As side dishes go, a big, steaming, golden baked potato is one of the showiest. It's also among the easiest and cheapest, which makes three very good reasons for its popularity. Unfortunately nothing in this world is perfect, and occasionally when you cut into your potato, you'll find a black spot inside. It's not dangerous, and you don't need to throw the potato away.
Black Spots on Potatoes
The black spots on potatoes are not at all the same thing as a moldy potato. With mold, the damage will always be at the surface of a potato or else in cracks and crevices where disease or damage has opened a path into the potato's interior. You won't find mold inside an apparently unblemished potato.
The black spots you'll see inside the potato are actually bruises, caused by the potatoes getting bumped and jostled as they made their way from the soil to a warehouse to a retailer and eventually to your home. The spots form when a bump bruises the internal cell walls of the potato, releasing enzymes that create a dark pigment called melanin.
Don't be too hard on your grower or grocer if you buy a bag of potatoes that contains a lot of dark spots. The bruises take a few days to form, so if they occur during harvest they may not even be present during the grading process. Then the potatoes are loaded and unloaded several times in bulk containers, cases or large sacks, before eventually ending up as the familiar 3-, 5- and 10-pound retail bags. At each step of the way, it's easy to bruise the spuds, as they're stacked and restacked, and very difficult to avoid.
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A Second Kind of Dark Spot
Bruises are easy to recognize. They'll look grey-blue in a raw potato, but darken during cooking to something approaching black or charcoal gray. They're relatively small, so it's easy enough to just scrape them out of the potato with your fork or butter knife and set the bruised bit at the side of the plate.
If you get a russet potato that's black inside or dark brown, with a sort of long tunnel running end to end, that's an entirely different problem. That's called "hollow heart," and it's an issue you'll usually see in years when growing conditions have been unpredictable and the potatoes have experienced periods of fast and slow growth.
Hollow heart is a deformity, not a disease, and it's not at all harmful. You can just scrape away the affected area, and eat the rest of the potato. Again, there really isn't any way the grower could detect this at the grading stage.
A Small Black Dot
Sometimes what you see on the potato isn't a bruise on the inside, but small black dots scattered across its surface. This is a different problem again, but equally harmless. If you look at a normal, healthy russet or other new potato, you'll notice that its surface is covered with a scattering of small freckle-like dots. Those mark the pores or "lenticels" where a potato's skin breathes.
Like the skin on an adolescent face, those pores sometimes get clogged. When they do – it happens when the fields get too wet – the lenticels will discolor after they shrink back to their normal size. There's no harm in eating the potato skin and all, but if the dots bother you, you can peel the potato and use a different one for baking.
Proper Handling Prevents Bruising
You can't control bruising that happens between the field and your home, but you can avoid damaging the potatoes any more. Always handle them gently, as opposed to just slinging your potatoes into the trunk or over the tailgate. They keep best in a cool, dry, dark place with good ventilation. Light will make them sprout, and humid or poorly ventilated spaces can cause mold.
Potatoes are more susceptible to bruising if they're cold, so your refrigerator isn't the best place for them. When they're cold, your potatoes will convert some of their starches to sugar, which is a natural antifreeze, and it changes their taste and their cooking qualities. If you've ever had fries or hash browns that seemed to darken much too quickly, that's why. It takes a week or two at room temperature for the process to reverse, and for the potatoes to go back to normal.
Fred Decker is a trained chef, former restaurateur and prolific freelance writer, with a special interest in all things related to food and nutrition. His work has appeared online on major sites including Livestrong.com, WorkingMother.com and the websites of the Houston Chronicle and San Francisco Chronicle; and offline in Canada's Foodservice & Hospitality magazine and his local daily newspaper. He was educated at Memorial University of Newfoundland and the Northern Alberta Institute of Technology.