What happens is that once the oxygen is used up, anaeorbic bacteria take over. They produce short chain organic acids like acetic (vinegar), lactic, propanoic etc. This lowers the pH which then stops further bacteria growth.
In pit silos, and concrete silos, air is eliminated by allowing the top to spoil which seals it. Using plastic or air tight silos like Harvesters (the big blue ones) reduces the spoilage. you can also store high moisture corn the same way.
When I was an undergrad at Purdue and working on the beef farm, we did some experiments with spraying organic acid on corn and then storing it in wooden bins. It work. The cool thing is that rumenants (i.e. cattle, sheep etc) use the acids for energy just like we use sugar. In fact the bacterial action in the rumen normally produces the same acids which are obsorbed into the blood and utilized for energy.
Ok, sorry, I didn't mean to bore you, when I get off on these tangents, people eyes tend to roll back into their sockets etc.
Larry