Getting Rid Of Acetaldehyde

[Screwtop]

Gregs statements may have sound scientific validity, however my kinesthetic learning style prevents me from agreeing :blink:

Screwy

 

[WitWonder]

My post was somewhat tongue in cheek, but the question was serious - why is the practise of open fermenting still continued to this day if it is highly likely (certain?) to introduce acetaldehyde in the final product?

 

[Greg.L]

My post was somewhat tongue in cheek, but the question was serious - why is the practise of open fermenting still continued to this day if it is highly likely (certain?) to introduce acetaldehyde in the final product?

I don't know enough about industrial brewing to know how common open fermenting is, but the principle is quite different on a large scale. The relative surface area is much smaller so the risk from air contact is smaller. Anything of 100L or less is generally at an extreme risk of oxidation, but if you keep the air out it doesn't matter. Keeping air excluded has the added benefit of protecting against infection, most infections need air to grow.

 

[glenwal]

An airlock will actually let in more oxygen (any nasties that are in the air) than glad wrap as the glad wrap is flexable and can expand and contract. During fermentation, the oxygen inside the fermenter is consumed, and CO2 is produced. With glad wrap the end result is a positive pressure inside (ie. excess quantity) of CO2, with an air lock the pressure equalises.

When a sample is drawn through the tap with glad wrap, the sample reduces the pressure inside and helps it to equalise with the external pressure, meaning no air is drawin into the fermenter. And even if more liquid is taken out than there is excess CO2 inside, the glad wrap lid will "deform" to displace the volume instead of sucking in outside air. With an air lock, drawing off a sample will reduce the pressure inside, which will suck air in through the airlock resulting in air inside the fermenter.

 

[MastersBrewery]

informative and amusing ... that how I like my threads h34r:

 

[mattyra]

My post was somewhat tongue in cheek, but the question was serious - why is the practise of open fermenting still continued to this day if it is highly likely (certain?) to introduce acetaldehyde in the final product?

Have you tasted VB. Obviously the best flavour is not the main goal when these people make beer :lol:

To add something to the discussion. I have only been brewing for a couple of years but have tried both methods and trying to make my brewing better. I didn't really notice any differance when using the lid or the glad wrap. I just come to the conclusion that if you are just fermenting your beer it won't really make much of a differance as long as you give a decent attempt at trying to keep the oxygen out (CO2 is heavier the O2 therefore sitting low in the fermenter and not letting the O2 in).

 

[Greg.L]

According to wikipedia the permeability of polythene wrap is 2000 cm3 μm m-2 d-1 kPa-1. Thats a pretty high figure for such a thin film. Holding it down with an o-ring won't help, if the co2 can flow out then the o2 can get in, remember the concentration gradient from out to in is pretty steep.

 

[glenwal]

According to wikipedia the permeability of polythene wrap is 2000 cm3 μm m-2 d-1 kPa-1. Thats a pretty high figure for such a thin film. Holding it down with an o-ring won't help, if the co2 can flow out then the o2 can get in, remember the concentration gradient from out to in is pretty steep.

Except the CO2 is heavier than air and the CO2 is lower so there isn't going to be an exchange of gases (not to mention the positive pressure from fermentation that will also prevent oxygen from flowing inwards)

 

[Greg.L]

Except the CO2 is heavier than air and the CO2 is lower so there isn't going to be an exchange of gases (not to mention the positive pressure from fermentation that will also prevent oxygen from flowing inwards)

Here's Dalton's law for you.

"The partial pressure of an ideal gas in a mixture is equal to the pressure it would exert if it occupied the same volume alone at the same temperature. This is because ideal gas molecules are so far apart that they don't interfere with each other at all. Actual real-world gases come very close to this ideal."

The o2 and co2 can both reach saturation irrespective of each individual concentration. Having co2 in there won't keep the o2 out at all, being heavier only helps keep the co2 in.

 

[kymba]

aww, Greg...please do not speak ill of our gas layers - Long live the thick, creamy, impervious blanket of CO2 that is Our Saviour & benevolent protector of our open fermentation vessels!

 

[OneEye]

For anyone that comes here for the original point of the thread... I found this on HomeBrewTalk.com which some may find useful... at least worth a shot I think.

"Either way, I barely noticed this when transfering to the keg and thought it was mild and would lager-out. 3 weeks later, I took a sample and definitely decided I couldnt drink a keg of the stuff. So I started doing some research. It turns out that acetylaldehyde is very volatile, and the fact that the keg was already carbed could be a huge benefit, as the escaping CO2 at warmer temps would bring the acetylaldehyde right with it.

I took the keg out of the kegerator, and burped the pressure relief valve every day or so for 5 days now. Additionally, I took some yeast cake, added about 8oz of wort to it, let it start fermenting for about 24h and pitched that.

The combination seems to have completely cleared up the problem after only a few days. It delays the whole process though, as I really need to re-lager the beer now, but at least I will have a (at this point it is promising) very good tasting Munich Helles."

 

[glenwal]

Here's Dalton's law for you.

"The partial pressure of an ideal gas in a mixture is equal to the pressure it would exert if it occupied the same volume alone at the same temperature. This is because ideal gas molecules are so far apart that they don't interfere with each other at all. Actual real-world gases come very close to this ideal."

The o2 and co2 can both reach saturation irrespective of each individual concentration. Having co2 in there won't keep the o2 out at all, being heavier only helps keep the co2 in.

Except there is a layer of solid in between in this case, and permeability of a solid does not follow Daltons law. The positive partial pressure of the CO2 inside the fermenter will reduce the total permeability of the sold (in this case - glad wrap)

 

[drsmurto]

A lot of brewers and winemakers (pros and amateurs) think they know a lot about O2 and it's impact on beer and wine but the fact people like myself are paid to research the impact of oxygen before, during and after fermentation should make it clear that neither industry has stopped trying to understand it, nore are they anywhere near really understanding it. We did a large scale trial during vintage this year looking at O2 during winemaking and are following it through monitoring the development, acetaldehyde production is one of hundreds of molecules we are tracking. In addition, i am currently writing a review on a closely related topic that should be published later this year, currently going through the peer review process.

As an FYI, the Journal of the Institute of Brewing is currently allowing free online access so I strongly suggest many of you make use of this unique opportunity (most research organisations including mine, both academic and private, pay $1000s per year per journal/publisher for access) to dispel many of the myths that circulate this forum. I can only dream.

Whilst there is a large positive pressure of CO2, gladwrap will be ok, not ideal but ok. Once that pressure drops (ie the gladwrap is not stretched to breaking point) the pressure is no longer enough to prevent O2 getting in. Gladwrap is a bacterial barrier, it is not designed to, nor does it prevent gas transfer. O2 and CO2 are miscible and despite the apparent difference in densities, environments at or close to atmospheric pressure will result in mixing of these 2 gases. I have spent and continue to spend a lot of time and effort removing and keeping O2 out of my experiments in the lab and am measuring the content down to 1 ppb. Even inside the standard corny keg (which i use as an inert gas chamber) there is a minimum pressure required to prevent O2 from getting back in. So if O2 can get into a sealed keg, with a slight positive pressure, then what hope does gladwrap have.

My 2 c, not intended as a lecture but seems to have come across that way.
Cheers
DrSmurto

p.s I have smelt pure acetaldehyde on numerous occasions, we use it to train up sensory panellists and I recently went through a rigorous training regime on faults and taints in wine, acetaldehyde was one of them and i rarely picked it as green apples. At varying concentrations, in different media the perception changes. When mixed with other volatile compunds this is further complicated due to a synergistic effect that may have positive or negative results. Sensory science is far from simple.

 

[gunbrew]

Interesting thread.
I went to a brew pub and saw 800 litre open fermentation vessels.
One was full, see photo.
The bar tender sent me into the brewery to have a look.
At the time I was in shock that they let a customer walk in there and I was thinking that people walking in there had to be an infection risk to the beer.
The place only made 2 beers a dark and a light, no idea what yeast.
Brewer was not there to quiz.
I asked the bar tender numerous questions for what ever that was worth, he said:
Open fermenting was only whilst there was a vigourous ferment, they had 2 large open fermenters.
Then they moved the beer to a large closed fermenter for the remainser of the ferment, visible at back of photo.
Then they moved the beer to closed conditioning tanks in a cool room.

 

[Greg.L]

Interesting thread.
I went to a brew pub and saw 800 litre open fermentation vessels.
One was full, see photo.
The bar tender sent me into the brewery to have a look.
At the time I was in shock that they let a customer walk in there and I was thinking that people walking in there had to be an infection risk to the beer.
The place only made 2 beers a dark and a light, no idea what yeast.
Brewer was not there to quiz.
I asked the bar tender numerous questions for what ever that was worth, he said:
Open fermenting was only whilst there was a vigourous ferment, they had 2 large open fermenters.
Then they moved the beer to a large closed fermenter for the remainser of the ferment, visible at back of photo.
Then they moved the beer to closed conditioning tanks in a cool room.

That makes sense, brief open fermentation then into sealed SS fermentation vessels. I have no problem with that.

Thanks for your input Dr Smurto. It is a very complex area with lots of complications.

 

[OneEye]

Thanks for all the input guys, especially Greg.L and Dr.S. I'll persist with trying to 'fix' this beer but future brews (at least the next couple at least) I'll try and throw a lid on.... I'll just have to try and find a relatively low profile airlock (maybe a small 3-piece?) so it will fit in my ferm chamber!

 

[Steve@PMF82]

My 2 c, not intended as a lecture but seems to have come across that way.
Cheers
DrSmurto

I guess that just depends on your POV eh? I found it to be quite informative along with many other great contributions in this thread.
So :icon_cheers:

 

[mattyra]

Thanks Dr What a read. Not meaning to spark anything up again but wouldn't the lid on the fermenting vessel be in the same position as the glad wrap. If the keg wasn't able to keep all of the O2 out then what hope does a plastic lid (that has a hole and airlock in it)?

 

[daemon]

Greg.L I'm curious that if you think Glad Wrap during fermentation is such a bad idea, what method do you use to transfer the beer into kegs / bottles that guarantees that there is no oxgen left in the keg / bottle?

The risk of oxidisation when transferring post-fermentation are far, far greater (IMHO) than during fermentation yet I don't know of any way to purge 100% of the oxygen from my kegs.

 

[Greg.L]

Greg.L I'm curious that if you think Glad Wrap during fermentation is such a bad idea, what method do you use to transfer the beer into kegs / bottles that guarantees that there is no oxgen left in the keg / bottle?

The risk of oxidisation when transferring post-fermentation are far, far greater (IMHO) than during fermentation yet I don't know of any way to purge 100% of the oxygen from my kegs.

I bottle condition, the yeast soak up the little bit of o2 in the bottles. I handle my beer/wine/cider as little as possible. The fact that some contact with air is inevitable when handling makes it more important to reduce air contact at other times, the effect tends to be cumulative.

As for lids v film, the lids are thicker hdpe rather than thin ldpe used for film, so the permeability is much lower. SS or glass are even better. The seals on a screw thread lid with an o-ring are much better, only a small amount of o2 can get past.