The Science Behind Green Potatoes: Chlorophyll and Solanine
Potatoes are a staple in many diets, but occasionally they can take on a peculiar green hue. This color change is caused by the potato's production of chlorophyll, the same pigment that makes leaves green. While chlorophyll itself is harmless, its presence is a crucial sign that the potato has also begun producing solanine, a natural, bitter-tasting toxin. Both compounds are triggered by the potato tuber's exposure to light during storage or growth.
The Role of Light Exposure
Potatoes are underground tubers, and their natural habitat is dark. When they are exposed to light, whether from store displays or kitchen counters, they interpret this as a signal to photosynthesize, producing chlorophyll. This process is the potato's way of preparing to sprout and grow new shoots. However, this same exposure to light also triggers the plant's defense mechanism, which is the production of glycoalkaloids like solanine. The amount of solanine increases with the duration and intensity of the light exposure.
Solanine: The Cause of the Bitter Taste
Solanine is a colorless, toxic glycoalkaloid that a potato produces as a natural defense against pests and diseases. It is a neurotoxin that, in high concentrations, can cause gastrointestinal upset, headaches, and other neurological symptoms. Fortunately, the characteristic bitter taste of solanine makes it unlikely for a person to eat enough to cause serious harm, as the flavor is a built-in warning system. The highest concentration of solanine is found in the skin and the area just beneath it, which is why peeling is an effective step in removing the toxin.
What to Do with Green or Bitter Potatoes
If you discover that your potatoes have turned green or taste bitter, your actions should depend on the severity of the issue.
- Mild Greening: If only a small area of the skin is green, you can simply peel away the green portion and a little extra flesh beneath it. According to the USDA, this is often enough to make the potato safe to eat. However, if the potato tastes bitter, you should throw it out.
- Extensive Greening or Bitterness: If the green color runs deep into the potato's flesh or if the potato has a strong bitter taste, it's best to discard it entirely. Cooking does not effectively destroy solanine.
Comparison Table: Safe vs. Unsafe Green Potatoes
| Characteristic | Mild Greening (Safe to Eat After Trimming) | Extensive Greening / Bitter Taste (Unsafe) |
|---|---|---|
| Appearance | Light green patch, typically on the surface only. | Deep green color extending into the flesh. |
| Taste | No noticeable bitter taste after peeling. | Distinctly bitter flavor, even after cooking. |
| Feeling | Firm texture. | Soft spots or shriveled appearance. |
| Action | Peel and trim away green areas and sprouts before cooking. | Discard the entire potato. |
Proper Storage is Key to Prevention
To prevent potatoes from turning green and developing solanine, proper storage is essential. As stated in an article by Purdue University, potatoes should be stored in complete darkness.
A simple and effective method:
- Store potatoes in a cool, dark, and dry place, such as a pantry, cellar, or cupboard.
- Ideal temperatures are between 45–50°F (7–10°C). Avoid storing them in the refrigerator, as the cold can cause starches to convert to sugar, affecting texture and flavor.
- Keep potatoes away from direct sunlight and artificial light, which can trigger chlorophyll and solanine production.
- Use a paper bag, mesh bag, or cardboard box for storage instead of a plastic bag. This allows for air circulation and helps prevent moisture buildup that can accelerate spoilage.
- Store potatoes separately from other produce, especially onions. Onions and potatoes both release gases that can cause the other to spoil faster.
Conclusion
Understanding what turns potatoes green and bitter is crucial for ensuring food safety in your kitchen. The harmless green chlorophyll acts as a visible warning sign for the presence of solanine, a natural toxin that causes bitterness and can be harmful if consumed in large quantities. While mild greening can be addressed by careful peeling and trimming, any potato that is extensively green or tastes bitter should be discarded. By adopting proper storage techniques—keeping potatoes in a cool, dark, and dry place—you can easily prevent this issue and enjoy your spuds safely.
