Pressuring Yeast

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Pressuring Yeast

Postby hoochlover » Sat Oct 10, 2015 1:05 pm

Sorry if this is the wrong forum for this question. Has anyone here ever experimented with different types of airlocks on their fermenters? After doing a lot of trial runs I noticed that if I close the fermenter completely and let pressure build, then release it, it seems to give more effect in regards to releasing the CO2 bubbles. A bit like taking the lid off a shaken up coke bottle. Of course it could just be the fact you see a lot more and there is not much actual difference. Why would this matter? Well the CO2 increases the acidity of the wash slowing the ethanol production by some percentage. It also increases the amount of time needed for settling. Having a stir plate in your fermenter would be the most productive way to do this but I am looking for a cheaper/macgyver type solution to it.

I'd like to have some sort of airlock which lets pressure build up to a certain amount, and then releases it back to atmospheric pressure. My first thought is having a fatter/longer airlock tube, if the CO2 has to push more water out of the way the pressure should be higher. But I think this won't release it back to atmospheric pressure and therefore not get the result I want. It would probably have a bigger pressure differential than the standard tiny airlocks though so it may be better than nothing. Is there some device which can do this? Has anyone experimented with airlocks and noticed any difference?
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Re: Pressuring Yeast

Postby Whiskyaugogo » Sat Oct 10, 2015 3:19 pm

G'day

A lot of people here don't use airlocks and I have never heard of a stirrer in the ferment (the fermentation does this itself). There is no scientific reason to use airlocks vs open fermenters except maybe wild yeast infection from unclean plastics etc.

What are you fermenting?
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Re: Pressuring Yeast

Postby hoochlover » Sat Oct 10, 2015 4:27 pm

Whiskyaugogo wrote:G'day

A lot of people here don't use airlocks and I have never heard of a stirrer in the ferment (the fermentation does this itself). There is no scientific reason to use airlocks vs open fermenters except maybe wild yeast infection from unclean plastics etc.

What are you fermenting?


Hi, at least some commercial breweries do stir their fermentations, not just their lees. It's to increase the speed of the fermentation and also to reduce foam buildup so they can fill their tanks higher. Some do it because of the type of yeast they use. They have stir plates inside so there is no chance of infection getting in as it's in a closed system.

I'm fermenting sugar for what it's worth.
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Re: Pressuring Yeast

Postby Whiskyaugogo » Sun Oct 11, 2015 12:09 pm

Sorry mate, thought you were talking Distilleries ;-)

If you were using your ferment for distilling, enhancing the yeast activity may cause unwanted flavours. As I said, a good ferment the yeast do a great job of agitating the wash :handgestures-thumbupleft:
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Re: Pressuring Yeast

Postby hoochlover » Sun Oct 11, 2015 12:53 pm

Whiskyaugogo wrote:Sorry mate, thought you were talking Distilleries ;-)

If you were using your ferment for distilling, enhancing the yeast activity may cause unwanted flavours. As I said, a good ferment the yeast do a great job of agitating the wash :handgestures-thumbupleft:


Yeah you could be right. The other thing to consider is agitating it may actually reduce unwanted flavours by reducing acidity and nutrient starvation hence reduce yeast cell breakdown. Until someone does the testing it's just guesswork. :) From my own point of view I want to limit the nutrients (yeast, salts, etc) to ferment out the sugar in the cleanest way possible. Whilst things like the tomato paste washes are great "Set and forget" washes that do have low unwanted flavours they aren't optimal by any measurement.

If you check my lowans yeast thread you can see with the right conditions you can ferment out ~4% wash in a few hours with the right start. And likely a 6-7% wash in 12-24 hours. People seem to usually wait 1-2 weeks for a 10% TPW. The longer yeast is in the wash the more unwanted flavours that are added to the wash. The higher the yeast reproduction the higher the esters/fusels that are made and the more heads/tails you get, etc.
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Re: Pressuring Yeast

Postby sp0rk » Sun Oct 11, 2015 1:55 pm

hoochlover wrote:If you check my lowans yeast thread you can see with the right conditions you can ferment out ~4% wash in a few hours with the right start. And likely a 6-7% wash in 12-24 hours. People seem to usually wait 1-2 weeks for a 10% TPW. The longer yeast is in the wash the more unwanted flavours that are added to the wash. The higher the yeast reproduction the higher the esters/fusels that are made and the more heads/tails you get, etc.

This is not completely true
A high yeast count (within reason) will clean up unwanted esters and other compounds, length of exposure to yeast isn't really a worry until you have cells dying and autolysis starts to happen
Have a read of Yeast by Chris White, a very informative book on all things yeast
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Re: Pressuring Yeast

Postby hoochlover » Sun Oct 11, 2015 4:01 pm

sp0rk wrote:
hoochlover wrote:If you check my lowans yeast thread you can see with the right conditions you can ferment out ~4% wash in a few hours with the right start. And likely a 6-7% wash in 12-24 hours. People seem to usually wait 1-2 weeks for a 10% TPW. The longer yeast is in the wash the more unwanted flavours that are added to the wash. The higher the yeast reproduction the higher the esters/fusels that are made and the more heads/tails you get, etc.

This is not completely true
A high yeast count (within reason) will clean up unwanted esters and other compounds, length of exposure to yeast isn't really a worry until you have cells dying and autolysis starts to happen
Have a read of Yeast by Chris White, a very informative book on all things yeast


Thanks for the suggestion. I'll give it a read.
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Re: Pressuring Yeast

Postby hoochlover » Sun Oct 11, 2015 7:02 pm

sp0rk wrote:Have a read of Yeast by Chris White, a very informative book on all things yeast


I really like this book so thanks for suggesting it. I've only read about 33% of it so far, the parts which I think are applicable to distilling. Chris White also has some of that work published on his companies website. Like the graph which is relevant to what you stated.

http://www.whitelabs.com/sites/default/ ... e_Line.pdf

Whilst there is a lot there that we can take as distillers there is a lot we can't necessarily draw from either. For instance that graph is likely from a beer brew and for a beer brew you want to have the lag phase appropriate for the tastes you are after. The majority of taste (ie esters, fusels) is produced is in the lag phase, that graph shows that ~66% of the diacetyl is. Reduce the lag phase and reduce the diacetyl, along with a tonne of other esters/fusels.

I think this is why the pitch rate for distillers is extremely important, the higher the pitch rate the less yeast growth you get and in theory less flavours produced. There is of course a few important things you need to change in your wash if you do pitch a lot of yeast. ie nutrients.

Since diacetyl boils at 88C, 10C higher than ethanol, in any reflux column it's much easier to strip it out than the alcohols which are very close to ethanol that are more likely to be produced in the autolysis of the yeast in the "resting phase". So personally I don't see much advantage as distillers to care about diacetyl much at all, the smearing of the heads components which have very similar boiling point to ethanol is much worse in my opinion than diacetyl. I think this is why it's prudent for distillers to get that wash and yeast separated as soon as it's done because you're going to stop any reactions from occurring that do occur if you don't. I can't see a reason why you would prefer the potential for less diacetyl.

I also cannot find any real scientific knowledge on when the so called "diacetyl rest" starts and stops. How can the yeast actually do anything when there is no sugar left? Yeast can reduce ethanol but only in the presence of oxygen which shouldn't be there in a finished fermenter. So where is the energy coming from exactly to "clean up" the brew? It seems to me once the CO2 stops there is no way anything can happen in the wash except the death of yeast and the attributable flavours it introduces. This would suggest the so called diacetyl rest can only happen whilst there is something to ferment and that by the end of CO2 activity it can no longer happen in any appreciable way except through autolysis and those resources being reclaimed which also introduce other unwanted flavours.

Personally I think a large problem when it comes to home distilling is there is so much disinformation spread due to people following beer/wine brewing science.
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Re: Pressuring Yeast

Postby WTDist » Sun Oct 11, 2015 7:34 pm

hoochlover wrote:
sp0rk wrote:Personally I think a large problem when it comes to home distilling is there is so much disinformation spread due to people following beer/wine brewing science.

good read :handgestures-thumbupleft: im one of those guys that takes on what i read here. i would experiment but i have little time to scratch my ass 8-}
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Re: Pressuring Yeast

Postby hoochlover » Sun Oct 11, 2015 8:06 pm

I think the main reason people leave their wash on the yeast cake after it's done is because most people don't have a good way to clarify it besides time and gravity. That and it's often hard to tell for something like beer when it's fully finished by hydrometer alone without a lot of experience on certain gear. People who don't distil will probably not notice having more of the "bad stuff" in there due to the low concentration of the wash.
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Re: Pressuring Yeast

Postby hoochlover » Sun Oct 11, 2015 8:47 pm

Here is a some data from that book that relates purely to brewing a beer and temperature impact on the fusels/esters. The same gas chromo done with distilling in mind would be highly interesting, maybe it already exists out there somewhere. It seems whitelabs offer a service where you can send them in a sample and have them do it. But in a testing mindset it's impossible to afford that with so many tests.
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Re: Pressuring Yeast

Postby Darwin award » Mon Oct 12, 2015 4:11 pm

"if I close the fermenter completely and let pressure build, then release it, it seems to give more effect in regards to releasing the CO2 bubbles."
I think all you are doing is causing the co2 to build up in your fermenter, then when you open it, you see it escaping back into the atmosphere,
I don't think you are actually somehow causing it to release more Co2, you are simply releasing it in one pulse....IDK maybe that stirs up the ferment a bit as well and increases activity,
much like giving your fermenter a bit of a shake can start it bubbling again.....
Hence I can't see any advantage in what you are suggesting...I imagine that an open ferment would actually release more co2 than a open / sealed / opened one....
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Re: Pressuring Yeast

Postby hoochlover » Mon Oct 12, 2015 5:02 pm

Darwin award wrote:I don't think you are actually somehow causing it to release more Co2, you are simply releasing it in one pulse....IDK maybe that stirs up the ferment a bit as well and increases activity,


Yeah I don't think I will make it release more CO2 in total, or not that much more anyhow if you're talking about the whole process. It's about forcing a way to have it release those reluctant bubbles more easily so less stay in the liquid. It's just an idea I had anyhow, I don't know what if any difference it will actually make but I like the thought of having some sort of "yeast powered" auto stirring device that does a better job than just having it open to the air. Whether that is possible I'm not sure.
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Re: Pressuring Yeast

Postby hoochlover » Tue Oct 13, 2015 1:34 pm

I uploaded a small video showing the pressure release. You can see that it does mix the yeast up a lot more than would otherwise be possible.

However this had no impact on my 2 hour 4% ABV fermentation, I tested another batch that was done that way for the whole thing and it fermented out in the same time. Maybe for a longer ferment it would help, not sure. It seems the only real way to improve the ferment time is a constant low pressure stirring mechanism. This CO2 pressure build up takes 5 to 10 mins to get a noticeable mixing impact. The pressure certainly reduces the foaming though, the foam can't grow whilst under pressure.

However after doing a bit more research it seems that fermenting under pressure may lower esters/fusels so still some more things to investigate along that front.


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Re: Pressuring Yeast

Postby Darwin award » Tue Oct 13, 2015 11:23 pm

Ah right, I get what you are saying.
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