What you see: Black-lined caverns inside your potatoes.
What it is: An injury of some kind. Possibly from pressure or from being stored too cold.
Eat or toss: If some of the potato still looks normal, cut around the black areas and eat.
Blackened cavities inside potatoes
First, let’s just acknowledge that the dark, cavernous holes in these potatoes have a decidedly nightmare-ish look to them. Black, dusty, strung with ambiguous-looking lines. Like, if you were really small and got lost in one of those caverns, you’d probably encounter a scary mythological beast.
But, it’s OK. This freakish look doesn’t necessarily spell doom for your dinner prep (though it probably will mean more precise chopping).
When I shared these images with University of Idaho potato expert Nora Olsen, she guessed these potatoes had somehow been under a lot of pressure (maybe by being at the bottom of a pile) or had been stored at too-cold temperatures. In any event, these uncomfortable experiences could have caused some of their inner cells to collapse and die. When cells die, or even just leak, cellular components normally kept separate mix and chemical reactions ensue. In this case those reactions led to the production of a type of melanin (from the same family of pigments that colors human skin), which is why the inner areas are so dark.
If pressure was the issue, then, when the potatoes were released from that pressure, their flesh bounced back enough to create air pockets where the damaged cells used to be. They may have also been dehydrated; with less water in each cell, the potato would be less likely to fill out the damaged area. But if it were simply a matter of being stored too cold, Olsen theorized that the sprouting could have lead those weird empty spaces to form. Sprouts would have pulled moisture and nutrients from the potato, possibly enough to leave us with cavities of emptiness (which is, coincidentally also the name of my new band).
The “dusty” look came about when bits of potato starch were released from busted cells and dried.
It’s easy to look at these potatoes and assume that mold or bacteria have taken over. But here are some reasons why that’s unlikely: the flesh is still firm and dry, making it unlikely that mold or bacteria is breaking it down. Additionally, the injuries are decidedly deep within the potatoes. Typically mold or bacteria enters through the exterior and you can trace their paths of destruction.
However, in the photo below, check out the potato with a brown hole in the background; in that case it’s clear that something did break the skin; but it would be OK to cut that area off because it’s clear that the surrounding flesh is still firm and dry.
In conclusion, these potatoes are still edible. If they experienced a crushing force, Olsen said, “probably the texture more than anything would be off.” She said she’d also cut the black areas away for aesthetic reasons.
“I would just cut that off and use the rest of it,” she said.
UPDATE: Since Olsen and I first talked about this issue, she sliced open the potato pictured below and 10 tiny goblins marched out. Kidding! While there were no apparent goblins, she suspects this tuber suffered a similar fate as the potatoes featured above. Her theory is that the potato was struck by chilling injury after being stored in a too-cold space, and further struggled as sprouts formed and pulled away water and nutrients. This potato, she concluded, was beyond hope.