Author Topic: observation of dissolved oxygen loss in wort  (Read 5687 times)

Offline klickitat jim

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Re: observation of dissolved oxygen loss in wort
« Reply #15 on: April 29, 2013, 04:54:50 PM »
I've given O2 some consideration, at one point almost ordered a regulator and stone. I currently splash aerate. Once when I drain my boil and again after cold crashing when I put it in the fermentor. I don't think I will change. Its not been a problem.

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Re: observation of dissolved oxygen loss in wort
« Reply #16 on: April 29, 2013, 04:59:33 PM »
So adding pure O2 before pitching is good. And adding excessive o2 before pitching will negatively affect the flavor. And aerating after pitching can be ok in certain situations like starters and high gravity beer or mead. But pure o2 after pitching is always bad. Is that right?
Adding pure O2 before pitching is good.

You can't add excessive O2 before pitching, it is not possible due to saturation.

Adding O2 to beer (not wort) negatively affects flavor.

Aerating after pitching in starters is fine because although that can affect the flavor stability in a negative way, you are not drinking your starter.

Pure O2 after pitching is not always bad, as long as it is done in a controlled, measured manner and you don't add so much that it is toxic to the yeast, and as long as it is done before fermentation has progressed too far (because then it can affect the flavor and stability).

Essentially, oxygen toxicity can be caused by oxygen radicals like superoxide (O2-) that are generated in and can damage the cell.  Superoxide is grabbed by superoxide dismutase, which alternately converts it to either hydrogen peroxide (H2O2) or molecular oxygen (O2).  Since the H2O2 can also damage the cell it is further degraded to water and oxygen (2 H2O2 -> 2 H2O + 2 O2).  This is the same reaction that happens during respiration in our bodies all of the time, and dealing with it is important enough that we have superoxide dismutase all over our bodies, circulating and in every cell.

Your google search may not have led to anything that the authors directly relate to brewing, but the yeast strains that are used in labs are derived from beer/bread strains and share nearly all of their genetics with our brewing strains.

You should at least be able to read the abstracts of some papers here:
http://onlinelibrary.wiley.com.offcampus.lib.washington.edu/doi/10.1002/yea.320070203/abstract
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3380282/
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Offline jjflash

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Re: observation of dissolved oxygen loss in wort
« Reply #17 on: April 29, 2013, 06:41:33 PM »
I think yeast oxygen toxicity is a wildly propagated urban myth for brewers.  No doubt you can kill most anything with excessive oxygen.  However, with our brewing practices this is unlikely to happen and needless worry. Excessive oxygen, in my opinion, is rarely a problem.

I do believe you can use excessive oxygen that negatively affects beer flavor, producing fusel alcohols and acetaldehyde.

I do believe that consistent control of dissolved oxygen in wort is critical to steady yeast growth and yeast production of desirable flavor compounds.

Low gravity beers <1.060 are very forgiving of mistakes and this information is not as applicable to these beers. High gravity beers >1.080 are much less forgiving of mistakes and this information is more important for their success.
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Offline majorvices

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observation of dissolved oxygen loss in wort
« Reply #18 on: April 30, 2013, 04:59:00 AM »
Am I missing something? A Google search of "oxygen toxicity in yeast" turned up nothing related to brewing. And in the "yeast" book, it says,"Generally you do no want to add oxygen later, as it can disturb the delicate balance of flavor and aroma compound creation." It also suggests, in high gravity beers, "adding oxygen between 12-18 hours after pitching can make a tremendous difference in attenuating the beer." But nothing about oxygen toxicity. Doesn't spinning fermenting wort on a stir plate introduce oxygen continually? Why would 30 seconds of oxygenation be a good thing for the yeast 10 minutes before pitching, but be a bad thing 10 minutes after pitching?

I don't mean to be a smarty pants but I'm suddenly cornfused about something I thought I understood!  ???

Pure o2 can be toxic to yeast. I have actually killed yeast in yeast starters before by adding pure o2 directly to the starter after pitching yeast.

Are you sure it was the o2? Before I got a stir plate I occasionally oxygenated starters without any apparent harm to the yeast.

Pretty sure. I hit it with a very long o2 blast. Never got any growth or action on a very fresh pack of yeast that swelled quickly in Wyeat packet then trasferred to stir plate. Nothing but spinning.
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Re: observation of dissolved oxygen loss in wort
« Reply #19 on: May 08, 2013, 05:23:45 AM »
So adding pure O2 before pitching is good. And adding excessive o2 before pitching will negatively affect the flavor. And aerating after pitching can be ok in certain situations like starters and high gravity beer or mead. But pure o2 after pitching is always bad. Is that right?
Adding pure O2 before pitching is good.

You can't add excessive O2 before pitching, it is not possible due to saturation.

Adding O2 to beer (not wort) negatively affects flavor.

Aerating after pitching in starters is fine because although that can affect the flavor stability in a negative way, you are not drinking your starter.

Pure O2 after pitching is not always bad, as long as it is done in a controlled, measured manner and you don't add so much that it is toxic to the yeast, and as long as it is done before fermentation has progressed too far (because then it can affect the flavor and stability).

Essentially, oxygen toxicity can be caused by oxygen radicals like superoxide (O2-) that are generated in and can damage the cell.  Superoxide is grabbed by superoxide dismutase, which alternately converts it to either hydrogen peroxide (H2O2) or molecular oxygen (O2).  Since the H2O2 can also damage the cell it is further degraded to water and oxygen (2 H2O2 -> 2 H2O + 2 O2).  This is the same reaction that happens during respiration in our bodies all of the time, and dealing with it is important enough that we have superoxide dismutase all over our bodies, circulating and in every cell.

Your google search may not have led to anything that the authors directly relate to brewing, but the yeast strains that are used in labs are derived from beer/bread strains and share nearly all of their genetics with our brewing strains.

You should at least be able to read the abstracts of some papers here:
http://onlinelibrary.wiley.com.offcampus.lib.washington.edu/doi/10.1002/yea.320070203/abstract
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3380282/


One website requires a login. The other doesn't really answer any brewing-specific questions. 
So too much oxygen kills yeast. But how much is too much? Is there a threshold ppm? Or is it the physical act of pure o2 bubbling thru the yeasty wort?

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Re: observation of dissolved oxygen loss in wort
« Reply #20 on: May 10, 2013, 10:29:38 AM »
One website requires a login. The other doesn't really answer any brewing-specific questions. 
So too much oxygen kills yeast. But how much is too much? Is there a threshold ppm? Or is it the physical act of pure o2 bubbling thru the yeasty wort?
I don't remember for sure, but I want to say it is something like 15 ppm.  I would not be surprised if it is strain and temperature dependent.  It's not really a concern because even if you can get that much in your wort, it will drop when you add the yeast.  It is only a constant high level that is toxic IIRC.  It is not a physical thing, it is a buildup of reactive oxygen species like superoxide and peroxide.
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DO meter accurate?
« Reply #21 on: May 10, 2013, 11:21:01 AM »
Are your DO meter readings accurate?  The DO meters I used in laboratories had a built in stirrer because they did not work properly unless the water was circulating.  I'm not sure what type of DO meter I was using or whether chemiluminescent DO meters need moving water to work properly. 
« Last Edit: May 10, 2013, 11:23:37 AM by kramerog »
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Re: observation of dissolved oxygen loss in wort
« Reply #22 on: May 10, 2013, 11:27:52 AM »
One website requires a login. The other doesn't really answer any brewing-specific questions. 
So too much oxygen kills yeast. But how much is too much? Is there a threshold ppm? Or is it the physical act of pure o2 bubbling thru the yeasty wort?
I don't remember for sure, but I want to say it is something like 15 ppm.  I would not be surprised if it is strain and temperature dependent.  It's not really a concern because even if you can get that much in your wort, it will drop when you add the yeast.  It is only a constant high level that is toxic IIRC.  It is not a physical thing, it is a buildup of reactive oxygen species like superoxide and peroxide.


Aha. Thanks for clearing that up for me.

Offline jjflash

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Re: DO meter accurate?
« Reply #23 on: May 11, 2013, 03:35:47 PM »
Are your DO meter readings accurate?  The DO meters I used in laboratories had a built in stirrer because they did not work properly unless the water was circulating.  I'm not sure what type of DO meter I was using or whether chemiluminescent DO meters need moving water to work properly.

The DO meter is in the glass carboy as it is being filled by pump, so it is always in well circulated wort.  This is a very high quality Hach LDO. Even if it was off a point or two, doesn't change the trend of sudden oxygen desaturation, of a high gravity wort, in very short period of time. I will run this experiment over the next several brew days to confirm this finding. 

My current message to myself on this - I should pitch yeast immediately upon completion of wort aeration/oxygenation.  My previous method was to fill the carboy, stop and do a yeast count, calculate my pitch volume, then pitch the yeast. This all the while the wort was desaturating....
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Offline veedo

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Re: observation of dissolved oxygen loss in wort
« Reply #24 on: July 06, 2013, 08:21:36 AM »
Very interesting.  Was about to buy a new o2 regulator with a flow meter, but now I'm not sure if its worth it.  Have you done any more tests with this?