What’s this black stuff?

The black areas in those potatoes are most likely internal black spot (internal bruising) or blackheart/internal discoloration, rather than mold.

From the photo, I notice that:

  • The dark patches are inside the potato flesh, not on the surface.
  • They appear firm and localized, not fuzzy or slimy.
  • Several potatoes have similar dark streaks or oval-shaped black areas, suggesting a problem that occurred during growth, harvesting, storage, or transport rather than a single rotten potato.

The most common causes are:

  1. Bruising during harvesting or handling
    • Impacts can damage cells inside the potato without breaking the skin.
    • The damaged tissue later turns dark brown or black.
  2. Storage conditions
    • Potatoes stored too cold or with poor ventilation can develop internal discoloration.
    • Oxygen deficiency inside large piles of potatoes can also cause dark centers (“blackheart”).
  3. Natural physiological disorders
    • Sometimes potatoes develop internal necrosis due to environmental stress while growing, such as heat or irregular watering.

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