Originally Posted by GilSwillBasementBrews
Anything post boil needs sanitizing.
What he said.
Originally Posted by smonteton
Does the co2 keep bacteria and infection at bay?
Sort of. There's a few things at work, though.
Alcohol beverages, beer in this case, are inherently inhospitable to bacterial infections. Not much, and certainly nothing that is known to be deadly or seriously harmful, can harbor itself in beer. That's obviously POST fermentation.
During the fermentation process, wort has a tendency to create a lot of yeast that in turn create a lot of CO2. This off-gassing does create a sort of "natural barrier" that protects the beer, but it doesn't mean you can be reckless with the beer. You can find examples of open fermenters in use at commercial breweries, but it does have risks. The concept of using wild yeast and souring, to most extents, is built around trying to replicate nature in a more perfect way.
What you're aiming for, though, is a fully sanitized environment from the time it cools in your boil kettle all the way to bottling/kegging. Everything that touches it should be thoroughly sanitized and a spray bottle/Vinator of Starsan are wonderful things. Oh, and don't blow a bunch of unknowns into your beer with a fan.