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Old 04-25-2011, 02:18 AM   #1
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Default Purpose of wort oxygenation

I was trying to figure out what the actual purpose of oxygenation was and I can't really find anything other that it just kick starts the yeast.

When oxygen is available, yeast can use the oxygen to completely oxidize the sugar and the resultant waste is CO2 and water. However, in an anaerobic environment (where there is no O2) the yeast produce CO2 and ethanol but produce less energy in the reaction.

Wouldn't making a larger starter be easier / better than adding oxygen to the wort, especially if you are going for a high abv beer?



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Old 04-25-2011, 02:43 AM   #2
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When you have an aerobic environment, the yeast cells multiply, dont they? That would give a larger number of actual yeast cells. You could do a larger yeaststarter and accomplish the same thing i would think. I am no yeast expert and am drawing my knowledge from reading stuff. I don't know if I am entirely accurate or not.



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Old 04-25-2011, 02:48 AM   #3
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Aerobic environment = yeast can process sugar into energy more efficiently, no alcohol production, mitosis (more yeasties) occurs

Anaerobic environment = yeast cannot completely process sugar and produce CO2 and Alcohol as waste at the expense of not getting as much energy out of the sugar, mitosis still occurs.

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Old 04-25-2011, 02:53 AM   #4
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I think this pretty much says it all... First section covers why, the rest of the info is just gravy...

Why Yeast Need Oxygen

Yeast use oxygen for cell membrane synthesis. Without oxygen, cell growth will be extremely limited. Yeast can only produce sterols and certain unsaturated fatty acids necessary for cell growth in the presence of oxygen.

Inadequate oxygenation will lead to inadequate yeast growth. Inadequate yeast growth can cause poor attenuation, inconsistent or long fermentations, production of undesirable flavor and aroma compounds, and produces yeast that are not fit for harvesting and re-pitching.

How Much Oxygen?

Oxygen requirement is variable depending on: yeast strain employed, original gravity of wort, and wort trub levels.

Some yeast strains have higher oxygen requirements than others. It is generally safe to assume that you need at least 10ppm of oxygen. 10ppm will supply adequate oxygen in most situations. Over-oxygenation is generally not a concern as the yeast will use all available oxygen within 3 to 9 hours of pitching and oxygen will come out of solution during that time as well. Under-oxygenation is a much bigger concern.

High original gravity (>1.065) wort, in addition to increasing osmotic stress on yeast, can cause problems with achieving adequate levels of dissolved oxygen. As the gravity of wort increases, solubility of oxygen decreases. Increased temperatures also decrease the solubility of wort.

The unsaturated fatty acids found in wort trub can be utilized by yeast for membrane synthesis. If wort trub levels are low, yeast will need to synthesize more of these lipids and therefore will require more oxygen.

Methods of Aeration / Oxygenation

Homebrewers have several aeration/oxygenation methods available to them: siphon sprays, whipping, splashing, shaking, pumping air through a stone with an aquarium pump, and injecting pure oxygen through a sintered stone. We have tested all of these methods using a dissolved oxygen meter and have found that, when using air, 8 ppm of oxygen in solution is the best that you can achieve. Injecting oxygen through a stone will allow much higher dissolved oxygen levels. The chart below shows methods tested and the results.


Method DO ppm Time
Siphon Spray 4 ppm 0 sec.
Splashing & Shaking 8 ppm 40 sec.
Aquarium Pump w/ stone 8 ppm 5 min
Pure Oxygen w/ stone 0-26ppm 60 sec (12ppm)

It was concluded that pumping compressed air through a stone is not an efficient way to provide adequate levels of DO. Traditional splashing and shaking, although laborious, is fairly efficient at dissolving up to 8 ppm oxygen. To increase levels of oxygen, the carboy headspace can be purged with pure oxygen prior to shaking. The easiest and most effective method remains injecting pure oxygen through a scintered stone.

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Old 04-25-2011, 03:52 AM   #5
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HAHAHAHAHA!!!! Thats funny. Anywho, YAY!!! I was somewhat right. Reading these forums has absorbed into my brain a bit. Now if I could just download the entire forum to my brain via bluetooth. Got an app for that?

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Old 04-25-2011, 03:56 AM   #6
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Thanks for the info.

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Old 04-25-2011, 03:59 AM   #7
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Quote:
Originally Posted by djsethall View Post
...now if I could just download the entire forum to my brain via bluetooth. Got an app for that?
"tank, I need an up-link."

haha.

but seriously... I was actually thinking the same exact thing as the OP since my last brew (imperial stout/stout PG). If oxygenating your wort is done to help yeast multiply, seems like this would be moot if you already had enough cells in your starter.
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Old 04-25-2011, 03:59 AM   #8
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Quote:
Originally Posted by Golddiggie View Post
I think this pretty much says it all... First section covers why, the rest of the info is just gravy...

Why Yeast Need Oxygen

Yeast use oxygen for cell membrane synthesis....
What he said.
But one point you made.
It is about having enough healthy (lots of good membranes) yeast at the beginning of the ferment. Strictly speaking, if they yeast were grown up in a high O2 environment in the starter (oxygenated, stirred, low carbs added continuously) - and this is possible in a commercial environment, then there is no need to oxygenate the actual wort. However for the hombrewer it is easier to just oxygenate the wort than to build a bioreactor to grow up the yeast.
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Old 04-25-2011, 04:14 AM   #9
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Originally Posted by giligson View Post
However for the hombrewer it is easier to just oxygenate the wort than to build a bioreactor to grow up the yeast.
Now I have an idea for my next project. Thanks!!!
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Old 04-25-2011, 05:02 AM   #10
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mmmmm... bioreactor... eeeexxcellent (wrings hands together sinisterly)


so does the mrmalty pitching calculator take into consideration aerated vs. non-aerated wort?



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