Sneaker

Recipes 

Third batch ever. I have it in secondary, and have checked the gravity twice, so that I'll know when it's ready to bottle. I'm using a wine thief to take a sample, which means I have to take off the stopper of the carboy. Doesn't this release all the CO2 and introduce oxygen?

Clonefarmer

Recipes 

CO2 is heavier than Oxygen so there should be a protective blanket on top of the beer.

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jeffmeh

Recipes 

No. CO2 is denser than air, so unless you really disturb the fermentor the amount of O2 that will make it through the CO2 blanket is nothing to worry about.

jds

Recipes 

And even if you do get a bit of O2 in the beer, it will still turn out fine. Honestly, beer is pretty resilient stuff, and it takes a lot of effort to screw it up badly.