Green vs. Red apples
Malic acid is a natural antifungal and is found in apple cider vinegar. Long before the young girl in the link below was born, I hypothesized that the tartness of green apples meant that their malic acid content would be much higher than the malic acid in sweet red apples.
As it turns out, I was right as proven by this wonderful girls science project 10 years ago. Do you suppose she is a FUPO head (fungus until proven otherwise) today?