Why Do Potatoes Turn Black After Cooking? [How To Store Them Properly]

If you love the flexibility of a good potato as a side dish, you have probably faced potatoes that discolor– turning a rusty color before cooking or a gray to black color after cooking.

This can be frustrating when you want your plates to be Pinterest perfect. The bad news is if the potatoes have changed color, you can’t undo it.

The good news is that you can prevent them from turning brown, and even if you don’t, they are still safe to eat. 

Potatoes turning black is a common phenomenon caused by oxidation, a chemical reaction that occurs when the potato is exposed to air. This reaction is more pronounced in potatoes due to their high starch content, which reacts with oxygen to change the potato’s color to gray, brown, or black. While unappealing, a potato that has turned black due to oxidation is still safe to eat, as this process does not affect its flavor or nutritional value. To prevent or minimize oxidation, store cut potatoes submerged in water or cook them immediately after cutting.

Because potatoes are starchy vegetables, they oxidize when they are exposed to air, turning from white to brown or black. Although this is not pretty, the texture and flavor of the potatoes have not changed, and they are still good to eat.

You can prevent this oxidation by storing sliced or cubed potatoes in water or salted water before you cook them. The water will prevent air from getting to the cut surface and starting the oxidation reaction.

You can also treat the water with some lemon juice or vinegar to lower the pH, which will help the potatoes keep their color while they cook.

Potatoes Oxidize When They Are Exposed To Air

You’ve seen apples turn brown when they are sliced and left exposed to air. The same process is what causes potatoes to change colors before, during, and after cooking.

Potatoes have an enzyme in them called polyphenol oxidase or tyrosinase. When you slice a potato, this enzyme is exposed to the oxygen in the air, and a chemical reaction occurs.

The discoloration of the potato is the result of this reaction called oxidation. 

It Is Safe To Eat Black Or Brown Potatoes

Whether your potatoes oxidize before or during the cooking process, you can rest assured knowing that they are still safe to eat. They may not look very nice, but the taste and texture will be the same. 

How To Prevent Potatoes From Turning Brown Before Cooking

Potatoes and Cooking Pot

When you are cutting up your potatoes to bake, roast, boil, or fry, you can take a few simple steps to prevent them from oxidizing.

Store Potatoes In Water Before Cooking

As you cut up the potatoes, put them in a bowl full of water and make sure that the water keeps them covered. Take them out of the water and pat dry if you are roasting or frying them.

To prevent potatoes from turning brown, it is best to store cut potatoes in water in the refrigerator for up to 24 hours. This is a good idea if you have a lot of prep to do for a big meal, and you need to spread out some of the work to make preparations easier. 

Soak Potatoes In Salt Water

If you are looking for a crispy outside on the potato, you can soak the potatoes in salt water. Combine two tablespoons of salt with 6-8 cups of water.

Soak the potatoes in this solution prior to baking or frying. Just before cooking, take the potatoes out of the water and pat dry.

Salt helps draw the water out of the potatoes, so this method will make your finished product crispier faster.

Reduce The pH Of The Soaking Water

Another simple way to keep potatoes from turning before cooking them is to add something slightly acidic to the water you soak the potatoes in.

A squeeze of lemon juice, a splash of vinegar, or a couple of teaspoons of fruit preservatives (ascorbic acid powder) will keep the potatoes from turning even after you take them out of the water.

How To Prevent Potatoes From Changing Colors During And After Cooking

You may have experienced the disappointment of opening up your crockpot after a full day of cooking a roast and vegetables only to find that the potatoes have turned black.

It’s a frustrating experience. These blackened potatoes are still safe to eat even though they are not pretty. 

This dramatic change is still just an oxidation reaction, but with heat added. That is why it is much more dramatic than the room-temperature pre-cooking reaction.  

To prevent oxidation, try soaking the potatoes in a slightly acidic bath before cooking. Add the juice from half a lemon or a couple of teaspoons of vinegar to the soaking water for your potatoes. Pour that liquid off before cooking.

In the crockpot or pressure cooker, make sure that the liquid you are cooking in covers the potatoes completely. This will help prevent oxidation. 

Pro Tip

If you are baking or roasting the potatoes, use a glass or stone baking dish instead of a metal one. Glass and stone will help discourage oxidation reactions on the potatoes and other starchy vegetables. 

Keeping Potatoes Warm Longer To Prevent Oxidation

After cooking, if you need to keep the potatoes warm for serving, you can keep them in a crockpot on the warm setting. This is most effective for mashed, smashed, or baked potatoes.

You can keep roasted or fried potatoes crispy in the oven by turning the oven down to 160 degrees.

If you line your baking sheet with parchment paper or use a glass or stone baking dish, the potatoes will be less likely to oxidize and change colors.

Storing Cooked Potatoes

Even after they are cooked, potatoes can continue to oxidize. The best way to reduce this possibility is to store them in plastic or glass air-tight containers.

Keep left-over potatoes in the refrigerator for up to 6 days of delicious lunches. 

Freezing Potatoes

Raw potatoes do not freeze well. The bags of frozen fries or hash browns from the grocery store have been partially cooked before they are frozen.

If you just try to freeze a raw potato, it will develop an unpleasant texture and lose its flavor when you try to thaw and cook it.

Plenty of Potatoes

On the other hand, you can freeze cooked potatoes. Mashed potatoes, cooked shredded potatoes, and boiled potatoes freeze reasonably well for about 3-4 weeks. They will decline in texture and flavor after that.

How To Know When Potatoes Have Gone Bad

If you encounter a potato and are concerned that it is not safe to eat, you should dispose of it. 

If a potato is genuinely rotten, you will know right away by the smell. Rotten potatoes smell awful. In the early stages of rotting, potatoes become shriveled and mushy. These potatoes should be immediately discarded. 

If your potatoes have sprouted small eyes but are still firm and creamy white, you can just cut out the little sprout and use the rest of the potato. 

As you are peeling potatoes, you will sometimes find dark spots and bruises. If the rest of the potato is firm and good, just cut out the bruised portion and go ahead and use the potato.

On occasion, you may cut into a potato that is black right in the middle. If it is, but the outside of the potato is still firm and creamy white, you can cut the good parts and use them. 

Nutritional Value In Potatoes

Potatoes come in a wide variety, from large russet potatoes to tiny sweet purple ones. 

Potatoes are high in fiber. Adding prepared potatoes to your meal can actually help you lose weight because you eat less and feel full for longer.

Eating more fiber can help keep cholesterol and blood glucose levels under control. Potatoes also have antioxidants, especially in the skins.

The more colorful types of potatoes like yellow, orange, and purple, have higher levels of antioxidants. Potatoes also have vitamin C, Vitamin B6, potassium, magnesium, and folates.

The trick to getting the benefits out of potatoes is in the preparation. Fried potatoes loaded with bacon and cheese are delicious, but they don’t add much nutritional value to your diet.

Instead, try roasting an assortment of colorful potatoes in a glass dish with a bit of olive oil, sea salt, pepper, and sage. You will have a tasty and healthy side dish without the extra fat.

Branch Out And Try New Varieties Of Potatoes

You have no doubt had a russet potato – a white potato with brown skin. But there are many more options to try to add interest to your meals.

We often think about sweet potatoes at Thanksgiving, but they are good all year round. Try them as a savory side dish by roasting them.

Red potatoes are soft and creamy white on the inside with, a very thin red skin. They are delicious boiled or roasted with onion.

Yukon gold potatoes are a little waxy and yet still fluffy with golden skin and yellow flesh. Purple potatoes are a bit sweet.

Depending on the variety, their skin ranges from gray to almost black, and the flesh is blue to dark purple. They have a similar texture to sweet potatoes and Red potatoes.

Final Thoughts

With a little preparation, you can keep your potatoes from oxidizing and turning brown or black. Soak them in water until right before cooking to prevent the oxidation process from starting.

If you are roasting the potatoes, prepare them beforehand by soaking them in water prepared with a squeeze of lemon juice or a splash of vinegar.

Use glass or stone baking dishes instead of metal to reduce the likelihood of oxidation.

The good news is that even if the potatoes do change colors, they are still safe to eat. 

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