Oxygen and Beer: When/how does it effect the brew?

I'm new to brewing and going on my fourth batch. I've scoured this resource and others to find out that oxygen can affect beer in a couple negative ways at various points in the brewing process. What I'm not quite clear on is how, when, to what extent, and to what likelihood the various oxygen contact points affect the beer. I've listed below some seemingly necessary points where the beer would come in contact with air. Can anyone share with me where the greatest risk is (and what the negative outcome would be) and the common methods to prevent? Or, is it just going to happen and isn't a big deal?

-Moving from primary to secondary (if doing so)--It seems necessary for there to be air contact, so how much is contact does it take for negative outcomes?

-Checking the specific gravity during fermentation when using an opaque fermenter

-For whatever reason, coming up short of 5 gallons, such that there is more space than ideal in the secondary fermenter (if using a secondary)

-If not using a secondary, and adding hops to primary for dry hopping purposes


-Stephen

Generally if you practice any reasonable level of precaution, oxidation is something that is not going to have an immediate effect on your beer quality. Eventually all beer will oxidize/stale.

SGM said:

-Moving from primary to secondary (if doing so)--It seems necessary for there to be air contact, so how much is contact does it take for negative outcomes?

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If you're going to use a secondary, yes there will be air contact. But there will be air contact at any point of racking and you will eventually rack even if not doing a secondary. Oxidation can be minimized by keeping the end of the siphon resting on the bottom of the transfer vessel and keeping the hose below the level of the beer. I've had several bottle conditioned beers (esp high gravity ones) last for over a year without excessive staling. That said, I opened a bottle that was about 2 years old and it was totally undrinkable.

SGM said:

-Checking the specific gravity during fermentation when using an opaque fermenter

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Generally not a problem since the beer in your fermenter is covered by a blanket of CO2. If you use something like a turkey baster or wine thief to get your sample, then you're not going to disturb the beer much.

SGM said:

-For whatever reason, coming up short of 5 gallons, such that there is more space than ideal in the secondary fermenter (if using a secondary)

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Not a good practice, but not a huge problem either since the beer will likely evolve off some CO2 to make that protective blanket.

SGM said:

-If not using a secondary, and adding hops to primary for dry hopping purposes

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If you're just lifting the cover or removing the stopper, for the same reasons as above, not a big problem.

Very good answer Hex23.

Perfect. Thanks for the response!

Thanks, just dryhopped my second IPA brew today (sanitized like a mofo, took the lid off and had someone drop the hops in) and was wondering the same thing.