Did I Over-aerate?

[GHBWNY]

I've been wondering for months why two recent back-to-back brews ended up (and still do) taste fusel-y. The general consensus on here is too warm a ferm temp. While that would have been my guess, too, it was definitely not the case with either of these two. I read an article this week called, "The Biochemistry of Yeast: Debunking the Myth of Yeast Respiration and Putting Oxygen in Its Proper Place", by Tracy Aquilla (@MoreBeer website) that gave me new food for thought, especially this:

"Another thing to remember is that the oxygen 'requirement' (that is, the aeration needs) of brewers’ yeast is strain-dependent and that what might be adequate for one strain could be insufficient or excessive for another. For this reason, it is probably best to be familiar with your yeast, to know when aeration is necessary, and to aerate the wort only to saturation (about 8 ppm of oxygen for most worts) upon pitching and then to stop. Keep in mind also that oxygen is beneficial even at levels well below saturation, so aerating even a little will actually help a lot."

Plus... "In certain styles of beer in which metabolic byproducts of yeast growth (such as VDKs, oxo-acids, fusel alcohols, and their derivative esters) are undesirable, it is even preferable not to aerate the cold wort. Avoiding aeration may be particularly desirable when fermenting high-gravity worts that will naturally result in the formation of more esters."

It's interesting that I decided with these two beers to really, REALLY aerate them. While I don't have a way to measure ppm O2, I wouldn't have thought it possible to over-aerate via my "rock-n-slosh-on-the lap-for 2 minutes" method (had always heard you cannot over-aerate by hand, and that you should try for a 2-inch layer of foam on top). But could I have? At least for those styles? Is there a chart that recommends ppm O2-per-style?

I'm going to recommend to myself not to aerate as vigorously with the next batch and see what happens.

 

[TheMadKing]

That flies in the face of a ton of empirical evidence that demonstrates that increased oxygen results in increased cell count. In a lab designed to multiply cells in the most efficient manner, they bubble O2 through a growth medium on a stir plate... I don't know what kind of study she has done, or what evidence she is presenting, but that's pretty much the opposite of what most microbiologists believe. O2 needs are thought to be growth dependent, not strain dependent. Basically, the more generations of yeast needed to reach saturation in your beer, the more oxygen needed to manufacture glycogen for healthy cell walls.

I'm skeptical to say the least.

 

[sky4meplease]

If you were to over oxygenate it would likely be with pure oxygen.
I experimented measuring DO in wort a couple years ago and could not get over 4ppm without pure oxygen.
Is this all grain or extract brewing?

 

[rkzi]

Scott Janish has a blog post about factors influencing ester and fusel production. The consensus seems to be that aeration decreases esters, while it does not affect fusel levels that much. This does not seem to apply for open fermentations, where the yeast has constant access to air but is still stated to produce higher amount of esters. In this case the effect of top pressure might play a larger role than oxygen.

 

[GHBWNY]

That flies in the face of a ton of empirical evidence that demonstrates that increased oxygen results in increased cell count. I'm skeptical to say the least.

I get that. It's what I was led to believe since beginning brewing (not that I actually checked out the empirical evidence to back up my beliefs). This article is not in as of itself "empirical evidence" (although having done some research myself, it certainly has the tone of that which is based upon empirical evidence), nor does the author imply that oxygen is not beneficial to fermentation --- just not needed.

My take away from this article is that brewer's yeast is unique in that it can reproduce through two different venues: respiration (aerobic) and fermentation (anaerobic). The author's point is that yeast DO NOT REQUIRE oxygen in order to survive. To wit,

"...yeast does not really require oxygen. Most animals will die after several minutes without oxygen; brewers’ yeast does not require it at all in the presence of sufficient nutrients, because it doesn’t need to respire. Saccharomyces species of yeast, in fact, are exceptional in that they represent the few rare species of yeast that have absolutely no requirement for oxygen and can grow under strict anaerobic conditions (2). (Most other yeasts, even those that can ferment sugar [for example, Brettanomyces], cannot grow without oxygen.) Yet the brewing literature and all brewing experience point to the need for oxygen for healthy fermentations."

Simply put, fermentation, being a process wherein the yeast choose feasting upon the overwhelming abundance of available sugar over consuming oxygen in order to propagate, means that fermentation does not "require" oxygen in order to take place. As for the role of oxygen in fermentation, the author says this:

"It is well-documented that yeast uses oxygen whenever it is available, even during fermentation, and yeast cells rapidly absorb essentially all of the oxygen made available to them. Yeast, however, will use the overwhelming majority (if not all) of the available oxygen in biosynthetic reactions, not for respiration.*

The dissolved oxygen levels in wort drop from saturation to near zero very quickly after pitching yeast, usually within 30 minutes under ideal conditions, because yeast absorbs the oxygen for eventual membrane biosynthesis. The oxygen enables the cells to grow much faster and to reach a higher cell density."

So, the article is not dismissing the importance of the role of oxygen in the fermentation process, but simply stating that yeast "do not require" oxygen in order to survive. Which brings me back to my original question: Did I add too much extra, unneeded, harmful? O2 to my wort for the style/type of beer I brewed? While 10-12 ppm of added O2 to cooled wort is the rule of thumb, since my aeration process is arbitrary at best, am I possibly doing more harm than good? Would it be better for now (or until I have a way of actually measuring ppm) to err in favor of NOT aerating at all, or very little, or continue to take the chance that over-aerating might be a disadvantageous possibility?

 

[SmokeyMcBong]

.Avoiding aeration may be particularly desirable when fermenting high-gravity worts

I have a hard time swallowing that line right there....

 

[kh54s10]

I don't know about the effects of too much aeration but I am fairly sure that you can not achieve that by "rock and slosh". Especially for only 2 minutes. I have read that no matter how long you slosh you will only get you so much, and that amount is less than generally recommended for most brews.

 

[TheMadKing]

I get that. It's what I was led to believe since beginning brewing (not that I actually checked out the empirical evidence to back up my beliefs). This article is not in as of itself "empirical evidence" (although having done some research myself, it certainly has the tone of that which is based upon empirical evidence), nor does the author imply that oxygen is not beneficial to fermentation --- just not needed.

My take away from this article is that brewer's yeast is unique in that it can reproduce through two different venues: respiration (aerobic) and fermentation (anaerobic). The author's point is that yeast DO NOT REQUIRE oxygen in order to survive. To wit,

"...yeast does not really require oxygen. Most animals will die after several minutes without oxygen; brewers’ yeast does not require it at all in the presence of sufficient nutrients, because it doesn’t need to respire. Saccharomyces species of yeast, in fact, are exceptional in that they represent the few rare species of yeast that have absolutely no requirement for oxygen and can grow under strict anaerobic conditions (2). (Most other yeasts, even those that can ferment sugar [for example, Brettanomyces], cannot grow without oxygen.) Yet the brewing literature and all brewing experience point to the need for oxygen for healthy fermentations."

Simply put, fermentation, being a process wherein the yeast choose feasting upon the overwhelming abundance of available sugar over consuming oxygen in order to propagate, means that fermentation does not "require" oxygen in order to take place. As for the role of oxygen in fermentation, the author says this:

"It is well-documented that yeast uses oxygen whenever it is available, even during fermentation, and yeast cells rapidly absorb essentially all of the oxygen made available to them. Yeast, however, will use the overwhelming majority (if not all) of the available oxygen in biosynthetic reactions, not for respiration.*

The dissolved oxygen levels in wort drop from saturation to near zero very quickly after pitching yeast, usually within 30 minutes under ideal conditions, because yeast absorbs the oxygen for eventual membrane biosynthesis. The oxygen enables the cells to grow much faster and to reach a higher cell density."

So, the article is not dismissing the importance of the role of oxygen in the fermentation process, but simply stating that yeast "do not require" oxygen in order to survive. Which brings me back to my original question: Did I add too much extra, unneeded, harmful? O2 to my wort for the style/type of beer I brewed? While 10-12 ppm of added O2 to cooled wort is the rule of thumb, since my aeration process is arbitrary at best, am I possibly doing more harm than good? Would it be better for now (or until I have a way of actually measuring ppm) to err in favor of NOT aerating at all, or very little, or continue to take the chance that over-aerating might be a disadvantageous possibility?

It's very unlikely that you are over oxygenating.

From what you've quoted, she's drawing a distinction between the actual production of alcohol (anaerobic respiration) and the growth phase of yeast, which is an essential part of beer production.

Unless you are pitching the exact number of cells that your beer needs to ferment, (no lag phase is required, and no new cells need to be produced), oxygen is 100% necessary. She even says this, in the quotes you've provided, that oxygen is needed for the multiplication process.

That's like saying you don't need eggs to make an omelette because eggs play no role in the cooking process.

Just because oxygen is not needed to produce alcohol, it is absolutely needed for producing healthy cell walls during cell budding, which is necessary for reaching a proper cell count, which is necessary to ensure that there are enough healthy cells to metabolize the sugars in your beer without producing esters and fusels.

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

I read the whole article, and what she's saying is basically exactly what we all know, and what I just said, that oxygen is used to produce healthy cell walls as the cells multiply toward saturation, and that oxygen is beneficial to most home brewers. She also contradicts herself several times throughout the article, and plays devils advocate to her own arguments resulting in no net assertions or knowledge gained. Overall, I don't think this is well written even if the science is sound. I especially don't like the readers ego stroking in the introduction designed to empower the reader into believing that they are now privy to secret science information that only "really smart people" know.

@ajdelange I noted that you had input on this article, and I would be really curious to hear your thoughts.

 

[GHBWNY]

It's very unlikely that you are over oxygenating.

From what you've quoted, she's drawing a distinction between the actual production of alcohol (anaerobic respiration) and the growth phase of yeast, which is an essential part of beer production.

Unless you are pitching the exact number of cells that your beer needs to ferment, (no lag phase is required, and no new cells need to be produced), oxygen is 100% necessary. She even says this, in the quotes you've provided, that oxygen is needed for the multiplication process.

That's like saying you don't need eggs to make an omelette because eggs play no role in the cooking process.

Just because oxygen is not needed to produce alcohol, it is absolutely needed for producing healthy cell walls during cell budding, which is necessary for reaching a proper cell count, which is necessary to ensure that there are enough healthy cells to metabolize the sugars in your beer without producing esters and fusels.

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

I read the whole article, and what she's saying is basically exactly what we all know, and what I just said, that oxygen is used to produce healthy cell walls as the cells multiply toward saturation, and that oxygen is beneficial to most home brewers. She also contradicts herself several times throughout the article, and plays devils advocate to her own arguments resulting in no net assertions or knowledge gained. Overall, I don't think this is well written even if the science is sound. I especially don't like the readers ego stroking in the introduction designed to empower the reader into believing that they are now privy to secret science information that only "really smart people" know.

@ajdelange I noted that you had input on this article, and I would be really curious to hear your thoughts.

I truly appreciate your perspective and feedback. And I don't disagree. It reads on the one hand as a kind of semantic 'near-myth', while on the other, a convincing, albeit scientifically-arguable proposition. I, too, am enough of a skeptic to not swallow everything I read H, L & S, which is why I brought this to the attention of the more-informed members of the forum, esp. in light of my concern over fusel production as it may/may not relate to over-aeration (if such a thing exists?)

 

[sky4meplease]

For the amount of O2 the OP dissolved into the wort with an agitation method it is doubtful the cause for high detectable fusel alcohols.
I would look at pitch rates and PH as a starting point for the cause especially if fermentation temperatures have been ruled out.

 

[Weezy]

Quite simply, and as has been stated already, you'll never over aerate a wort by rocking a carboy. So the answer is clearly no. Excess oxygen isn't causing your hot alcohol production. My guess is stressed yeast or poor temperature control. You may have under aerated.

You say temps were fine. Are you using a temperature controlled environment like a bar fridge with a temp controller or did you just push it in the corner of the closet?

The detailed discussion of the life cycle of sacc is fine and fun, but it might be a bit far in the weeds for the problem at hand.

 

[Kent88]

My take away from this article is that brewer's yeast is unique in that it can reproduce through two different venues: respiration (aerobic) and fermentation (anaerobic).

They are not unique in this, there are other microbes that also do this. (edit: if you're picky, you could claim a difference between fermentation and anerobic respiration)

I want to say that some microbes in the digestive tract of ruminants also undergo anaerobic respiration. I think even people who are enduring grueling physical challenges where they can't possibly be getting enough oxygen have something interesting happening in their muscles that ends up in a little lactic acid production.

A quick search turned up this. KhanAcademy is good with math, at least, maybe they've done well with cellular biology.

I would be beyond surprised if you over-aerated just by shaking the fermenter.

I'm going to stick with using my "aquarium-style" aerator. From what I've gleaned from brulosophy's aeration experiments (you might find this one particularly interesting) along with C. White and Jamil Z's Yeast book, I believe I will get good results from using that device and, in high gravity beers, adding an extra shot of air between 12 and 18 hours. I do finally have a high-gravity test subject.

I think (again, gleaning info from others, very little first hand experience with this) where people get in trouble is thinking they can compensate for low yeast pitching rate with increased oxygenation.

 

[DurtyChemist]

You say temps were fine. Are you using a temperature controlled environment like a bar fridge with a temp controller or did you just push it in the corner of the closet?

This. Are you controlling fermentation temperature within a degree or two OR are you pitching yeast and letting it sit at ambient temperatures? If you are controlling temperature how are you controlling it? Mini fridge and a digital controller? Cool Brew Bag? T-Shirt Trick?

 

[GHBWNY]

This. Are you controlling fermentation temperature within a degree or two OR are you pitching yeast and letting it sit at ambient temperatures? If you are controlling temperature how are you controlling it? Mini fridge and a digital controller? Cool Brew Bag? T-Shirt Trick?

As for ferm temp control itself, I'm all for it and I realize mine could always be better. My Brew Year's Resolution is getting a mini-fridge (already have the STC-1000) and making a ferm-control chamber. But for the time being, my "ferm temperature control" has consisted of amb temp control + swamp cooler when necessary, and it has so far worked to keep the fermenter at ~62-64F (amb.) for 2-3 weeks. You might be thinking, "but he doesn't know about exothermic reaction!" Yeah, I do. That said, my understanding is that fusels are produced from "too warm a ferm temp", which by my interpretation (and correct me if I'm wrong), is too high a ferm temp for the entire fermentation period, E-R notwithstanding. I could understand fusels in the finished product if the amb. temp for the two batches in question had been at a steady, say ~70-80F for 2-3 weeks. But over 3 years of brewing under these conditions, I've not had a problem with fusel production. Although I've never measured the [progress of] internal fermentation temp over an extended period, I would be skeptical in the case of these two "fusel" batches that a temporary temperature variation due to E-R might result in an entire 5-gallon batch being warm enough long enough to create fusels. But I could be wrong.

 

[kh54s10]

It is my understanding that fusels can be created by high fermentation temperatures for a fairly short time. I would think at least 24 hours though. The most critical time being at high krausen, or in other words, the most active portion of the fermentation.

 

[sky4meplease]

As for ferm temp control itself, I'm all for it and I realize mine could always be better. My Brew Year's Resolution is getting a mini-fridge (already have the STC-1000) and making a ferm-control chamber. But for the time being, my "ferm temperature control" has consisted of amb temp control + swamp cooler when necessary, and it has so far worked to keep the fermenter at ~62-64F (amb.) for 2-3 weeks. You might be thinking, "but he doesn't know about exothermic reaction!" Yeah, I do. That said, my understanding is that fusels are produced from "too warm a ferm temp", which by my interpretation (and correct me if I'm wrong), is too high a ferm temp for the entire fermentation period, E-R notwithstanding. I could understand fusels in the finished product if the amb. temp for the two batches in question had been at a steady, say ~70-80F for 2-3 weeks. But over 3 years of brewing under these conditions, I've not had a problem with fusel production. Although I've never measured the [progress of] internal fermentation temp over an extended period, I would be skeptical in the case of these two "fusel" batches that a temporary temperature variation due to E-R might result in an entire 5-gallon batch being warm enough long enough to create fusels. But I could be wrong.

If you never had a problem before then what changed?
Beer style? (Much lighter or darker than previous beers)
ABV? (Higher or lower than usual)
Yeast? (Strain, pitch rates, harvested or fresh)
Water (Change in source)
Sanitation
PH (Do you have a way to check before and after fermentation)

If you don't think it is fermentation temperature and no one seems to think you over oxygenated then let's move on to other possible causes.

 

[madscientist451]

I've been wondering for months why two recent back-to-back brews ended up (and still do) taste fusel-y. The general consensus on here is too warm a ferm temp. While that would have been my guess, too, it was definitely not the case with either of these two.

If you don't have any fermentation temperature control, I would suggest changing that before looking at any other variable if you are perceiving flavor problems in your beer.

There have been several Brulosopy experiments on aeration. Here's the one where they compared a 3 minute shake to no shake at all:

http://brulosophy.com/2015/05/25/wort-aeration-pt-1-shaken-vs-nothing-exbeeriment-results/

 

[505-Brewer]

As for ferm temp control itself, I'm all for it and I realize mine could always be better. My Brew Year's Resolution is getting a mini-fridge (already have the STC-1000) and making a ferm-control chamber. But for the time being, my "ferm temperature control" has consisted of amb temp control + swamp cooler when necessary, and it has so far worked to keep the fermenter at ~62-64F (amb.) for 2-3 weeks. You might be thinking, "but he doesn't know about exothermic reaction!" Yeah, I do. That said, my understanding is that fusels are produced from "too warm a ferm temp", which by my interpretation (and correct me if I'm wrong), is too high a ferm temp for the entire fermentation period, E-R notwithstanding. I could understand fusels in the finished product if the amb. temp for the two batches in question had been at a steady, say ~70-80F for 2-3 weeks. But over 3 years of brewing under these conditions, I've not had a problem with fusel production. Although I've never measured the [progress of] internal fermentation temp over an extended period, I would be skeptical in the case of these two "fusel" batches that a temporary temperature variation due to E-R might result in an entire 5-gallon batch being warm enough long enough to create fusels. But I could be wrong.

As others have said you most certainly did not add too much O2. Its quite difficult to do this even with pure O2.

1 - how are you monitoring the temperature of your fermentation? You say your controlling ambient but wort inside a carboy can easily go way up do you know the temp of the wort by measuring it directly? If so your only guessing.

2 - what kind of yeast and how are you pitching it ?

3 - if this is new then something has changed. Bigger beers? New process ?

Hope you get it solved. Fusel ruin a beer and generally dont age out.
Good luck!

 

[GHBWNY]

As others have said you most certainly did not add too much O2. Its quite difficult to do this even with pure O2.

1 - how are you monitoring the temperature of your fermentation? You say your controlling ambient but wort inside a carboy can easily go way up do you know the temp of the wort by measuring it directly? If so your only guessing.

2 - what kind of yeast and how are you pitching it ?

3 - if this is new then something has changed. Bigger beers? New process ?

Hope you get it solved. Fusel ruin a beer and generally dont age out.
Good luck!

1. I monitor the temp of my fermentation by monitoring the ambient temp surrounding the fermenter. As I stated previously, I don't have an "internal" temperature control vehicle for the fermenter, but will be building a ferm chamber w/STC-1000 soon. As needed, I use a swamp cooler. My cellar, where a SMaSH IPA is fermenting right now, is at a very steady 62F amb and will be throughout this fermentation. Even with exothermic reaction, there should be no plausible reason for this ferm (or those in the past) to get too warm.

2. Yeast naturally varies with brew. I haven't done a starter yet, so I use fresh dry rehydrated. I cool and mechanically aerate wort, pitch rehydrated yeast and give it a gentle stir.

3. In general, nothing new in the process.