Dodgy Cauliflowers

[Tomas]

My Cauliflowers were just ripe so I laid the leaves over the flower to keep them white but in a couple of days they turned mildew. I thought perhaps the flowers were a little damp, so with the next one's coming ripe I did'nt lay the leaves over I just left them, and blow me they went all mildew as well. Any one got any idea's what happened ? Could it be some disease or some bug ? Any advice would be most welcome.Thanks.

Tomas.