Sweet potato with a white, “web-like” pattern

What you see: A sweet potato with white, spiderweb-like patches inside. You’re particularly likely to see this in older sweet potatoes that have sprouted.
What it is: A pithy, older sweet potato. It’s lost moisture. In those white areas, its pigments and other components are breaking down and being redistributed.
Eat or toss: It’s still safe to eat! And could easily be fine. But I can’t promise it will be top quality. Consider using it in a dish where sweet potatoes play a supporting, rather than starring, role. 

You can’t quite tell in the image, but reader Kai R., of Arlington, Va. reports that this was a massive sweet potato; about the size of her forearm. She placed it on her counter, didn’t quite get to it before an international trip and then returned to find it had sprouted wildly (#canrelate). She cut off the sprouts and attempted to root them in water and then contemplated why the remaining sweet potato had this white, meshy patch. So what happened? I asked Cole Gregorie, a sweet potato specialist at Louisiana State University’s Sweet Potato Research Station. He suspects we’re seeing evidence of age and a repartitioning of resources within the potato to support sprouting. 

“This is what I would call becoming pithy,” he explained. “You’re gonna start losing your sweetness, you’re gonna start getting a little bit drier.” 

The sweet potato is certainly still safe to eat, he said, it just may not taste as good. 

Why would a sweet potato get pithy?

After a sweet potato is harvested, Gregorie said, it spends about six to eight weeks converting starches to sugars and marching toward its maximum sweetness. 

But once all those starches have been turned to sugars, things start to go downhill quality-wise. That’s because the sweet potato starts to turn its energy toward sprouting. (Tip from Gregorie: Keeping sweet potatoes between 65 and 70 degrees will slow or delay sprouting.) As it pivots toward its next stage of life, it harvests goodies from cells within the sweet potatoes to fuel the sprouts. 

“The potato is going to start trying to repartition the sugars and the nitrogen and all the other stored minerals in the potato to grow shoots,” he explained. 

Take beta-carotene, for example, a pigment that makes sweet potatoes orange and that our bodies convert to Vitamin A. Gregorie said the sweet potato breaks it down, most likely to collect its nitrogen to fuel the sprouts. 

“When they strip it of that, you lose the orange color,” he said. The process is similar to how trees recirculate nutrients before they shed their leaves in the fall, he said. 

While this was a particularly large sweet potato, Gregorie said that wouldn’t impact the likelihood of going pithy. The bigger issue may have been that this was a sweet potato stored on the counter during a Mid-Atlantic summer. Warmer temperatures will speed along sprouting, leading to pithiness.

What is the white stuff inside a “pithy” sweet potato?

Basically it’s a matrix of spent cells stripped of their beta carotene and other components. Not to be too dramatic or anything. 

“You deflate a cell and the cellular membrane is still there,” Gregorie explained. If the cells were still plump, the sweet potato’s surface would still look smooth and flush. Those cells donated their moisture, nitrogen, and other materials to the growth of the sprouts, but, he said, “when they start to dry out, it looks almost like a little webbing.”

What are the wet, white spots around the edge of this sweet potato?

Sweet potato latex! It’s a natural substance that sweet potatoes use for defense. If this sweet potato were more fresh, you’d probably see larger beads oozing out of this potato; as the potato has lost moisture, the latex has dried up too. On the other hand, this sweet potato was in a kitchen in a more humid part of the country, so it was probably losing moisture at a slower rate. Based on age, genetics and other factors, sweet potatoes can vary in terms of how much latex they produce, how much you might see and how that latex might behave when you’re prepping your meal.