Wort Aeration

[WoodlandBrew]

Oxygen quickly comes out of solution. My last brew day was a beer with OG 1.090+ with 20+ppm O2. Pitched yeast 30 minutes after reading. By three hours later O2 sat was down to 16ppm.

In "Principles of Brewing Science" Fix attributes this to the yeast using the oxygen to produce sterols. (p95 in the paper back second addition)

 

[JJFlash]

In "Principles of Brewing Science" Fix attributes this to the yeast using the oxygen to produce sterols. (p95 in the paper back second addition)

Absolutely correct! That is why we are putting in oxygen.

I failed to mention I use yeast off a stir plate that has been cooled, the liquid decanted, then only the yeast is pitched. So the yeast is pitched in hibernation stage and not at full Krausen already working. So there must be some lag time...

I have attributed most of this sudden drop to the oxygen quickly coming out of solution. Most certainly could be all/most yeast oxygen uptake. Perhaps next brew day I should delay pitching the yeast by several hours and recording the oxygen saturation drop over time. Would be more beneficial information.

 

[Hamsterbite]

Oxygen quickly comes out of solution. My last brew day was a beer with OG 1.090+ with 20+ppm O2. Pitched yeast 30 minutes after reading. By three hours later O2 sat was down to 16ppm.

For the past few years I have hit my desired oxygen level then pulled my dissolved oxygen meter out. Past few brews I have been leaving it in to see just how quickly the oxygen comes out of solution. Much quicker than I even anticipated. That is why for big beers extra doses of oxygen are recommended in the first 24 hours.

Some brewers will add large quantity of yeast and less oxygen, others will add less yeast more oxygen. Both methods do work. It all depends upon your yeast. If you are using 1056 and want a very clean profile then pitch lots of yeast - doesn't matter. However, if you are brewing Belgian style with 540 and high OG the beer is very dependent upon yeast flavor - then less yeast and more oxygen. Most yeast flavors are derived in the first 72 hours with abundant yeast growth.

These are just my personal observations from brewing Belgian beers for many years. Your brewing techniques can significantly change many of these variables.

That's what I would expect with wort that has been oxygenated beyond the point of equilibrium, which near as I can determine is somewhere between 8-9 ppm. You can certainly force more pure O2 into solution, but to keep it at the desired level for a given amount of time, I suspect, you would need to fill the headspace with a proportionate volume of O2, and not more. Of course, the yeast are going to be converting it to CO2 at the same time, so there's probably no practical way to keep the desired O2 levels where you want them. You can't seal the headspace, and CO2 is going to displace any air and/ or O2. Im sure there's a way to do it with the right lab equipment, but that's not ever going to be practical for home brewers.

That said, you need to have some way of knowing when to stop adding O2. When the fermentation is done, you obviously want all of the O2 gone.
I think we have some good rules of thumb, but I would like to better understand some of the variables involved. We know that strain, gravity, temperature, fermenter geometry, headspace, etc. all have an effect on the duration of the ferment and hence the consumption requirements/rates for the O2.

 

[WoodlandBrew]

That's what I would expect with wort that has been oxygenated beyond the point of equilibrium, which near as I can determine is somewhere between 8-9 ppm. You can certainly force more pure O2 into solution, but to keep it at the desired level for a given amount of time, I suspect, you would need to fill the headspace with a proportionate volume of O2, and not more. Of course, the yeast are going to be converting it to CO2 at the same time, so there's probably no practical way to keep the desired O2 levels where you want them. You can't seal the headspace, and CO2 is going to displace any air and/ or O2. Im sure there's a way to do it with the right lab equipment, but that's not ever going to be practical for home brewers.

That said, you need to have some way of knowing when to stop adding O2. When the fermentation is done, you obviously want all of the O2 gone.
I think we have some good rules of thumb, but I would like to better understand some of the variables involved. We know that strain, gravity, temperature, fermenter geometry, headspace, etc. all have an effect on the duration of the ferment and hence the consumption requirements/rates for the O2.

Read the chapter on fermentation in "Principles of Brewing Science" by George Fix It will explain this all to you. It's the best explanation I have read. He keeps it simple enough to be understandable even if you don't have a degree in micro biology.

 

[Hamsterbite]

Read the chapter on fermentation in "Principles of Brewing Science" by George Fix It will explain this all to you. It's the best explanation I have read. He keeps it simple enough to be understandable even if you don't have a degree in micro biology.

Thanks for the recommendation. I look forward to getting this book.