blackish inside ring around potatoes; cause
 

I recently bought a sack of russet potatoes and microwave each one
before I cut it up into sections to fry or to boil in soup. However I
am noticing underneath the skin layer a blackish sort of material or
discoloration. Is this caused by the potato in too cold of temperature
and may have frozen? Or is it caused by insects or bacteria or molds?

Anyone know of a blackish discoloration of potatoes underneath the
skin layer?

Archimedes Plutonium
whole entire Universe is just one big atom where dots
of the electron-dot-cloud are galaxies