Visual and Olfactory Warning Signs
Recognizing a potentially poisonous sweet potato begins with a simple visual and olfactory inspection. A healthy sweet potato should be firm and have a smooth, unblemished skin. If you observe any of the following, it's best to discard the root vegetable to avoid the risk of foodborne illness.
Mold Growth
One of the most obvious signs of spoilage is the presence of mold. Mold can appear as fuzzy patches of white, green, black, or even purplish growth on the skin. While some might be tempted to cut off the moldy portion, this is not a recommended practice for porous vegetables like sweet potatoes. Mold can send mycotoxins deep into the flesh, even if not visibly apparent, which can cause illness. For this reason, if you see mold, the entire potato should be discarded to ensure safety.
Discoloration and Dark Spots
Beyond mold, discoloration can be a key indicator. Dark or black spots on the skin, and especially dark, dry patches on the inside, signal that the sweet potato is past its prime. While a small dark spot might be cut away if the rest of the potato is firm and healthy, extensive discoloration is a red flag. For purple sweet potatoes, discoloration can be harder to spot, but mushy or overly wrinkled texture is a good indicator.
Wrinkled or Mushy Texture
A fresh, healthy sweet potato is firm to the touch. As it ages and spoils, the skin will begin to wrinkle and the flesh will soften, sometimes becoming soft and squishy. If the sweet potato feels soft or leaks a mysterious, sticky liquid, it is a clear sign of rot and should be thrown out immediately.
Off-Putting Odor
Trust your nose when inspecting sweet potatoes. A bad sweet potato will develop an off, sour, or musty smell. This is a sign that the vegetable is beginning to rot and should not be consumed, even if other signs aren't as prominent.
The Role of Sprouting and Taste
While mold and texture are the primary indicators of spoilage, sprouting and taste can also offer important clues about a sweet potato's edibility.
Sprouting: A Potential Indicator
Sweet potatoes, like regular potatoes, can develop sprouts when stored for too long. The growth of large, stalky, purplish sprouts is a sign of an aged sweet potato. These sprouts contain compounds called glycoalkaloids, which can be toxic in large quantities. For sweet potatoes that are still firm and have only small, minor sprouts, you can trim the sprouts off and cook the potato immediately. However, if the sprouts are significant and the potato shows other signs of rot, it's safer to discard it entirely.
The Bitter Taste Test
Sometimes, a sweet potato that appears relatively normal on the outside may have an off or bitter taste when cooked. This bitterness is often a sign of high glycoalkaloid concentration, which can be caused by improper storage, frost damage, or fungal infections like black rot. While the taste is often a natural deterrent, do not consume a sweet potato that tastes unusually bitter, as it can indicate high levels of toxic compounds.
Sweet Potatoes vs. Regular Potatoes
A common misconception is that sweet potatoes are as toxic as regular potatoes when they show signs of spoilage or greening. The reality is quite different, and understanding the distinction is important for food safety. The following table highlights the key differences.
| Feature | Sweet Potatoes | Regular Potatoes |
|---|---|---|
| Botanical Family | Morning Glory Family (Convolvulaceae) | Nightshade Family (Solanaceae) |
| Toxin in Sprouts/Green Parts | Glycoalkaloids (produced when infected or aged) | Solanine (produced naturally, higher in green/sprouted parts) |
| Toxin Level | Relatively low in natural toxins. | Potentially toxic when green or sprouted, especially in large amounts. |
| Primary Spoilage Cause | Mold, bacteria, and rot. | Greening, sprouting, and bruising. |
| Toxicity Risk in Tubers | Low risk for humans unless severely molded or rotten. | Higher risk; green parts and sprouts should always be removed. |
| Can you eat it raw? | Safe in moderation, though can cause discomfort. | Never consume raw due to high solanine content. |
Proper Storage to Prevent Spoilage
To prevent your sweet potatoes from spoiling and potentially becoming toxic, proper storage is essential. They should be stored in a cool, dry, and dark place with good air circulation, such as a pantry or cellar, to maximize their shelf life. The U.S. Sweet Potato Council recommends avoiding refrigeration for uncooked sweet potatoes, as the cold temperature can cause them to develop a hard center and an unpleasant taste. Stored correctly, sweet potatoes can last for several weeks. Cooked sweet potatoes should be refrigerated and consumed within a few days to prevent spoilage.
Conclusion
In summary, determining if a sweet potato is poisonous is less about inherent toxicity and more about identifying clear signs of decay and spoilage. A sweet potato that is soft, moldy, smelly, or extensively discolored should be discarded immediately. While minor sprouting can sometimes be salvaged by removing the sprouts, a pronounced bitter taste or extensive mold growth indicates that the entire vegetable is compromised. By performing a simple visual and olfactory inspection, and storing them properly, you can safely enjoy this nutritious vegetable and avoid foodborne illness. When in doubt, it is always safest to throw it out.
What to Do If You Eat a Bad Sweet Potato
If you believe you have eaten a bad or moldy sweet potato, monitor yourself for symptoms of food poisoning such as nausea, vomiting, or diarrhea. While most cases are mild, severe symptoms or persistent illness require medical attention. Stay hydrated and consult a doctor, especially if symptoms worsen.
Key Takeaways
- Visible Mold: Do not eat sweet potatoes with any mold growth, regardless of how small the patch is, as toxins can spread invisibly.
- Soft or Mushy Texture: A squishy or leaking sweet potato is a clear sign of rot and should be discarded.
- Foul Odor: A sour or musty smell is a reliable indicator that the sweet potato has gone bad.
- Significant Sprouting: While minor sprouts can be cut away, large, prominent sprouts can produce toxic glycoalkaloids, especially when accompanied by a bitter taste.
- Bitter Taste: Never eat a sweet potato that tastes unusually bitter, as this can signal high levels of toxic compounds.
- Proper Storage: Store sweet potatoes in a cool, dark, and dry place away from the refrigerator to prevent premature spoilage.
- Don't Confuse with Regular Potatoes: The glycoalkaloid toxicity risk in sweet potatoes is generally much lower than the solanine risk in green or sprouted regular potatoes.
