I remember visiting a potato farm about 30 years ago. The farmer was growing them in rich, black soil. After harvest, the potatoes were run through a machine that was filled with red volcanic soil. The potatoes were lightly coated in this soil which apparently increased their value at market as potatoes grown in red soil were desirable. I also heard a comment that the potatoes kept better when coated in red soil. Not sure that I would buy those potatoes in the video purely based on principle.