Extra aeration impact on final ABV?

[Kent88]

This weekend I made a high-gravity Belgian Ale, and I aerated with a "aquarium-style" aerator right after adding yeast, and again about 18 hours after pitching yeast, as recommended in Jamil Z & Chris White's Yeast book (and multiple sources around the internets).

I have been working under the impression that alcohol is developed during anaerobic respiration, so wouldn't re-aerating during krausen give the yeast another chance to consume sugars aerobically, thus not producing alcohol, for a little while longer? Has anyone looked into what, if any, kind of difference this makes to the ABV of the resulting beer?

I wouldn't think it would make a huge difference, but I don't know.

 

[MVKTR2]

Don't add oxygen after the first 24 hours or you run the risk of oxidized beer. The oxygen aids cell splitting/yeast growth and as you point out isn't a part of the yeasts conversion of sugar into alcohol and co2. The only reason we add oxygen when brewing is for yeast growth, thus why a stir plate is so good for building a yeast starter.

 

[MVKTR2]

To actually answer your question I'm sure brewing scientists have looked at it but it's impractical for beer production for the reasons stated above. Oxygen is beers mortal enemy!

 

[sky4meplease]

I too have read the excerpt in the yeast book.
I think the idea is to provide the newly budded cells from the exponential growth phase a shot of 02 as you did the yeast you pitched initially. That is why you wait 12-18 hours to allow for cell division.
The yeast quickly take up this new 02 which helps with fermentation and attenuation.
I suppose if you wait too long to do this you risk oxidation.
Also stated is the need for pure 02 above 1.092.
As far as affecting the ABV I suppose if the yeast stress out or give up prematurely due poor health it would negatively affect attenuation and ultimately ABV.

 

[Kent88]

This wasn't about oxidation of the final product or what would happen if the yeast didn't get enough oxygen.

More about what amount of sugar is being consumed by yeast while it is going through aerobic fermentation and not producing alcohol. From what I understand ABV is figured by looking at gravity at the beginning and end of fermentation, but what if more of that sugar than usual is being consumed in the presence of oxygen and not producing alcohol.

Am I making any sense?

I assumed that the impact would be low, but I'm curious.

 

[DaWhip]

You are correct about the differences between ABV produced during aerobic & anaerobic fermentation, but there is the fabulous third scenario - The Crabtree Effect. Aerobic Fermentation produces ethanol if in the presence of a significant concentration of glucose (i.e. wort).

Alcohol Production:
The alcohol production industry is highly dependent upon the Crabtree active Saccharomyces cerevisiae. Yeast produces alcohol only under anaerobic conditions (which must be maintained for higher alcohol output!). Under aerobic conditions, oxidative phosphorylation takes place, which stops the use of glycolytic pathway. But, if excess of glucose (substrate) is supplied to the culture, then Crabtree effect takes place, and respiration is inhibited even if aerobic condition prevails! This leads to excess production of alcohol rather than biomass production. So, Crabtree comes to a favorable use in alcohol industry.

http://www.biotechnologyforums.com/thread-2251.html