Aeration of starter, and NOT the wort - discussion.

Ok, so I forgot to aerate my wort but have discovered that this is a strategy used to create a cleaner ferment. As the oxygen is only needed for bulk cell division and not so much for fermentation. Pitching a properly sized starter should be sufficient. Anyone have experience with this?

If you do, do you think you'd be able to use a warmer fermentation regime? My Imperial Stout has been in the high 70's all week. Still bubbling, day 6. If it's estery (Edinburough WLP028) I'm not too worried as the other flavors will be strong to balance. I'm mostly concerned about acetaldehyde.

Anyhow, interested in what others out there have to say on the subject. thanks for the input!

No value to add to your thread. I do like your spirit though! I look forward to hearing how your beer turns out. Please do share it here on HBT. Many myths have been debunked here because a fellow didn't think the world was flat. Or something like that.


Cheers!

Kana

Lies! The world is flat and you must rehydrate your yeast!

I do like this idea though in the OP. I'm interested in the results.

pretty sure o2 and warm fermentation are two very different things. Ive made starters and fermented beer warm when i was a beginner and they tasted like plastic.

@Dan & Hello: http://theflatearthsociety.org/cms/
@poptarts: O2 & temp are related in that, oxygen is not needed for fermentation (only for cell multiplication) and by oxygenating your starter (to GROW yeast) then pitching into a NON oxygenated wort (to ferment) one will have a cleaner beer due to the lack of yeast products produced during the cell division phase.

This cleaner wort may counter the ester production of a warmer fermentation.

As I continue to research, I'm suspecting that this will be the case to some small extent. My biggest issue will be the acetaldehyde (green apple) flavor, which is reportedly able to be cleaned up with time. This one's going to sit for a while.

I just took a gravity (refractometer), but it was from a plugged spigot and is questionable (particles in suspension). Current gravity is 1.065, still day 6. Tastes decent though. Thinking of repitching another, stronger alcohol tolerant yeast, OG was 1.085. Luckily I'm using a spigotted bucket for primary on this one so I can taste and gravity read it as I go with minimal contamination concerns.

jbock,

I see a different situation. The technique you mention (heavy oxygen in the starter, low oxygen in the wort) is a common practice amongst Belgian brewers. The direct outcome of this is an increase in ester production. The increased esters are formed because the yeast have to work without oxygen and are stressed more than if they had a lot of oxygen present. The reason it works so well for the Belgians is because the starter creates enough cells to get through the beer and the practice of temperature ramping through fermentation gives a boost to the fermentation as well.

This approach is the opposite of brewing for a "clean" beer. For a clean beer you would oxygenate the starter and the wort so the yeast never get stressed. Clean meaning low esters in the final product.

Below is the source material regarding not aerating wort...

"If possible, don't! The reason is that it is not the wort that needs the oxygen, it is the yeast. By oxgenating the wort instead of the yeast starter, it will cause an over production of cells due to the excessive oxygen presence. This then leads to the production of unwanted esters and higher alcohols that will compromise beer flavor.

When oxygenating starters, you cannot use pure O2... the reason is that the uptake occurs too fast and without a dissolved O2 meter ($$$), you cannot tell when to stop. The way to properly do this one is to aerate using a high pressure aquarium pump, sterile air filter and a stainless steel aeration stone, all of which are redily available. It is virtually impossible to over-aerate using air, so you will avoid oxygen toxicity problems that will occur if trying to do this with pure oxygen. ", Eric Watson, Beertools.com

Wow, that quote goes against everything I've heard... It's true that esters are formed when yeast are multiplying, but they also throw esters when stressed. If there aren't enough cells in the wort, it is a stressful environment. Also I've only heard about higher alcohols being thrown if the beer ferments too warm. The experts I've heard (jamil, Gordon strong, Chris white, countless professional brewers) all say that oxygenation of the wort is key, especially with bigger beers. Some beers even need multiple doses of oxygen over time. This is all to keep the yeast healthy and to make sure the beer finishes to terminal gravity.

I'm no expert, but that's the first I've heard of someone advocating for no oxygenation.


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Here is a link to a Danstar article on the subject.
http://www.danstaryeast.com/articles/aeration-and-starter-versus-wort

The yeast won't be stressed if they have enough oxygen on-board for the full fermentation. Whether they get that before hitting the wort or after really doesn't matter to the yeast. That's why pitching dry yeast without aerating wort works.

Interesting topic for discussion as it is confusing. Increased in ester production is commonly associated with stressed yeast. Yeast are stressed due to low amounts of nutrients available to reinforce cell walls; budding new cells is stressful; inability to multiply due to poor nutrient environment (including o2), and more I'm sure.

So, it would seem, perhaps simply so, that if you can reduce or eliminate the factors that induce stress, the yeast will produce limited esters.

One thing I've often wondered about is why some yeast are particularly eatery and others are not. It almost seems like a lot of the estery yeasts are more flocculant...perhaps dropping out and leaving a stressful environment for the yeast still in suspension? (too much food stripped of mineral nutrients and o2, and not enough help?). Except Belgian and hefe yeasts, I guess, so this isn't so accurate.

It's all for the same purpose when you boil it down.... temp control, cell count, nutrients, o2....it's all to provide a relatively stress free environment for the yeast. Temp is the easiest thing to control during fermentation. It'd be ideal to have all factors satisfied, such that we could control ester production by changing ferm temps alone (which is pretty much what we do).

The thing to remember that a starter doesn't create ALL the yeast that are needed to ferment the beer- the proper pitching rate (and not overpitching) also allows for yeast reproduction. An overpitched beer will taste 'flat' due to the yeast not reproducing and giving the flavor characteristics as part of that.

I would still aerate the wort, in a properly pitched beer. That would mean less stress for the yeast (esters) as they reproduce.

You absolutely don't want to make all of the yeast for your beer in a starter. No argument there. But, the yeast don't decide to take up oxygen real-time as they are multiplying. They take up available oxygen before they start multiplying (in the case of aerated wort) or before and during the reproductive phase (in the case of an aerated starter). The point being, the yeast are capable of taking on enough excess oxygen in a well aerated starter to go through a healthy fermentation if you pitch at a normal rate.

However..... I think most home brewers tend to underpitch and pay poor attention to yeast health, so aerating your wort is cheap and easy insurance to make sure you have a healthy fermentation. Underpitching AND underaerating would certainly be a recipe for disaster.

jbock,

I do not know your experience level or if you are just throwing things out for the sake of conversation, but a few of your threads here are totally contrary to brewing practice that has been in place for centuries.

You need to aerate wort because boiling for 60-90 minutes takes all of the oxygen out of it. I think what is lacking in the quote you posted was the ability to control how much oxygen to put in the wort. I just purchased a size "E" medical oxygen tank (full) on Craig's list for $20. Purchased a regulator on Ebay for $20. This will let me measure the oxygen for my starters and wort for $40.

I think it is more in terms of under aerating or properly aerating rather than no oxygen at all.

Keep it simple - for "normal" low ester beers, put some oxygen in your starter and put some oxygen in your wort. Your yeast will perform as you want.

boydster said:

You absolutely don't want to make all of the yeast for your beer in a starter.

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Why?


why is growing yeast in the starter instead of the wort any different? do we need the ester produced at the time in our beer? can't we force ester production by bumping the ferm temp? Can't we limit ester production by reducing ferm temp?

I'm not saying you're wrong, I just want someone to explain why.

Weezy said:

Why?


why is growing yeast in the starter instead of the wort any different? do we need the ester produced at the time in our beer? can't we force ester production by bumping the ferm temp? Can't we limit ester production by reducing ferm temp?

I'm not saying you're wrong, I just want someone to explain why.

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It's not that simple. During the reproductive phase, some of the character and flavor of the beer is created, and that is desirable. An overpitched beer, where that doesn't happen, is ok but may be bland and sort of 'flat' tasting, without character. An underpitched beer may exhibit flavors from the stress of that- phenols and esters, for example.

You can get more esters by fermenting too warm, of course- but the flavors from an overpitched, warm fermentation may not be desirable and pleasant.

Yooper, that all sounds like common arguments that we've read a thousand times on here.

But, you're Yooper. I'll assume you're right and that the 'character' you mention are esters/phenols created during the reproduction phase which can't be had any other way. If that's true, ok.

Overpitching? my understanding from JZ comments is that Overpitching is actually uncommon. Specifically, it needs to be an extremely large overpitch to appreciably impact the beer.

The Daystar link is informative, although it often seems the dry yeast shops don't get much respect. We always use the words like the 'yeast uses the oxygen in reproduction'. if that article is accurate, the yeast internalize the o2 and build up their lipids for use in reproduction, where the children take the nutrients with them with successive generations. can't the starter be healthy enough, aerated enough, and big enough of a colony to reproduce appropriately n the worth?

Weezy said:

Yooper, that all sounds like common arguments that we've read a thousand times on here.

But, you're Yooper. I'll assume you're right and that the 'character' you mention are esters/phenols created during the reproduction phase which can't be had any other way. If that's true, ok.

Overpitching? my understanding from JZ comments is that Overpitching is actually uncommon. Specifically, it needs to be an extremely large overpitch to appreciably impact the beer.

The Daystar link is informative, although it often seems the dry yeast shops don't get much respect. We always use the words like the 'yeast uses the oxygen in reproduction'. if that article is accurate, the yeast internalize the o2 and build up their lipids for use in reproduction, where the children take the nutrients with them with successive generations. can't the starter be healthy enough, aerated enough, and big enough of a colony to reproduce appropriately n the worth?

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Yes, overpitching is uncommon and unlikely- but the point is that is the only way to avoid yeast growth and reproduction (and hence the need for oxygen in the wort). I don't use dry yeast as often as some- I may use it once, and then save it in my yeast fridge, so then it's liquid yeast and not dry- so I don't have much experience in using it as dry yeast and I don't have the specifics of not aerating vs aerating when Danstar says it's not needed for dry yeast.

Lots of things happen during the yeast's life stages, from formation of compounds (like diacetyl) and esters to fermentation and then some "clean up" when the yeast even digest some of their own waste products. It's not as simple as folks are trying to make it by leaving it all up to a starter and/or aeration of the wort. Yeast, although simple organisms, do go through a rather complex process.

We understand yeast go through a complex cycle during (and prior, in starters) fermentation. The question at hand is does properly sized and aerated starter contain enough healthy, fortified, yeast capable of doing the job w/o aerated wort. The Danstar link, not only for dry yeast but for starters, seems to say yes.

Nobody understands this well enough to say one way or another, but it may be short sided to say it must be done a certain way.

Yooper said:

Yes, overpitching is uncommon and unlikely- but the point is that is the only way to avoid yeast growth and reproduction (and hence the need for oxygen in the wort).

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You don't need oxygen in the wort for yeast to reproduce. An aerated starter will provide O2 for the yeast to grow in the starter, then once that growth phase is complete (well, really, things are happening concurrently) the additional O2 that the starter is still being exposed to is taken up by the yeast (now in a pitchable-colony) to build a reserve that is then used during the main fermentation. They will reproduce without aerated wort in those circumstances.

Again, though, there are limiting factors at work - how much will your yeast need to reproduce, how much oxygen are they taking on, how sure are you about your initial cell count when you pitch - that make it tough to say with certainty that you met all of the conditions the yeast need for a healthy fermentation in wort that hasn't been aerated. Expensive lab equipment could help with that, but isn't exactly practical at the home brewing scale.

Here are some things I picked up from the Practical Brewing Course at UC Davis:

Yeast require the following:
Energy (sugars)
Nitrogen (amino acids)
Lipid (Needs oxygen for sterol synthesis and denaturing of fatty acids)
Sulfur
Vitamins
Minerals(including zinc)

In the absence of oxygen, yeast is unable to synthesize the unsaturated fatty acids and sterols it needs for its membranes. Oxygen promotes yeast growth, not fermentation. Yeast are classified into four groups based on their oxygen requirement:
Group 1: requires 1/2 air saturation
Group 2: requires air saturation (7.1mg/L, 10P wort at 15C)
Group 3: requires O2 saturation (33.8mg/L)
Group 4: not satisfied even by O2 saturation (not common in brewing yeast)

There is no differentiation between a starter and the finished wort with regard to the oxygen requirement...yeast need it to grow, period.

We tend to focus on viability (live cells), but vitality is just as critical and without oxygen during yeast growth, vitality suffers.

Most breweries use oxygen saturation in the wort prior to pitching, but all of them use some form of oxygen introduction.

Liquid yeast is the predominant yeast used in the brewing industry.

helibrewer said:

Here are some things I picked up from the Practical Brewing Course at UC Davis:

Yeast require the following:
Energy (sugars)
Nitrogen (amino acids)
Lipid (Needs oxygen for sterol synthesis and denaturing of fatty acids)
Sulfur
Vitamins
Minerals(including zinc)

In the absence of oxygen, yeast is unable to synthesize the unsaturated fatty acids and sterols it needs for its membranes. Oxygen promotes yeast growth, not fermentation. Yeast are classified into four groups based on their oxygen requirement:
Group 1: requires 1/2 air saturation
Group 2: requires air saturation (7.1mg/L, 10P wort at 15C)
Group 3: requires O2 saturation (33.8mg/L)
Group 4: not satisfied even by O2 saturation (not common in brewing yeast)

There is no differentiation between a starter and the finished wort with regard to the oxygen requirement...yeast need it to grow, period.

We tend to focus on viability (live cells), but vitality is just as critical and without oxygen during yeast growth, vitality suffers.

Most breweries use oxygen saturation in the wort prior to pitching, but all of them use some form of oxygen introduction.

Liquid yeast is the predominant yeast used in the brewing industry.

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Worth noting along with all of this info is that breweries are often repitching a slurry almost directly from a prior fermentation. That means the yeast has used most, if not all, of the oxygen it took up for the previous brew.

boydster said:

Worth noting along with all of this info is that breweries are often repitching a slurry almost directly from a prior fermentation. That means the yeast has used most, if not all, of the oxygen it took up for the previous brew.

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Also, of course they have used up the oxygen in the starter wort. That is what I was saying. That is why oxygenating a starter does not replace oxygenating the wort.

Yooper said:

Also, of course they have used up the oxygen in the starter wort. That is what I was saying. That is why oxygenating a starter does not replace oxygenating the wort.

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That's not entirely true though. They don't brew beer under constant-aeration conditions like we would do with a starter, the beer would suffer greatly. The yeast need a certain amount of oxygen to ferment the starter - this is how the colony is built up, which we want. If you are aerating your starter, they take up oxygen in excess of what is needed to grow in just the starter, so the yeast is leaving the starter front-end loaded with excess O2 that can be used to ferment the wort. The yeast won't just stop taking up oxygen in the starter because they have a big enough colony, they continue taking it up until they can't take up any more. If you are aerating your starter constantly (like with a stirplate) then the entire colony that you are about to pitch is taking up oxygen even after it has finished dividing, leaving plenty of O2 reserves for it to draw from when it needs to start dividing again once pitched into the wort. There's no "off-switch" or anything to indicate to the yeast when to stop taking up O2, other than its natural limit of how much it can hold in reserve. As it uses up that reserve, if there is more O2 available to it, it will replenish the reserve. Yeast is great at scavenging nutrients, and it will continually be looking for available nutrients that it requires. As you introduce those nutrients, if it can physically take them in, it will, even if it doesn't need them immediately.

To look at it another way. You can supply the yeast in a starter with oxygen that meets one of three conditions.
1) Not enough oxygen to ferment the starter properly
2) Exactly enough oxygen to ferment the starter properly, but no more
3) More than enough oxygen to ferment the starter properly

In cases 1 and 2, your yeast will suffer if you don't introduce oxygen to your wort. In case 3, whether the yeast have enough oxygen in reserve for the full fermentation depends on how much excess O2 the yeast had available to it, your intended pitch rate, and how accurately you know your actual cell count. If you are pitching in excess of .75 million cells per ml per degree P, and you are pitching a starter that had oxygen available to it even after the colony peaked, then the entire colony was able to maximize its on-board O2 reserve and that should be sufficient for a healthy fermentation, just as it would be with dry yeast which has the same benefit of being front-end loaded with the sterols it needs. That's the ideal scenario for someone who is planning not to aerate their wort. The yeast can still reproduce when it hits the wort, because it has already taken up what it needs to form new cell walls for daughter cells.

The Danstar link directly says oxegenating the starter can replace oxygenating the wort. The point is the yeast stock up, lipids are built, fully primed to make babies. They need no more oxygen unless the wort is high gravity and they'd be expected to make more than normal babies. its the same scenario as why dry yeast doesn't need aerated wort. the yeast are fully ready, healthy, with everything they need to bud 2-3 times. This is the same scenario as dry yeast not needing aerated wort. They have everything they need already.

The point Weezy is making a definite strategy used by some famous Belgian beer brands. I read "Brew like a monk" and Classic Styles "Belgian ale" in which both authors confirmed that the path to the interesting Belgian beers is to have a large amount of healthy yeast pitched into under aerated wort.

I plan to try this for my next hefeweizen in hopes of creating more esters. Aeration like many things in brewing is a tool to be used for fine tuning.

At our August brew club meeting, Zech Laughbaum, the microbiologist for Fat Heads Brewery was our guest speaker. He said MANY times essentially: If you're not oxygenating your starters & your wort, you are abusing your yeast. Y'all can do as you please, but imma continue to love on my yeast...


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boydster said:

and you are pitching a starter that had oxygen available to it even after the colony peaked, then the entire colony was able to maximize its on-board O2 reserve and that should be sufficient for a healthy fermentation

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Can you point me to where I can learn more about S. cerevisiae oxygen metabolism under different conditions?

As I understand it oxygen handling is more complex than that and depends in part on growth phase and nutrient availability, with particular importance of oxygen availability during the lag phase for reproductive health and that at other growth stages oxygen is used in other ways.

The yeast don't need oxygen, they need sterols and other lipids, which are taken up from the medium as well...New Belgium did experiments with olive oil in place of aeration and got good performance out of the yeast that way.

The yeast take up and use oxygen to synthesize sterols and lipids (through acetyl CoA) which are then in turn used in subsequent growth stages. They don't take up oxygen and then carry it around as an "oxygen reserve", and there certainly are regulatory mechanisms for oxygen metabolism.

I'm also not sure dry yeast doesn't benefit from oxygenated wort. Just like with rehydrating, though the performance may be acceptable without it, it doesn't mean its optimal.

1.085 needs oxygen or a massive starter. I'm guessing you used a starter sized with further growth in mind. That yeast is way over stressed.

Wow, I hit a home-run with this question. Thanks everyone for chiming in, so many great comments and insights.

For what it's worth, I'm planning on repitching a fresh starter (maybe WLP90 SD Super). Thinking of continuing down this interesting experiment and NOT aerting my wort. I'll keep you posted on how it progresses.

The original starter was a WLP28 vile pitched into a 1 gallon, mild-ale wort (1 of 5, each on a different yeast). With about an inch of slurry, I decanted and pitched into a 3 gallon wort. I don't believe I took a gravity on it as I didn't foresee needing one with a starter. In hindsight I wish I had.

Re: cjgenever's comment: Is it truly a "stress" when under-pitching?
Re: Bassman's comment: You can't measure oxygen for your starter with a tank and regulator meaningfully. You need a dissolved oxygen meter.

Sure a meter is fine, but the nature of the original comment was to not aerate at all because one can't measure exactly. Well, I don't see homebrewing to be that exact of a science. I have been using the little red tanks with a aeration stone for 1 minute at a time for years with many great fermentations. I just switched to a real regulator to try and pursue some strategies as this thread highlights.

Regarding your strategy of not adding any oxygen to your wort, I would add a little. In both the Belgian brewing books, the brewers they spent time with under-aerated on purpose, but there was some oxygen involved in the process. Especially with high gravity brewing.

I've got nothing to contribute other than thanks for the knowledge gained by reading this debate. I read every post, and there's some interesting arguments here. I'd like to see your results Jbock.

If you did a one gallon starter with intermittent shaking you should have had just the right amount (or a little more) of yeast for a three gal high gravity brew.

Yes, underpitching is stressful in the sense that the yeast are too involved with reproduction. The only reproduction you want is enough to flavor the beer. More than that leads to poor attenuation or stalled ferments.

Ew, an imperial stout in the high 70s??? Esters aside I'd worry about some serious fusels that would make it taste like 25% ABV.

TastyAdventure said:

Ew, an imperial stout in the high 70s??? Esters aside I'd worry about some serious fusels that would make it taste like 25% ABV.

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boydster said:

That's why pitching dry yeast without aerating wort works.

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I know the Danstar FAQ says you can do this, but anecdotally, the only time I ever tried this, I ended up with a massive banana-bomb. Had to dump the batch, it was undrinkable. I now aerate/oxygenate every batch, regardless of whether I'm pitching (rehydrated) dry yeast or a decanted liquid yeast starter.

How has this thread gotten this far without someone suggesting Olive Oil? LOL...I oxygenate my starters and my wort. The preferred level of oxygenation at the commercial level is impossible to achieve at home without pure O2, so I'm not going to reinvent the wheel.

There are always threads challenging conventional wisdom here and it's healthy, but sometimes I wonder why people don't just throw some grain into their mouths with warm water and a swig of yeast. Hey..it'll be beer!

Yeah, I aerate with filtered air through a stone. I also add a touch of evoo at the end of boil for high gravity. Cheap, easy, very effective. My yeast are always happy little workers with this setup.

Couple basic questions to help me follow along.

1. How long to yeast cells live (days, weeks, months)?
2. All organisms live to evolve and reproduce. So how do yeast cell generations after the original pitch grow and reproduce in a oxygen void environment?
3. How big of a starter would it take to ferment a beer and not get any reproduction from the yeast (example: 1qt slurry at start and 1qt slurry at the end)?