[klickitat jim]

The O2 that escapes is gone, not the O2 that is absorbed, right.

[Phil_M]

But is the oxygen in the bubbles really absorbed back into the wort, or is it just encapsulated in the foamy bubbles? Once the bubbles bursts, the O2 is just released back into the air, not into the wort. Just like using a stone, if the O2 is bubbling to the surface it is escaping, not absorbing. It would seem that any O2 absorption occurs during the shaking, not as a result of the collapsing foam.

It's not the air in the bubbles that's driving the oxygenation of the starter, it's the surface area. Oxygen will dissolve into wort at a rate that's based on surface area and pressure. By maximizing the surface area of the wort, there's then more wort touching air. A diffusion stone works similarly. Folks don't just put a blanket of O2 on the beer and let it dissolve into the wort, they use an aeration wand. That wand creates thousands of tiny bubbles, which again increase the surface area of the wort that's in contact with oxygen. Running the stone too hard such that the bubbles break the surface doesn't mean that you're not oxygenating the wort, just that you're wasting O2.

[a10t2]

Based on Mark's previous comments, the purpose of the foam is to expose at least some of the cells directly to the atmosphere, akin to being streaked on a plate.

[S. cerevisiae]

But is the oxygen in the bubbles really absorbed back into the wort, or is it just encapsulated in the foamy bubbles? Once the bubbles bursts, the O2 is just released back into the air, not into the wort. Just like using a stone, if the O2 is bubbling to the surface it is escaping, not absorbing. It would seem that any O2 absorption occurs during the shaking, not as a result of the collapsing foam.

You are comparing apples to oranges.  Bubbling a gas through a liquid is not the same thing as a gas-liquid foam. The ratio of liquid to gas is inverted in a gas-liquid foam.  A gas-liquid foam is composed of pockets of gas entrapped in extremely thin layers of liquid.  O₂ is absorbed at the boundary between the liquid and the gas.  It does not take long to saturate a liquid when the depth is less than the thickness of a human hair and gas appears on both sides. We are taking about a depth measured in nanometers.  The liquid will saturate based on Henry's law.  The only way to force more O₂ to dissolve is to increase the pressure of the gas (as we do with CO₂ when force carbonating a keg).  Pure O₂ saturates at 40ppm because pure O₂ contain five times the amount of O₂ as air.

Now, the $10,000 question here is do the cells pick up any non-dissolved O₂ when the culture is pitched before shaking?  Dissolved O₂ from air peaks at around 8 parts per million.  The O₂ in air is 21 parts per hundred.  If a wort bubble is the same thickness as a soap bubble, we are looking at a range of 10 to 1,000 nanometers. The diameter of Saccharomyces cell ranges from 5 to 10 micrometers.

[ultravista]

According to Chris White, dissolved O₂is taken up by the yeast during the first thirty minutes.  An Erlenmeyer is a miserable vessel in which to make a shaken, not stirred starter due to its geometry.

Doh! I was ready to buy a rubber stopper for my 5L flask. Is a straight-walled bottle materially better?

[S. cerevisiae]

Why such a bad vessel?

It's a cone.  The pressure increases as the wort is forced into the cone.

I got about the same amount of foam as in pictures you have posted. I used a sold stopped to seal it up and gave it a good vertical shaking.

It only looks like you obtained the same amount of foam.   First off, the starter in the photos is only 600ml in volume. Secondly, there is more foam per inch in a cylinder than in a cone, and the media bottle gets wider from bottom to top.    An Erlenmeyer flask is a compromise piece of culturing glassware at best.  It is a poor man's Fernbach flask, which has a short and broad cone in order to maximize surface area.   

https://en.wikipedia.org/wiki/Fernbach_flask

The fact that Erlenmeyer flasks and stir plates became the gold standard in home brewing instead of being seen as the compromise devices that they are blows my mind. A stir plate is a poor man's compromise orbital shaker. 
 

[Stevie]

The original volume was 1000ml. After shaking there was about 1400ml of foam and the liquid volume was about 600ml. The flasks lowest graduation is 1000ml, so those are obviously SWAG estimates. Like I mentioned, my jugs were of questionable cleanliness as they had not been touched in over two years. I cleaned one today during post brew clean up and will give it a shot for the kolsch I am brewing a few weeks from now.

Edit - I wonder if there is a foam stabilizer that could be utilized without harming the yeast or inhibiting their ability to access the O2. Maybe very small touch of agar agar or xanthan gum?

[S. cerevisiae]

Edit - I wonder if there is a foam stabilizer that could be utilized without harming the yeast or inhibiting their ability to access the O2. Maybe very small touch of agar agar or xanthan gum?

Why would you want add foam stabilizer?  The wort that is in gas-liquid foam form is saturated by the time the foam collapses.  After working with a class O3/O4 strain¹, I can say without reservation that most of the strains that are sold by Wyeast and White Labs fall into class O1 or class O2 with respect to O₂ demand.  Class O1 oxygen demands can be met by 4ppm dissolved O₂ (a.k.a. half air saturated wort).  Class O2 oxygen demands can be met by 8ppm dissolved O₂ (a.k.a. fully air saturated wort).  There are yeast performance downsides to over oxgenation.

[1] B.H. Kirsop, Oxygen in Brewery Fermentation, http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1974.tb03614.x/pdf

[Stevie]

I was going there off of the idea that the juice is the foam. If 30min or foam is good, well ok.

[S. cerevisiae]

I was going there off of the idea that the juice is the foam. Is 30min or foam is good, well ok.

Five minutes of foam is okay.  Do not think of the foam as some kind of secret sauce where magical things happen to the yeast cells.  It is little more than a low-tech way to ensure that the medium is well aerated.   

[Stevie]

I suppose this method may be why the wine whip/mix-stir aeration method works well for wort. I get a dense foam that last hours when using my mix-stir. That is by far my favorite piece of low tech and practically unbreakable piece of kit.

[klickitat jim]

Just a side note, blowing Oxygen through wort is not a waste of oxygen. I've seen a waste of oxygen. I know how a waste of oxygen thinks.

Back to regular programing

[ultravista]

Do you attach a drill to the mix-stir?

[HoosierBrew]

Do you attach a drill to the mix-stir?

Yep. Love my mix stir. I use it to whip up the wort until it gets to the top of the bucket, then pitch.

[klickitat jim]

Do you attach a drill to the mix-stir?

Yep. Love my mix stir. I use it to whip up the wort until it gets to the top of the bucket, then pitch.

I've heard Zainashef say numerous times not to do that because once the stuff that makes foam has made foam it will never make foam again.