Why don't we agitate during fermentation?

[springer]

I have to say the quality of his products is top notch. If it works out for me I will have to buy a few more . I have two 1/2 barrels and three 1/4 that I want to use as fermenters . I already used the 1/2 a few times but with a stopper and airstop

 

[Edcculus]

wasn't walking the barrel used towards the end of fermentation? Just like when I swirl the carboy a few days after active fermentation is complete just to rouse the yeast a little .

And conditioning is done after the active fermentation is completed.

I asked why do it during an active fermentation . Because the yeast are doing a pretty good job of it on their own.

Oh, I thought you were talking about rousing at the end of fermentation. I don't claim to be an expert, but it seems to me if you pitch enough yeast, using a stir plate for a whole batch is probably useless. That is unless you are trying to achieve a very specific goal, like a really dry beer with no adjuncts.

I also know we can't compare everything we do to commercial brewers, but you don't see them mixing up thier fermenting wort. I guess I'm trying to say that I don't fully understand the point of this. Why would I want to constantly stir my fermenting wort when I can get desired attenuation through proper aeration and pitch rates?

 

[david_42]

Even if the top of a flask is left completely open (rarely the case) how is the oxygen getting in there once it is full of co2?

Two reasons: 1. air-entrainment due to friction 2. yeast give off very little CO2 during their growth.

 

[Bonysplicer]

I'd like to see it done both on a closed setup like yours, but also done in a typical carboy/airlock setup that most folks have. I have a feeling the results would be quite different. That perhaps in a closed environment, purged of o2 it would work great, and their would be no oxydation worries...but in a "real world" or typical hb'ers situation it would be a setup for disaster.

Your statement shows a lack of understanding of physical chemistry. Check out references to Henry's Law. In any fermenter situation, carboy or otherwise, gases exist in equilibrium between two phases, gaseous (headspace) and dissolved gas in solution. the rate of transfer in this equilibrium is a surface area limited function.

For example, when you use an oxygen stone or fish tank bubbler to pump o2 through your wort, the wort picks us a high level of o2 quickly due to surface area to volume ratios of tiny bubbles and the high partial pressure of o2. Similarly, boiled, degased starter wort picks up oxygen because whirlpool agitation increases surface area exposure, but still the wort will only dissolve enough o2 gas to be in equilibrium with the partial pressure of o2 in the headspace. So relative to the gas/liquid interface stirring merely hastens the balance of equilibrium.

BUT in a fermenter yeast use o2 and "fart out" co2 into solution So the partial pressure of dissolved o2 decreases over time and the partial pressure of co2 increases over time. Additionally, the total pressure in the headspace is regulated by the airlock/blow off. So as the co2 builds up in solution it increases the partial pressure of gaseous co2 (equilibrium). But since the total pressure is fixed, gas is driven off through the airlock. That gas is a mixture of co2 and o2. Over time the faction o2 in the headspace limits toward zero through being driven off through airlock and being used by the yeast.

My understanding is that "oxidation flavors" are caused by excess dissolved o2. From this it would seem prudent to drive off excess dissolved oxygen as quickly as possible, prehaps through agitation in an oxygen defficient environment.

 

[lamarguy]

Why would I want to constantly stir my fermenting wort when I can get desired attenuation through proper aeration and pitch rates?

The objective is maximize the movement of the yeast throughout the wort. A stir plate is an effective means to achieve constant yeast movement. The secondary objective is to speed the conditioning process.

For example, studies have shown leaving cold break in the fermenter increases the nucleation sites for CO2 during active fermentation, which allows the CO2 to be released more readily from solution. This induces stronger currents (swirling) within the wort, a "natural" method for yeast movement. We're just talking about augmenting that process with mechanical motion.

 

[wildwest450]

Ah! It's not a matter of disliking your explanation! I certainly did not mean to offend. I was just looking for a bit more of a scientific explanation than "Oxidized beer is not yummy" I was merely conjecturing and offering my thoughts on the situation

Then go talk to a scientist, this board is to give advice, not provide you with "scientific" explanations of everything. I've brewed enough beer to know you don't want to put your carboy on a stir plate.

But please, feel free to do so and report back with the results.

 

[oldschool]

A fermenter is not a closed system, it out-gases.

Also, O2 CAN come back the other way if the pressure on the outside exceeds the pressure on the inside. This happens most often when you put an airlock on while the wort is still warm.

Maybe slightly..but not for long. The wort will start to outgas and form a CO2 blanket over the beer since it is heavier than the O2. I respect the Rev's opinions but sometimes i wish someone would say "I'm not sure, I have not tried that sort of thing. You should try it and educate all of us." I once posted a thread basically saying that, "here is what i did, these are my results" and almost everyone told me that i had to be wrong.

 

[Revvy]

I respect the Rev's opinions but sometimes i wish someone would say "I'm not sure, I have not tried that sort of thing. You should try it and educate all of us."

Uh, I think I said that, TWICE in this thread....

If you don't like our explanation, and have your own theory then why don't you try it and prove us wrong? Me personally, I don't want to risk 5 gallons of beer to know if I am wrong or not.

Then YOU do it...make up a 10 gallon batch of beer....split it into two fermenters, pitch EXACTLY one packet of dry yeast into each batch....Spin one with a stirbar, leave the other alone. Bottle and come back in 6 weeks and see if half the batch tastes like cardboard.

Actually THREE times, I also discussed Larmarguy's experiment and offer some ideas as to that as well.

 

[JKoravos]

I've been thinking of adding agitation to my next fermenter. I don't see any reason that it would have anything other than a positive affect on the fermentation. The agitation doesn't need to be terribly vigorous and probably not even continuous to get maximum attenuation out of the yeast. You'd likely have to adjust your brewing process a bit for slightly higher attenuation, but in the long run it's probably an extremely consistent fermentation method.

Oxidation shouldn't be a concern at all. I'm not sure why it would be, there's no oxygen in there.

 

[remilard]

I've brewed enough beer to know you don't want to put your carboy on a stir plate.

How can you know something when you lack anecdotal observation or even a rudimentary understanding of why it would be true?

Bonysplicer has a point in that the oxidation argument, that is stated as a matter of fact, is laughable. It blows me away that somebody can think that agitating the beer would change the composition, apparently via magic, of the gas that is in contact with the surface. It certain would change the surface area exposed to gas, but that doesn't matter if all of the gas is inert (as it was right before the magic happened).

Also laughable, that two HBT posters with more street cred than Bonysplicer are doing the same damn thing and nobody is calling them stupid.

My 2 cents, I think recirculating the beer with a pump is a more promising approach (and one practiced by a number of commercial breweries).

My other 2 cents, this is the wrong message board to use the word "why" on.

 

[JKoravos]

BTW, the reason you get oxygen into the wort in a starter on a stirplate is due to gas diffusion. There is a direct path between the wort and the outside air and since there is also a concentration gradient between the interior or the flask and the exterior air, oxygen will enter the flask. If anyone really wants to understand how this works, research Fick's Law of Diffusion.

In a fermenter with an airlock, there's no way for oxygen, or any other gas, to enter the headspace once the fermenter is closed, except for the rare case where the gas in the fermenter is much warmer than the ambient temp and the contraction of the gas as it cools sucks exterior air backwards through the airlock.

 

[oldschool]

Actually THREE times, I also discussed Larmarguy's experiment and offer some ideas as to that as well.[/QUOTE]

True you did. I'm not saying we should stir our beer. You know where i am coming from.

 

[mordantly]

so what does "wet cardboard" taste like? and don't use the object in the definition. i know what paper tastes like, but im not about to imbibe cardboard to analize the flavor profile.

 

[Revvy]

so what does "wet cardboard" taste like? and don't use the object in the definition. i know what paper tastes like, but im not about to imbibe cardboard to analize the flavor profile.

Most of those taste descriptors actually comes from the memory of what a taste or smell invokes rather than an actually flavor. The same thing goes for the "bandaid" one often mentioned, or the "wet horseblanket" mentioned in wine. It may not be logical and it may not be the actual smell or taste if you did suck on wet cardboard, but some of them are "archetype" and a lot of people can inherently understand.

It may stem from the "supertaster" gene found in some people, like how if some folks try to eat something with cilantro it tastes like soap in their mouth. Or those folks who understand the concept of "Umami" in food, which some say is the fifth taste, and other's say it doesn't exist. That's why some of these may be universal....buried in some bizarre genetic code in our brain...it's really fascinating.

But a lot people have no problem understanding the taste or concept of wet cardboard with thinking about it or tasting a beer with it in there, they may not have ever tasted wet cardboard...but their brain tends to "know" what it is like.....Or would taste like if they actually did.

To people in their 40's if you say "wallpaper paste" it invokes the memory of a certain kind of paste glue that many of us used in elementary school (which I don't know if it still exists in the era of gluesticks and such)...But many kids know what it smells like, as well as may have actually injested it.

At the same time, others may have the same chemical traits on a mollecular level like the smell/taste in invokes...like, iirc Acetaldehyde which we percieve as "green apples" is actually the chemical that gives green apples their distinctive taste...If I recall correctly.

THis is actually a great podcast about taste.....except this guy devoted his life to actually tasting wet carboard, horseblanket, dirt, long before he made his carreer as a wine critic;

Basic Brewing Radio
Gary Vaynerchuk of Wine Library TV brings the thunder to BBR and gives us his perspectives on the art of tasting as he samples homebrew.

Click to listen, Mp-3

 

[oldschool]

The only beers I have had that smelled like this are porters. not good!

 

[mordantly]

Revvy, the link doesn't work. can you try again?

 

[bmckee56]

I make a considerable amount of wine at home each year and one of the things I do to my wines is to gently shake the carboy to release trapped CO2 from the wine to aide in clearing. I also use a vacuum pump to remove the trapped CO2. Also, the wine is typically racked off the yeast and sediment prior to any significant amount of shaking to de-gas.

I can understand the OP questioning why this practice is not done with beer and I also see the point of keeping O2 exposure to a minimum. In all, It is an interesting thread.

Oh..... I take no stand either way here, cause I have a long way to go before I can offer up any significant input as it relates to Home Brewed Beer.

Salute!

 

[remilard]

so what does "wet cardboard" taste like? and don't use the object in the definition. i know what paper tastes like, but im not about to imbibe cardboard to analize the flavor profile.

Wet cardboard and wet paper taste similar. I think you'll know it when you taste it. It also tastes just like it smells.

Alternately, buy a beer, take the cap off, recap it, shake it up a bunch and leave it as hot as possible (preferably around 100 F or more) for about a week and then chill it and drink it.

Note that trans-2-nonenal tastes like paper or cardboard but there are other products of oxidation in beer that taste like other things (and are desirable in some beers).

 

[Revvy]

Revvy, the link doesn't work. can you try again?

I fixed it!!! reclick the linky.

 

[Bob]

My understanding is that "oxidation flavors" are caused by excess dissolved o2. From this it would seem prudent to drive off excess dissolved oxygen as quickly as possible, prehaps through agitation in an oxygen defficient environment.

Your statement shows a lack of understanding of the brewing process.



Oxidation flavors are indeed caused by excess dissolved oxygen. However, the prime source for oxidation off-flavors hasn't anything to do with fermentation. It has to do with the mash.

There is a phenomenon called hot side aeration which sets up the precursors for in-package staling and development of off-flavors that evoke wet cardboard or paper. Hot side aeration (HSA) is caused when sweet wort pics up too much oxygen, usually through excessive agitation.

Before you go all wobbly about HSA affecting your beer, though, take my advice and stop worrying about it. HSA is of concern to large beer factories, where they're pumping wort at hundreds of gallons per minute. In order to induce HSA-derived flavor precursors in your wort, you'd have to pump it through a garden hose at a high rate of speed and shoot it into your kettle.

That said, you can pick up off-flavors from air post-ferment, but it's not from the introduction of oxygen. It's through the introduction of non-S. cerevisae microorganisms - in other words, contamination. The same flavors associated with HSA can also come from contamination.

I mean to say, how many production breweries still use open fermentation? If ever there was a situation where green-beer oxidation would be virtually guaranteed, it's then. It doesn't happen, because it happens on the other end of the brewhouse. Contamination is also unlikely, provided an open ferment is conducted properly, because infecting microorganisms cannot withstand the environment of high krauesen.

Agitation can be beneficial, however. Yeast strains which are excessively flocculent - Ringwood springs to mind - often need to be roused periodically during the ferment, in order to maintain contact with the wort. Whether it's twice-daily stirring with a sanitized implement or constant agitation with a sanitized submersible pump - I've done both - extremely flocculent strains sometimes need the physical assist. I have to note I've never experienced staling precursors developing with those methods.

It is good to keep beer away from air after bitter-wort aeration and the onset of the ferment. But it's for different reasons than the development of flavor precursors of oxidation. The moral of the story is "stop worrying about it".

Oh, and about de-gassing: Vintners de-gas their product because it's intended to be still; I for one don't like fizzy Sauvignon, and I'm sure you don't either. Brewers intend their product to be quick (carbonated); a good conditioning regime will take into consideration the amount of dissolved CO2 in the green beer before conditioning and add a proportionate amount of priming solution to reach a targeted volume. Thus de-gassing is a waste of time.

Plus it adds to global warming.

Have fun,

Bob

 

[JKoravos]

Another thought I've had for rousing yeast is to run a stainless tube down to the bottom of my fermenter and force some CO2 through the tube once or twice a day to rouse the yeast. It's probably a little easier than constant agitation and it still gets the yeast back up in suspension.

 

[Bob]

CO2 agitation works well. It works especially well in conical fermenters - connect the CO2 line to the bottom valve of the cone, set to 20psi (or so), and gently crack the valve. Conical or not, use caution, though, because it has a tendency to foam like crazy.

Bob

 

[mordantly]

hrmmmm. easier than groping and shaking my carboys..

 

[Revvy]

hrmmmm. easier than groping and shaking my carboys..

Uh, you "grope" your carboys? You pervert you.

You know what's next.....

But remember....

 

[mordantly]

i hug it, kiss it, shake it, whisper sweet tales to it in the night..... how will my beer get pregnant when i swear she wore a rubber? well okay a few of these i do regulary behind closed closets with a carboy. i swirl it and rock it to keep my yeast infection to a maximum.

 

[silverbrewer]

I am reading this post as I was thinking of very gently continuosly stiring my fermenter so the internal cooling coils would have the wort passing over them.
Are you lot in agreement that the yeast action causes enough currents within the fermenter to make a stirrer redundant?

 

[JesseRC]

I swirls mine , gentle shake after the most of the fermentation is over with. It helps clean the sides off and rouses the yeast just before I up the fermenter up to 68-69F. I dont do this during the 1st 5 days cus fermentation is already going strong. I consider my fermenters closed systems and I dont think the beer is getting oxidized. What does it buy me, well probably nothing if I just let is sit long enough, but on a dry light ale , its just peace of mind that it gone as far as it can go . On stouts I hardly ever swirl, as I want them a little sweet.

 

[JVD_X]

I've been thinking of adding agitation to my next fermenter. I don't see any reason that it would have anything other than a positive affect on the fermentation. The agitation doesn't need to be terribly vigorous and probably not even continuous to get maximum attenuation out of the yeast. You'd likely have to adjust your brewing process a bit for slightly higher attenuation, but in the long run it's probably an extremely consistent fermentation method.

Oxidation shouldn't be a concern at all. I'm not sure why it would be, there's no oxygen in there.

You could pressurize o2 into a keg then wait for high krausen and put the keg under vacuum. Just a crazy idea I suppose

 

[Hermit]

Your statement shows a lack of understanding of physical chemistry. Check out references to Henry's Law. In any fermenter situation, carboy or otherwise, gases exist in equilibrium between two phases, gaseous (headspace) and dissolved gas in solution. the rate of transfer in this equilibrium is a surface area limited function.

For example, when you use an oxygen stone or fish tank bubbler to pump o2 through your wort, the wort picks us a high level of o2 quickly due to surface area to volume ratios of tiny bubbles and the high partial pressure of o2. Similarly, boiled, degased starter wort picks up oxygen because whirlpool agitation increases surface area exposure, but still the wort will only dissolve enough o2 gas to be in equilibrium with the partial pressure of o2 in the headspace. So relative to the gas/liquid interface stirring merely hastens the balance of equilibrium.

BUT in a fermenter yeast use o2 and "fart out" co2 into solution So the partial pressure of dissolved o2 decreases over time and the partial pressure of co2 increases over time. Additionally, the total pressure in the headspace is regulated by the airlock/blow off. So as the co2 builds up in solution it increases the partial pressure of gaseous co2 (equilibrium). But since the total pressure is fixed, gas is driven off through the airlock. That gas is a mixture of co2 and o2. Over time the faction o2 in the headspace limits toward zero through being driven off through airlock and being used by the yeast.

My understanding is that "oxidation flavors" are caused by excess dissolved o2. From this it would seem prudent to drive off excess dissolved oxygen as quickly as possible, prehaps through agitation in an oxygen defficient environment.

I just racked for the first time last night and was surprised by the amount of gas that came out. I thought it had reinvigorated the yeast but I'm told it was probably just excess CO2 coming out of solution. There was still some activity this morning, which might be fermentation but wouldn't getting the CO2 out be beneficial also?

 

[corncob]

Maybe I am naive about what I read on the internet, but I have been trying to brew something remotely close to Samuel Smith's Organic Pale Ale since I first started brewing. I read this:

http://www.merchantduvin.com/pages/5_breweries/samsmith_yorkshire.html

I bought four vials of WLP037 Yorkshire Square Ale Yeast. I have a batch of 1.045 bitter w/ fuggles and goldings in the closet at 65*.

And I've been swirling it something awful twice a day since the bubbles started. I'll let you all know in a few weeks. Ahhhhhh science!