What Causes Green Potatoes

Posted on: June 7th, 2012 by Annette Welsford No Comments

Potatoes are one of the most nourishing foods on earth. But they can also be poisonous.

You must never eat potatoes leaves. Commonly referred to as “potato greens”, the leaves are poisonous, and even eating the smallest amount, can make a person extremely ill.

While the tuber itself is normally totally safe to eat, if any part of it has turned green, this is an indication of toxins.

This potato needs to be peeled and all the green flesh should be removed.

The Poison in Potatoes

The poison ingredient found in potato leaves is solanine, which is very toxic, even in very small quantities. It is also found in the sprouts that emerge from the eyes of tubers. And when the tuber itself starts to go green, this shows that solanine is present.

Before cooking potatoes, all sprouts should be removed, and all green sections cut off. If the flesh is green, peel and discard the skin, even if it doesn’t look particularly green. If cooked potato tastes bitter, chances are it contains solanine, so don’t eat it.

What Makes a Potato Tuber Turn Green

Solanin is a natural toxin that is triggered as a natural defence against pests and fungus. Most highly concentrated in the skin (and of course the leaves), it is both odourless and colourless.

When the potato is exposed to light, chlorophyll forms in the skin and upper layers of the potato flesh, which causes it to turn green. The chlorophyll isn’t toxic – in fact it is perfectly harmless – but the areas where the chlorophyll forms coincide with high concentrations of solanine.

While the potato is growing, the tubers must be protected from natural sunlight. What potato growers do is to pull the soil up against the growing stem; a procedure known as hilling or ridging. If they don’t do this, and the tuber is exposed to sunlight, the tubers will turn green and become toxic.

The same applies to potatoes that are subjected to artificial light in shops or when you store them at home.

Solanum Tuberosum Poisoning

Don’t underestimate the effect of potato poisoning. According to the US National Institute of Health, people have died as a result of potato poisoning, although the concede that this happens rarely – and it seems from other sources, that there hasn’t been a death from potato poisoning for decades.

According to the NIH, symptoms of poisoning include (in alphabetical order):

  • a loss of sensation
  • abdominal pain
  • delirium
  • diarrhoea
  • dilated pupils
  • fever
  • hallucinations
  • headaches
  • hypothermia (which presents as a lower than normal body temperature)
  • paralysis
  • shock
  • slow pulse
  • slowed breathing
  • vision change
  • vomiting

Having said that vomiting is one of the symptoms, the NIH warns that you should never try to induce vomiting unless instructed to do so by a health care professional or medical doctor. Rather seek urgent medical assistance.

Storing Potatoes

Once potatoes have been harvested, they should be kept in a cool, dark place to prevent the eyes from sprouting and the skin and flesh from turning green. Then need to “breath” so should not be stored in plastic. This will shorten their shelf life, as will storing them alongside onions.

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