aerobic vs anaerobic fermentation

[BernardSmith]

I am a skeptical guy. My background is in the social sciences, not the physical sciences and I am always looking for proof whenever I hear some claim or other.
I understand that yeast requires oxygen to reproduce but may require less (or no oxygen) when reproduction is of less importance to us compared to the yeast's activity in converting sugar into alcohol.
So, the rule of thumb seems to be that in the early stage of making wine we pitch the yeast into large buckets without sealed lids and airlocks (aerobic fermentation) . Later when the yeast has reproduced enough and has converted almost all the sugar to alcohol we rack the wine into a smaller container and seal it with an airlock (anaerobic fermentation). My question is how much O2 does the yeast need to reproduce? Might there be enough O2 in water that has neither been distilled nor filtered through reverse osmosis? Has anyone measured the activity of yeast in a known quantity of must in an open bucket compared to a sealed carboy? I know that we are supposed to stir the must twice a day to introduce additional air into the wine but how necessary is this? Has anyone checked to see if a failure to do so really inhibits the reproduction of the yeast or indeed degrades or kills the yeast or puts it into such stress that off flavors result?

 

[JohnT]

OK,

I understand your confusion.

The terms used are confusing and incorrect. All Fermentation (the process of converting sugar to alcohol), does not require oxygen. All fermentation performed by yeast is anerobic. For the sake of clarity, lets just use the term Fermentation and reproduction.

Reproduction is an Aerobic process. Yeast needs minimal amounts of oxygen for a healthy reproduction. I believe that I have read that yeast needs about 8 or 16 ppm (parts per million) of oxygen.

So we have only Anerobic fermentation and aerobic reproduction.

In simple terms, yeast uses oxygen in the development of healthy cell walls. as yeast splits, without the benefit of oxygen, the yeast's cell walls get progressively "unhealthy".

Primary fermentors are cheifly used for a number of reasons (here are but a few).

1) to provide extra room due to the high level of fermentation occuring during the first week or so.

2) to allow for the introduction of minimal amounts of oxygen to be introduced during the "lag" phase of fermentation (where reproduction in mostly concentrated).

3) to allow for punchdowns (forcing the grape skin "cap" back into the wine).

Wine is normally transferred to a secondary fermentor when fermentation is nearly complete. While in the primary, the CO2 expelled by the yeast protects the wine against any foreign bacteria. Once fermentation is on the decline, the wine must be place in a more air-tight environment to keep it safe.

 

[BeerAlchemist]

First, let me clear that up a little bit for you. The difference between aerobic and anaerobic fermentation is not based on whether or not a container is sealed, it is based off the availability of oxygen to the yeast (ie I could inject O2 into solution and seal a container, its still going to be aerobic). When the oxygen levels of the solution (must/wine in this case) deplete the yeast shift gears and go into anaerobic fermentation. So, during aerobic fermentation the yeast are producing very little alcohol, they are using the oxygen as a key component of reproduction with significant CO2 production. When the O2 is used up and the yeast turn anaerobic is when the yeast begin producing the bulk of the alcohol.

Deficiencies in oxygen create a high stress environment and is detrimental to the ability of the yeast to reproduce. This will result in a number of defects to the wine and possibly destroy it.

I can tell you the O2 needs for yeast in beer, but I don't know how much is needed in wine...yet.

 

[JohnT]

First, let me clear that up a little bit for you. The difference between aerobic and anaerobic fermentation is not based on whether or not a container is sealed, it is based off the availability of oxygen to the yeast (ie I could inject O2 into solution and seal a container, its still going to be aerobic). When the oxygen levels of the solution (must/wine in this case) deplete the yeast shift gears and go into anaerobic fermentation. So, during aerobic fermentation the yeast are producing very little alcohol, they are using the oxygen as a key component of reproduction with significant CO2 production. When the O2 is used up and the yeast turn anaerobic is when the yeast begin producing the bulk of the alcohol.

Deficiencies in oxygen create a high stress environment and is detrimental to the ability of the yeast to reproduce. This will result in a number of defects to the wine and possibly destroy it.

I can tell you the O2 needs for yeast in beer, but I don't know how much is needed in wine...yet. However, for a successful fermentation yeast

BA.

Fermentation requires and uses no Oxygen. All fermentation is Anerobic.
Reproduction will use oxygen in the process, thus making it Aerobic.

It does not matter if oxygen is present. If it is not USED, then it is considered as Anerobic.

 

[BeerAlchemist]

OK,
All fermentation performed by yeast is anerobic.

Certain yeasts, including sacc c are unique in that they can create alcohol both aerobically and anaerobically. Yeast activity, fermentation, in a high glucose aerobic environment is called the crabtree effect.

 

[BeerAlchemist]

BA.

Fermentation requires and uses no Oxygen. All fermentation is Anerobic.
Reproduction will use oxygen in the process, thus making it Aerobic.

It does not matter if oxygen is present. If it is not USED, then it is considered as Anerobic.

Sorry, do not want to be rude or anything, but that is incorrect.

 

[robie]

I can't remember the thread title, but only a few weeks ago there was some arguing going on about this subject (Seems every few weeks someone wants to questions this, so they bring it up). One person (only one of all of "us" posting on that thread!) quoted a true scientific study by a yeast packet manufacturer. They had measured the amount of O2 contained in non-stirred must. That amount was not considered enough, at least for their yeast strain. You will need to find it yourself.

There have been many studies done on this, so the internet should be a good place to start searching.

Based on your post, sounds to me like you already know what the scientists and researchers are saying. So, I assume you are wanting to hear about personal experiences.

What you will hear on here will be personal experiences, even years of such, none of which will really prove much of anything.

There is something call "best practices" as opposed to, "It has always worked for me, so?", or "Just get by practices".

For instance - In spite of the research that says otherwise, many even commercial wineries will put chardonnay grape juice and yeast in a sealed stainless steel container; never stirring, never oxygenating never openng until fermentation is thought to be finished. Their wine turns out just fine; maybe even award winning. They do this year after year. What does this prove?

We all have our opinions. Me? I strive to follow the best practices methods, regardless of what others do.

Think of it as - best practices give you the greatest changes of success, while the others, though they work for some over and over again, in the end, they are more apt to fail. It's a percentage thing.

 

[JohnT]

From Wikipedia.....

The fermentation process does not require oxygen. If oxygen is present, some species of yeast (e.g., Kluyveromyces lactis or Kluyveromyces lipolytica) will oxidize pyruvate completely to carbon dioxide and water. Thus, these species of yeast will produce ethanol only in an anaerobic environment. This process is called cellular respiration.


And the definition of Anaerobic...

Occurring in the absence of oxygen or not requiring oxygen to live. Anaerobic bacteria produce energy from food molecules without the presence of oxygen. Compare aerobic.


All fermentation is anaerobic.

 

[BeerAlchemist]

From Wikipedia.....

The fermentation process does not require oxygen. If oxygen is present, some species of yeast (e.g., Kluyveromyces lactis or Kluyveromyces lipolytica) will oxidize pyruvate completely to carbon dioxide and water. Thus, these species of yeast will produce ethanol only in an anaerobic environment. This process is called cellular respiration.


And the definition of Anaerobic...

Occurring in the absence of oxygen or not requiring oxygen to live. Anaerobic bacteria produce energy from food molecules without the presence of oxygen. Compare aerobic.


All fermentation is anaerobic.

I see you managed to leave out the other short paragraph under "Effect of Oxygen." Here it is the section in its entirety so as to introduce some level of academic honesty:

"The fermentation process does not require oxygen. If oxygen is present, some species of yeast (e.g., Kluyveromyces lactis or Kluyveromyces lipolytica) will oxidize pyruvate completely to carbon dioxide and water. Thus, these species of yeast will produce ethanol only in an anaerobic environment. This process is called cellular respiration.

However, many yeasts such as the commonly used baker's yeast Saccharomyces cerevisiae, or fission yeast Schizosaccharomyces pombe, prefer fermentation to respiration. These yeasts will produce ethanol even under aerobic conditions, if they are provided with the right kind of nutrition."

http://en.wikipedia.org/wiki/Fermentation_(biochemistry)

 

[BeerAlchemist]

For instance - In spite of the research that says otherwise, many even commercial wineries will put chardonnay grape juice and yeast in a sealed stainless steel container; never stirring, never oxygenating never openng until fermentation is thought to be finished. Their wine turns out just fine; maybe even award winning. They do this year after year. What does this prove?

I know its a rhetorical question...but...it proves nothing really. There is still oxygen added to the solution during stemming and pressing so the white wine goes into the sealed fermentor with, perhaps, plenty of oxygen if measured. Or a larger yeast culture is added so there doesn't need to be much growth. Perhaps plenty of nutrients were provied so their stress load is less. In brewing there are those, particularly Belgian brewers, who argue that a certain level of stress on the yeast can produce positive flavors so why not wine...its pretty much the same yeast after all. So, yeah, it pretty much proves nothing. I'm there with you, best practices and all.

 

[BobF]

I see you managed to leave out the other short paragraph under "Effect of Oxygen." Here it is the section in its entirety so as to introduce some level of academic honesty:

"The fermentation process does not require oxygen. If oxygen is present, some species of yeast (e.g., Kluyveromyces lactis or Kluyveromyces lipolytica) will oxidize pyruvate completely to carbon dioxide and water. Thus, these species of yeast will produce ethanol only in an anaerobic environment. This process is called cellular respiration.

However, many yeasts such as the commonly used baker's yeast Saccharomyces cerevisiae, or fission yeast Schizosaccharomyces pombe, prefer fermentation to respiration. These yeasts will produce ethanol even under aerobic conditions, if they are provided with the right kind of nutrition."

http://en.wikipedia.org/wiki/Fermentation_(biochemistry)

Are we making wine or baking bread?

 

[BobF]

Wine yeast does NOT require the winemaker to shut off the oxygen supply to work anaerobically.

There are, however, plenty of very good reasons to keep oxygen reduced once the yeast is done using what it needs.

 

[BeerAlchemist]

Are we making wine or baking bread?

Its sacc c...wine, bread, beer, it does it all.

 

[spaniel]

Most microbes will preferentially use oxygen if it is present vs going into anaerobic mode (fermentation = alcohol). This is because fuel (glucose) is typically a precious resource and aerobic respiration yields ~18X as much energy per glucose molecule consumed compared to anaerobic fermentation.

BeerAlchemist is correct that some yeast species exhibit a different trait called the "Crabtree effect" where, in high glucose environments (ie must), they will still product alcohol. The Darwinian reason is obvious; raising the alcohol content of their environment keeps the microbial competition down, and they can afford to do it as long as glucose is in abundant supply. Once glucose concentrations go down, they will stop making alcohol if they have oxygen.

So, when glucose concentration is high in must (the first few days after you pitch yeast), even if the yeast gets oxygen you will get alcohol produced. But as glucose is used up, you have to take away all oxygen or the yeast will stop producing alcohol and just burn the yeast aerobically while producing biomass (reproducing).

Also note that while the yeast is in high gear over the first few days, so much CO2 is coming off the must that it forms a blanket that pushes air away and prevents oxygen from reaching the surface of the must and diffusing into solution to any significant degree. And the concentration of gas in any liquid is pretty darn low, so anyone thinking the O2 introduced when mashing grapes and preparing the must is going to be present for more than a few hours once the yeast spin up to speed are mistaken.

Anaerobic respiration is a stressful process. It is easier to reproduce when some oxygen is present, so putting all the above together with this, this is why it a) is acceptable to let some O2 in at first, and b) you must pitch a batch with a big enough culture of yeast, or they may not get sufficient biomass in place before they stop reproducing to do a proper job turning the must into wine.

Clearly O2 is not required to ferment wine, to any significant extent. My white wine ferments perfectly happily pressing the juice into carbuoys with airlocks, then adding yeast. It does not go as fast as red in an open top fermenter...and I don't want it to, either.

Just the opinion of a cell and molecular biologist. YMMV.

 

[ckassotis]

The idea that you need to take the oxygen away to produce good wines seems counter-productive to me. It seems to run counter to the growing return to the barrique/amphora method of winemaking throughout many European countries. I have had the pleasure to try some of these wines on a recent trip to Sicily, among them COS, and they are really something special. Remarkable mineral-rich whites, intensely aromatic, and certainly nothing "wrong" with them due to their larger than average oxygen exposure during fermentation and even long-term aging.

 

[spaniel]

The idea that you need to take the oxygen away to produce good wines seems counter-productive to me. It seems to run counter to the growing return to the barrique/amphora method of winemaking throughout many European countries. I have had the pleasure to try some of these wines on a recent trip to Sicily, among them COS, and they are really something special. Remarkable mineral-rich whites, intensely aromatic, and certainly nothing "wrong" with them due to their larger than average oxygen exposure during fermentation and even long-term aging.

Are you suggesting we simply do away with the convention of putting secondaries under airlocks? Allow as much oxygen into wine as possible? I have no experience with the wines you reference, but 2 years ago I took the risk of leaving excessive headspace in a batch of white wine (pure laziness and busyness) and the result was that I poured it down the drain to free up the carbuoy...the first and last time I made such a mistake....

 

[BernardSmith]

I didn't mean to start a war. Sorry. I guess my question is really whether anyone has measured the amount of dissolved oxygen in the water or must to see if there is enough O2 to enable yeast to reproduce for a week without adding more O2 either by stirring or through exposure of the surface of the must to the air. If there is, then it should make no difference if we seal the primary and add an airlock, and if there is not then it is not only best practice but in fact really necessary to add O2 during the first few days after pitching the yeast. The follow -up question would be IF there was insufficient O2 in the must to last more than a couple of days, whether the action of the CO2 in bubbling up to the surface would be sufficient to introduce enough O2 to the wine through agitation at the surface to preclude the need to stir.

 

[spaniel]

The O2 in solution will not last anywhere near a week. But IMHO as long as your starter culture is approximately the right size you shouldn't worry about it. My white wine goes straight into airlocked carbuoys...I've put sealed caps on primaries with airlocks. I've never had a batch stick.

 

[JohnT]

I see you managed to leave out the other short paragraph under "Effect of Oxygen." Here it is the section in its entirety so as to introduce some level of academic honesty:

"The fermentation process does not require oxygen. If oxygen is present, some species of yeast (e.g., Kluyveromyces lactis or Kluyveromyces lipolytica) will oxidize pyruvate completely to carbon dioxide and water. Thus, these species of yeast will produce ethanol only in an anaerobic environment. This process is called cellular respiration.

However, many yeasts such as the commonly used baker's yeast Saccharomyces cerevisiae, or fission yeast Schizosaccharomyces pombe, prefer fermentation to respiration. These yeasts will produce ethanol even under aerobic conditions, if they are provided with the right kind of nutrition."

http://en.wikipedia.org/wiki/Fermentation_%28biochemistry%29

Yes, in the presence of oxygen (anerobic conditions), the fermentation process, however, DOES NOT MAKE USE OF THAT OXYGEN, thus it is still an ANEROBIC process!

 

[ckassotis]

Are you suggesting we simply do away with the convention of putting secondaries under airlocks? Allow as much oxygen into wine as possible? I have no experience with the wines you reference, but 2 years ago I took the risk of leaving excessive headspace in a batch of white wine (pure laziness and busyness) and the result was that I poured it down the drain to free up the carbuoy...the first and last time I made such a mistake....

If you want to make sherry, sure. Sherry producers do just that, and then successfully market their product. But no, I'm not suggesting that. What I'm saying is that it isn't as simple as what was being said. Clearly this technique works fine without oxidizing wine, so suggesting that oxygen must be removed to produce wine is simply not true.

That being said, I have to agree with JohnT here. We teach fermentation as a process that does not use oxygen here at the University. I know we've been quoting Wikipedia here, but here is a section from the Biology textbook that we use here:

"There are two mechanisms by which certain cells can oxidize organic fuel and generate ATP WITHOUT the use of oxygen: anaerobic respiration and fermentation. Fermentation is a way of harvesting chemical energy without using either oxygen or any electron transport chain - in other words, without cellular respiration. How can food be oxidized without cellular respiration? Remember, oxidation simply refers to the loss of electrons to an electron acceptor. so it does not need to involve oxygen. Glycolysis oxidizes glucose to two molecules of pyruvate. The oxidizing agent of glyolysis is NAD+, and neither oxygen nor any electron transport chain is involved. Fermentation is an expansion of glycolysis that allows for the continuous generation of ATP by the substrate-level phosphorylation of glycolysis. In alcoholic fermentation, pyruvate is converted to ethanol in two steps. The first step releases carbon dioxide from the pyruvate, which is converted to the two-carbon compound acetaldehyde. In the second step, acetaldehyde is reduced by NADH to ethanol. This regenerates the supply of NAD+ needed for the continuation of glycolysis and thus the continuation of fermentation."