Hi David,
Having worked in a lab for 20 years means I know that what you just wrote is only half correct. As you are obviously aware milk is pasteurised and will spoil within a couple of days of opening. Milk doesn't go into second hand containers for that reason. Milk is nutrient rich, just like wort.
Milk is also only held at 72C for 15 seconds. When someone starts trying to HTST pasteurise their wort and store it for a while, then I'll worry.
Within a couple days of opening, my cubes of botulism are happily fermenting away. With yeast. Non-wild yeast.
Kai, I think we are talking about why someones fermenter blew up like a balloon without addition of yeast. Obviously it is the result of spoilage organisms.
Its when they start putting milk in second hand plastic containers you should worry about.
cheers
Darren
Botulism? who knows, apparently the toxin is tasteless. Maybe you are volunteering to do a trial?