Apparently there have been studies and manufacturer recommendations that say you need not aerate or oxygenate dry yeast; it already comes with everything it needs. On my last couple of ale batches I let the O2 tank sit idle, just let the wort fall into the fermenter, nothing more. Results were good. On my lager batch, now nearing the end of fermentation, I went ahead and gave it an O2 treatment. What do you all think on this matter?

Last year I tried no aeration on a couple batches using S-04 and S-05 yeasts. I found my attenuation was lower than expected. However, I was also just pitching the yeast directly on top of the wort and that was using 1 package of yeast per 6 US Gallons of wort. A little low I think.

I've also learned that properly rehydrating the yeast improves viability up to 20% in dry yeast which is a lot of extra cells. If I had done that it may have made the difference. For now I'm sticking to aeration and rehydration of my dry yeasts. Anything to reduce the lag phase and help the yeast reproduce quickly and start fermenting has to be better for the wort.

On my next batch I am going to add yeast energizer once the lag phase is done. I want to see if that improves fermentation time or attenuation at all. If nothing else it will make for thicker yeast cell walls which will make the yeast better for re-pitching later...

While it wouldn't stand up to scientific standards of scrutiny, this experiment got me rethinking my dry yeast procedures:
http://www.youtube.com/watch?v=vOrfmzpDmPk

I would think that it depends on your pitching rate. If you pitch enough packets then you shouldn't need to aerate/oxygenate. Oxygen is used for the growth phase of your yeast population. When oxygen is around, they do not ferment, they reproduce. When you oxygenate your wort, your trying to develop a big enough population to do the fermentation. So if you pitch enough yeast packets up front, your population should be big enough (1 million bugs per ml of wort per degree plato). Higher gravity beers are more likely to need oxygen due to the need for a larger population to efficiently ferment the wort. Lagers need a bigger population because the lower temps result in a slower fermentation...more bugs get it done faster.

Mr. Malty suggests that 2 packs of dry yeast should be enough total population for a 1.050 ale to give you a point of reference.

Here's the opinion of a Danstar guru I found online:

"I found a response to questions about starters and oxygenations from Dr. Clayton Cone at Danstar/Lalleland/Lalvin, a leading manufacturer of dry yeast, that I found pretty interesting. Basically he says that dry yeast come packed with the amount of lipids needed to triple the yeast cell count. After those lipids have been used up, additional oxygenation is required for healthy cell growth. For brewing a 5 gallon beer between 3% and 5% alcohol, no additional yeast or oxygen are needed apart from what is available in a single 11g packet. For higher alcohol content beer, you either need to pitch additional yeast or oxygenate to allow for yeast growth. I’m not sure what Danstar considers a proper pitching rate, so that is something I will have to investigate. I do know that Jamil recommends pitching about 10g of yeast on average for an average gravity 5 gallon batch in Brewing Classic Styles."

You oxygenated at the end of fermentation?

Sorry, Spider, if my post was ambiguous. I meant to say that my lager still hasn't reached FG so I can't give an opinion on it yet, but no, I didn't oxygenate after fermentation had begun. I did it the normal way.

Spelt, your comments make sense. The sample in the youtube experiment was OG 1.047 and he used what would be one packet for 5 gallons. I've always thrown in about 3 packets of ale yeast for 10 gallons and 90% of my beers are OGs under 1.055, so I guess that's why O2 isn't necessary for them. I'm going to save the O2 bottle for liquid yeasts, higher OGs, and lagers.

Beers made with dry yeast should be oxygenated as it simply helps the yeast to get going through their aerobic respiration phase which leads to proper cell reproduction (budding). If you are pitching lots of dry yeast in an average gravity wort, than this is not such a big deal, but with higher gravities, oxygen can help in reaching a proper terminal gravity as well as faster fermentations.