It probably has something to do with the yeast and sugars used in the manufacture of the ethanol. Seems to provide a medium for accelerated growth of mildew.
Mildew on the exterior of ethanol storage tanks has been a persistent problem. Most coating manufacturers have added a mildewcide in their finish coats to arrest this problem. This approach, in my experience, has not proven very effective. PPG/Ameron manufacturers a polysiloxane, PSX700...
