Degassing science?

[mpelechaty]

Hi,

I am looking for a good resource which describes the science behind degassing.

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

 

[MedsenFey]

There isn't a lot of science behind degassing. There is good data that shows fermenting under CO2 pressure inhibits yeast, though you have to get above 7 atmospheres to bring their reproduction to a halt. However, even under as little as 0.3 atmospheres of CO2 pressure, the time required for maximal growth of the yeast may be doubled. In theory, if you could keep the CO2 in solution even lower with a continuous vacuum, you might be able to speed fermentation complete up by a few hours (maybe even a day).

I don't think there is any definitive data on CO2 causing harsh or "off" flavors. Most esters are actually a plus in mead. I can tell you that I don't bother actively de-gassing most of my meads. I aerate them during the initial fermentation, and I will swirl them (under airlock) some during the fermentation to keep the yeast in suspension, which will cause some de-gassing as a by product. However, I don't keep doing it until all gas release stops so I'm sure the amount of de-gassing I accomplish is probably quite small. I'm quite lazy when it comes to de-gassing, but this has not prevented me from producing great meads.

After fermentation is complete, I let things de-gass passively at room temperature and they go flat in a couple of days.

If anyone ever produces any studies showing that aggressive stirring/de-gassing produces better results, I'll start doing it. Anecdotally, there are some folks over at GotMead using stir-plates for continuous stirring/de-gassing and the initial impressions are favorable, so it may be that this will prove to be a useful thing.

Medsen

 

[lsmith47]

So now I'm confused about degassing. Aeration is good at the beginning, CO2 is bad throughout. However, later oxygen is bad, so wouldn't anything like aggressive stirring also be bad?

 

[Yooper]

So now I'm confused about degassing. Aeration is good at the beginning, CO2 is bad throughout. However, later oxygen is bad, so wouldn't anything like aggressive stirring also be bad?

Certainly! But...........oxidation doesn't occur until after the yeast are finished using oxygen and the yeast stops producing as much co2. So, early in fermentation, you can degas and stir.

You can definitely (and should) stir mead and wine in primary, especially if you're using fruit that may float or form a "cap".

Once fermentation slows, at an SG of roughly 1.020-1.010, you will want to ensure that you are under airlock and stop stirring.

I was at the NHC last year when the mead panel discussed degassing, and were all in favor of it. I'm a believer, in that I believe that they know what they are talking about. But I'm a lazy winemaker, and don't even remember to stir my musts every day let alone degas my meads.

 

[mpelechaty]

There isn't a lot of science behind degassing. There is good data that shows fermenting under CO2 pressure inhibits yeast, though you have to get above 7 atmospheres to bring their reproduction to a halt. However, even under as little as 0.3 atmospheres of CO2 pressure, the time required for maximal growth of the yeast may be doubled. In theory, if you could keep the CO2 in solution even lower with a continuous vacuum, you might be able to speed fermentation complete up by a few hours (maybe even a day).

I don't think there is any definitive data on CO2 causing harsh or "off" flavors. Most esters are actually a plus in mead. I can tell you that I don't bother actively de-gassing most of my meads. I aerate them during the initial fermentation, and I will swirl them (under airlock) some during the fermentation to keep the yeast in suspension, which will cause some de-gassing as a by product. However, I don't keep doing it until all gas release stops so I'm sure the amount of de-gassing I accomplish is probably quite small. I'm quite lazy when it comes to de-gassing, but this has not prevented me from producing great meads.

After fermentation is complete, I let things de-gass passively at room temperature and they go flat in a couple of days.

If anyone ever produces any studies showing that aggressive stirring/de-gassing produces better results, I'll start doing it. Anecdotally, there are some folks over at GotMead using stir-plates for continuous stirring/de-gassing and the initial impressions are favorable, so it may be that this will prove to be a useful thing.

Medsen

How long do you typically age your mead for if you don't mind me asking?