Yeast and Oxygen

From articles that I have read in Winemaker magazine, they seem to frequently reference how oxygen is good for fermentations in the early stages. However, they never really define when these early stages are (e.g. 3 days, 7 days, etc.). Does anybody know approximately how long form the beginning of fermentation does the yeast go from aerobic to anaerobic?

You really shouldn't judge your fermentation based on days, rather by hydrometer reading. Normally once your fermentation gets down to around 1.010 you either snap down the lid and add an airlock to your primary or rack to your secondary and add an airlock.

The way I understood it, and I could be wrong*, but the yeast need oxygen when reproducing at the beginning of fermentation. Once they've reached their more or less maximum numbers, they begin to switch from reproduction mode to fermentation mode and go anaerobic. In other words, they stop multiplying and start eating sugar. Once the sugar has been fermented out, they can go into a dormant stage, and if more sugar is added they can start multiplying again and start a refermentation. It's kind of a cycle the yeast goes through. This is why it's vitally important to add potassium sorbate if the wine is to be sweetened, since the sorbate interferes with the yeast's ability to reproduce, and metabisulfite removes the oxygen the yeast needs to reproduce in their aerobic stage. So the live yeast eventually dies out and no new yeast is produced to keep eating the sugar.


*It's happened once before.

OH NO!!!

Not this topic again. (LOL)

Tom_S has got it correct. O2 is important during the reproductive (or "Lag") phase of fermentation.

The question is this, though.. Just how much O2 is needed.

I usually airate the must for the first one to 2 days by simply splashing the must around with a punch down tool. I have found this to be just fine. I also leave the must covered under a sheet of plastic.

JohnT said:

OH NO!!!

Not this topic again. (LOL)

Tom_S has got it correct. O2 is important during the reproductive (or "Lag") phase of fermentation.

The question is this, though.. Just how much O2 is needed.

I usually airate the must for the first one to 2 days by simply splashing the must around with a punch down tool. I have found this to be just fine. I also leave the must covered under a sheet of plastic.

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I hear you on the "Oh No!!!"

It is done very differently from one experienced wine maker to another and it tends to turn out just fine for all. It is kind of like asking the question, 'Which is better, red or white"?

During the primary phase, I like to aerate my red kit wines each day by giving them a lite stir with a little splashing. I never completely seal up my reds during primary. I even aerate my whites at least once during primary, usually on day 2 or 3.

As Julie said, it is not so much the number of days as it is the rate of fermentation, and is based on the SG. Since most kit manufacturers say that when the SG gets to 1.020 to 1.010 to seal up the wine under air lock, they must think that is the time the yeast no longer need oxygen, but again, that is just a ballpark and strictly my own interpretation. Though the act of sealing doesn't actually change the state from aerobic to anaerobic, it does say, "No more oxygen, please." That sort of makes sense to me, anyway.

This discussion can get very technical and also a little heated sometimes, so I won't say anymore than what is my opinion and what works for me.

Ok, since it has caused heated debate we will end it here. Thanks for the tips, lol!

This kind of debate is what makes the forum interesting. I believe that punching down wine during the lag phase at least 3-4 times a day provides sufficient oxygen. Failure to do so could result in an oxygen deficient must. I ferment in anywhere from 225L to 500L plastic tubs.

s0615353 said:

Ok, since it has caused heated debate we will end it here. Thanks for the tips, lol!

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WHAT?? Quit already? I haven't even had the chance to bring up the definition of the word anarobic!

[biting tongue]

s0615353 said:

Ok, since it has caused heated debate we will end it here. Thanks for the tips, lol!

Click to expand...

We are just giving you a hard time. This subject has caused heated debate, but really, it is a very good subject to discuss, so don't let us deter you. I think it is very important, because without some understanding of this, it is not easy to understand the whys for healthy yeast and completed fermentations.

I gave you a small bit of my opinion and so should others. Come on, guys and gals!!! Don't be shy.

Here's some more of my opinion. Before one starts fermentation, there is always going to be at least some oxygen present in the must. In most cases one adds water and stirs. If not, pouring the must into a fermeter bucket is going to load up the O2. In a pail, hopefully one will stir it up well, so it will have some O2 added. Even if one does nothing, under normal circumstances a certain amount of O2 is going to find its way into the must, although it just might not be enough to supply what the yeast need. The actual amount needed is discussed on one yeast provider's website, but I can't remember which.

Before fermentation, I would always recommend stirring and splashing in some O2, even with a white kit. Lots don't stir a white kit before or after pitching the yeast; they lock down the lid and add an air lock. I just will not do this, myself. You will find many who do this and do it very successfully... go figure.

There is definitely an aerobic phase and a separate anaerobic phase. Yeast tend to do most of their multiplication during the aerobic phase, when O2 is present. This tells me that if one doesn't provide a healthy aerobic phase, the number of yeast available to finish the job might all be seriously depleted before fermentation is complete. Maybe some stuck fermentations could be because there are no more healthy yeast left... I never considered this before now.

Some studies say yeast metabolize the sugars more during the anaerobic phase. Some people argue the aerobic phase is not necessary and site some wines made in a special process in isolation of O2 in France. While this might be possible under special circumstances, it is not the norm.

Many believe the reason to apply an air lock after fermentation slows is because there is no longer enough CO2 being produced to protect the wine. I also believe this is true, but I will add that by this time the yeast are likely at or well into the anaerobic phase and need isolated from O2.

Comments?

JohnT said:

WHAT?? Quit already? I haven't even had the chance to bring up the definition of the word anarobic!

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(I'll start the fight!)

There is no definition for the word - anarobic. That word does not exists!
See how easy it is...

Just kidding!!! John, Bob, I know you are getting close to the breaking point. Come on, let's have it. I know you both have a lot to offer.

OK ... I'll say just a little bit, that has no bearing on practical application ...

The wine benefits from being isolated from O2. The yeast doesn't care.

That is the only thing I would change about your fine write-up

robie said:

(I'll start the fight!)

There is no definition for the word - anarobic. That word does not exists!
See how easy it is...

Just kidding!!! John, Bob, I know you are getting close to the breaking point. Come on, let's have it. I know you both have a lot to offer.

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I thought that it was a rule of this forum that the "over 50" crowd is allowed typo's... LOL

Kick a man when he is down! I suppose the next thing on this thread is a discussion over the high quality of welches grape juice....

((Let's drag Wade in ...))

Don't sweat the spelling, John. If correct spelling was a requirement, Wade wouldn't be here!

One more thought on O2. Part of the reason that whites require extra protection is that they are presumably fermented much cooler and slower than reds.

Lower temps means O2 can be more easily dissolved into the wine where it does damage.

Reds OTOH, are fermented at temps that, when combined with the sparging effect of CO2 in more active fermentation (relative), make it more difficult to actually get O2 dissolved into the wine.

It's not the CO2 'blanket' that protects the wine. It's O2 being blown out by CO2. At the tail end of AF, temps fall and CO2 release slows, presenting better opportunities for O2 to make it's way in.

Sounds right to me!

That sounds right to me, also. Just be mindful that after fermentation starts, whites don't usually need a lot of stirring compared to a red. Under the same conditions, the whites will oxidize much quicker than reds.

Same is true during later racking, a white should not be splash racked if possible.

Is this because white wines do not have the extra tannin to help preserve them?

s0615353 said:

Is this because white wines do not have the extra tannin to help preserve them?

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In part, that is correct, but tannins will only protect so much as far as O2. It is the little buggies in the air that I am more afeared of!