At one of the KBF functions this past year Jim Rutledge shared a story about a bad run that Four Roses had a number of years ago due to musty/contaminated corn. He said that one of their QA folks who is really sensitive to must picked it up and they rejected an entire batch. They alerted the other dsitillers as well to look out for the bad grain. Due to the nature of the musty contaminated batch, every piece of equipment had to be cleaned or sterilized and the batch was sold off to be redistilled a vodka. This was all done at a considerable expense.
If a distiller is prepared to kill an entire run due to an off flavor, killing a single off barrel is an easy choice and is just a cost of doing business.