Green Spuds

I don’t know about you but I find the cleaned spuds we buy from the shops go green really quicky, even stored in the cupboards away from light. It might be the fact that they are clean with all of the soil washed off, or it could be that they were ‘turning’ anyway before I got them. I don’t grow potatoes myself so have to look closely at the ones I do buy, which isn’t always easy when they are stored in brown paper sacks. 

Have you ever wondered how toxic green potatoes are? I don’t even eat the green crisps when I buy a packet so it’s been instilled into me never to eat the green bits. 

Green-Skinned Potatoes

Why do potatoes turn green? The green is chlorophyll, caused by the potatoes being exposed to light. Chlorophyll is not poisonous. But the same conditions that promote chlorophyll production also increase the formation of solanine, which is poisonous. So the green is an indicator of likely trouble, but is not trouble itself.

Potatoes can also have dangerously high levels of poisonous solanine without being green. This can happen if the potatoes are diseased or damaged, or they are stored in warm temperatures, or they experience a spring frost and make only stunted growth as a result.

Solanine is one of the potato plant’s natural defenses against diseases such as late blight, and against pest attacks.

Just discarding all green-skinned potatoes won’t remove all the solanine from our plates. Solanine is a glycoalkaloid found at some level in all nightshade crops. 

Apparently the amount of solanine in an average-sized serving of potatoes is easily broken down by the body so we don’t need to worry. Green skins contain 1500-2200 mg/kg total glycoalkaloids though which can be poisonous.

The British Medical Journal of 8 December 1979 reports that there is normally a high concentration-gradient between the peel and the flesh, but this is lost when potatoes are exposed to light or stored in adverse conditions. This means the level of solanine quickly drops as you peel deeper into the potato, unless the potatoes were exposed to light or were stored in a warm place for several weeks or more.

Green Potato Myths, Dispelled

The Department of Animal Science at Cornell University says that solanum-type glycoalkaloids are not destroyed by cooking. There isn’t any real evidence to say it increase arthritis conditions either.

“Solanine is water-soluble, so boiling lowers the levels.” An infamous 1979 case of 78 London school children getting very sick after eating boiled potatoes that had been stored improperly over the summer vacation seems to prove this belief not true. (All made a full recovery.)

The US National Institutes of Health advises never to eat potatoes that are green under the skin. This is ambiguous and has been interpreted to mean either: throw out all potatoes with any green bits, or cut off the green skin and also any green flesh under the skin and eat the rest of the potato. Most of us  seem to cut off the green bits and use the rest.

10 Steps to Safe and Healthy Potato Eating

1. If you do grow potatoes, try to cover them fully with soil or mulch, so that they are not exposed to light.

2. Give plants enough space so that the developing potatoes are not crowded and pushed up above the soil surface.

3. If mowing to reduce weeds before mechanical harvest, keep the length of time between mowing and harvest to a minimum. For the same reason, harvest soon after removing mulch. Hand digging can be done without removing weeds or mulch first, but there is a limit on how much one person can hand-harvest.

4. When harvesting, minimize damage to the tubers.

5. When sorting potatoes for storage, do not put all the ones showing any green in the same container. Leave the green-skinned potatoes mixed with the others, so that no-one gets a higher amount than average.

6. When storing potatoes, keep them in the dark, and cool. Don’t store them for longer than necessary. There seems no need to worry about storage up to one year or so, as generations of potato growers have provided for their family needs this way.

7. Apparently there is no reason to use green potatoes sooner than others. Nor is there apparently any advantage to storing them longer in the hope of de-toxifying them.

8. When preparing potatoes for eating, cut off and compost the green bits. Don’t use all the greened potatoes in the same meal. Reduce the risk by mixing greened and plenty of non-greened potatoes.

9. When eating, spit out any potato that tastes bitter.

10. Enjoy eating your potatoes fried, boiled, mashed, chipped, baked or roasted.