Degassing Science?

Hi,

I posted this in the mead forum, but haven't had any luck.

I am looking for a good resource which describes the science behind degassing mead during the primary fermentation.

What I have gathered thus far is that the co2 produced during fermentation can be toxic to the yeast which will cause them to produce esters which cause off or harsh flavors. Is that correct?

Cheers,
Michael J. Pelechaty

If CO2 is toxic to yeast, why do the wee beasties insist on producing CO2?

Cheers!

What's wrong with shaking or stirring? Did you mix your honey with warm water or just dump it in? When I did it, it wasn't glumpy, so....

day_trippr said:

If CO2 is toxic to yeast, why do the wee beasties insist on producing CO2?

Cheers!

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Probably for the same reason they insist on producing alcohol which is also toxic to yeast.

Attempting to de-gas during active fermentation would seem to be an exercise in futility.

day_trippr said:

If CO2 is toxic to yeast, why do the wee beasties insist on producing CO2?

Cheers!

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You insist on producing feces and yet would probably be discontent to hang out in a pile of crap.

discnjh said:

You insist on producing feces and yet would probably be discontent to hang out in a pile of crap.

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Bad analogy. While I do insist on producing excrement, I don't live, eat and respire in said production

Cheerss!

day_trippr said:

Bad analogy. While I do insist on producing excrement, I don't live, eat and respire in said production

Cheerss!

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If you were stuck in a carboy you would!

skipper1953 said:

Probably for the same reason they insist on producing alcohol which is also toxic to yeast.[...]

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I suspect this is another defective analogy. A given strain of yeast will simply stop digesting sugars once the alcohol level reaches the limit of its tolerance...

Cheers!

day_trippr said:

I suspect this is another defective analogy. A given strain of yeast will simply stop digesting sugars once the alcohol level reaches the limit of its tolerance...

Cheers!

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And wouldn't the just do the same when they reach the CO2 level of their tolerance?

http://www.abgbrew.com/pdf/ibssupplement.pdf if you're interested. apparently the american brewer's guild believes that CO2 can be bad for yeast, even if you don't.

discnjh said:

And wouldn't the just do the same when they reach the CO2 level of their tolerance?

http://www.abgbrew.com/pdf/ibssupplement.pdf if you're interested. apparently the american brewer's guild believes that CO2 can be bad for yeast, even if you don't.

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Classic case of "context is everything".

"The yeast essentially suffocates in high CO2 environments, and the uptake of nutrients is inhibited. It is important to note that it is not CO2 pressure alone which cause inhibition of yeast, but rather saturation of the yeast cells with CO2 (saturation can build up while yeast is in a tank under pressure)."

My yeast don't ferment in a pressurized environment. They are happy yeast...

Cheers!

day_trippr said:

Classic case of "context is everything".

"The yeast essentially suffocates in high CO2 environments, and the uptake of nutrients is inhibited. It is important to note that it is not CO2 pressure alone which cause inhibition of yeast, but rather saturation of the yeast cells with CO2 (saturation can build up while yeast is in a tank under pressure)."

My yeast don't ferment in a pressurized environment. They are happy yeast...

Cheers!

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You didn't have much context when you said that CO2 can't be toxic to yeast because yeast produce it.

Look, I'm not claiming that CO2 toxicity is a problem on a homebrew scale. Merely that the "yeast make it, so it can't be toxic" argument isn't really valid. And with that, I'm done.

discnjh said:

You didn't have much context when you said that CO2 can't be toxic to yeast because yeast produce it.

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That claim would be an extrapolation of what I actually wrote.

Look, I'm not claiming that CO2 toxicity is a problem on a homebrew scale. Merely that the "yeast make it, so it can't be toxic" argument isn't really valid. And with that, I'm done.

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You were done before this

Cheers!

day_trippr said:

"The yeast essentially suffocates in high CO2 environments, and the uptake of nutrients is inhibited. It is important to note that it is not CO2 pressure alone which cause inhibition of yeast, but rather saturation of the yeast cells with CO2 (saturation can build up while yeast is in a tank under pressure)."

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This may be spot on but it looks a little suspicious. The yeast are not respiring at any time in a normal fermentation so it is hard to imagine them "suffocating" in the usual sense of the word. If suffocate does not have its usual meaning then what does it mean? And then the word "saturate". What does it mean here? In the usual context it means that whatever it is that is being saturated has taken up as much of whatever it is that is doing the saturating under the particular conditions that pertain at the time. Thousands of years of brewing/meadmaking/winemaking experience have shown that yeast operate just fine when the medium is saturated with CO2 to the levels attendant on fermentation at atmospheric pressure i.e. the partial pressure of CO2 over the surface of the wort or must is 1 atm. The saturation level for CO2 under these conditions is a bit less than 1 volume. They also do fine under pressure of an extra atmosphere or 2 but when the pressure gets higher than that, and it doesn't have to be CO2 pressure - hydrostatic pressure is detrimental too, performance begins to fall off. In lager brewing lagering, or part of lagering, is often carried out at modest pressure without formation of esters or other apparent damage to the beer.

If, despite the evidence to the contrary, you still believe CO2 is poisoning your yeast you can easily lower the pressure of CO2 within the fermenting liquid by lowering the partial pressure of CO2 over the liquid. This can be done by sweeping out the headspace with any gas that does not have a detrimental effect on the beer/mead/wine. Nitrogen would be a good choice. Air would not as it contains oxygen.

Nothing. I have been agitating it, but I was more looking for a scientific paper describing the yeasts biology and what actually happens when too much c02 is present. The knowledge I described having is just broscience as of now and I would like to understand it as "real" science.

I'm not as concerned with the actually mixability of the honey as I am with producing a good mead quickly. I have heard from multiple people that degassing can help, but I would like to get a more scientific explanation as to why.


Cheers,
Michael

mpelechaty said:

Nothing. I have been agitating it, but I was more looking for a scientific paper describing the yeasts biology and what actually happens when too much c02 is present. The knowledge I described having is just broscience as of now and I would like to understand it as "real" science.

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Well, if you wanted to pay 42 dollars there's an article called "Effect of carbon dioxide on yeast growth and fermentation". Or find a library with access to the journal, Enzyme and Microbial Technology.

ScienceDirect - Enzyme and Microbial Technology : Effect of carbon dioxide on yeast growth and fermentation

discnjh said:

Well, if you wanted to pay 42 dollars there's an article called "Effect of carbon dioxide on yeast growth and fermentation". Or find a library with access to the journal, Enzyme and Microbial Technology.

ScienceDirect - Enzyme and Microbial Technology : Effect of carbon dioxide on yeast growth and fermentation

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Thanks! I think I may be able to get it for free when I get back to school via the university.

"If CO2 is toxic to yeast, why do the wee beasties insist on producing CO2?"

CO2 is toxic to human cells at various levels and we insist on producing it. Wild yeast produce CO2 and it diffuses away from them, but in the context of home brewing, they are stuck in a fermentation vessel constantly exposed.

Mcsuck said:

"If CO2 is toxic to yeast, why do the wee beasties insist on producing CO2?"

CO2 is toxic to human cells at various levels and we insist on producing it. Wild yeast produce CO2 and it diffuses away from them, but in the context of home brewing, they are stuck in a fermentation vessel constantly exposed.

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So the basis of my original response was obviously tongue in cheek (and I assume most of the responses to that were as well) but here's the deal: "toxic" is not a binary condition. CO2 is not "toxic" to man below the atmospheric levels that we have adapted to, and alcohol is not considered "toxic" at modest levels.

Yeasts are beasts that are most likely one of the oldest forms of life on this particular planet. They evolved on their own for bazillions of years, and the fact that they exhale CO2 and pee alcohol into their own environment, yet continue to thrive, is a clear statement of what conditions they are happy to live in.

Along comes man, who discovers the magic of yeast, and enslaves the poor things to do his bidding. And if man is smart, he doesn't foist conditions upon his tiny minions that are detrimental to them. That means, for instance, not sealing their environment such that conditions exceed their comfort zone (eg: don't seal the fermenter causing CO2 to rise to toxic levels) and don't expose them to alcohol levels beyond what they are capable of producing on their own.

Left on their own, yeast won't kill themselves...

Cheers!

day_trippr said:

Bad analogy. While I do insist on producing excrement, I don't live, eat and respire in said production

Cheerss!

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Arguably, your yeast isn't respiring but whatever.

tCan said:

Arguably, your yeast isn't respiring but whatever.

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You need a really powerful microscope to see their tiny lungs...

Cheers!