Hollow heart indicates an open cavity in the center of a potato that turns brown in more severe cases. Its cause is debated: some report it is a physiological disorder caused by not properly rotating fields (planting the same crop in the same lot for multiple growing cycles); others report it is caused by irregular or excessive watering (accelerated by late season rains). Packing sheds use ultrasonic machinery to scan and cull potatoes with excessive hollow heart. A certain amount of hollow heart is allowed as per USDA Good Delivery Guidelines.