Yeast life, aerobic to anaerobic - when do they transform?

[shanek17]

How do you know when to add an airlock to your fermenter? I have heard different things about this before and honestly iv been just kinda been winging it for now. But I did just make a big expensive batch of clover honey mead and now I feel I Should have some more information on how to do this properly!

I recall hearing that when 80% of the sugar has been eaten then its safe to put on the airlock, or when the fermentation activity is dying down. I just want to know roughly when the yeast are going from their aerobic (oxygen phase) and then to anaerobic (no oxygen phase).

Is there much of a difference between wine yeast and beer yeast on this matter?

 

[shanek17]

really, Nothing ? Have I stumped the great members of the wine forum ?!

I think this is my first thread with 0 activity!

 

[JohnT]

My take on it is that there is really no "hard and fast" rule on this. What I normally do is to ferment to the point where we are under 2 or 3% sugar remaining (I ferment dry).

The reason for adding an airlock is that you are comming to the end of fermentation. It is during fermentation that the yeast creates a protective "blanket" of positive pressure CO2. This removes the risk of any kind of bacteria related problems. The call to add an airlock should be made when fermentation is slowing down and a lot less CO2 gas is being produced.

 

[Dugger]

I've always thought that the aerobic stage is during fermentation when the yeast is consuming sugar and the anaerobic stage is after fermentation when the yeast do something else (with acids?) but I don't really know that for sure. Perhaps one of our resident chemists can jump in and clarify this.
As you note, most look to airlock protection when fermentation is winding down - I use 1.010 as my guideline.
Don't know about differences between wine and beer use regarding aerobic vs. anaerobic.

 

[ibglowin]

I usually snap the lid and add the airlock when the SG gets down around 1.025.

There is a good article on Understanding Yeast in Winemaker Magazine. There are a couple of paragraphs in the article that discuss the importance of oxygen in alcoholic fermentation.

 

[PCharles]

How do you know when to add an airlock to your fermenter? I have heard different things about this before and honestly iv been just kinda been winging it for now. But I did just make a big expensive batch of clover honey mead and now I feel I Should have some more information on how to do this properly!

I recall hearing that when 80% of the sugar has been eaten then its safe to put on the airlock, or when the fermentation activity is dying down. I just want to know roughly when the yeast are going from their aerobic (oxygen phase) and then to anaerobic (no oxygen phase).

Is there much of a difference between wine yeast and beer yeast on this matter?

Shanek17, It is very important to have adequate oxygenation for yeast to get started turning sugar into CO2 and alcohol. Once the process starts, it’s a bit like a fire. It will burn until certain conditions are met. As a winemaker, you will want to have a complete fermentation (for dry wine). Things such as alcohol content, pH, and nutrients can affect the ability of the yeast to reach its maximum objective. There are a variety of methods and process to get to this point of completion. Kit wines are put under air lock in the primary right off. If you're making wine from grapes, you may just through a sheet over the primary, while punching down the cap several times per day. Once fermentation nears completion, it becomes more important to protect the wine from unwanted contaminants. Low pH and high alcohol provide a natural defense.

The anaerobic phase is often referred to as malolactic fermentation. In this phase, an anaerobic bacteria is introduced into the wine. This is usually done just after pressing, though some add it earlier, and some later. This anaerobic bacteria convert malic acid to lactic acid, knocking the edge off the wines sharp taste. This is a rather brief description... I just wanted to give you an introduction to malolactic bacteria. This phase lasts 3-4 weeks. Completion of MLF (malolactic fermentation) (it's really not fermentation at all by the way) is usually tested for. Let me also add that not all wines are put through MLF. Some wines go into MLF on their own, without adding the MLF bacteria.

Once MLF is complete, the wine is put up for long term storage. Sulfite is added at this time to protect the wine. Wineries will keep wine in barrels for several years. During this phase, it is important to keep containers topped off. Sulfite is usually added periodically. Sulfite levels are usually tested to make sure levels are where they should be.

I encourage you to read articles, posts, books, from other wine makers. I enjoy WineMaker Magazine and have found it quite helpful. Kits are a good way to start off, just to get down the basics of the process.

I hope this helps.... Sorry for being so long winded.

PCharles

 

[MalvinaScordaad]

How do you know when to add an airlock to your fermenter? I have heard different things about this before and honestly iv been just kinda been winging it for now. But I did just make a big expensive batch of clover honey mead and now I feel I Should have some more information on how to do this properly!

I recall hearing that when 80% of the sugar has been eaten then its safe to put on the airlock, or when the fermentation activity is dying down. I just want to know roughly when the yeast are going from their aerobic (oxygen phase) and then to anaerobic (no oxygen phase).

Is there much of a difference between wine yeast and beer yeast on this matter?

You need some O2 for the yeast to grow at the beginning of the fermentation. After that they can do just fine without 02. When the cap is formed it holds in the Co2 which protects the fermenting wine. Yet the cap needs to be submerged and mixed it so it does not dry out and grow bacteria. When you punch down the cap you are also introducing O2. All this is fine however with a Mead I assume, or a Red or White Juice you do not have a cap. In these cases you need to keep the Co2 layer over the fermenting wine. So an air lock should be in place from the beginning or as soon as possible when to activity of the ferment will not blow through the air lock. You can use a white sock on the neck of the carboy if you are foaming over but as soon as possible an Air lock should be used. You need to think of it as a white wine process. You should also reduce the headspace as much as possible as the fermentation continues and allows you to top up the fermenting carboy without foaming over.
Malvina

 

[JohnT]

Shanek17,
The anaerobic phase is often referred to as malolactic fermentation. In this phase, an anaerobic bacteria is introduced into the wine. This is usually done just after pressing, though some add it earlier, and some later. This anaerobic bacteria convert malic acid to lactic acid, knocking the edge off the wines sharp taste. This is a rather brief description... I just wanted to give you an introduction to malolactic bacteria. This phase lasts 3-4 weeks. Completion of MLF (malolactic fermentation) (it's really not fermentation at all by the way) is usually tested for. Let me also add that not all wines are put through MLF. Some wines go into MLF on their own, without adding the MLF bacteria.

PCharles

Correct me if I am worng, but ...

Fermentation (the process of converting sugar into alcohol) is, in itself, anaerobic. This is in that no oxygen is required for the conversion of sugar to alcohol. The addition of oxygen during fermentation is required for yeast to reproduce and increase its biomas, but not required for fermentation.

I have never know MLF to be referred (in itself) as the anerobic phase but simply as MLF.

 

[ibglowin]

From Winemaking 101 on ECKraus

Fermentation Stages

A wine fermentation has two distinct stages: primary and secondary--also sometimes described as aerobic and anaerobic fermentations.


* The Primary Fermentation will typically last for the first three to five days. On average, 70 percent of the fermentation activity will occur during these first few days. And in most cases, you will notice considerable foaming during this time of rapid fermentation.

The primary fermentation is also called an aerobic fermentation because the fermentation vessel is allowed to be opened to the air. This air plays an important roll in the multiplication of the yeast cells.

Here's how important. The little packets of yeast that is generally called for in a five gallon wine recipe will typically be multiplied up to 100 to 200 times during the few days of primary/aerobic fermentation. Without air this multiplying stage is hindered. That is why it is important that you do not use an air-lock during the first few days of a fermentation and allow the fermentation to be open to air.

Alcohol is being produced during the primary fermentation as well, but a significant portion of the yeast's energy is being devoted to reproducing itself.


* The Secondary Fermentation is when the remaining 30 percent of of fermentation activity will occur. Unlike the typical four to seven days the primary fermentation takes, the secondary fermentation will usually last anywhere from one to two weeks depending on the amount of nutrient and sugars still available.

So as you can start to see, the secondary fermentation is much slower with less activity at any given time. You will also notice the activity becoming slower and slower with each passing day.

The secondary fermentation is an anaerobic fermentation which means that air exposure is to be kept to a minimum. This can easily be done by attaching an air-lock to the fermentation vessel.

It is this reduction in air exposure during the secondary fermentation that entices the yeast to forget about multiplying and start giving its energy completely to making alcohol.


The term Anaerobic Fermentation in wine making is sometimes used instead of the "MLF" term. MLF is also sometimes called "secondary fermentation" in some circles which can make it even more confusing to budding winemakers who first hear the term normally when a wine is racked to secondary container to finish out. Kinda confusing but thats the way it is it seems.

 

[JohnT]

so secondary fermentation and MLF are both called anerobic fermentation.

I knew that both secondary and MLF execute without oxygen. Thus they are called anerobic (as opposed to aerobic). I just never heard of MLF being referred to (and acknowledged) when one says "anerobic fermentation".

 

[BobF]

Technically speaking, I've always heard that primary fermentation happens in two stages; aerobic and anaerobic, and that secondary fermentation is what is done when making Champagne.

It has become common to refer to the remainder of the primary ferment after transfer to the secondary vessel as the secondary fermentation.

 

[MalvinaScordaad]

so secondary fermentation and MLF are both called anerobic fermentation.

I knew that both secondary and MLF execute without oxygen. Thus they are called anerobic (as opposed to aerobic). I just never heard of MLF being referred to (and acknowledged) when one says "anerobic fermentation".

This is getting more confusing then it needs to be. First yeast when cultured is exposed to some oxygen. It allows for yeast development. As vats are pumped over yeast is exposed to further o2 it also helps somewhat but it has nothing to do with the actual chemical reaction that is taking place. But to be very clear there is only one anerobic fermentation that converts Sugar to Alcohol. O2 has nothing to do with it. This is called Primary Fermentation but a better term is Alcohol Fermentation. Now some Kit makers and juice makers transfer the ferment into another container before the AF is complete. They call this a Secondary Fermentation. Why? who knows. It is not Secondary to anything. It is still the Primary fermentation. It is still an AF fermentation and It is still Anerobic. If you need anything else to convince you of this think of Carbonic Maceration of Beaujolais Noveau Wines all fermented completely in the absence of Oxygen. Completely Anerobic. The "malolactic fermentation" refers to the conversion of the grape acid malate to lactate conducted by members of the lactic acid bacteria. ML Fermentations are not anerobic or areboic but a dicarboxylic reaction. But ML bacteria work best when not exposed to oxygen. When making a sparkling wine a second AF is employed to create Co2 in the bottle. The EC Kraus paper is wrong and the more I read it is dumb. All Juice ferments should be under air lock from the very beginning and never fermented with an open top. If you have no Cap as in grape fermenting you expose the fermenting wine to bacteria. All White Wine is fermented in this fashion in a closed top with air lock to let Co2 escape. I really get annoyed when bad advice is giving especially by a Company who should know better.
Malvina

 

[PCharles]

I consider MLF to be anaerobic as it utilizes bactaria that are anerobes. From a microbiological term, anaerobes do not grow well in the presence of oxigen. I work in a lab. We culture for anaerobes using a closed environment. Fortunetly the bacteria used in the MLF process are not as fussy as all this sounds. Anaerobes do just fine in barrels, often making a long term home in the wood. Barrels are not are tight though. I just refer to phases as Primary Fermentation, Secondary Fermentation, MLF Fermentation (not a true fermentation), and Bulk Aging. Each phase is specific to the kind of wine you are making, Red, White, Fruit. That's the way I look at it, and I'm sure you will get many other opinions. The important thing is to understand what is going on in each phase.

 

[MalvinaScordaad]

I consider MLF to be anaerobic as it utilizes bactaria that are anerobes. From a microbiological term, anaerobes do not grow well in the presence of oxigen. I work in a lab. We culture for anaerobes using a closed environment. Fortunetly the bacteria used in the MLF process are not as fussy as all this sounds. Anaerobes do just fine in barrels, often making a long term home in the wood. Barrels are not are tight though. I just refer to phases as Primary Fermentation, Secondary Fermentation, MLF Fermentation (not a true fermentation), and Bulk Aging. Each phase is specific to the kind of wine you are making, Red, White, Fruit. That's the way I look at it, and I'm sure you will get many other opinions. The important thing is to understand what is going on in each phase.

I will not argue Biology with you however there is no AF fermentation that includes an aerobic phase. There is no difference in AF between Primary and Secondary AF. Yeast converts Sugar to Alcohol in one process. While it may be true that yeast can benefit from some exposure to Oxygen that Oxygen is never part of the conversion of Sugar to Alcohol. All the terms primary and secondary do is confuse winemakers. At least referring to the MLF as a secondary, which is also a misnomer, makes more sense as it is at least another reaction that produces c02. There is NO REACTION that depends on Oxygen to ferment wine. That is why the EC Kraus paper is wrong and misleading as a guide to new winemakers as it is portrayed as Winemaking 101.

Now in actual practice you say it is important to understand what is going on in each phase. Well then I challenge you to tell me the exact point you go from Primary to Secondary Phase of AF. If it actually existed if should be pretty easy to tell. That is if it exists in the first place. But it doesn't.

It is not about opinions it is what is fact. And lastly it makes no difference if you are fermenting Juice Red or White, or Fresh grapes. The biological processes involved are exactly the same.

Here is Winemaking 101 There are 2 steps to making wine one mandatory the other optional. AF and MLF in that order. AF can benefit from some oxygen for yeast growth and MLF does not benefit from oxygen for ML bacteria health.

Malvina

 

[JohnT]

This is getting more confusing then it needs to be. First yeast when cultured is exposed to some oxygen. It allows for yeast development. As vats are pumped over yeast is exposed to further o2 it also helps somewhat but it has nothing to do with the actual chemical reaction that is taking place. But to be very clear there is only one anerobic fermentation that converts Sugar to Alcohol. O2 has nothing to do with it. This is called Primary Fermentation but a better term is Alcohol Fermentation. Now some Kit makers and juice makers transfer the ferment into another container before the AF is complete. They call this a Secondary Fermentation. Why? who knows. It is not Secondary to anything. It is still the Primary fermentation. It is still an AF fermentation and It is still Anerobic. If you need anything else to convince you of this think of Carbonic Maceration of Beaujolais Noveau Wines all fermented completely in the absence of Oxygen. Completely Anerobic. The "malolactic fermentation" refers to the conversion of the grape acid malate to lactate conducted by members of the lactic acid bacteria. ML Fermentations are not anerobic or areboic but a dicarboxylic reaction. But ML bacteria work best when not exposed to oxygen. When making a sparkling wine a second AF is employed to create Co2 in the bottle. The EC Kraus paper is wrong and the more I read it is dumb. All Juice ferments should be under air lock from the very beginning and never fermented with an open top. If you have no Cap as in grape fermenting you expose the fermenting wine to bacteria. All White Wine is fermented in this fashion in a closed top with air lock to let Co2 escape. I really get annoyed when bad advice is giving especially by a Company who should know better.
Malvina

Malvina,

Thank you. That was my understanding too.

johnT.

 

[robie]

Yeast need oxygen to begin development and to multiply to great numbers. They multiply faster and better if oxygen is present. I know you can't, but if you could somehow remove all oxygen from the must, not do a yeast starter, but sprinkle the yeast into that oxygen free must, pump off all the oxygen above that must, and keep the must oxygen free, the yeast will not develop properly or in great number. The result will be a stuck fermentation and/or a huge H2S problem from highly stressed yeast. (Again, I know; this scenario is not possible in ordinary circumstances.)

During what kit makers refer to as primary, oxygen is present (aerobic) and assists the development of the yeast, as explained above. You can think of this as the aerobic alcohol fermentation phase. During this phase, one can usually get away with sealing up the fermenter because the must is going to naturally have lots of oxygen in it already. Especially with kits, one has to do a lot of stirring to make sure the must is well mixed with the added water. This insures the must is loaded with oxygen. (The reason why I always stir my wine all during primary alcoholic fermentation is to make sure there is enough oxygen for proper aerobic yeast action. may not be necessary, but - just to be sure. Do I HAVE TO? Probably not.)

When the SG gets down to about 1.020 to 1.040, the kit makers have you either transfer the wine to a carboy and add an air lock, or have you snap down the lid on the fermenter bucket and add an air lock. The idea here is to begin restricting the access of oxygen (anaerobic) to your wine. This is for the benefit of the yeast, as well as for the wine - to slow oxidation. You can think of this as the beginning of the anaerobic alcoholic fermentation phase. During this phase, yeast multiplication lessens significantly (not enough oxygen) but not entirely.

This is not exact, but it makes the point as to why the air lock is necessary at SG 1.020 to 1.040. If you don't restrict oxygen at this stage, the yeast will continue to work, but all the nice things that they can impart during anaerobic likely won't happen or at least they will be less.

The idea of the second phase of alcoholic fermentation being referred to as secondary fermentation has always been a question for me. If you speak to many pro wine makers and ask them what is secondary fermentation, most will likely say it is MLF.

Those Beaujolais Noveau Wines, which are alcohol fermented without the presence of oxygen, is another matter. I can't say how they get away with it, but I doubt there really is any method for removing ALL oxygen, 100%, but I can't say this as a fact. Whether or not one likes this wine, considering this is a special wine, which has its unique flavor profile, one might use this as an example of how a wine turns out when it does not go through a true aerobic phase.

 

[BobF]

It is not necessary to cut off oxygen for the sake of yeast. Cutting off oxygen in the late stage of AF/primary ferment is for the purpose of protecting against oxidation.

Many people ferment many wines to dryness without ever cutting off the yeasts oxygen supply.

 

[JDC]

I would trust a yeast company's info

From the Wyeast web site

"Oxygenation/Aeration

Oxygen is a necessary nutrient for proper yeast growth. Yeast requires oxygen for the synthesis of sterols. Sterols are membrane lipids which help maintain cellular fluidity and permeability enabling cells to grow and bud. Every time a cell buds the cellular sterol content is diluted. Once the level becomes too low (in approximately 3-4 doublings) the cells lose the ability to bud. Sterol content generally is the limiting factor of yeast growth. Synthesis of sterols occurs only when oxygen is present. Thus, it is critical to supply the yeast with appropriate levels of oxygen.

Yeast require 8 to 16 ppm of oxygen. Oxygen is typically dissolved into the must during crushing/destemming and then during pump-over/punching down for red wines fermented on skins. The most that atmospheric oxygen can provide to must is about 8 ppm. For this reason, it may be necessary to rack the wine or pump-over shortly after inoculation.

Pure oxygen can also be used to provide adequate oxygen in the must. Oxygen can be injected using a scintered stone. It is important to note that too much oxygen can be added using pure oxygen. Up to 40 ppm can be achieved with pure oxygen, but it is best to keep the dissolved oxygen levels below 20 ppm.

High sugar levels and high must temperatures both make it more difficult to dissolve oxygen into must. For high sugar musts or musts that have high temperatures, additional oxygenation/aeration may be necessary."

 

[robie]

It is not necessary to cut off oxygen for the sake of yeast. Cutting off oxygen in the late stage of AF/primary ferment is for the purpose of protecting against oxidation.

Many people ferment many wines to dryness without ever cutting off the yeasts oxygen supply.

I am sure many people do. There are always exceptions.

Don't want to argue with you, Bob, but what you are saying is there is no anaerobic phase for the yeast or at least that there is no advantage in providing this stage. Just don't think the research experts at places like U.C. Davis agree with that.

 

[BobF]

I am sure many people do. There are always exceptions.

Don't want to argue with you, Bob, but what you are saying is there is no anaerobic phase for the yeast or at least that there is no advantage in providing this stage. Just don't think the research experts at places like U.C. Davis agree with that.

I'm not saying there isn't an anaerobic phase. I'm saying it isn't up to the winemaker to "turn off the oxygen supply". Yeast quit using oxygen when they need to quit as part of their life cycle.

There are obviously good reasons to reduce exposure of wine to oxygen. Getting yeast to do the right just doesn't happen to be one of them.