[homoeccentricus]

Some brewers add their dry hops somewhere during (presumably at the end of) primary fermentation, the reasoning being that the still active yeast will consume the oxygen that is introduced with the hops.

Does this really make a difference? If so, what trigger should I use to add the hops?

[Iliff Ave]

I thought the main reason is that as yeast falls out of suspension, it will strip out hop aroma. I personally dry hop after FG has been reach and most of the yeast has settled (or in the keg) but have no experience doing it any other way.

[rabeb25]

Ferment, crash cool to drop yeast. Raise back up to 68, dryhop.

[HoosierBrew]

Ferment, crash cool to drop yeast. Raise back up to 68, dryhop.

+1.  Same thing I do.

[homebrewdad7]

On the last IPA that I did, I waited until fermentation was done.  I then added a very small amount of simple sugar with my dry hops, the thinking being that the active fermentation would help prevent oxidation. 

This was certainly no side by side comparison, ala Brulosophy, but this did happen to be the very best beer I've ever brewed.

[homoeccentricus]

Ferment, crash cool to drop yeast. Raise back up to 68, dryhop.

Why yes, but that does not answer my question. 

[rabeb25]

Ok then, Yeast only consumes oxygen in the initial phase of growth ( I am sure Mark will correct my laymans terms). So there for that would not be the case.

[S. cerevisiae]

Ok then, Yeast only consumes oxygen in the initial phase of growth ( I am sure Mark will correct my laymans terms). So there for that would not be the case.

Actually, yeast cells consume O₂ whenever it is available, which is why the "Don't rack to secondary because it will oxidize your beer" mantra is yet another home brewer created myth.

[denny]

Some brewers add their dry hops somewhere during (presumably at the end of) primary fermentation, the reasoning being that the still active yeast will consume the oxygen that is introduced with the hops.

Does this really make a difference? If so, what trigger should I use to add the hops?

I have never experienced a problem with oxygen introduced by dry hops.  I wonder if it's more theoretical than real.  I have experienced less than ideal results by dry hopping when the beer is still on the yeast, though.  I noticed high levels of geraniol, a rose like quality.  I started xferring the beer before dry hopping and haven't noticed it since.

[HoosierBrew]

I have never experienced a problem with oxygen introduced by dry hops.  I wonder if it's more theoretical than real.  I have experienced less than ideal results by dry hopping when the beer is still on the yeast, though.  I noticed high levels of geraniol, a rose like quality.  I started xferring the beer before dry hopping and haven't noticed it since.

That's my experience too, Denny. It's why I prefer to dry hop (fairly) clear beer.

[narcout]

Actually, yeast cells consume O₂ whenever it is available, which is why the "Don't rack to secondary because it will oxidize your beer" mantra is yet another home brewer created myth.

Is there a temperature below which they will stop consuming oxygen?

[hopfenundmalz]

Some brewers add their dry hops somewhere during (presumably at the end of) primary fermentation, the reasoning being that the still active yeast will consume the oxygen that is introduced with the hops.

Does this really make a difference? If so, what trigger should I use to add the hops?

I have never experienced a problem with oxygen introduced by dry hops.  I wonder if it's more theoretical than real.  I have experienced less than ideal results by dry hopping when the beer is still on the yeast, though.  I noticed high levels of geraniol, a rose like quality.  I started xferring the beer before dry hopping and haven't noticed it since.

That is a biotransformation that happens with the yeast, somewhere online I saw data showing the geraniol and linalol going up during fermentation. Adding dry hops to active yeast will give more. Some brewers are after that, Matt Bryndilson for one who talks about adding the dry hops with about 1 degree Plato left. Another brewer says the O2 added gives the yeast a little bump,and they help to give a lower FG to the finished beer.

On the other hand brewers like Vinnie Cilurzo says he drops the yeast before dry hopping, as they will take the resins out if you don't. 

[homebrewdad7]

Somebody needs to get Marshall over at Brulosophy to add this to his list of exBEERiments...

[S. cerevisiae]

Is there a temperature below which they will stop consuming oxygen?

Yes, but it is below the range of a home refrigerator.

[HoosierBrew]

Matt Bryndilson for one who talks about adding the dry hops with about 1 degree Plato left. Another brewer says the O2 added gives the yeast a little bump,and they help to give a lower FG to the finished beer.

On the other hand brewers like Vinnie Cilurzo says he drops the yeast before dry hopping, as they will take the resins out if you don't. 

I prefer Vinnie's method for my beers, but OTOH I've had FW's beers and they do not suck, to say the least.
Dry hopping is one of those techniques where there are lots of ways to do it and they are all at least good. Personal preference after that.