That unsettling black ring is usually something called an internal black spot: a bruise hidden deep inside the potato, caused by pressure, rough handling, or poor storage. The outside can look perfect while the inside quietly darkens, forming grayish or black rings or patches that feel firm and smooth, not slimy or fuzzy. Sometimes temperature stress or natural vascular “veins” simply oxidize and darken, especially after cutting or cooking.

In most cases, it’s safe to eat. Just cut away the darkened area and check the rest: it should smell normal, feel firm, and look like regular potato. If it’s soft, slimy, sour, musty, green, or truly moldy, throw it out. To avoid future surprises, choose potatoes without soft spots, store them in a cool, dark, ventilated place, and buy from stores with fast-moving produce. Then bake, mash, and roast without fear.