Aeration or No Aeration

[SplitHops]

A question on Aeration; If aeration is mainly to oxygenate your wort to help yeast produce more rapidly, and a more viable proliferation, do I really need to aerate the wort if I have already grown my yeast starter to over 4 billion cells for say a five gallon sample of beer.

I would think since oxygen can cause staling or infuse unwanted other yeast into the beer, would it be safe to say if I have grown a strong yeast starter, that skipping this step would be better?

Appreciate anyone's educated thoughts on this matter.

Thank you

[MarkTrent]

A question on Aeration; If aeration is mainly to oxygenate your wort to help yeast produce more rapidly, and a more viable proliferation, do I really need to aerate the wort if I have already grown my yeast starter to over 4 billion cells for say a five gallon sample of beer.

I would think since oxygen can cause staling or infuse unwanted other yeast into the beer, would it be safe to say if I have grown a strong yeast starter, that skipping this step would be better?

Appreciate anyone's educated thoughts on this matter.

Thank you

While O2 does impact reproduction, perhaps the most important part to consider is the the effects of lipids near the end of fermentation. Lipids are metabolized by the yeast cell from squalene and without O2 this metabolite (lipids) cannot be formed. Lipids make the cell wall elastic and fluid which not only helps with reproduction but also intake of sugars and output of alcohols near the end of fermentation. Once the fermentation is anaerobic, lipids cannot be formed and with each new bud the lipids from the mother cell are shared equally with the new daughter cell. With plenty of O2 a yeast cell can contain up to 5% lipids. So in an anaerobic environment, after the first doubling the new yeast cell now contains 2.5% lipids and after the next split the cell contains 1.25% and then 0.63%. It is at this point that the cell wall becomes leathery, may not be able to bud and is more challenged to uptake sugar and remove alcohol. The build up of alcohol within the cell can become toxic and deadly. Now for a <5% alcohol beer these three doublings should be sufficient to fully ferment the beer but for a bigger beer more doubling may be needed. This is dependant on pitching rate as the more yeast pitched the fewer doublings required but pitching rate also has an impact on the flavor of the beer. So all this boiled down; if you can supply plenty of O2 in your propagation and with an adequate pitching rate a <5% alcohol beer may not need supplemental O2 for good fermentation. For larger beers or lower pitching rates O2 at pitching may be required. When re-pitching, the yeast is poor in O2, therefore additional O2 at pitching may always be necessary. Source: http://www.danstaryeast.com/articles...er-versus-wort

[SplitHops]

While O2 does impact reproduction, perhaps the most important part to consider is the the effects of lipids near the end of fermentation. Lipids are metabolized by the yeast cell from squalene and without O2 this metabolite (lipids) cannot be formed. Lipids make the cell wall elastic and fluid which not only helps with reproduction but also intake of sugars and output of alcohols near the end of fermentation. Once the fermentation is anaerobic, lipids cannot be formed and with each new bud the lipids from the mother cell are shared equally with the new daughter cell. With plenty of O2 a yeast cell can contain up to 5% lipids. So in an anaerobic environment, after the first doubling the new yeast cell now contains 2.5% lipids and after the next split the cell contains 1.25% and then 0.63%. It is at this point that the cell wall becomes leathery, may not be able to bud and is more challenged to uptake sugar and remove alcohol. The build up of alcohol within the cell can become toxic and deadly. Now for a <5% alcohol beer these three doublings should be sufficient to fully ferment the beer but for a bigger beer more doubling may be needed. This is dependant on pitching rate as the more yeast pitched the fewer doublings required but pitching rate also has an impact on the flavor of the beer. So all this boiled down; if you can supply plenty of O2 in your propagation and with an adequate pitching rate a <5% alcohol beer may not need supplemental O2 for good fermentation. For larger beers or lower pitching rates O2 at pitching may be required. When re-pitching, the yeast is poor in O2, therefore additional O2 at pitching may always be necessary. Source: http://www.danstaryeast.com/articles...er-versus-wort

Excellent answer and makes perfect scene, thank you for the detailed answer. Very helpful

[mmussen]

Always aerate. The old rule of thumb is 1 million cells/mL/Plato. Meaning that in a 5 gallon batch you'd want about 2 smack packs. And at that level aeration is still recommended for fermentation. O2 will not carry over into the final beer if you time the aeration correctly - the yeast will absorb it right away.

[MarkTrent]

Always aerate. The old rule of thumb is 1 million cells/mL/Plato. Meaning that in a 5 gallon batch you'd want about 2 smack packs. And at that level aeration is still recommended for fermentation. O2 will not carry over into the final beer if you time the aeration correctly - the yeast will absorb it right away.

Yes this is good advice. I think I got carried away in explaining why O2 is needed and got away from practical advice. As noted above adding O2 at pitching will not cause oxidation of the finished product and it is not hard to avoid contamination when aerating. In addition there is no practical method to know how successfully you have provided O2 in your propagation. It is very challenging without a proper propagator and these are very expensive. However, for small propagations, orbital shakers have been shown scientifically to provide aeration levels as high as propagators. It could be assumed that a stir plate may provide adequate O2 but I'm not aware of any science that has proven that. So, with all that said, aeration of all beer at pitching, regardless of size, is good insurance against under attenuation and will help to produce consistently flavorful beer.

[SplitHops]

Mmussen thank you.

Always aerate. The old rule of thumb is 1 million cells/mL/Plato. Meaning that in a 5 gallon batch you'd want about 2 smack packs. And at that level aeration is still recommended for fermentation. O2 will not carry over into the final beer if you time the aeration correctly - the yeast will absorb it right away.

MMussen as I mentioned I am growing my yeast so my question was not of a how much rather if I have enough already is it really necessary to add oxygen. As in an earlier response the answer was that oxygen also plays an important roll in not only fermentation and proliferation of yeast but also has a strong result in creating other attributes along the way.

[ubrewbeer]

MMussen as I mentioned I am growing my yeast so my question was not of a how much rather if I have enough already is it really necessary to add oxygen. As in an earlier response the answer was that oxygen also plays an important roll in not only fermentation and proliferation of yeast but also has a strong result in creating other attributes along the way.

Is there such a thing as adding too much yeast?

[jordanquintao]

Is there such a thing as adding too much yeast?

If you pitch all cells needed reproduction may be not occur. Esters are create in reproduction phase. You will have zero esters in your beer. All these guys will stand in your started. May be will have the same profile of a overpitched beer.

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[Brewtech11]

Olive oil

As an interesting aside, New Belgium did some experimentation about 10 years ago where they forewent aeration in favor of adding olive oil to the wort. Olive oil is a most excellent source of unsaturated fatty acids which yeast require for reproduction and cell wall manufacture. If I recall their fermentations were quite successful and the beers were within parameters on taste panel. I don't believe the intention was ever to replace aeration, rather it was an academic exercise, and an interesting one at that.