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Why are my sweet potatoes turning green when I bake them?

Quick Answers

There are a few common reasons why sweet potatoes may turn green when baked:

  • Exposure to light – Sweet potatoes produce chlorophyll when exposed to light, turning them green.
  • Cooking at high temperatures – Cooking sweet potatoes at very high temperatures can cause a reaction that turns them green.
  • Age/maturity – More mature sweet potatoes are more likely to turn green when baked.

While strange looking, green sweet potatoes are still safe to eat. The green color does not indicate spoilage or poisoning. It is simply an aesthetic issue. The green color comes from increased chlorophyll production, which is not harmful. However, it can impart a bitter taste.

What Causes Sweet Potatoes to Turn Green?

Sweet potatoes, especially those with lighter flesh, contain chlorophyll and other pigments that give them their orange color. When exposed to light, sweet potatoes ramp up production of chlorophyll and begin to turn green. This is why sweet potatoes are typically cured and stored in complete darkness after harvest. Any light exposure during storage or transport can trigger partial greening.

Additionally, cooking sweet potatoes at very high temperatures may facilitate a reaction between chlorophyll and amino acids that turns the potatoes green. This effect is exacerbated if the sweet potatoes are already partially green before cooking due to light exposure.

Finally, the age and maturity of the sweet potato also plays a role. More mature sweet potatoes that are beginning to sprout or decay are more likely to turn green when baked versus fresh, young tubers.

Light Exposure

Sweet potatoes, like regular white potatoes, undergo a process called photosynthesis. During photosynthesis, the potatoes produce chlorophyll, giving them their vibrant orange-yellow hues. If sweet potatoes are exposed to sunlight or artificial lighting, the increased light triggers an increase in chlorophyll production. This causes green pigments to accumulate in the flesh.

Sweet potatoes are typically cured and stored in complete darkness directly after harvest. Curing involves holding the sweet potatoes at a warm, humid temperature for 5-7 days to heal any cuts and scrapes and seal in moisture. After curing, the tubers are moved to a dark, cool, dry storage area. This prevents chlorophyll formation and greening while the potatoes await sale and distribution.

Issues can arise if the sweet potatoes are not cured and stored properly. Even brief light exposure during transport from the field or sorting and packaging at distribution centers can be enough to jump start chlorophyll production and greening. Produce handlers must take care to minimize light exposure through all supply chain steps.

Cooking at High Temperatures

In addition to light exposure, cooking sweet potatoes at excessively high temperatures may also induce greening. When heated to very high temperatures, compounds in the sweet potatoes can go through the Maillard reaction. This is a chemical reaction between amino acids and reducing sugars that gives browned food its distinctive flavor. It is the same reaction that causes bread to turn golden brown and develop a toasted flavor during baking.

As part of the Maillard reaction, residual chlorophyll in the sweet potato reacts with amino acids and turns green. The higher the cooking temperature, the more intense the green color. Baking, broiling, grilling, and frying are more likely to induce greening versus lower temperature cooking methods like steaming, boiling, or slow roasting.

Preventing excess browning and caramelization helps limit greening when cooking sweet potatoes. Cook them at lower temperatures for longer periods to achieve a tender texture without going overboard on the Maillard reaction.

Maturity and Age

Mature, older sweet potatoes are also more likely to develop green patches and discoloration when cooked. As the tubers age, their chlorophyll levels slowly rise in preparation for sprouting and plant growth. Though invisible on the surface, these increased chlorophyll levels mean the aging tubers are primed for greening.

Additionally, over the-hill sweet potatoes may be starting to decay internally. This decay releases sugars and acids that can react with chlorophyll and cause greening during cooking. The condition of the sweet potato matters greatly in its proclivity for greening.

To minimize greening, cook only fresh, young sweet potatoes that display no signs of sprouting or decay. Avoid using sweet potatoes that have sat in storage for extended periods. Check them carefully for sprouts or soft spots before purchasing.

Is it Safe to Eat Green Sweet Potatoes?

While visually unappealing, green sweet potatoes are safe to eat. The green color does not indicate spoilage, disease, or contamination of any kind. It is simply a cosmetic change due to chlorophyll and has no bearing on the tuber’s edibility.

However, green sweet potatoes are often described as having a bitter, metallic taste. The green patches will likely taste more bitter and unpleasant than the normal orange flesh. Some may find the taste too unpalatable to eat.

If the greening is mild, you can simply cut away the affected parts of the potato. Any green patches or discoloration can be removed before cooking and eating the remaining normal colored flesh. For potatoes that are extensively green, however, it is best to discard the entire tuber.

Not Mold or Spoilage

When seeing green or blue patches on food, people often mistakenly think it is mold. However, the greening on sweet potatoes is not at all related to mold growth. It is simply the overproduction of chlorophyll, which is harmless.

Fresh sweet potatoes are around 80% water. This moisture content makes it very difficult for mold to grow, as mold requires drier conditions. If you spot actual fuzzy mold on a sweet potato, then yes, it is spoiled and should be discarded.

But green or blue-green areas without fuzz or mold are not an indication of spoilage. The potato can still be eaten if the off-color parts are removed.

Not Caused by Poisoning

Some also worry that greensweet potatoes have been poisoned in some way. Perhaps exposure to chemicals or toxins turned them green?

Rest assured this is not the case at all. There are no common toxins that turn sweet potatoes green when applied to the exterior or taken up by the plant. The green color change happens naturally from increased chlorophyll levels.

So while green sweet potatoes look unnatural, they are not toxic or poisonous in any way. You can eat them after removing the colored parts.

Not Underripe or Overripe

The greening also does not indicate anything about the maturity level or ripeness of the sweet potato. An immature, underripe sweet potato can turn green just as easily as an overripe, sprouted potato.

Young, freshly harvested sweet potatoes can start to exhibit greening after just a few days if exposed to light during curing and storage. Light exposure triggers chlorophyll production in potatoes of any maturity level.

However, older, near rotting potatoes do green more easily and extensively since their chlorophyll levels are already high in preparation for plant growth and sprouting. But again, greening can occur in new or old tubers. It is not strictly tied to ripeness.

Preventing Sweet Potatoes from Turning Green

To avoid having your baked sweet potatoes come out of the oven with unappetizing green patches, follow these tips for selecting and storing potatoes as well as preparing and baking them properly.

Choose Firm, Unblemished Potatoes

Carefully inspect sweet potatoes at the store when purchasing them. Choose potatoes that are firm with tight, unwrinkled skin. Avoid any potatoes that have soft spots, breaks in the skin, or show signs of sprouting or mold growth.

Check that the potato’s skin and flesh under any cracks or cuts looks creamy white or orange-yellow. Pass on any tubers with dark bluish-green tints visible through damaged skin.

Store in a Dark, Cool Place

Keep sweet potatoes in a well-ventilated, cool, dark place around 55-60°F after purchase. Do not refrigerate them. The low temperature of the refrigerator can adversely affect the potato’s starch content and texture.

Avoid placing sweet potatoes in sunlit areas or near light sources. Light exposure causes greening to develop slowly over time. Store them in a dark pantry or cupboard instead.

Bake at 350-400°F

When baking sweet potatoes, aim for oven temperatures between 350-400°F. Baking much hotter than 400°F can facilitate greater greening through the Maillard reaction.

The moist, protected environment inside a foil wrapped potato provides ideal conditions for greening at high heat. Bake unwrapped or loosely wrapped in foil to allow moisture to escape and prevent a robust Maillard reaction.

Let the natural sugars in the sweet potato caramelize and brown slowly at a more moderate heat instead of blistering the exterior at really high temperatures.

Parboil Before Baking

Parboiling sweet potatoes for 10-15 minutes before baking helps retard greening as well. The brief boiling helps leach out some of the oxidizing enzymes and chlorophyll content before they go into the oven.

After parboiling until just tender but not fully cooked, you can finish baking the potatoes at 350°F until done. This two-step process minimizes the potential for greening.

Cook Thoroughly Before Eating

Make sure your baked sweet potatoes are completely tender throughout before eating them. Dense, undercooked portions are more likely to develop green patches than fully cooked flesh.

Use a fork to check for doneness. It should slide smoothly through the entire potato without resistance when fully cooked. This ensures the flesh cooks evenly, thereby avoiding underdone sections that may turn green.

What to Do With Green Sweet Potatoes

While green sweet potatoes are edible, you may still want to avoid eating them due to the off-putting color and bitter taste. Here are a few options for using up accidentally greened sweet potatoes.

Cut Away Green Parts

If the greening is minor, simply trim off the green portions of the flesh before eating. The remaining normal colored sections of the baked potato can still be consumed and enjoyed.

Just take care to remove all of the green-hued areas, as these will have an unpleasant bitter taste. The unsightly color can be cut away while retaining much of the edible potato.

Make Sweet Potato Fries

For sweet potatoes baked until they have moderate greening throughout, try turning them into fries instead of eating them whole. When cut into fries or wedges, the thin pieces of potato cook through fully, helping reduce bitterness.

Toss the fries with olive oil, salt, and spices. Roast at 400°F until deeply browned and crispy. The caramelized exterior and robust seasoning helps mask any off-flavors from chlorophyll development.

Mash, Puree, or Blend

Mashing, pureeing, or blending thoroughly combines the sweet potato flesh until uniform. This helps dilute any green patches or bitterness.

While the mash may take on a slightly duller green tone, the bold orange pigments in the rest of the potato should dominate. The deep flavors of butter, brown sugar, cinnamon, and nutmeg also help override the bitter taste.

Make Sweet Potato Pie

For very green potatoes, hide the unappetizing color and flavor by turning them into sweet potato pie. Bake the potatoes until soft and scoop the flesh from the skins.

Puree the green sweet potato flesh with eggs, sugar, cream, and pumpkin pie spice. The bold pie filling ingredients help mask the off-putting green color and taste.

Pour the pie filling into a prepared pie crust. Bake until set and topped with browned meringue if desired. The green sweet potatoes become a creamy orange custard in pie form.

Feed to Livestock

If the greening is too severe to salvage the sweet potatoes for human consumption, you can feed them to livestock. Chickens, pigs, cattle, and horses can safely eat sweet potatoes regardless of their color.

Chop or mash the green potatoes to make them easier to consume. The animals likely will not mind the odd color or bitter taste the way we do.

You can also bury extremely green or rotten potatoes into a compost pile. Over time they will break down into rich soil for your garden.

Frequently Asked Questions

Are green sweet potatoes poisonous?

No, green sweet potatoes are not poisonous. The green color is caused by increased chlorophyll levels, not toxins or contaminants. They are safe to eat though may taste more bitter.

Can you eat parts of sweet potato that are green?

You can eat the green parts of sweet potatoes, but they often have an unpleasant bitter taste. It is best to cut away any green areas and eat only the normally colored orange flesh.

What causes the green in sweet potatoes?

Green in sweet potatoes is caused primarily by exposure to light, which stimulates chlorophyll production and greening. Cooking at high heat and the potatoes’ age can also contribute to greening through chemical reactions.

Are green potatoes safe to eat?

Green potatoes are safe to eat, but tend to taste bitter and unpleasant. You can remove green areas and eat the rest. Severely green potatoes are best discarded or used for non-food purposes.

Can you still eat a sweet potato if it’s green?

Yes, you can still eat a sweet potato or parts of it even if it has turned green. The green sections will likely be more bitter tasting. Removing green areas can allow you to eat the rest of the potato.

Is it bad to eat green sweet potatoes?

Green sweet potatoes are not harmful or toxic, but they frequently taste bitter. Many people find them too unpalatable to eat. Cooking methods like mashing or making pie can help offset the bitterness.

What happens if you eat green potatoes?

Eating a green potato will likely give you an unpleasant bitter flavor but is not dangerous. Some solanine buildup may cause minor stomach upset if very large quantities of green potatoes are eaten.

Conclusion

Sweet potatoes can turn an unnatural green color when baked due to reactions between chlorophyll and amino acids at high heat. While this outward greening may seem odd, rest assured it poses no safety risks.

Choose firm, fresh potatoes and store them properly to limit greening potential. When cooking, bake at moderate temperatures and allow potatoes to fully soften. If they still turn green, remove the discolored sections, make fries or pie, or feed to livestock to put those green potatoes to use.