[JJeffers09]

I need to go make an olive oil, flour, juicy ipa...

[Philbrew]

If you pitch a single packet of dry yeast into 5 gallons of wort, there will be several replication periods.

because the cell count of dry yeast is so high, most of the time there is no need for cell growth and therefore no need for aeration. 

Assuming growth=replication, Denny's statement seems incorrect.  Hence my extrapolation that if this is correct, you couldn't overpitch using a yeast cake.  Except that I'm certain that using a full yeast cake results in a drastic overpitch.

My understanding is that dry yeast doesn't need oxygen because it has sterol reserves already built up in whatever science-y way they go about making it.

Exactly.  But there is massive growth in the number of yeast cells!  4 replications (read 4 doublings) means that there will be 16 times as many cells in the yeast cake as compared to the original pitch.
What Narcout quoted from Lallemond said that there is enough lipids in dry yeast to accomplish 4 replications.  Anything more will require additional O2.

[denny]

Exactly.  But there is massive growth in the number of yeast cells!  4 replications (read 4 doublings) means that there will be 16 times as many cells in the yeast cake as compared to the original pitch.
What Narcout quoted from Lallemond said that there is enough lipids in dry yeast to accomplish 4 replications.  Anything more will require additional O2.

3-4 replications is the commonly quoted target number.

[Saccharomyces]

Isn't aeration not all that necessary if you pitch enough healthy yeast?

That is correct.   O₂ demand is lessened if one pitches a starter at high krausen as well.

[denny]

Isn't aeration not all that necessary if you pitch enough healthy yeast?

That is correct.   O₂ demand is lessened if one pitches a starter at high krausen as well.

Good to see ya, Sacc!

[Saccharomyces]

It is nice be back, Denny.

[Philbrew]

Keep in mind the viability of the age of the packet you are getting.  Even with how slowly dry yeast drop-off, I can't imagine that 100% of the cells are ready to rock especially when the packet has a bit of age on it. Not all survive the rehydration stage either (whether its in wort or water).

Yes, that is why I think some aeration is a good idea even if you are pitching dry yeast.

In the last year and a half, I've pitched either dry yeast or slurry.

- I pump into the fermenter and I splash the stream around to create as much foam as possible if I'm pitching rehydrated dry yeast.

- If I'm pitching slurry, I get out the O2 stone.

[Philbrew]

I need to go make an olive oil, flour, juicy ipa...

Good idea!  Denny (and Gary) will really drink it up and enjoy as long as you hop it with lots and lots of Fuggles.

[denny]

I need to go make an olive oil, flour, juicy ipa...

Good idea!  Denny (and Gary) will really drink it up and enjoy as long as you hop it with lots and lots of Fuggles.

 

[Backyard Bruise-master]

I've been slowly making my way through White & Zainasheff's Yeast(y) tome; this topic comes up at page 75.
Long story short, adding enough O2 leads to a faster fermentation and improved attenuation.  8-10ppm is the target for most wort, and shaking only gets you in the high 2s.

Not saying anyone's process is wrong, especially if you're satisfied with the results, but why leave anything to chance?  A healthy pitch is just the start.  What about the rest of the race to FG? 

[Saccharomyces]

O₂ demand is strain specific.  Most of the brewing strains available to homebrewers fall into O₂ classes O1 & O2.  The O₂ demand for class O1 yeast strains can be met with half air saturated wort (4ppm).  The O₂ demand for class O2 yeast strains can be met with air saturated wort (8ppm).  The outliers that are available to homebrewers are the Yorkshire strains, which are usually class O3/O4.  The O₂ demand for these strains is so high that it cannot be met with pure O₂ saturated wort (40ppm).  That is why Yorkshire breweries rouse and aerate fermenting beer with a fish tail.

Brian Kirsop's seminal paper on O₂ demand: http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1974.tb03614.x/pdf

[brewinhard]

The outliers that are available to homebrewers are the Yorkshire strains, which are usually class O3/O4.  The O₂ demand for these strains is so high that it cannot be met with pure O₂ saturated wort (40ppm).  That is why Yorkshire breweries rouse and aerate fermenting beer with a fish tail.

Can underation of these strains result in more diacetyl production?

[ynotbrusum]

Sacc - I don't know what a fish tail is, but I don't think my wife will let me get one!  I second the welcome back to a great contributor here.  Nice article reference.  I will read this tonight.

[69franx]

Isn't aeration not all that necessary if you pitch enough healthy yeast?

That is correct.   O₂ demand is lessened if one pitches a starter at high krausen as well.

Good to see ya, Sacc!

+1 Sacch

[Joe Sr.]

Isn't aeration not all that necessary if you pitch enough healthy yeast?

That is correct.   O₂ demand is lessened if one pitches a starter at high krausen as well.

Good to see ya, Sacc!

+1 Sacch

Yes.  Good to see youse.  Just kegged a bitter using 1768 at your recommendation.