Beer Forum

Here's the case study: APA with an OG of 1.048, 11 gallons in the fermentor, 69*F fermentation temp, using 19g of US-05.
http://www.mrmalty.com/calc/calc.html

If I'm not keeping/harvesting the old yeast (post-fermentation) is there any point in adding O2 to the fermentor?

I seem to recall from an archive (though I can't remember which one) that O2 is necessary for yeast growth & propagation and long term "health". However, I also seemed to remember (again, still don't remember where) that someone declared O2 as unnecessary if you pitch the correct amount as the yeast don't need to replicate nearly the same as if they were underpitched.

Thoughts?

(OK - I know it isn't hard to add O2 and I "could" just do it anyway; but that's not the point )

I would think that the O2 would be necessary anyway. Just because the yeast are in "fermentation mode" doesn't mean that they are not reproducing. Some less viable yeast is floculating, and others are reproducing. Obviously not at the rate that happens during the acclimation phase.

This is just my intuition. This question is probably best asked of Chris White.


Mylo

http://www.danstaryeast.com/library/aer ... _wort.html

"Lallemand packs the maximum amount of lipids into the cell wall that is possible during the aerobic production of the yeast at the factory. When you inoculate this yeast into a starter or into the mash, the yeast can double about three time before it runs out of lipids and the growth will stop. There is about 5% lipids in the dry yeast.

In a very general view:

At each doubling it will split the lipids with out making more lipids (no O2). The first split leaves 2.5% for each daughter cell. The second split leaves 1.25% for each daughter cell. The next split leaves 0.63%. This is the low level that stops yeast multiplication. Unless you add O2 the reproduction will stop.

When you produce 3-5% alcohol beer this is no problem. It is when you produce higher alcohol beer or inoculate at a lower rate, that you need to add O2 to produce more yeast and for alcohol tolerance near the end of fermentation. You definitely need added O2 when you reuse the yeast for the next inoculum."

Thoughts?
p.s. Yep, Lallemand does not manufacture US-05

In your specific case of a 12 Plato APA with with the proper amount of dry yeast, it would seem oxygenation is not necessary.

http://www.danstaryeast.com/library/aer ... _wort.html
http://www.fermentis.com/FO/60-Beer/60-23_faqCB.asp

In slight contrast to the Danstar link above (saying 3 reproductions are fine), Greg Noonan claims that ales generally grow 5 to 8 times the pitching rate and lagers 3 to 5. (New Brewing Lager Beer, p. 167) Perhaps Dr. Cone is taking into account that homebrewery transfers are not exactly quiet on average. Anyone else have a reference as to how many times yeast should reproduce in an ale/lager to produce the correct ester and phenol profile?

*edit* Good work on the Danstar info! Just beat me to it!