[denny]

Successive batches. The beers were weeks apart and the first was green while the second keg was kicking. No true triangle tests, just my own errorful palette and memory.

With all due respect, then you really don't know for certain.  Not that your opinion doesn't matter.

[mabrungard]

Martin, remember that even in the presence of air the fermentation will still be anaerobic due to the Crabtree effect. The metabolic pathways used by the yeast in open vs. closed fermentation will probably not be dramatically different, but there may be some difference.

I've been reading a few academic papers on oxygen and how it relates to yeast sterols. I need to read a bit more and wrap my head around things but I believe that open fermentation, broadly speaking, should keep the average yeast sterol composition by weight significantly higher than a closed fermentation. What is the difference in beer flavors expressed by yeast whose dry weight basis is 1% ergosterol vs 0.2% ergosterol? I don't know.

Doesn't the Crabtree effect have something more to do with the production of alcohol due to the concentration of sugars in the media? I'm not really sure.

However, I do agree that the metabolic condition for the yeast under that yeast foam blanket should be primarily anaerobic. I just wonder if there is some sort of effect from micro-oxygenation of the overall system on the yeast? 

[S. cerevisiae]

techbrau, it pays to search before posting.  Most of the information that you posted in the last couple of posts has been posted to the forum many times.

[S. cerevisiae]

And as a scientist and a Bayesian, I'm far more interested in discussing the points I made in my previous post than harping on misused, fundamentally flawed frequentist significance testing on poorly controlled experiments with sample sizes far too small to be meaningful.

You are going to find yourself very frustrated in this hobby.  One of the more influential brewers to enter and leave the hobby while I was on hiatus based a huge number of conclusions on one-shot experiments that contained tiny sample sizes.  There was no attempt to encourage others to repeat his results. You as well as I know that is not how science works, but many of his results have become gold standards that you will have to work very hard and make many enemies to tarnish.

To be completely honest I had a bit of an ulterior motive when I let Shaken, Not Stirred loose in the community (I started with British brewers first because they tend to be less dogmatic).  While I have believed that it is a solid low-cost, low-tech, and practical way to make and pitch a healthy starter for over two decades,  I needed to know if the results were repeatable as well as under what conditions did the method not meet expectations.  Are there still unknowns?  Of course, there will always be unknowns because we are dealing with biological organisms.  However, I am now very comfortable suggesting the method to other brewers who are looking for a way to make and pitch a healthy starter that is easy to perform and low cost. 

I remember what it was like to be cash strapped when I first started brew.  I had moved up to a detached home from a non-detached home a couple of years earlier, and I was still a single man.  I was not robbing Peter to Paul like a lot of house poor people, but discretionary income was in short supply.  After having lived through that experience, I did not want see a single new brewer put off moving up to using liquid cultures because he/she could not afford to purchase a stir plate and an Erlenmeyer flask when I knew that they were not necessary to propagate yeast.

With the above said, you will find that even the most technical brewers in this hobby are not pure scientists because most have an engineering bent, which means they are practitioners just like medical doctors where their worlds are combination of theory plus practice.  You will not find much in the way of support for basic science without an immediate application within the community, and most of the basic science that is conducted will be inherently flawed due to small sample sizes and poorly designed experiments.  It is just a fact of life.

[S. cerevisiae]

Like what? I did do some searching, and didn't find anything at all dealing quantitatively with absolute levels of ergosterol. And while lots of posts qualitatively touch on pitch rate, UFA/ergosterol reserves, and wort aeration individually in a hand-wavey manner, I haven't seen any discussion about a quantitative, unified model of  growth/fermentative performance that takes into account all of these factors.

I am talking about the Crabtree effect. The gravity at which the Crabtree effect kicks in, which you probably copied from somewhere else without understanding how the 1.008 figure was calculated and under what wort composition.  I laid these numbers and calculations out in several threads in such a way as to be accessible to the layman.  O₂ solubility with respect to gravity as well as the importance of cellular health and increased pitching rates with high gravity wort due to the effects of osmotic pressure and ethanol on turgor pressure has also been covered several times with supporting citations.  You are acting like this information is new to everyone.   

The AHA Forum is not a tech journal.  It is a hobby site with people with disparate backgrounds.  What you call hand waving is an attempt to make the complex information accessible without bogging people down.  Finding the balance between what is and is not too nuts and bolts is an art form.

[S. cerevisiae]

I did remember the 1.008 figure from something probably you posted, but please don't jump to unfounded ad-hominem conclusions and assume that I don't understand that the 1.008 is derived from the fact that the underlying mechanism is a glucose concentration of > ~0.3%, and wort sugar is nearly always less than 10% glucose. 1.008 is ~2% sugar by weight, giving a glucose concentration of ~0.2% assuming the sugar is comprised of 10% glucose.

The glucose level in extract is rarely 10% or less.  The average mash is conducted at approximately 150F.   At that temperature, the extract will contain roughly 14% glucose, which yields 0.28% glucose w/v for an S.G. of 1.008.

What I have not seen is all of the relevant information about the interactions between pitching rate, nutrient reserves, and dissolved oxygen laid out on the table and discussed at once quantitatively. I'm doing my own research into this, but do you have any nuts and bolts insights?

Trust me, I do not avoid this stuff because I do not desire to have a neat and orderly solution. It's just that a monkey wrench eventually gets thrown into the works that completely invalidates my work every time I attempt to do so, which is why I have reached the point where I have decided that any attempt to produce model that covers all brewing yeast strains is a fool's errand.  There are too many variables.   For example, we pitch an O1 yeast strain into 8ppm wort.  The mother cells can top off their ergosterol reserves using 2ppm before entering the logarithmic phase.  How is the remaining O₂ used?  One can take a linear approach and say that the mother cells and the first generation of daughter cells will use it equally, but is that really how the excess O₂ will be used? 

As far as open fermentation versus closed fermentation goes, my hypothesis at this point is that difference lies in reduced top pressure.  Unless the yeast head is overflowing the fermentation vessel, it is blanketed by CO₂. The CO₂ blanket prevents significant O₂ pickup.  If you ever get the opportunity to visit a Yorkshire-style brewery, you will discover that they spray the fermenting beer down on top of the fermentation to aerate the culture.  If open fermentation allowed for O₂ pickup during fermentation, this step would not be necessary. 

[S. cerevisiae]

How about a real world analysis:  http://www.brewingwithbriess.com/Assets/PDFs/Briess_PISB_CBWPilsenLightDME.pdf

As far as the other stuff, go ahead and knock yourself out.  You will discover like I did that it is a fool's errand.  If it could be done, it would have already been done.

[S. cerevisiae]

Like I said, feel free to knock yourself out.