Yeast Pre-Oxygenation - Oxygenate your yeast, not your wort.

[Bobby_M]

In my 18 years of brewing, I never heard of this or thought about it on my own.

https://academic.oup.com/femsyr/article/9/2/226/568736

The basic idea: Most of us know, at various levels of understanding, that yeast needs oxygen, hence all the shaking and pour wort and whatever other gadgets one might employ. It's the one time in the entire brewing process where oxygen is not only OK but welcomed into the process. The yeast use oxygen for creating cell walls when reproducing. For a more digestible version:

https://wyeastlab.com/resource/home-enthusiast-oxygenation-aeration/

I've always understood that in the cases where you're pitching yeast in some cell quantity that would definitely require or benefit from additional reproduction that getting oxygen into the wort was really important. For example, something like a 1.060 ale wort being pitched with a one-two month old pack of Omega without making a starter. Cell growth is definitely needed and oxygen will enable it. The rub is that putting the oxygen in the wort just after pitching is arguably damaging for the same reason that oxygen damages beer on the hot side and post fermentation cold side. The amount of damage is debatable, but not really whether it happens or not. It's one of the reasons why people debate how long it's OK to delay pitching and whether oxygen should go in before or after pitching (doing it after means the yeast is there to conceivably use it up faster).

TLDR - Less oxygen damage will occur if you combine the liquid yeast with some fresh wort in a smaller sanitized container where you can oxygenate the yeast in isolation.

This is what we're doing in a starter on a stir plate. On particularly delicate beer styles, one is encouraged to cold crash a starter to be able to decant the very oxidized wort out of there so as not to taint the beer with it.

In order to make a more sense of it; here are a few approaches to fermentation.

1. Pitching more than enough yeast. This is dumping enough cells to fully attenuate the wort with no reproduction needed. You get very little yeast character out of this and no oxygen is needed.
a. A ton of dry yeast
b. A huge starter

2. Pitching nearly enough yeast into your batch's wort. Some reproduction is necessary for full attenuation. You will get some yeast character and some oxygen is needed.
a. some dry yeast
b. a semi-fresh liquid pack give or take
*less cells than a calculator says is required for the gravity/volume.

3. Pitching barely enough yeast into your batch's wort. A LOT of reproduction is necessary for rull attenuation. You will get maximum yeast character and a lot of oxygen is needed. Is it possible that the amount of O2 needed here could damage the wort to some degree?
a. one pack of dry yeast in a very high gravity wort or fermented at lager temps for example.
b. an old/aging pack of liquid yeast.
*significantly less pitch than the calculator wants.

The pre-oxygenation concept comes in where you'd otherwise add it into the batch's wort directly, but you don't either because you don't want a ton of estery yeast character or you want to limit oxidation damage no matter how small.

For example, in 2a you'd rehydrate in a container and then add some wort and hit it with O2. Same in 2b, but no rehydration. The other application would be where you can't really grow enough yeast even in a starter, perhaps because you don't have enough yeast to pitch into a huge starter, or your starter vessel isn't big enough for the calculated need. Maybe you need a 4L starter but only have a 2L flask. Grow a 2L starter, decant the spent wort, dilute with some batch wort and "preoxynate" then pitch.

I'm not really making any definitive claims here. I'm bringing it up for fuel for conversation. So, what's up? Have you heard of this pre-oxygenation technique before? Have you tried it?

I just did for the first time on an American Pilsner (aka a Hoppy American Lager). 2L starter, crash, decant, dilute with 2 liters of wort, oxygenation with a stone for 30 seconds, let it rest while the remaining wort was chilling down to the final pitching temperature.

 

[day_trippr]

I've never seen this recommendation so certainly haven't done it

I do 10 gallon batches with typical OGs in the 70-75 point range, and I do over-built starters to keep a yeast line going for up to a year. I typically do 5 liter starters a few days before the brew, give them a good jump with straight O2, then let them run on a stir plate for 24 hours before crashing and decanting into pint size mason jars. When I pitch I follow with 4 minutes of O2 at 0.5 LPM for each carboy, based on Chris White's stated practice as expressed in Yeast (he did 2 minutes at 1 LPM, but I think that is less effective due to lower efficiency).

Anyway....to switch to this "new" process, aside from not gassing the carboys, I just need to add fresh wort to the decanted starter, and gas that up before pitching. Seems simple enough.

I'll keep this in mind, and on my next batch I'll do one carboy my traditional way and use the above procedure for the other and see what happens...

Cheers!

 

[Willy]

Would a starter with an active stir bar produce any oxygen? Curious. No idea.

Never tried that unless my stir bar adds some oxygen. I usually rock a bucket.

Curious to hear experiments on this.

 

[mashdar]

On some level, is this a brief vitality starter?

Is the idea to use part of the wort post-boil, or DME early?

Total O2 in solution would be lower with low volume. If yeast can't keep up, might need to do slower, longer O2 delivery. 20 min at 0.1 lpm?

I wonder how long for the DO to drop.

 

[day_trippr]

I wonder how long for the DO to drop.

I had possession of a decent DO meter about a decade ago and did a few experiments while I had it. One was seeing how fast the O2 was removed from strike liquor using bakers yeast with a bit of corn sugar; the other was seeing how fast the O2 I added to a carboy of freshly pitched wort disappeared. In both cases there was very little O2 remaining after 6 hours, and within 12 hours there was no measurable O2 remaining (I was actually pretty impressed with the strike water deaeration thing)...

Cheers!

 

[mashdar]

I'd be concerned about getting sufficient O2, then; If getting 10-12 ppm is useful (presumably so given the popularity of oxygenation), and if it takes hours for it to get absorbed, won't the total oxygen in 1/2 gallon be too low, even if we hit 40ppm? (And at what point is it toxic?)

I'm just thinking out loud.

 

[BrewnWKopperKat]

The podcast episode "Controlling Oxygen in Beer with Colin Kaminski" has a segment that talks about doing this.

eta: also "Beer Process Control with Colin Kaminski" starting at about minute 30.

 

[Climb]

This is the first I have heard of preoxygenation. Bobby, thanks for your post and giving this technique broader exposure. It's an interesting technique and could be a handy tool to keep in ones brewing repertoire. I wonder, do we know that preoxygenation is really necessary? Does anyone know of research that has shown that oxygenating wort is detrimental to the beer produced? What was the level of oxygen concentration and what was the detrimental impact to the beer? What does the LODO community say about preoxygenating a starter versus oxygenating wort? As is common, some knowledge only creates more questions. I am interested in input from others that have more knowledge in this area than I.

From my read of the paper, of the first link, they oxygenated the yeast slurry at 20 C for 8 hours using oxygen and a membrane sparger. The paper states "oxygen", so I assume that was pure oxygen and not atmospheric air and I assume that a membrane sparger would be more efficient at dissolving gas in a liquid than a sintered stone. But how would they only get an oxygen concentration of 8 mg L-1 (that's 8 ppm right?) in the yeast slurry, when the Wyeast article shows up to 12 ppm in 60 seconds using pure oxygen with a sintered stone in wort. Would the difference between oxygenating a yeast slurry and wort be that different? Was the oxygen concentration of the yeast slurry being controlled? I didn't see any mention of that.

It seems to me that this preoxygenation technique would be most applicable to high gravity wort that can't hold all the oxygen in saturation the yeast need during fermentation, even though the paper used 12 degree plato wort.

The paper also states, "... although industrial applications of this technique are scarce. This is due to the inconsistent and limited scientific studies and the lack of knowledge regarding the biochemical background of the preoxygenation of yeast cells." I think this summarizes why most have not heard of preoxygenation before.

 

[DBhomebrew]

Echoes of some points in Saccharomyces's explanations in favor of his Shaken Not Stirred starters.

 

[AdjunctBrewer]

Some things I'm not clear on:

1.) How much damage really occurs when oxygenating 5 gallons of wort for a period of time (is there quantifiable and noticeable "damage" to the wort?)
2.) Is it better to a.) pitch the yeast first and then oxygenate or b.) oxygenate and then pitch the yeast

For the pre-oxygenate process above:

3.) What (smaller) quantity of wort should be oxygenated and innoculated?
4.) How fast is the oxygen used in the smaller quantity of wort?
5.) Should the yeast be pitched before or after oxygenating the new smaller quantity of wort?
6.) How long should one wait to pitch this smaller quantity of newly innoculated and oxygenated wort?
7.) Is there a noticeable difference in the outcome of the beer?
8.) Is there an advantage and can this concept be effectively employed with dry yeast even though they don't need the oxygen?

It's an interesting concept, but just like all of the other homebrew yeast concepts - shaken not stirred, rehydrate vs don't, stir plate vs air pump, etc... what metrics can the homebrewer employ to qualify and quantify this new process?

Aside from the standard, "It started ferementing right away" or "it's the most vigorous fermentation i've seen", homebrewers generally believe in these things on the basis of "I've always done it that way" or "That's how Grandpa, Dad, Uncle or Papazian did it" or the everfaithful "look at all of my medals" as if rehydrating yeast got them a bunch of medals.

 

[Willy]

The podcast episode "Controlling Oxygen in Beer with Colin Kaminski" has a segment that talks about doing this.

Here's a link to the podcast

 

[Willy]

Also - here's an older HBT thread on oxygen in starters. (From 2020)

https://www.homebrewtalk.com/threads/adding-oxygen-to-yeast-starters.679972/

 

[Miraculix]

There's a limit of dissolved oxygen and with a lower amount of liquid, the total amount of oxygen will be lower than with the full amount of liquid.

Might be worth checking how fast the yeast takes in all the dissolved oxygen in the starter flask, after adding the wort and oxygenating it. If the oxygen would be gone in 30 minutes, one could re-oxygenate the starter wort multiple times and in this way compensate for the relatively small volume of liquid.

 

[DavidWood2115]

This is really cool, thanks for sharing this Bobby.

The journal article Bobby links above discusses preoxygenation of the yeast slurry in the absence of maltose (using some complicated apparatus that I don’t fully understand). Unfortunately that means their results don’t directly indicate what would happen in the presence of fresh wort. To more closely approximate their results, I think adding distilled or RO water to dilute the yeast slurry and then putting it on a stir plate with a slow O2 feed would be a closer approximation.

I think the key difference is that if you oxygenate in the presence of maltose you will get yeast growth. But without maltose, you get the changes discussed in the paper. Which is better? Don’t have a clue.

 

[BrewnWKopperKat]

Here's a link to the podcast

Also episode 269 ("Beer Process Control with Colin Kaminski") starting at around 30:00.

 

[Bobby_M]

Some things I'm not clear on:

1.) How much damage really occurs when oxygenating 5 gallons of wort for a period of time (is there quantifiable and noticeable "damage" to the wort?)

I don't think anyone knows for sure other than the fact that oxygen is in the process of tearing everything apart at all times. It's like asking how much rust is OK on a car before it's not OK anymore.

2.) Is it better to a.) pitch the yeast first and then oxygenate or b.) oxygenate and then pitch the yeast

If you are going to oxygenate in the beer's full batch of wort, there's no reason to have oxygen sitting in there without the special guests there to take it.

For the pre-oxygenate process above:

3.) What (smaller) quantity of wort should be oxygenated and innoculated?

No idea. There's probably some threshold where it's enough to keep oversaturation at bay given some minimally controllable oxygen source. I think the last thing you'd want to do is bring a thimble of wort up to 20ppm and start killing the yeast you already have in there.

4.) How fast is the oxygen used in the smaller quantity of wort?

Same mystery as above.

5.) Should the yeast be pitched before or after oxygenating the new smaller quantity of wort?

The idea is that the yeast would probably be in the container and there would be no reason to try to build up some concentration if the yeast is going to start taking it up right away.

6.) How long should one wait to pitch this smaller quantity of newly innoculated and oxygenated wort?

As long as it would take for the yeast to uptake the oxygen.

7.) Is there a noticeable difference in the outcome of the beer?

This is kind of the same question as #1. It would only be a difference if the process of satisfying yeast sterol reserves in the whole wort had a noticeable oxidative quality.

8.) Is there an advantage and can this concept be effectively employed with dry yeast even though they don't need the oxygen?

Dry yeast doesn't "need" oxygen if you're pitching enough of it but all yeast will eventually need it if it has to reproduce.

It's an interesting concept, but just like all of the other homebrew yeast concepts - shaken not stirred, rehydrate vs don't, stir plate vs air pump, etc... what metrics can the homebrewer employ to qualify and quantify this new process?

Split batch experimentation is the only way I'd prove it to myself as a benefit.

Aside from the standard, "It started ferementing right away" or "it's the most vigorous fermentation i've seen", homebrewers generally believe in these things on the basis of "I've always done it that way" or "That's how Grandpa, Dad, Uncle or Papazian did it" or the everfaithful "look at all of my medals" as if rehydrating yeast got them a bunch of medals.

All the medals anyone gets is a pretty good sign of constant reassessment of process, or maybe constant dumb luck. With yeast handling, it's much more about troubleshooting fermentation problems retrospectively so you don't repeat the same mistake. As a judge, fermentation flaws are probably the biggest issue after cold side/packaging oxidation damage. Realize I'm just bringing this up as food for thought. There are plenty of brewers that are not even considering ANY part of yeast "precision" neither calculating pitch rates nor oxygenating anything and I'm sure a subset of those people are having a wonderful time with their beer.

 

[day_trippr]

fwiw, if memory serves, in Yeast Chris White related bringing wort to over 40ppm O2 sat with no noticeable issues...

Cheers!

 

[BrewnWKopperKat]

dry yeast side topic based on

8.) Is there an advantage and can this concept be effectively employed with dry yeast even though they don't need the oxygen?

and

Dry yeast doesn't "need" oxygen if you're pitching enough of it but all yeast will eventually need it if it has to reproduce.

but not 'aimed' at anyone specific.

There's some discussion on using dry yeast, in the context of oxygen management, in #293 in about the last 10 minutes. Also Zainasheff, in a Zymugry Live event (Aug 2023?) and in his new book (2024) talks about benefits he sees from rehydration (including faster starts).

 

[AdjunctBrewer]

I don't think anyone knows for sure other than the fact that oxygen is in the process of tearing everything apart at all times. It's like asking how much rust is OK on a car before it's not OK anymore.

If you are going to oxygenate in the beer's full batch of wort, there's no reason to have oxygen sitting in there without the special guests there to take it.

No idea. There's probably some threshold where it's enough to keep oversaturation at bay given some minimally controllable oxygen source. I think the last thing you'd want to do is bring a thimble of wort up to 20ppm and start killing the yeast you already have in there.

Same mystery as above.

The idea is that the yeast would probably be in the container and there would be no reason to try to build up some concentration if the yeast is going to start taking it up right away.

As long as it would take for the yeast to uptake the oxygen.

This is kind of the same question as #1. It would only be a difference if the process of satisfying yeast sterol reserves in the whole wort had a noticeable oxidative quality.

Dry yeast doesn't "need" oxygen if you're pitching enough of it but all yeast will eventually need it if it has to reproduce.

Split batch experimentation is the only way I'd prove it to myself as a benefit.

All the medals anyone gets is a pretty good sign of constant reassessment of process, or maybe constant dumb luck. With yeast handling, it's much more about troubleshooting fermentation problems retrospectively so you don't repeat the same mistake. As a judge, fermentation flaws are probably the biggest issue after cold side/packaging oxidation damage. Realize I'm just bringing this up as food for thought. There are plenty of brewers that are not even considering ANY part of yeast "precision" neither calculating pitch rates nor oxygenating anything and I'm sure a subset of those people are having a wonderful time with their beer.

Thanks for answering the questions. You've exemplified my point, as there are no specific answers to guide the homebrewer in this process. Most homebrewers don't own DO meters and aren't precise in anything homebrewing but still make good (to them?) beer.

Homebrewing doesn't have to be by guess and by golly but sometimes with new procedures you just have to try it and revise it based on the results.

Hopefully those who try this will post back with some answers on what did/didn't work for them and their observations on the final beer.

 

[Broothru]

I’m having a bit of difficulty sussing out the step-by-step of these competing processes. Maybe (probably) my dilemma is due to either advancing dementia, or (more likely) too much ‘holiday.’ Since I process data in a highly linear fashion, could someone compose a simple “Oxygenation for Dummies” to get me past this intellectual roadblock?

My normal process is to step-propagate liquid yeast with the final SG of starter wort near the same value as my predicted wort. I oxygenate the starter for :30 seconds @ .4L/min., add a pinch of nutrient and spin the magnet, hoping to hit high krausen just before pitching time on brew day. So far, so good?

I gather from the comments that at this point, rather than oxygenating the main wort, I should first pitch the prepared starter and the hit it with O2. But then the question is, how much O2? Looks like 20~40 ppm saturation, but how do I calculate/guesstimate how long and at what flow rate will it take for a 6.5 batch volume to reach that saturation without a DO meter to measure it (assume SL pressure, 16C/61F).

Help! I’m too math challenged and hungover to even attempt this calculation without outside guidance. My reasoning and comprehension capabilities ended up in a heap along side the spent wrapping paper and turkey carcass.

 

[AdjunctBrewer]

I gather from the comments that at this point, rather than oxygenating the main wort, I should first pitch the prepared starter and the hit it with O2.

Instead of pitching the yeast into the main (say 6.5 gal) volume of wort you would withdraw (say 0.5-1.0 gal) a smaller volume of wort, pitch the yeast into that smaller volume and oxygenate that smaller volume of wort. You would then pitch that smaller volume back into the larger volume ideally at the point all of the oxygen has been consumed in the smaller volume. The idea being that you're only potentially oxidising the smaller volume while giving the yeast the benefit of the oxygen.

 

[Bassman2003]

Great topic Bobby. I recently acquired a passable DO meter and have been employing oxygenation measures on my batches. The measurement of how much oxygen is needed in your wort can be eye opening. Since using the DO meter I have put a lot more O2 in my wort which has resulted in meteoric yeast activity. I will be soon tasting all of the batches to see how they turned out.

While adding so much O2 into my wort I thought about this same topic. Damage vs assistance. My first thoughts are towards the amount of O2. It takes a lot more oxygen to get 5.5 gallons up to 12-18ppm compared to 2L at 12-18ppm.

- How much O2 does the yeast actually consume and need?
- How much gets wasted and just sits in the wort?
- How much goes out of solution before the yeast get to it?
- How long does the O2 hang around in the wort for the yeast to eventually consume?

Only oxygenating the starter brings about other questions:

- With only 2L, will the yeast get enough oxygen?
- Do you oxygenate multiple times?
- How much oxygen can the yeast store? When they hit the wort, there will be none, so will the oxygen taken up in the starter be enough when reproduction starts?

It would seem that the cells present in the starter will become 'super cells' that are like Olympic athletes. They will get right to work. But as they divide there will be no fuel for the newly created cells. (that is if the oxygen added to the batch wort lingers). Will this end up starving the last round of created cells? So the first round are super fit and the last round are weak? Or there is no 'last round' because all of the oxygen ran out?

 

[Bobby_M]

It's a difficult topic to really reach hard conclusions on and I had a hard time arranging my thoughts in the initial post because there are so many digressions you might take.

People that are generally careless about yeast pitch nuance and mechanics don't always have "problems". Even when they do, they don't necessarily attribute the problem to an aspect of yeast handling because it does take time to learn about the cause and effect in that realm. Be careful to realize when I say "careless", I mean innocently ignorant and not in a derogatory way.

Pitching any amount of yeast, in any condition, with or without oxygen or aeration, will ferment the wort into beer 99.99% of the time. Just that fact alone makes people less motivated to talk about the how and whys.

 

[corncob]

I'm going to change my user name to "innocently ignorant."

 

[corncob]

I have never owned an oxygen bottle, so I don't know anything about anything. I mostly brew English ales of moderate gravity, and I've never entered a competition, although I would like to one day. One of the great things about brewing is that it can be done successfully at very different levels of sophistication.

This discussion reminded me of an old video I saw on you tube recently, which was a recorded presentation from a Canadian brew pub on how they handle Ringwood. The guy said that they preferred to top crop and immediately pitch into the next batch, but if the timing didn't line up, they would fill a bucket with the fresh wort and pitch refrigerated top-cropped slurry into that. It would form an explosive krausen in less than an hour and then they pitched that into the batch. I wonder if some of the dynamics of the massive overpitch becoming the pitch for the whole batch are part of this. Obviously the ringwood brewery was worried about rapid fermentation onset (due to open fermentation) rather than O2 exposure, but there seems to be a parallel.

I've always wondered about oxygenating wort. All the yeast stains we currently have were developed and selected in breweries that didn't oxygenate. I wonder if the beer was very different back then, or if the practice just makes up for the small scales and irregular schedules homebrewers and craft brewers have to cope with.

Perhaps it has to do with the near-universal adoption of closed fermentation.

 

[Bobby_M]

Great topic Bobby. I recently acquired a passable DO meter and have been employing oxygenation measures on my batches. The measurement of how much oxygen is needed in your wort can be eye opening. Since using the DO meter I have put a lot more O2 in my wort which has resulted in meteoric yeast activity. I will be soon tasting all of the batches to see how they turned out.

This is good to hear. I've probably been under-dosing for fear of toxicity but post #18 and this one allay those fears a good deal. I want a DO meter so bad.

While adding so much O2 into my wort I thought about this same topic. Damage vs assistance. My first thoughts are towards the amount of O2. It takes a lot more oxygen to get 5.5 gallons up to 12-18ppm compared to 2L at 12-18ppm.

- How much O2 does the yeast actually consume and need?
- How much gets wasted and just sits in the wort?
- How much goes out of solution before the yeast get to it?
- How long does the O2 hang around in the wort for the yeast to eventually consume?

Only oxygenating the starter brings about other questions:

- With only 2L, will the yeast get enough oxygen?
- Do you oxygenate multiple times?
- How much oxygen can the yeast store? When they hit the wort, there will be none, so will the oxygen taken up in the starter be enough when reproduction starts?

I agree that all these questions need to be answered to really grasp whether it's a viable technique for any given beer.

It would seem that the cells present in the starter will become 'super cells' that are like Olympic athletes. They will get right to work. But as they divide there will be no fuel for the newly created cells. (that is if the oxygen added to the batch wort lingers). Will this end up starving the last round of created cells? So the first round are super fit and the last round are weak? Or there is no 'last round' because all of the oxygen ran out?

My understanding (which is painfully limited) is that the parent cell will split its sterols with the new bud and that budding and later cell growth will halt once oxygen and sterols are depleted. Then they go to work fermenting. If the job of fermenting the whole batch needs "A LOT" more cells than you currently have, I think the main decision that has to be made is whether you want the growth to happen in your batch of beer or not.

Yes? Well, I suppose you can just put some cells in the batch and feed it some oxygen a couple times to make sure they can reproduce and grow (whatever enough means). You can't just keep feeding oxygen the whole time because ethanol production is ideally anaerobic, and like I'm speculating there is an oxidation damage threshold somewhere anyway. Note if someone is hung up on if it's really a concern, just taste the wort that results from stirring a starter for 24 hours to get a sense of its extreme conclusion.

No? Get all/most of the growth in a starter. This wouldn't really be good for something like an ESB or Weise bier because of the highly diminished yeast character.

 

[Bobby_M]

I'm going to change my user name to "innocently ignorant."

Not if I don't beat you to it. It's at least a beer name.

 

[Bobby_M]

I've always wondered about oxygenating wort. All the yeast stains we currently have were developed and selected in breweries that didn't oxygenate. I wonder if the beer was very different back then, or if the practice just makes up for the small scales and irregular schedules homebrewers and craft brewers have to cope with.

Perhaps it has to do with the near-universal adoption of closed fermentation.

Yes, I think it has a lot to do with the modern homebrewer behavior of buying a tiny container of aging/old slurry and essentially being tasked to bring it back from the edge of death. Breweries of the past were slinging huge fresh slurries.

 

[corncob]

Yes, I think it has a lot to do with the modern homebrewer behavior of buying a tiny container of aging/old slurry and essentially being tasked to bring it back from the edge of death. Breweries of the past were slinging huge fresh slurries.

I get successful results with moderate to excessive pitches of top crop slurry that is 2-4 weeks old, no starter, no O2. I say "successful" because, not having a point of comparison, my process might be good or bad. I like the beer, at least, and I get consistency with attenuation and flavor. Based on what I read here, I have short lag times.

I've always wanted to schedule brews so I could pitch directly from one batch to the other, as God intended, just to see what would happen, but I've never done it. I suspect that real direct repitching of clean, active yeast covers a multitude of sins.

 

[Broothru]

Instead of pitching the yeast into the main (say 6.5 gal) volume of wort you would withdraw (say 0.5-1.0 gal) a smaller volume of wort, pitch the yeast into that smaller volume and oxygenate that smaller volume of wort. You would then pitch that smaller volume back into the larger volume ideally at the point all of the oxygen has been consumed in the smaller volume. The idea being that you're only potentially oxidising the smaller volume while giving the yeast the benefit of the oxygen.

OK, thanks. I'm finally getting the picture. In a way, you're using a gallon or so of the post boil wort almost like the final step up in propagation, then pitching that portion into the remaining volume of the wort without oxygenating the entire 6.5 gallons of wort.

It seems like the DO in the 'final step up' should be mostly consumed in less than 6~8 hours if the yeast being pitched is highly viable or at high krausen from the previous step up. Then the yeast will have sufficient glycogen reserves to feast and bud new daughter cells on the fresh wort without the need for additional oxygen.

 

[sibelman]

To me, this idea seems sensible: yeast need oxygen to reproduce. Once there's enough yeast cells, no more need, I guess. Anaerobic respiration thereafter.

In other words start with enough cells somehow, and skip aeration/oxygenation.

I'm not seeing this as a revolutionary change. The main idea: do any needed cell reproduction outside the main body of wort, which never gets aerated/oxygenated cuz there's no need and it might be a bad thing. Cool.

 

[mashdar]

(Assuming a clean yeast profile,) Is there any need for aerobic activity in the wort at all if there is a sufficient quantity of healthy yeast present? And how many is that? 4.5 million cells per mL per degree P for a normal gravity ale? (6x normal calculator value)

 

[sibelman]

Is there any need for aerobic activity in the wort at all if there is a sufficient quantity of healthy yeast present?

This is a fine question. I've imagined active fermentation being aerobic, followed by slower anaerobic fermentation. Based on no relevant knowledge whatsoever. I read most of Yeast by Chris White a few years ago, but don't recall...

Many claim dry yeast doesn't require (added) oxygen. Of course, even freshly chilled wort is gonna have considerable oxygen in it...

 

[Bobby_M]

I get successful results with moderate to excessive pitches of top crop slurry that is 2-4 weeks old, no starter, no O2. I say "successful" because, not having a point of comparison, my process might be good or bad. I like the beer, at least, and I get consistency with attenuation and flavor. Based on what I read here, I have short lag times.

I've always wanted to schedule brews so I could pitch directly from one batch to the other, as God intended, just to see what would happen, but I've never done it. I suspect that real direct repitching of clean, active yeast covers a multitude of sins.

I think being happy with the beer consistently is a good enough reason to not change anything.

The thing I can't wrap my head around is that a colony of yeast that never sees any oxygen shouldn't really be sustainable in theory because it shouldn't be able to reproduce and it doesn't live forever. I assume that typical wort handling is getting SOME oxygen in play.

 

[Bobby_M]

Many claim dry yeast doesn't require (added) oxygen. Of course, even freshly chilled wort is gonna have considerable oxygen in it...

The claim is true enough I think. The sterol reserves are "full" at the time the cells are dried so when they are properly revived/rehydrated, they can reproduce in the batch wort "AS IF" you had just given fresh oxygen to a liquid slurry that was somewhat sterol-depleted.

The nuance though, is how much yeast you pitch vs. how much is needed. The extreme example is, one dry yeast cell, no matter how fat and happy is is going in will not have the horsepower to ferment anything and certainly not enough sterols to reproduce enough.

One pack is often not enough for high gravity ales or normal to high gravity lagers and if it is enough to get the job done, it may not ferment as clean as it would with more. Clean isn't always the goal, but just sayin.

 

[sibelman]

A thing I wonder: don't the yeast "want" to reproduce even if there's more than enough to ferment the wort? They don't know how many yeast cells there are, and don't decide to not reproduce just 'cuz I pitched more than enough healthy cells. They just do what yeast do.

I imagine a happy yeast cell has all it needs to do what yeast does: ingest sugar, excrete alcohol & CO2, and divide. I don't need my yeasties to be happy, as long as there's enough of 'em to get the job done. But I want them to be happy. Don't I?

 

[mashdar]

They don't know how many yeast cells there are, and don't decide to not reproduce just 'cuz I pitched more than enough healthy cells. They just do what yeast do.

Based on Kai's results for starter populations, they do seem to have some sense of population density.

 

[oldschool]

I’ve read about this in a few different books or at least it is touched on. I was always under the impression that this is done in a brewery when they don’t have a sufficient way to “rouse” the harvest yeast. Essentially they don’t have a yeast dosing system that adequately disperses the yeast into the cold wort. So they add the pitching about of yeast to a dedicated tanks, then add wort, then mix and/or aerate, then pitch the entire contents to the fermenter. I never read that they avoid aeration of the main wort in this process.
I always pitched chilled starters. Decant leaving the yeast, add in some wort to the flask when I start filling the fermenter giving it some shakes while tinkering with the temp and then pitch when it’s completely dispersed- some strains take a lot of shaking. But then I hit the fermenter with O2 anyway.
That said once I realized that I didn’t have any oxygen so I just repeated the process as usual and didn’t hit the fermenter with anything O2. The fermented out clean and completely like normal but took two extra days or so. Omega west coast 1

 

[Bassman2003]

This is good to hear. I've probably been under-dosing for fear of toxicity but post #18 and this one allay those fears a good deal. I want a DO meter so bad.

This is the one I got. Keep your eyes on Ebay as I found a seller that was selling them new for $120-$180. https://www.vernier.com/product/go-direct-optical-dissolved-oxygen-probe/

Optical is the only way you want to go and it is basically only useful for oxygenation due to the temperature constraints. But that is the most important place to use a DO meter anyway outside of experiments and system testing. This model is in use with others' I know and it is accurate and easy to use with its app.

 

[corncob]

I think being happy with the beer consistently is a good enough reason to not change anything.

The thing I can't wrap my head around is that a colony of yeast that never sees any oxygen shouldn't really be sustainable in theory because it shouldn't be able to reproduce and it doesn't live forever. I assume that typical wort handling is getting SOME oxygen in play.

Exactly. We now have the technology (and the desire) to keep DO in the ppb range throughout. But we're using yeast that adapted in a very different environment. I wonder if we would still be able to keep these old cultures going without the parallel development of microscopes, glycol, and propagation methods. Certainly, we homebrewers would be out in the cold no matter what--I'm thinking about small commercial brewers.

I think about that picture of the open fermentation in wooden vats in the pilsner urquell basement. I bet that Culture is stable and vital as long as they keep brewing with it. But I bet that beer would be all cardboard dull caramel if they sent a bottle to my local store.

I think, as homebrewers, we're trying to do two different things, fundamentally, with yeast. This method gets at that concept.