No Wort Aeration, Pitching Dry Yeast Theory

[SJW]

I have been doing a lot of research on Not aerating the wort when pitching dry yeast as recomendend by the Danstar website. The question is asked half way down the page.
http://www.danstaryeast.com/faq.html

Also I found this on Youtube, very interesting.


The only time yeast need oxygen is to reproduce. Dont packets of dry yeast supply you with all the yeast you need? And I have heard dry yeast doesnt need nearly as much oxygen as liquid yeast. So what's the point of this aerating crap with dry yeast? My theory is that yeast are needlessly reproducing when they should be getting to the good stuff, making alcohol. I realize this goes totally against what we have all heard and read but I think it is something to take into consideration and I am going to test this theory on my next batch. I will let you know how it turns out.

Steve

 

[Phrak]

Interesting theory Steve. I'm sorry I can't offer any technical insights into this topic, but it will be interesting to watch the debate

Maybe ping Jamil an email and see if he's got any thoughts on the topic?

Tim

 

[Ross]

Steve,

Glad to see i inspired you into a little research & it bears out my thoughts/findings



cheers Ross

 

[Jazzafish]

I have been doing a lot of research on Not aerating the wort when pitching dry yeast as recomendend by the Danstar website. The question is asked half way down the page.
http://www.danstaryeast.com/faq.html

Also I found this on Youtube, very interesting.


The only time yeast need oxygen is to reproduce. Dont packets of dry yeast supply you with all the yeast you need? And I have heard dry yeast doesnt need nearly as much oxygen as liquid yeast. So what's the point of this aerating crap with dry yeast? My theory is that yeast are needlessly reproducing when they should be getting to the good stuff, making alcohol. I realize this goes totally against what we have all heard and read but I think it is something to take into consideration and I am going to test this theory on my next batch. I will let you know how it turns out.

Steve

The yeast still reproduces. Think about it, you are only putting in say 14g per packet... but are left with a whole slurry after fermentation, plus the yeast in suspension.

When you test this theory, please split the batch into two side by side fermentations... and pay attention to the following, as I believe they will be areas affected:

Grams of yeast per litre of wort pitched
Lag Time of fermentation
Temperature of fermentation
Duration of fermentation
Final Gravity of beer
Taste of beer (comparison)

Cheers,
Jarrad

 

[Stuster]

One thing to consider is that higher levels of oxygen from aeration will lead to the yeast producing lower ester levels. So it depends on what you are aiming for. You might want to aerate well with dry lager yeast, but not bother with the dry wheat beer yeast. That's the theory anyway and it'd be good to see what happens in a homebrew situation.

 

[tdh]

Found this on the Lallemand site -

AERATION AND STARTER VERSUS WORT
Can you please comment on the strategy of trying to aerate/oxygenate the yeast while they are in a STARTER rather than aerating the wort itself. (Please let me abuse the language and science a bit and just say that yeast need "a big swallow of oxygen" before they ferment beer.)

I understand that this is exactly your strategy in the production of dry yeast--i.e. dry yeast can be pitched into unaerated wort because they have already taken their big swallow of oxygen. How feasible is it for a homebrewer to grow up a starter in similar fashion? Is continuous aeration of the starter required? A stir plate?

If I have no stir plate, and no gas transfer equipment of any kind, is there a practical procedure I can follow to grow yeast whose oxygen requirements are already met? Letting air into the starter jug and shaking it, repeating this over several days, etc? Any temperature dependency? Any minerals or nutrients I can add to the starter to increase the yeast's efficiency at storing up oxygen-related compounds? Thank you for sharing your expertise.

- Matt


RESPONSES:

Yeast need a trace amount of oxygen in an anaerobic fermentation such as brewing to produce lipids in the cell wall. With out O2 the cell cannot metabolize the squalene to the next step which is a lipid. The lipids make the cell wall elastic and fluid. This allows the mother cell to produce babies, buds, in the early part of the fermentation and keeps the cell wall fluid as the alcohol level increases. With out lipids the cell wall becomes leathery and prevents bud from being formed at the beginning of the fermentation and slows down the sugar from transporting into the cell and prevents the alcohol from transporting out of the cell near the end of the fermentation. The alcohol level builds up inside the cell and becomes toxic then deadly.

Lallemand packs the maximum amount of lipids into the cell wall that is possible during the aerobic production of the yeast at the factory. When you inoculate this yeast into a starter or into the mash, the yeast can double about three time before it runs out of lipids and the growth will stop. There is about 5% lipids in the dry yeast.

In a very general view:

At each doubling it will split the lipids with out making more lipids (no O2). The first split leaves 2.5% for each daughter cell. The second split leaves 1.25% for each daughter cell. The next split leaves 0.63%. This is the low level that stops yeast multiplication. Unless you add O2 the reproduction will stop.

When you produce 3-5% alcohol beer this is no problem. It is when you produce higher alcohol beer or inoculate at a lower rate, that you need to add O2 to produce more yeast and for alcohol tolerance near the end of fermentation. You definitely need added O2 when you reuse the yeast for the next inoculum.

If you prepare a starter culture you will need added O2. in the starter and perhaps in the main mash as a precaution. You will need to follow the precautions as mentioned above. If the mash is designed to produce 3-5% alcohol you may not need added O2. Brewing above that needs added O2.

Regarding your comment about growing your own yeast that will not need added O2 in the fermenter; The Lallemand yeast factory grows yeast under a different metabolic pathway than you will have in your starter culture. We feed the media to the aerobic fermentation at a rate that will keep the sugar levels below 0.2% at all times to maintain the Pasteur Effect. This builds cell mass with minimum to no alcohol production. As the sugar level rises above 0.2% the Crabtree Effect begins and no matter how much air you feed the fermentation, alcohol + CO2 are the main by-products. Your starter culture will have a much higher level of sugar. You will produce some cell mass but mostly alcohol and CO2 no matter how much air you add by stirrer or bubbles.

Dr. Clayton Cone


tdh

 

[Thirsty Boy]

Its my understanding (mainly from Jamil, but also from a few other sources) that the best, most consistent flavour profile in a beer is produced when the yeast have to double 4 times in order to reach the correct cell density for the wort they are in. This may or may not be correct, but assuming it is...... then according to the answer above from Dr Cone, the dried yeast can only really double 3 times before it runs out of lipids... unless you add O2.

So without 02: Either you are pitching too much yeast into a beer, and it reaches the right cell density before it runs out of puff, but also before it has doubled 4 times - giving you a sub optimal result flavour wise OR you are pitching less than or the right amount of yeast into the beer, but it cannot reproduce enough times to reach the optimal cell density, and you might have trouble with under attenuation or stressed yeast off flavours.

Whereas if you do add 02: you can pitch the right amount of yeast to get optimal cell density after 4 rounds of the yeast doubling and they can do it because they can manufacture some lipids along the way. As a bonus they yeast will be healthy and robust and should do their job without producing any nasty flavours. They will also be in decent enough shape so that you could harvest some yeast to re-pitch into your next brew.

It might be right or wrong, but thats the way I think about it, and the way I treat my wort follows from there.

Thirsty

 

[SJW]

The yeast still reproduces. Think about it, you are only putting in say 14g per packet... but are left with a whole slurry after fermentation, plus the yeast in suspension.

Interesting Jarrad, but from the Danstar site they say the yeast accumulates sufficient amounts of unsaturated fatty acids and sterols to produce enough biomass in the first stage of fermentation.
I think the only way to reslove this is to try it. And the fealing I a getting is Ross uses this method or has used it and it works.

No, there is no need to aerate the wort but it does not harm the yeast either. During its aerobic production, dry yeast accumulates sufficient amounts of unsaturated fatty acids and sterols to produce enough biomass in the first stage of fermentation. The only reason to aerate the wort when using wet yeast is to provide the yeast with oxygen so that it can produce sterols and unsaturated fatty acids which are important parts of the cell membrane and therefore essential for biomass production.

 

[matti]

Whether you pitch the yeast dry or rehydrate it will not matter that much.
But without getting in to the science of yeast it is advisable but not neccesary to aerate the wort.
The reason above should be enough explanation.

(Pitching dry will kill some yeast and to boost yeast growth you need a wee bit extra O2.)

Providing you're brewing practices are sound, SJW, I very much doubt that that you'd notice the difference in the final brew.

This yeast talk should be left to those who intend to getting their "repoducibility factor" as close to 1 as possible.

There is another way to get that factor of reproducibility down.
Make larger batches. ^_^

 

[neonmeate]

the anti-aeration theory was propounded here a couple of years ago:
http://www.beertools.com/html/articles.php?view=245
http://www.beertools.com/html/articles.php?view=251

now, i very rarely use dried yeast, and obviously feeding a starter o2 in the way that this guy describes is quite different to just throwing in the yeast packet. i can't be bothered doing that with my starters, so my current procedure is:
when i pitch a starter from liquid yeast, or make a beer with high gravity, i aerate.
when i repitch a heap of slurry, like most of a cake, i dont aerate. (provided the yeast isnt tired out from lots of generations or a high-grav fermentation)

 

[kenworthy]

intersting and good luck with the experiment something similar happened to me unintentionaly finished my brew ,bit pissy by that stage forgot to aerate the wort added my stater yeast to it ,next day realized what I done but found my brew was fermenting normally that had me wondering beer came out fine.Oh yeah I used dry yeast

 

[Thirsty Boy]

Is it perhaps merely a matter of playing it safe??

You might be more than able to get away with not aerating, or with pitching more yeast than optimum... but it might give you a result that is less than you were looking for - on the other hand, I haven't seen an argument that aerating your wort (in the correct way) can actually do the beer any harm.

So for the minimal effort involved, you take that area of concern out of your brewing. Depends on how much effort you are willing ot go to and whether you think the "safe" factor is worth it.

I do, but I am also on a quest for that reproducibility factor of 1 ..... its about 1:15 atm, but I'm working on it

 

[SJW]

So for the minimal effort involved, you take that area of concern out of your brewing. Depends on how much effort you are willing ot go to and whether you think the "safe" factor is worth it.

Well said, and good point!

 

[Screwtop]

My last two experiments using rehydrated S-189 in two batches (one oxygenated prior to pitching and one not) produced the same results both times (4 batches). The wort which was oxygenated to 12ppm had a longer lag time and took 4 days longer to ferment to a stable gravity, both achieved the same rate of AA% in both tests, taste tests to follow. One of the earlier oxygenated batches is on tap and exhibits Acetyl but that could be due to early filtering and not allowing time for the yeast to clean up.

 

[underback]

Intentional or not, most of us would be introducing some O2 into our worts simply by the transfer to fermenter. Probably enough for the dry yeast to have an adequate supply for the task.

Cheers

 

[Darren]

Intentional or not, most of us would be introducing some O2 into our worts simply by the transfer to fermenter. Probably enough for the dry yeast to have an adequate supply for the task.

Cheers

Thats the way I see it. Again many of you are reading too much into yeast O2 requirements at the HB level (<100 litres).


cheers

Darren

 

[Screwtop]

Intentional or not, most of us would be introducing some O2 into our worts simply by the transfer to fermenter. Probably enough for the dry yeast to have an adequate supply for the task.

Cheers

That's what I thought, although I don't splash the wort around much, after chilling then overnight in the ferm fridge to get it down to 9C



Zero on the DO Meter

After a 25 second burst of oxygen via a .5 micron ss diffuser.

 

[SJW]

Thats the way I see it. Again many of you are reading too much into yeast O2 requirements at the HB level (<100 litres).


cheers

Darren

I agree with Darren only because I think he is correct. I pitched a S-189 yesterday into a AG wort that was chill to 50 in the kettle then tranfered via pvc hose and no splash to the fermenter, then chilled to 12 in the fermentation fridge o/night, then I just tipped the yeast in on top and did not even stir in, and I had active fermentation quicker than if I had gone to all the troble of airating. I would of bet my left nut that this was not going to fire up!

Steve

 

[Darren]

Screwie,

What is optimal DO level for yeast in beer?

cheers

Darren

 

[tangent]

I agree with Darren only because I think he is correct.

hahaha as opposed to "I agree with Darren because he looks good in high heels."