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Why Do Potatoes Turn Green? (And Are They Safe to Eat?)

Why Do Potatoes Turn Green? (And Are They Safe to Eat?)
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When you realize that your potatoes have started turning green, you’re faced with the dilemma of whether to throw them away or salvage them for some good eating. How do you decide which way to go with this decision?

Well, ask a bunch of people what they do. You will find that some cut their losses and toss the green potatoes while others cut away the green parts and use the rest anyway. And both may be good options. Read on!

However, green potatoes are more than food from a Dr. Seuss story, a St. Patrick’s Day stunt, or a strange green curiosity. They also can be quite harmful. The green color and bitter taste that potatoes can develop can also indicate the presence of a dangerous substance.

This article addresses all that you need to know about green potatoes: whether they pose a risk to your health or are okay to eat, how to inspect, how to store them, and the best way to handle them carefully when they are brought home.

Why Do Potatoes Turn Green Anyway?

Potatoes turning green may sound as if it is a supervillain’s sinister plot but it is instead a very natural process. When potatoes are placed in the light, they produce chlorophyll, the same green pigment that gives plants and algae their green color. So that’s why this process is routine in nature.

This process causes the most light-skinned potatoes to change from yellow or light brown to green. This process actually also occurs in dark-skinned potatoes too, though the dark pigments may mask it.

You can actually tell if a dark-colored potato is turning green just by scratching off a little part of the skin and checking for any existing green patches underneath.

Chlorophyll also enables plants to harvest energy from the sun through the process of photosynthesis. Through this process, plants produce carbohydrates and oxygen from the sunlight, water, and carbon dioxide.

The chlorophyll that gives potatoes this green color is entirely harmless. In fact, chlorophyll is present in many plant foods that you eat every day.

So green potatoes are harmless then? Afraid not. Greening in potatoes can signal the production of something potentially harmful — a toxic plant compound called solanine.

Green Potatoes Can Be Toxic to Eat

When potatoes produce chlorophyll, it can also encourage the production of compounds that protect the potato against damage from fungi, insects, or bacteria. Unfortunately, these compounds can be toxic to humans as well.

Solanine, the toxin that potatoes produce, works by stopping an enzyme involved in breaking down certain neurotransmitters. And it can also break down cell membranes and can negatively affect your intestine’s permeability.

Solanine usually is present in low levels in the skin and flesh of potatoes as well as in higher concentrations in the potato. If exposed to sunlight or if they are damaged, potatoes produce more of it.

Chlorophyll is a good indicator of the presence of high levels of solanine in a potato but it isn’t a perfect measure. Although the same conditions encourage the production of both solanine and chlorophyll, they are produced independently of each other.

That’s why you can’t always be sure that chlorophyll equals solanine in a plant.

In fact, depending on variety, one potato may turn green very quickly yet contain moderate levels of solanine. Another may green slowly yet provide the highest levels of solanine.

How Much Solanine Is Too Much?

It’s difficult to say precisely how much solanine will make you feel sick. It differs for every person and depends on a person’s individual tolerance and body size. There have been specific instances of poisoning but it is best not to find out the hard way!

Solanine poisoning includes nausea, diarrhea, vomiting, headaches, and stomach pain. Mild symptoms should improve in 24 hours but who wants all of that just for the risk of eating a green potato?

In extreme cases, severe effects have been reported, such as paralysis, coma, convulsions, breathing problems, or even death. So you will want to take this possibility seriously.

Can You Cook Green Potatoes?

Solanine levels are highest in the potato skin. So peeling a green potato will help reduce the levels. Peeling a potato at home removes 30% of its toxic compounds. That still leaves 70% in the potato. A potato has a high concentration of solanine. A peeled potato might still contain enough to make you sick.

Cooking methods such as baking, microwaving, or frying do not reduce solanine levels significantly. They do not make green potatoes safe enough to eat. If a potato has just a few green spots, cut them out, or you can peel the potato. Remove the eyes of the potato too.

If the potato is very green or tastes bitter (the most significant sign of solanine), it’s best to throw it away. Don’t take the chance and make a family member very sick.

How to Stop the March Toward Green

Fortunately, solanine poisoning is very rare. However, solanine poisoning may be underreported because of the common symptoms with food poisoning or stomach viruses. Some people would never consider that a potato may be making them sick.

Potatoes that contain too much solanine usually do not make it to the grocery store. However, if they are not handled properly, potatoes can produce solanine after they have reached the supermarket or while in your kitchen.

Therefore, correct potato storage is vital for preventing high solanine counts from developing.

Physical damage, too much exposure to light, and high or low temperatures are the main reasons that stimulate potatoes to produce solanine.

Before buying potatoes, inspect them to make sure they have not been damaged or started greening. You may already know that you should store potatoes in a dark, cool place at your home, such as a basement.

Keep the potatoes in an opaque sack or plastic bag. That bag should shield them from light.

Storing potatoes in a refrigerator is not ideal. It’s too cold for potato storage. Some studies have shown increased solanine levels due to refrigerator storage.

Also, your pantry is probably too warm for long-term storage. Some homes have a piece of furniture they call a potato box that is an excellent place to store these potatoes as soon as you bring them home from the store.

If you don’t have a cool place to store potatoes, purchase the amount you plan to use that week. Store the potatoes in an opaque bag in the back of a cabinet or drawer. There, they will be best protected from light and warmth.

Green potatoes are a must to be taken seriously. The green color itself is not harmful; however, it may indicate the presence of solanine. Peeling green potatoes can help reduce solanine levels. Once a potato turns green, throw it away.

Inspect potatoes before buying them. Once you purchase food in a store, keep the food safe by storing and using it promptly. Don’t overbuy quantities of potatoes and then rotate the potatoes.

Types of Potatoes and How Soon They Turn Green

A russet potato loose or in a bag can turn green in a few days, especially in a time when customer sales are slow or a store does not rotate the display. You can probably see the effect of the light on the other side of a potato bag.

Yellow varieties, such as Yukon Gold, have fragile skin and can turn green quickly. Fingerlings, especially the Russian Banana variety, also tend to turn green immediately. If you see several green potatoes at a grocery store, ask the produce employee to bring out more potatoes.

The ideal environment for storing potatoes is 45 to 50 degrees F and 90 to 95 percent relative humidity and darkness. Store potatoes in a basement or cellar. Keep the potatoes away from warm areas.

If potatoes are eaten soon, they can be stored in your cupboard or a paper sack. Other stresses, such as light, cold, heat, or injury to the potato, increase the production of solanine. Proper storage prevents potatoes from turning green.

The height of hills often is reduced throughout the season by rain or irrigation. This water level is the reason why hills usually are so high. They are protected from exposure to light this way.

When hills are not large enough, potatoes can grow too close to the soil surface.

Some potatoes have longer stolons (stems or runners), making the potatoes grow further away from the plant. In these cases, a massive hill is essential to keep these potatoes covered with soil.

In summary, the following steps can help prevent greening:

  • Plant seedlings at proper depths (4 to 6 inches).
  • Hill or mound potato plants with soil while they are emerging and after they are about 4 to 6 inches tall. If growth is rapid and potatoes grow close to the surface, more hilling can be done. Use caution to avoid accidentally cutting roots and tubers.
  • Eliminate exposure to light after storing.