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Why Do Potatoes Turn Green? Are They Safe To Eat?

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Potatoes are a kitchen staple and the building blocks of many recipes. They’re in every culture and they’re just swell to have around. Nearly everything good to eat has some sort of potato in it, no matter how it’s cooked. This is not only the most filling vegetable, it’s also possibly the most delicious. 

So what do you do when you reach into your cupboard for those last 4-5 potatoes and they’ve all got a green tinge to them ? Why do potatoes turn green, and is there anything you can do about it ? Can you eat the green parts ? Let’s take a look.

potato green

Why do potatoes turn green ?

Potatoes turn green when they contain elevated levels of solanine, a type of natural poison primarily found in potatoes and nightshade. The green color appears because it is actually the pigment chlorophyll (green), which develops when the potato tubers are exposed to sunlight. And prolonged exposure to sunlight leads to the development of solanine. 

So green potatoes are green because they’ve been exposed to sunlight, and this has also triggered the development of a poison in them. This can happen due to poor storage, or because potatoes sometimes grow near the surface of the soil and farmers don’t manage to cover them with more soil in due time. 

Generally, commercial potato crops are closely monitored to ensure they don’t turn out green, and are usually stored very well. 

Is it safe to eat green potatoes ?

We recommend you don’t eat the green part of the potato, as that is where the most amount of solanine is. Always peel your potatoes, because solanine is mostly concentrated in the outer layer. In the case of green potatoes, it depends on how much green there is. 

If it’s a green end and you have a large potato, cut off the green and another half inch past that and you should be fine. If it’s a very small potato and it has a green end, we recommend throwing out the entire potato because almost all of it could have high solanine levels. 

Solanine – what is it ?

Solanine is a type of natural poison, specifically a glycolalkaloid (a combination of sugars with alkaloids). Solanine is most common in potato greens, leaves, and stems, because those are the ones exposed to direct sunlight. It’s also found in the poisonous nightshade flower. 

Why does solanine exist ? It’s the plant’s natural defense against being eaten, but as humans we don’t eat the top part of the potato plant, we only eat the root. So this means most of the time we’re safe, since the root does not reach the sunlight and does not usually develop high levels of solanine. when and if it does develop, it’s mostly found in the outer layer of potatoes. 

Read also: Why Are Potatoes So Filling ?

Solanine is usually triggered by direct sunlight exposure, as in several days, and by overly long storage. Unfortunately solanine is not easily destroyed by cooking. The only thing that seems to work is to deep-fry potatoes at 210 C/410 F for a minimum of 10 minutes, leading to about 40% less solanine. However fries exposed to that heat for that amount of time are likely halfway burnt.

Does this mean you should never eat potatoes ? Of course not, you can eat potatoes every day if you want, as long as you don’t reach a toxic, or even lethal dose. 

Signs of solanine poisoning

The toxic solanine dose is 2-3 mg/kg of body weight, and lethal doses are 5-6 mg /kg body. Meaning a 100 kg person (220 lbs) should eat less than 200-300 mg of solanine per day. How do you measure solanine ? Farmers try to keep solanine levels under 0.2 mg/gr of potato.

So based on that, 200 mg of pure solanine is equivalent to 1000 gr (1 kg or 2.2 lbs). We are unsure who can eat that much pure potato on their own in one sitting, but the warning should be there regardless.

Is solanine also found in other nightshade veggies ? No, solanine is restricted to the potato. Eggplants, tomatoes, and bell peppers are all fine, though they have their own toxicity to people who are sensitive to nightshades in general. There are many types of toxins found in nightshades. 

Can you fix green potatoes ?

Green potatoes cannot be truly fixed, since solanine development is not reversible. This means the only thing you can do, if your potatoes have turned green, is to cut off the green parts. Or discard them completely, if they’ve become particularly green or they’re very small and completely green. 

You can, however, store your potatoes in a way that prevents solanine from developing. This means storing potatoes in a cool, dry place, and completely dark. No trace of sunlight should be around those potatoes. 

For best results try not to buy in bulk, as in more than 3-4 pounds at a time so you can actually go through them in due time. 

green potato

Why do potatoes turn black ?

Potatoes turn black due to oxidation. This is because the enzymes in potatoes (tyrosinase) gain access to oxygen, and in turn darken. You won’t notice this in potatoes with the peel still on, because it acts as an insulation. But peeled and cut potatoes eventually turn black when exposed to air for several hours. 

The only way to stop this altogether you need to prevent the cut potatoes from reaching the air. The best method is to completely submerge the cut potatoes in cold water, making sure not a single edge is exposed. 

While the black part of the potato may look odd, it won’t hurt you. This also happens to boiled potatoes that are then drained and left to sit for too long without any coating of fat (butter, oil, lard, something).

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