oxygenating wort - larger capacity systems

[foxy]

It can't be. Lactate is the byproduct of anaerobic fermentation. The pH doesn't drop until it makes the switch.

Well when it has made the switch it is the co2 that scrubs any remaining oxygen from the wort.

 

[Sadfield]

Well when it has made the switch it is the co2 that scrubs any remaining oxygen from the wort.

..... and we're back here.

How does it go into anaerobic mode if there is oxygen? Isn't the definition of anaerobic respiration, respiration in the absence of oxygen? Don't living organism always favour aerobic, as it's around twenty times more efficient at releasing energy?

 

[foxy]

..... and we're back here.

No were not the question was from peebee quote. "What happens with that (marginally) excess oxygen when the yeast never really needed it to do the job? I only presume it just ends up as more yeast than is strictly necessary?

The answer is, 'The co2 produced by the yeast scrubs the excess oxygen from the wort'.

 

[peebee]

How does it go into anaerobic mode if there is oxygen? Isn't the definition of anaerobic respiration, respiration in the absence of oxygen? Don't living organism always favour aerobic, as it's around twenty times more efficient at releasing energy?

Not for yeast! I wouldn't be surprised if it were you who pointed it out to me? Yeast can't be bothered with all that complicated "aerobic" business if there's loads of food about (and it gets a steal on the competition), but it does need oxygen to synthesis the stuff to grow with. Crabtree effect - Wikipedia

 

[Sadfield]

Not for yeast! I wouldn't be surprised if it were you who pointed it out to me? Yeast can't be bothered with all that complicated "aerobic" business if there's loads of food about (and it gets a steal on the competition), but it does need oxygen to synthesis the stuff to grow with. Crabtree effect - Wikipedia

Good point, that's true. I was thinking generally about moving from aerobic to anaerobic whilst still having oxygen present.

Either way, there isn't scrubbing of oxygen by CO2. By the point at which fermentation is taking place and producing CO2, oxygen has already depleted in the first hours of the lag phase. Even when introduced during fermentation, such as rousing a Yorkshire square, oxygen is uptaken by the yeast. Otherwise, why would they do it, if it was only going to get scrubbed by CO2?

 

[Agentgonzo]

Yeast was on earth before the earth started producing oxygen

Where are you getting this from?

"The first yeast originated hundreds of millions of years ago"

"The Great Oxidation Event ... was a time interval when the Earth's atmosphere and the shallow ocean first experienced a rise in the amount of oxygen. This occurred approximately 2.4–2.0 Ga (billion years) ago"

 

[foxy]

Good point, that's true. I was thinking generally about moving from aerobic to anaerobic whilst still having oxygen present.

Either way, there isn't scrubbing of oxygen by CO2. By the point at which fermentation is taking place and producing CO2, oxygen has already depleted in the first hours of the lag phase. Even when introduced during fermentation, such as rousing a Yorkshire square, oxygen is uptaken by the yeast. Otherwise, why would they do it, if it was only going to get scrubbed by CO2?

From Ted Goldammer, a well known brewing microbiologist, The Brewers Hand Book.

Fermentation Phase​

The fermentation phase quickly follows the growth phase when the oxygen supply has been depleted. Fermentation is an anaerobic process. In fact, any remaining oxygen in the wort is "scrubbed," i.e. stripped out of solution by the carbon dioxide bubbles produced by the yeast.

 

[Sadfield]

@Agentgonzo The Great Oxidation Event? I thought that was the recent trend for NEIPA.

 

[foxy]

Where are you getting this from?

"The first yeast originated hundreds of millions of years ago"

"The Great Oxidation Event ... was a time interval when the Earth's atmosphere and the shallow ocean first experienced a rise in the amount of oxygen. This occurred approximately 2.4–2.0 Ga (billion years) ago"

https://gizmodo.com/yeast-kept-life-on-earth-alive-before-the-rise-of-oxyge-5829259

 

[Sadfield]

 

[foxy]

How can it scrub something that has already been depleted. That makes **** all sense, regardless of the blokes CV.

He isn't the only one who has stated that the co2 scrubs any remaining oxygen from the wort. Christopher Boulton and David Quain cover it their book, 'Brewing yeast and fermentation' That is where I first read about it.

 

[Wynne]

I think @foxy is correct.

It is a common misunderstanding (that I used to share) that when yeast cells are introduced into oxygenated wort, they first respire, using the oxygen present to breakdown glucose completely, to produce energy, water and carbon dioxide until the oxygen runs out then switch to anaerobic fermentation. This is incorrect.

From the start, the yeast respiration pathway is inhibited by the high concentration of glucose in wort (“the Crabtree effect”). Instead, after a period of adaptation (“the lag phase”), the yeast use the anaerobic fermentation pathway to partially breakdown glucose to produce energy, ethanol and carbon dioxide. The importance of oxygen in wort is that the yeast use it to synthesise sterols which are used in cell membranes so important for cell division during “the growth phase” of the yeast. During the growth phase, oxygen in wort becomes depleted - probably as a result of a combination of sterol synthesis by yeast and stripping as a result of carbon dioxide generation - and the growth phase comes to an end.

 

[foxy]

I think @foxy is correct.

It is a common misunderstanding (that I used to share) that when yeast cells are introduced into oxygenated wort, they first respire, using the oxygen present to breakdown glucose completely, to produce energy, water and carbon dioxide until the oxygen runs out then switch to anaerobic fermentation. This is incorrect.

From the start, the yeast respiration pathway is inhibited by the high concentration of glucose in wort (“the Crabtree effect”). Instead, after a period of adaptation (“the lag phase”), the yeast use the anaerobic fermentation pathway to partially breakdown glucose to produce energy, ethanol and carbon dioxide. The importance of oxygen in wort is that the yeast use it to synthesise sterols which are used in cell membranes so important for cell division during “the growth phase” of the yeast. During the growth phase, oxygen in wort becomes depleted - probably as a result of a combination of sterol synthesis by yeast and stripping as a result of carbon dioxide generation - and the growth phase comes to an end.

Thank you, also to add, there is oxygen left in the fermenting vessel even after the yeast has taken its fair share and the co2 has done its scrubbing there is still oxygen left in the finished product.
Eliminating oxygen from go to whoa is nigh impossible, we live with, and probably enjoy the level of oxidised beer we consume.

 

[Sadfield]

During the growth phase, oxygen in wort becomes depleted - probably as a result of a combination of sterol synthesis by yeast and stripping as a result of carbon dioxide generation - and the growth phase comes to an end.

You've missed the point. Oxygen is depleted very quickly and to a point where there isn't anything for the latterly produced co2 to scrub off. Look at the graph posted earlier, regardless of initial DO level, the recording is zero after 210 minutes.

"Some yeast strains have higher oxygen requirements than others. However, it is generally safe to assume that you need at least 10 ppm (mg/L) of oxygen. 10 ppm 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.'

https://wyeastlab.com/resource/prof...ve higher,adequate oxygen in most situations.

 

[foxy]

You've missed the point. Oxygen is depleted very quickly and to a point where there isn't anything for the latterly produced co2 to scrub off. Look at the graph posted earlier, regardless of initial DO level, the recording is zero after 210 minutes.

"Some yeast strains have higher oxygen requirements than others. However, it is generally safe to assume that you need at least 10 ppm (mg/L) of oxygen. 10 ppm 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.'

https://wyeastlab.com/resource/prof...ve higher,adequate oxygen in most situations.

I haven't missed the point. The graph shows zero, but in reality there is O2 left, even after the co2 has scrubbed the O2, brewers expect an inclusion of O2 in the finished product after fermentation. I forget the figure but there is a certain amount which they can live with.

 

[Sadfield]

I haven't missed the point. The graph shows zero, but in reality there is O2 left, even after the co2 has scrubbed the O2, brewers expect an inclusion of O2 in the finished product after fermentation. I forget the figure but there is a certain amount which they can live with.

This is laughable.

1) If it's measured zero, it will be zero. That's how measurement works.

2) How can the initially introduced oxygen remain into the finished product, if by your assertion it all gets scrubbed off by co2 during vigorous fermentation?

Redox reactions and O2 pickup post fermentation would explain it. If we're talking about oxidation in packaged beer.

 

[foxy]

This is laughable.

1) If it's measured zero, it will be zero. That's how measurement works.

2) How can the initially introduced oxygen remain into the finished product, if by your assertion it all gets scrubbed off by co2 during vigorous fermentation?

Redox reactions and O2 pickup post fermentation would explain it. If we're talking about oxidation in packaged beer.

It will not be zero, Put in the rest of the results and the size of the fermenter used in the experiment, it is nigh impossible to achieve zero O2.

 

[Sadfield]

is nigh impossible

So, possible.

 

[Wynne]

You've missed the point. Oxygen is depleted very quickly and to a point where there isn't anything for the latterly produced co2 to scrub off. Look at the graph posted earlier, regardless of initial DO level, the recording is zero after 210 minutes.

"Some yeast strains have higher oxygen requirements than others. However, it is generally safe to assume that you need at least 10 ppm (mg/L) of oxygen. 10 ppm 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.'

https://wyeastlab.com/resource/prof...ve higher,adequate oxygen in most situations.

@Sadfield - please would you provide a reference for the chart that you copied earlier. It is difficult to assess it properly without reviewing it in the context of the original paper for which it was produced.

The chart does indeed show a rapid decline of dissolved oxygen to zero although the level of accuracy for the measurement of “zero” is not shown in your post so trace levels of oxygen below the level accuracy of the method of measurement could still be present. I agree with your point in a later post about other possible causes of oxidation (and, hence, beer ageing) in packaged beer and also with @foxy’s point that brewer’s tolerate a level of dissolved oxygen in final packaged product.

As to whether “I missed the point” or not, the “point” I was seeking to make was to address your comment “I was thinking generally about moving from aerobic to anaerobic whilst still having oxygen present”. There is no switch from aerobic respiration to anaerobic fermentation in a normal brewing fermentation because of the Crabtree effect (as @peebee pointed out originally) which inhibits aerobic respiration. Having previously misunderstood this myself, I am keen that others do not make the same mistake.

 

[peebee]

Goodness me! You're both still at? (I'm not talking about Wynne who's just posted too).

You both appear to be arguing over your interpretation of "scrubbing" used by a foreign author in a foreign book. I'd also cast a doubtful eye on the language used, but when I've been in similar arguments, I've been reminded that we share a common language from 2-300 years ago and the language in the two nations (UK and US) have diverged just a little ever since.

So, to put it another way: The yeast has started fermenting and evolving CO2. The headspace above the beer becomes increasingly enriched with CO2, and the concentration of O2 in the headspace falls away. Physics steps in (partial pressure) and forces excess O2 in solution that can no longer be held in solution by the partial pressure of O2 over the beer (and isn't nabbed by any passing yeast cells) to escape from the beer. If someone in the USA wants to call that "scrubbing", so be it.

(From a schoolboy grasp of physics, don't quote me as truly accurate, but it's heading the right way?).