potato is preparing to grow a new plant. This shift initiates internal changes that are important to understand before consumption.
The Chemical Change: Understanding Solanine and Toxicity
The process of sprouting is accompanied by the production of compounds known as glycoalkaloids, primarily solanine and chaconine, which are the potato’s natural defense mechanism against pests and disease. These compounds are present in all potatoes, but their concentration increases significantly when the tuber is exposed to light or begins to sprout. When the concentration of these toxins rises above a certain threshold, the potato can become unsafe to eat.
A major visual warning sign is the greening of the potato skin, which often occurs alongside solanine production. The green color itself comes from chlorophyll, which is harmless, but its presence signals that the potato has been exposed to light, stimulating the production of the toxic glycoalkaloids. The highest levels of solanine are concentrated in the sprouts, the eyes, and the green areas of the skin.
Potatoes containing elevated levels of these glycoalkaloids will often have a bitter taste. Ingesting too much solanine can lead to minor poisoning, with symptoms typically including nausea, vomiting, abdominal pain, and diarrhea. While severe poisoning is rare, it can cause more serious neurological effects like headaches, dizziness, and confusion. For most people, a potato with a solanine content of up to 200 milligrams per kilogram is recognized as safe, but concentrations rise rapidly in green or heavily sprouted areas.
Handling and Preparation of Mildly Sprouted Potatoes
If a potato is only mildly sprouted, it may still be safely prepared for consumption, provided it remains firm to the touch. A soft, shriveled, or mushy potato indicates significant water loss and a higher concentration of undesirable compounds, and should be discarded regardless of sprout size. Any potato with extensive green discoloration should also be thrown away.
To prepare a mildly sprouted potato, use a paring knife or vegetable peeler to completely remove the sprouts and the surrounding “eyes.” It is important to peel the skin thoroughly, as the concentration of solanine is highest near the surface. Any remaining green areas must be entirely cut away, often requiring the removal of at least an eighth of an inch of the tuber flesh.
After removing the sprouts and green sections, the remaining potato should be cooked, which can slightly reduce the overall glycoalkaloid content. However, cooking methods like boiling or baking do not completely eliminate the toxins, as glycoalkaloids are relatively heat-stable. The most important safety measure is the complete physical removal of the sprouts and green tissue before cooking.
Optimal Storage Conditions to Halt Sprouting
Preventing potatoes from sprouting involves controlling three primary environmental factors: temperature, light, and airflow. The ideal storage environment is cool, dark, and dry, which slows the metabolic processes that trigger sprouting. A temperature between 40°F and 50°F is recommended to keep potatoes dormant.
Storing potatoes in a cool area, like a dark pantry or basement, is preferable to refrigeration. Overly cold temperatures convert starches into sugars, resulting in a sweeter taste and sometimes a darker color when cooked. The storage location must be dark, as any exposure to light promotes the production of chlorophyll and the toxic solanine. A cardboard box or paper bag can provide the necessary darkness and absorb moisture.
Proper airflow is also necessary to prevent the buildup of moisture, which can encourage rot and sprouting. Potatoes should be kept in breathable containers like mesh bags or ventilated boxes, rather than sealed plastic bags.
Finally, potatoes must be stored separately from ethylene-producing produce, such as apples, onions, and bananas. The ethylene gas released by these items is a natural plant hormone that significantly accelerates the sprouting process in potatoes.