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Old 12-27-2012, 06:18 PM   #91
eastoak
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It was strong for about 3 days then almost nothing and today is 7 days since brewing. As I've said I'm used to seeing healthy fermentation for considerably longer. Does oxygen shorten the fermentation period?
I am going to transfer tomorrow but just as I've always done and not try to fix something that isn't obviously broken. Maybe that activity will restart it and maybe the tighter head space inthe carboy will play a role. Time will tell...
unless you have exactly the same conditions inside a fermentor from batch to batch you will see different looking "things" from outside the fermentor; the bubbles, krausen, smells and so on.

as far as the O2 i copied the following from the wyeast website:

Oxygen is a critical additive in brewing. Oxygen is the only necessary nutrient not naturally found in wort. Adding adequate oxygen to wort requires a fundamental understanding of why yeast need oxygen, how much oxygen they need, and how to get oxygen into solution and the factors affecting solubility of oxygen.
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 12-28-2012, 06:26 PM   #92
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Thanks eastok for all that. I didn't think to go to Wyeast's site. I'm using their products and they must be experts in their field. I did transfer to the carboy yesterday and there was a good layer of scum (!) in the bucket. I use an S airlock in the secondary and I'm seeing bubbles again. This airlock also helps to guage the CO2 coming off the brew in the absence of bubbles unlike the 3 piece pot style airlock I use in primary. It was quite lively immediately after transfer, perhaps becaise of the agitation, and is much less so now. The only thing I did prior to transferring was measure the SG which is a bit pointless. I've never done so before so have nothing to compare with, it clearly HAS been fermenting and is clearly not finished. It was about 1015 (from 1050)

Just a thought, and maybe this is a bit more ON topic, I understand/believe/agree with the concept of aeration or oxygenation but it enters as bubbles of gas which rise and break at the surface. Isn't that evidence that the air or oxygen is leaving the brew?

Concerning the figures above How do we convert ppm (parts per million?) in to a useable figure like liters per min and time?

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Old 12-28-2012, 06:45 PM   #93
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Just a thought, and maybe this is a bit more ON topic, I understand/believe/agree with the concept of aeration or oxygenation but it enters as bubbles of gas which rise and break at the surface. Isn't that evidence that the air or oxygen is leaving the brew?
i'm not sure what the speed of oxidation is but once the O2 is in there and causing oxidation there is no going back. not sure if the bubbles we see coming out are O2 or CO2 (i think CO2) but there are other smarter folks here that would know.
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