After par boiling potato fries I dried them and put them in a spare freezer to cool. It was getting late so I left them overnight. In the morn they had turned blackish. What caused this? Did I not par boil them enough? Was it the freezing? My intent was to par boil, dry, cool and deep fry until cooked but not browned. Then freeze and do the final deep fry the next day for a cook out. Any help would be appreciated.