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Does Yeast Need Air?


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#1 Wade's Wines

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Posted 31 March 2011 - 04:23 AM

I know some of us are wanting clarification on this. Is fermenting an anaerobic or aerobic process, and does yeast need oxygen or air to do its' thing? Can it ferment without air exposure, and if so why do we give it lots of it when it's fermenting? Please clarify, Oh Wine Gurus and Scientists (here's an etc. to cover all the rest of us!)!
Thanks!
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#2 Noontime

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Posted 31 March 2011 - 04:29 AM

I'm probably at the same level of knowledge as you and am not providing the expert, 100% confident answer you're looking for, but...

I believe the fermentation process of converting sugars to alcohol is anerobic, while the reproduction process requires some O2; so you need some O2 to build the colony but then you don't for fermentation. That's the way I understand it anyway, and I look forward to hearing the experts as well.
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#3 Lin Dixie

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Posted 31 March 2011 - 06:29 AM

I'm no scientist (according to my husband I'm a mad scientist, but that's a different story), but I found this online at this website.

"Yeast cells will use oxygen if it is present, and break down sugars all the
way to CO2 and H2O. In the absence of oxygen, yeast will switch to an
alternative pathway that does not require oxygen. The end products of this
pathway are CO2 and ethanol. The first pathway yields a lot more energy per
sugar molecule consumed, and so it is the "preferred" pathway if oxygen is
present. Paul Mahoney, Ph.D."

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#4 saramc

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Posted 31 March 2011 - 07:19 AM

Hey Wade, did this question stem from my comment in 'Blackberry Hasn't Started Fermentation Yet'? I was curious as to why some people put their ferment under airlock right out the door and others don't airlock until SG reaches certain point or certain # of days. Will be interested to watch the feedback on this. The bottom line, for winemaking which is preferred. Good topic Colonel!! smileytoast.gif
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#5 Tomer1

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Posted 31 March 2011 - 07:42 AM

I would say it depends on the wine your making,
White wines are very prone to oxidation so you would noramlly try to minimize oxygen and get fermentation going to creat a protective co2 layer.
Red musts contain natural anti oxidants (tannins) so oxidation is less of an issue and less care is needed.
My advice may or may not be backed by actually personal expirience and should be treated as such. :)

#6 tgoose55

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Posted 31 March 2011 - 08:52 AM

I know some of us are wanting clarification on this. Is fermenting an anaerobic or aerobic process, and does yeast need oxygen or air to do its' thing? Can it ferment without air exposure, and if so why do we give it lots of it when it's fermenting? Please clarify, Oh Wine Gurus and Scientists (here's an etc. to cover all the rest of us!)!
Thanks!


Fermentation is an anaerobic (no oxygen required) process that requires to two steps. The first step is known as glycolysis and the second step is fermentation. These two processes when combined result in the production of energy (Adenosine triphosphate (ATP) - Energy for Cells), but also creates waste products like ethanol and Carbon Dioxide.

This process begins with glycolysis (glyco = glucose (sugar) and lysis = breaks). During glycolysis, glucose is broken down several times until you end up with two molecules know as pyruvate. Other events occur such as ADP (adenosine diphosphate) has a Phosophate added creating ATP (cellular energy). Finally NAD is converted to NADH through a redox reaction. During glycolysis oxygen is not required.

Here is a very indepth video on glycolysis:
Glycolysis Animation - Youtube

Fermentation does not make energy for cells, instead it releases the Hydrogen from NADH and gets rid of pryuvate. This turns NADH into NAD, through the process of oxidation (losing electrons). For this to occur the pyruvate accepts the electrons, known as reduction, from the NADH. When this occurs the NADH is converted to NAD and pyruvate is converted to an end product. In yeast this is ethanol. As the pyruvate is converted to ethanol CO2 is released and overtime ethanol is created. In our bodies fermentation results in the production of lactic acid.

Fermentation is required not for the creation of energy (ATP). The process is required for NADH to be reduced to NAD. This way the NAD can be used in glycolysis. If fermentation (for an organism that is strictly a fermentor) never occurred the levels of NADH would go up, until there was no more NAD to be converted to NADH, remember this occurs during glycolysis.

Here is an indepth video of fermentation:
Fermentation Animation - YouTube

Glycolysis and fermentation do not require oxygen. If oxygen is available the yeast will not under go fermentation. Pasteur noted this in his experiments. When oxygen was added to yeast, ethanol was not produced. However the yeast cells reproduced rapidly. The reason for this rapid reproduction, yeast cells were using aerobic respiration to create ATP. Aerobic respiration results in a lot more ATP than glycolysis/fermentation. Since the cells have a greater amount of energy they can reproduce more often.

To answer your questions:
Is fermenting an anaerobic or aerobic process?
Fermentation is an anaerobic process.

Can it ferment without air exposure?
The only way for fermentation to occur is under low levels of oxygen.

Does yeast need oxygen or air to do its' thing? If so why do we give it lots of it when it's fermenting?
Here is where I make my connection. The yeast do require air while fermenting. Not to convert the sugar to ethanol. Rather to create more energy from the sugar into ATP. This increased level of ATP allows the yeast to reproduce faster. The more yeast cells present would result in more cells able to under go fermentation. Since you do not have an air stone (the oxygen that is pumped into a fish tank and bubbles), must flowing down and splashing like a waterfall, or any other device to agitate the must to create bubbles. Opening your primary fermenter and stirring it a few times does not create a 100% oxygen rich environment. It provides a bit of oxygen to assist the creation of ATP from aerobic respiration to help with reproduction. However the amount of oxygen is not great enough to stop all the yeast cells from under going fermentation. If the oxygen supply was constant throughout the entire process you would receive no ethanol.

Rob

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#7 charcole

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Posted 31 March 2011 - 09:03 AM

Good question,Im only acouple years into this hobbie and make only fruit wines,blueberry,salmonberry rhubarb,raspberry and red huckleberry,Isteam juice all my fruit,mix all the ingredients in plastic pail what the 24 hrs,make a yeast starter,then siphon must from pail to carboy and add the yeast starter,put under airlock,so far been happy with the results.This site is great appreciate all the good feed back,have learned alot smileytoast.gif

#8 Doc N

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Posted 31 March 2011 - 09:04 AM

Here is an article I found:

Oxygen requirements of yeasts.
W Visser, W A Scheffers, W H Batenburg-van der Vegte, and J P van Dijken
Department of Microbiology and Enzymology, Delft University of Technology, The Netherlands.
This article has been cited by other articles in PMC.
Abstract
Type species of 75 yeast genera were examined for their ability to grow anaerobically in complex and mineral media. To define anaerobic conditions, we added a redox indicator, resazurin, to the media to determine low redox potentials. All strains tested were capable of fermenting glucose to ethanol in oxygen-limited shake-flask cultures, even those of species generally regarded as nonfermentative. However, only 23% of the yeast species tested grew under anaerobic conditions. A comparative study with a number of selected strains revealed that Saccharomyces cerevisiae stands out as a yeast capable of rapid growth at low redox potentials. Other yeasts, such as Torulaspora delbrueckii and Candida tropicalis, grew poorly mu max, 0.03 and 0.05 h-1, respectively) under anaerobic conditions in mineral medium supplemented with Tween 80 and ergosterol. The latter organisms grew rapidly under oxygen limitation and then displayed a high rate of alcoholic fermentation. It can be concluded that these yeasts have hitherto-unidentified oxygen requirements for growth.
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#9 Tomer1

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Posted 31 March 2011 - 09:50 AM

Carbonic maceration is the perfect example of winemaking under complete lack of oxygen during the process.
First it starts with enzymatic convertion of sugars to ethanol (1-2% ethanol) then it switches to normal mathabolic convertion.
My advice may or may not be backed by actually personal expirience and should be treated as such. :)

#10 gregorio

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Posted 31 March 2011 - 09:55 AM

I know some of us are wanting clarification on this. Is fermenting an anaerobic or aerobic process, and does yeast need oxygen or air to do its' thing? Can it ferment without air exposure, and if so why do we give it lots of it when it's fermenting? Please clarify, Oh Wine Gurus and Scientists (here's an etc. to cover all the rest of us!)!
Thanks!


The entire fermentation process can be completed in an anaerobic environment. However, that assumes you start with a fully developed colony. It does not account for their growth needs. Yeast do need O2 during the expansion phase. As stated earlier, yeast use O2 to help produce energy that will expand the colony rapidly. If too little O2 is present during the expansion phase, the colony will struggle and could create an environment that will be ripe for H2S production. Another problem with too little O2 during expansion is that the newly formed yeast will not have a strong enough lipid layer and will end up being less alcohol tolerant.
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#11 Crazy Run Ranch

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Posted 31 March 2011 - 10:18 AM

The entire fermentation process can be completed in an anaerobic environment. However, that assumes you start with a fully developed colony. It does not account for their growth needs. Yeast do need O2 during the expansion phase. As stated earlier, yeast use O2 to help produce energy that will expand the colony rapidly. If too little O2 is present during the expansion phase, the colony will struggle and could create an environment that will be ripe for H2S production. Another problem with too little O2 during expansion is that the newly formed yeast will not have a strong enough lipid layer and will end up being less alcohol tolerant.


This sounds reasonable, yeast needs O2 to grow and reproduce. But if a fermentation were then completed in an anaerobic environment, there would probably be problems late in fermentation with H2S production. On the practical side, we know that O2 management is extremely important late in fermentation as well, maybe more important with varietals like Syrah. So how do we match up good practice with the theoretical possibility of fully developed yeast finishing the job w/o O2?

#12 gregorio

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Posted 31 March 2011 - 10:43 AM

This sounds reasonable, yeast needs O2 to grow and reproduce. But if a fermentation were then completed in an anaerobic environment, there would probably be problems late in fermentation with H2S production. On the practical side, we know that O2 management is extremely important late in fermentation as well, maybe more important with varietals like Syrah. So how do we match up good practice with the theoretical possibility of fully developed yeast finishing the job w/o O2?


Not necessarily. Carbonic maceration is often used in France with Pinot and maybe even Syrah without any H2S problems. I have never used nor ever plan to use this technique but it was required learning in class. In practical operation over there, the yeast see almost no O2 even in the expansion phase but the professors indicate that this would present the most risk.

I agree that some varietals seem to like more O2 even at the latter stages but could that be due to the way the inital stages were treated WRT O2 and nutrient? I don't have any hard data but I cannot remember having a late ferment O2 shortage since following a more stringent nutrient/oxygenation regimine during the lag and expansion phases. Prior ferments were not so clean.
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#13 Wade's Wines

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Posted 31 March 2011 - 11:07 AM

Thanks, everybody, I think I may be beginning to understand! :)
Yes, Sara, the post was spurred to answer your question in the Blackberry thread. Thought we'd find out a lot more if it had its' own thread. Thanks! :)
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#14 Doyle

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Posted 31 March 2011 - 11:40 AM

Lots of good info in this thread. Thanks.

#15 Howie

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Posted 31 March 2011 - 12:58 PM

Here's a good article that mentions all types of yeast - wine, beer, baking, etc.: http://en.wikipedia.org/wiki/Yeast
Howie Hart




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