why do potatoes turn black

Why do Potatoes can Change to Black or Brown?

Why do potatoes turn black or brown? That’s one interesting question. When potatoes change their color, people often assume the tubers themselves are damaged or the one cooking them made a mistake at some point. But that’s not necessarily true. Instead, the reason for potatoes having a darker-than-usual appearance has something to do with their varieties and the conditions where they were grown.

Cooked potatoes turn black or brown due to oxidation after being exposed to air for several minutes. This process, commonly known as after-cooking darkening, results from a reaction between the iron and chlorogenic acid naturally found in potatoes. But there’s more!

When both of these substances interact in the presence of heat, they form ferrous-chlorogenic acid. As soon as the new chemical comes into contact with air, it’s oxidized to create the dark-colored ferri-dichlorogenic acid. This compound is the reason for the black or brown tone present in cooked potatoes.

The amount of darkening that takes place and how fast it occurs is in direct proportion to the chlorogenic acid and iron quantities present in the potato. At the same time, the concentration of these substances depends on the potato variety, the way it was grown, and the storage conditions, such as temperature and length of time.

Overall, the quantity of chlorogenic acid in a potato increases the longer it has been stored at lower temperatures.

Still, one study showed how some potato varieties were more likely to turn black regardless of environmental conditions.

A few Potato Varieties and Their Likelihood of Turning Black After Cooking:

Potato variety
Probability of turning black after cooking
Irish Cobbler
Red Warba
Russet Rural
White Rural

After-cooking Darkening, Enzymatic Browning, or Blackheart?

Now that you know why potatoes get dark after you have cooked them, you may have another question: Why do potatoes turn black before cooking? Once again, oxidation is at fault!

Once you remove the skin of a fruit or vegetable such as the potato, it loses its protective layer against the elements becoming vulnerable to oxidation. That process is known as enzymatic browning.

This process takes place when oxygen reacts with the enzymes found in produce. As you may know, potatoes are rich in phenolic compounds. They also contain the enzyme polyphenol oxidase or PPO.

Whenever the flesh of a potato comes in contact with oxygen, the enzyme PPO enters into action to oxidize these phytochemicals. That reaction creates melanin.

Melanin gives raw potatoes, apples, and other fruits and veggies that unpleasant taste and brown color that you may be familiar with.

Can you Eat Potatoes that Turned Black or Brown?

You may eat potatoes that have turned black, but it largely depends on the cause. For example, if the potatoes turned black due to after-cooking darkening, you could consume them without problems.

It won’t harm you (as long as they haven’t been left at room temperature for many hours) or affect the potato in any significant way aside from the unattractive appearance.

Raw potatoes that have turned brown after peeling or slicing may be a different story. Enzymatic browning will cause tubers to look and taste kind of meh. Furthermore, the process also oxidizes nutrients such as vitamin C, effectively destroying many elements that make potatoes so awesome.

Generally speaking, a slight discoloration is not a problem, but if the brown gets too intense, you might as well toss it away.

Potatoes may also be black inside as a result of blackheart. The condition, also known as heat necrosis, occurs whenever tubers are grown at high temperatures such as 90° F or above and stored below 35° F for a long time.

There is no way you can tell if potatoes have blackheart by just looking at them. If you like to cook potatoes whole, you might get an unpleasant surprise as you get ready to dig in.

potato with dark center

The only way to determine if blackheart is present is by cutting tubers in half. You will notice how the centers are black while the rest seems OK.

So can you eat them? The answer is nope, at least not the black part. Besides looking awful, they won’t taste good at all.

Now, the are two things you can do. First, always cut potatoes before cooking them to know if the condition is there. Second, get rid of the dark sections and eat the rest if you don’t feel like throwing away an otherwise perfect potato.

You may not be able to stop it from appearing, but at least you can tell if it’s there before it’s too late.

What can you do to the Potatoes, so They Don't Change Color Before Cooking?

Let’s see if we can do something about that brown coloring that appears out of nowhere. The simplest way to prevent enzymatic browning is to cover raw potatoes with water once you have peeled, cut, chopped, or sliced them.

In other words, take a bowl, place your potatoes in there, and fill it with enough water to cover them completely. They should be fine for a couple of hours, even outside the fridge.

potatoes pieces in water

If, for some reason, you can’t use them until the next day, place them inside the fridge. Your refrigerator can keep them in good shape for around 24 hours. However, keep in mind once you get them out of the water, the enzymatic browning will resume.

Can you Stop Enzymatic Browning for Good?

There’s a simple trick you can use to protect your potatoes for good from the ravaging effects of oxidation by enzymatic browning. First, proceed to cover your potatoes with water as you did before.

Now, add one teaspoon of distilled white vinegar or lemon juice for every 64 ounces of water. That amount of liquid should be more than enough to safeguard your potatoes against any browning without messing up the flavor. Again, the idea is to lower the pH, which prevents the oxidation reaction from taking place.

In the following video, you will see what happens when potatoes react with air and how to protect them from the insidious reaction with oxygen:

How to Keep Potatoes from Blackening After Cooking

There’s a sure-fire way to avoid oxygen from messing up your beloved potato dishes. It is as easy as lowering the water pH before soaking your potatoes. The procedure goes as follows:

  • Soak potatoes in water while making sure they are entirely covered
  • Add white vinegar or lemon juice to the water
  • Apply the ratio of 1:64 (one teaspoon of vinegar or lemon juice per 64 ounces of water)
  • Leave them in water for 5 minutes
  • Drain the water
  • Cook the potatoes

If you are boiling potatoes, make sure they remain submerged in water at all times. When baking or roasting, remember to use parchment paper or a ceramic sheet to prevent the potatoes from oxidizing.

Refrain from leaving potatoes outside once you are done cooking, so keep them inside cooking containers on a low setting if you need to do something else before serving.

Do Potatoes get bad in the Fridge?

The fridge is the best place where you can store cooked potatoes. They last around seven days without any issues as long as you place them in plastic or glass containers away from the oxidizing action of air.

Should you Freeze raw Potatoes?

You must never store raw potatoes in the freezer as that is a recipe for developing blackheart. However, cooked potatoes that have been mashed, fried, roasted, or boiled will do quite well in the freezer for about a month. After that time, they will slowly turn bland until becoming unacceptable to any palate.

Why do potatoes turn black? Many things can affect potatoes and turn them brown or black for different reasons. Some of them have a quick fix, while others don’t.

Fortunately, now you can identify them and execute a plan to save your spuds with your new knowledge. Put the techniques to the test and be amazed by the results.