Yeast and Oxygen

[Veets]

I've read many posts that talk about active yeast "cleaning up" or scavenging oxygen late in a fermentation. For example, small amounts oxygen picked up in transferring to a secondary fermenter, or oxygen introduced when opening a fermenter for dry hopping, or oxygen introduced when bottling, etc. The theory is that the yeast will use the oxygen and so the beer won't be affected by the oxygen.

On the other hand, I've read many posts (usually beginners) asking about whether they should add oxygen so that the yeast could carbonate the fermented beer (e.g., when adding priming sugar, etc.). The responses I've read typically say that oxygen is only necessary during the yeast's growth phase, and that once the wort (or beer) is full of the active yeast then they'll happily chow on sugars without needing oxygen around to do their job. And that this is true even after cold-crashing a beer before bottling, where fewer yeast are remaining in the beer.

So, my "Brew Science" question is this: if the remaining yeast in an already-fermented beer (or mostly fermented beer) don't need oxygen in order to continue munching sugars and making CO2, is it really true that if oxygen is present then they will use it and prevent the beer from becoming oxygen-spoiled (cardboard taste, etc.)? Do they really "scavenge" oxygen? Or is that just a theory based on the knowledge that they need and use oxygen at the beginning of fermentation? In other words, is there any hard (published) evidence to back up the scavenging theory? (I'm sure that there are some strongly-held beliefs, so that's why I'm posting in the Brew Science forum rather than the Fermentation and Yeast forum)

Thanks for any helpful replies!

P.S. I am relaxed. I also realize that some people think that the small amounts of O2 won't make a difference and I shouldn't worry about it. I'm still interested to know the brew science.

 

[TheHopfather]

I've never once seen any data to back up the whole yeast scavenging oxygen thing. It seems to be one of those home brew myths that everyone takes as gospel. Yeast do take up oxygen during the growth phase, I don't think anyone disputes that, but during active fermentation?

It would be cool if someone with a DO meter could do some tests, I'd be interested to see the results. What are the DO levels in the beer before and after bottling and again after carbonating? I have seen a lot of pictures posted online showing NEIPA's that have gone brown in a matter of weeks after bottling, so I think it is safe to assume that even if yeast are scavenging oxygen, they aren't getting all of it. NEIPA's seem to be hyper sensitive to O2 pickup, it is interesting to see just how quickly they can oxidize.

Edit: Interesting article that goes into oxygen's role in wort. It doesn't really answer your question, but does explain how and why yeast use oxygen;

https://www.morebeer.com/articles/oxygen_in_fermentation

 

[mongoose33]

Yeast like to use oxygen if present, but if not, they can metabolize in other ways.

I've never read anyone suggest adding O2 to the process while bottling. Where are you seeing that?

A good rule of thumb is that the only place you want to introduce oxygen intentionally is when you pitch the yeast or when you make a starter; prior to that it's not helpful, and once fermentation is finished, it's not helpful either--and may well be detrimental.

I've followed the mantra of getting as much oxygen out of my post-fermentation beer as i can. There's enough evidence to suggest staling or oxidation as a result of O2 in the beer, so the best approach, IMO, and in my practices, is to do everything I can to avoid it.

BTW, one should be careful with posts and such when someone says "I couldn't taste any difference" as a result of doing a process or procedure. The difference may or may not actually be there.

There are certain hop flavors, for instance, that aren't perceivable by some people. Others may not be as able to readily taste oxidation, or other off flavors. That doesn't mean they're there--it just might mean the person reporting can't taste them.

 

[ScrewyBrewer]

I believe yeast consume oxygen during their aerobic phase, while they are building up strength and multiplying. Once the oxygen has been depleted the yeast switch into an anaerobic phase. That's when they begin converting sugars into Co2 and alcohol. In short, initially yeast benefits by the presence of oxygen, but once fermentation begins the addition of oxygen increases the level of diacetyl and off flavors.

Once all the sugars have been consumed, the yeast cells begin consuming diacetyl and other flavor precursors that cause off flavors in beer. After building up their energy reserves, by consuming flavor precursors, the cells prepare to go dormant. With the addition of priming sugar, when bottle conditioning, the yeast will wake up to convert the sugar into Co2 and alcohol again. I believe the yeast can do this while still in an anaerobic state.

 

[Veets]

Edit: Interesting article that goes into oxygen's role in wort. It doesn't really answer your question, but does explain how and why yeast use oxygen;
https://www.morebeer.com/articles/oxygen_in_fermentation

Excellent article, Hopfather. Thanks a bunch!

I've never read anyone suggest adding O2 to the process while bottling. Where are you seeing that?

To be clear, I didn't mean to suggest that anyone was recommending it. But I have seen people ask about whether it should be done. Here are a couple examples

https://www.homebrewtalk.com/forum/...-from-fermentation-to-bottling-bucket.329639/ ("Am I going to just end up oxidizing the brew, or would it help because I'm bottling and oxygenate the brew helping the yeast have the o2 to carbonate the brew better")

https://www.homebrewtalk.com/forum/threads/repitching-for-conditioning-an-eisbock.227116/ ("should i oxygenate the beer again (do i want aerobic fermentation or anaerobic) for my bottle conditioning?")

 

[bucketnative]

I've never read anyone suggest adding O2 to the process while bottling. Where are you seeing that?

EDIT to remove reference to Brew Like a Monk (I'm now not sure that's where I read the following: XXXX, one of the brew master's at one of the old Belgian breweries mentioned conditioning with the bottles on their sides. From what I remember, it was so that there was a greater surface area at the beer/air interface for oxygen to be available to yeast during the conditioning phase. I don't have that book with me anymore, or I would get a direct quote. Granted it's not adding O2, but at least someone was thinking about it during conditioning phase.

 

[chris000]

yeast never uses up all the O2 in the headspace during bottle conditioning; homebrewer myth.

next myth: to do EVERYTHING imaginable to avoid O2 is the way to get good beer.
and if you want to be absolutely true to style/clone, controlling the level of oxidation becomes the challenge

those who boil and cool liquor the day before they fill a storage keg; good for you. there's nothing wrong with it, just complete overkill IMO (especially when you drink it up in 1-3 months anyway)

I know, some ppl will not like it, but since sanitizer pushing seems to be current homebrew's accepted practice (at least on here), there are easier (chemical) methods to get rid of O2. and now don't tell me those you push sanitizer would have an issue with putting chemicals into their beer

 

[ajdelange]

From MBAA's 'Beer Packaging, 2nd Edition

"Generally, a 12-oz. (355-mL) bottle
of beer containing less than 0.5 mL of headspace air has
adequate shelf life for most local distribution scenarios.
Bottle conditioning or retaining a small amount of
yeast in the beer can help reduce oxygen content quickly
and extend shelf life. Also available are crowns with
oxygen-scavenging liners, which absorb oxygen in the
beer headspace, and oxygen barrier crown liners, which
can help keep oxygen from entering the crowned package.
Brewers should be aware that some of these liners “scalp”
or absorb hop aroma compounds."

I'd say professional brewers do indeed do EVERYTHING they can to exclude as much O2 as possible from their packages (and even so have trouble getting down to 0.5 mL airs).

 

[chris000]

0.5ml headspace isn't much...
TPO is a topic and there are different solutions to it (foam, enzymes, ascorbic, etc.).
and don't forget the goal there is very long shelf life at room temperature

 

[ajdelange]

Keep in mind that 0.5 ml in a 355 mL bottle is 100*0.18*.5/355 = 0.025% O2. That's pretty darn small.

The goal is, as it says in the quote "adequate shelf life for most local distribution scenarios." which isn't typically very long.

I found in my cooler a keg of Pils which I brewed almost 2 yrs ago. It is still pretty darn good and a large part of the reason for that is that it was protected from air (though it was oxygenated entering the fermenter) from the time it left the kettle up to the time it hit the glass. This is despite the fact that it was warm for two weeks until I got home after refusing to pay a technician $650 to unscrew a refrigerant pressure switch and screw in a new one.

 

[ajdelange]

I've never once seen any data to back up the whole yeast scavenging oxygen thing. It seems to be one of those home brew myths that everyone takes as gospel.

From MBAA's 'Beer Packaging, 2nd Edition

"Bottle conditioning or retaining a small amount of
yeast in the beer can help reduce oxygen content quickly
and extend shelf life.

It's not data but it strongly suggests that the data support scavenging as commercial brewers would not be likely to engage in the practice of including yeast in the package if it didn't work. Note that a commercial operation does not need to drop $100K on a Krones bottling machine with double pre-evacuation to use this technique to extend shelf life.

 

[chris000]

the ever lasting discussion commercial vs. homebrew, isn't it?
depending where you shift the scope, one gets different answers - at least IMHO
what I mean by that; commercial breweries have to be commercially successful. there are some that are very much so, despite selling oxidized beer.
homebrewers don't sell beer, as long as they like what they make they are "successful". and while expectations will vary, so does their equipment. I bet there are more who drink green beer than lager for 2 years.
To me personally it has to be stable for two months in the fridge and that is an entire different ballpark than commercial. Just watching for oxygen will not get you into long shelflifes (flash past., filtering, etc.)
I read once a paper about how much oxidation consumers would consider optimal; it wasn't zero...
Anyway, that was when I started to rethink of how much of that realistically applies to me personally and what's parcticle for me

 

[chris000]

It's not data but it strongly suggests that the data support scavenging as commercial brewers would not be likely to engage in the practice of including yeast in the package if it didn't work. Note that a commercial operation does not need to drop $100K on a Krones bottling machine with double pre-evacuation to use this technique to extend shelf life.

not sure where you going with this one. having yeast in the bottle is (in terms of volume sold) not a real option for a commercial brewer. it is the exception and only applies to certain styles.
yeast will not use up all the O2 in the headspace and displacement is not an option since the bottle is closed (different than a fermentor).
regarding cost, beer-foam is free

 

[TheHopfather]

It's not data but it strongly suggests that the data support scavenging as commercial brewers would not be likely to engage in the practice of including yeast in the package if it didn't work. Note that a commercial operation does not need to drop $100K on a Krones bottling machine with double pre-evacuation to use this technique to extend shelf life.

Oh, I'm sure the yeast scavenge some oxygen, I wasn't trying to claim that is the case. What I was saying is that there isn't any data out there that proves anything either way. I think the yeast are scavenging some oxygen (because that's what the internet says happens), the question is how much?

I'd actually really like to see data from a test with a DO meter.

 

[ajdelange]

the ever lasting discussion commercial vs. homebrew, isn't it?
depending where you shift the scope, one gets different answers - at least IMHO
what I mean by that; commercial breweries have to be commercially successful. there are some that are very much so, despite selling oxidized beer.

Yes, some do sell oxidized beer. When I visited Pilsner Urquel they had sinks - a big no - no today. This was quite a while ago - so long that when I commented in some forum that 'If PU is oxidized, I want oxidized" it this absolutely put George Fix's knickers in a knot.

homebrewers don't sell beer, as long as they like what they make they are "successful". and while expectations will vary, so does their equipment. I bet there are more who drink green beer than lager for 2 years.

There is as much variety in commercial brewing as in home brewing. These days any home brewer who knows a couple of lawyers and brokers is a commercial brewer (if not for long). All that aside, the science is the same whether you are a commercial operator, an extract brewer or someone who has won the Ninkasi medal.

To me personally it has to be stable for two months in the fridge and that is an entire different ballpark than commercial.

Not really. If a commercial guy's beers don't move in 2 months, he'll lose his shelf space. There are just too many competitors out there vying for it.

Just watching for oxygen will not get you into long shelflifes (flash past., filtering, etc.)

Perhaps not by itself (beer must also be biologically stable) but it is a sine qua non.

Anyway, that was when I started to rethink of how much of that realistically applies to me personally and what's parcticle for me

You must try to resist the temptation to try to promulgate your personal preferences as globally applicable. This doesn't mean that your thoughts aren't valuable - just that not everyone has your tastes nor customers.

not sure where you going with this one. having yeast in the bottle is (in terms of volume sold) not a real option for a commercial brewer.

It certainly is. Have you never had a beer advertising "Flashengarung" or "Med gisting in fles"? Lots of commercial brewers do it abroad and many imitate the practice in the US as well.

it is the exception and only applies to certain styles.

You won't find it in Stella or Bud but I'll bet you'll find it in some of InBev's portfolio. More to the point: if the MBAA recommends it in their manual on packaging practice then you can be sure lots of American brewers are doing it. Perhaps you are unfamiliar with MBAA. It is the Master Brewers Association of America. At one time it was only the big boys (and at one time the journal was published in German) but today, while the big boys are still there, so are lots and lots of smaller breweries.

yeast will not use up all the O2 in the headspace

Down to the last molecule? No, of course not, but enough to, in the words of MBAA, "reduce oxygen content quickly and extend shelf life.

and displacement is not an option since the bottle is closed (different than a fermentor)
regarding cost, beer-foam is free

Now it's my turn to be confused. Many large breweries use bottling machines that displace the volume above the beer with foam by knocking the filled bottle or shooting a jet of warm water into it.

 

[ajdelange]

What I was saying is that there isn't any data out there that proves anything either way. I think the yeast are scavenging some oxygen (because that's what the internet says happens), the question is how much?

I am sure the data is out there - ton's of it. Look back through the ASBC and MBAA TQ archives and I'm sure you will find some. The fact that yeast do scavenge oxygen is so well known that MBAA includes it in their bottling guidelines.

I'd actually really like to see data from a test with a DO meter.

In a meaningful test some beer would be brewed and split into two batches one of which would be bottled without yeast and the other with. After some time the crowns would be pierced and the headspace gas cancelled. As I say, I am sure this has been done but I don't know where to point you any more specifically than 'the literature'.

I have inoculated aerated wort with yeast and watched the numbers roll off on a DO meter. They scavenge it fast. In checking on my worts if I over shoot the maximum the meter will read (20 mg/L) the obvious solution would be to dilute 1:1 and read again but by the time the dilution is prepared, the yeast have consumed so much O2 that the second reading is meaningless.

 

[chris000]

ajdelange,
much appreciate your feedback; always great reading some other perspective!

Reagrding the volume of Flaschengärung; it is significantly less than the rest. Just a ballpark figure; in Germany the volume of Heifeweizen (which is not all finished in the bottle, but certainly represents the largest vol. of beer of this type) used to be around the 8%.
Regarding the O2 during bottle ferm. If you fill flat (all air, no foam), the yeast metabolizes 30-50% of the O2 depending on the fermentables/carbonation. It'll may be less in headspace measurements, but that;s because it diffuses into the beer, so a complete test setup would need to account for that as well.
my note on the fermentor vs bottle might have not been clear; I was referring to the fermentation part (not filling) in so far that they are very different systems; one vents and displaces and the bottle doesn't (one has a high dilution factor, the other not)