Why don't we agitate during fermentation?

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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.
 
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.
 
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. :D

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
 
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! :mug:
 
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).
 
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.

:p

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. :p

Have fun,

Bob
 
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.
 
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
 
hrmmmm. easier than groping and shaking my carboys..

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

You know what's next.....

motivator2903225.jpg

But remember....

motivator7072222.jpg
 
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.
 
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?
 
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.
 
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
 
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?
 
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!
 
Hey corncob, how'd your beer turn out? I'm working on a SS Pale Ale right now... curious as to how you liked the Yorkshire yeast...


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!
 
I have heard agitation is good as long as you have an airlock or blow off tube on your fermenter. By agitiating the yeast you are in a sense creating a larger surface area for the yeast to absorb nutrients from the wort. As long as oxygen is not being introduced agitiation is good. It can also help speed up the primary fermentation time.
 
I have heard agitation is good as long as you have an airlock or blow off tube on your fermenter.

Agitation is certainly beneficial for decreasing fermentation time.

The jury is still out on potential flavor regressions (e.g., increased esters, fusels) compared to a non-stirred fermentation.
 
The original large scale stir bar idea was discussed here.

I plan to use a closed, positive pressure vessel to conduct the fermentation test. I'll likely split a 5.5 gallon batch and ferment at the same temperature.

sanke-3.jpg




Yes, the size of the stir bar and centrifugal force is certainly a design concern. The goal is to achieve minimal agitation at the bottom of the fermenter, not a vigorous whirlpool. I believe that can be achieved with a 3" - 4" stir bar and a large 6" computer fan.

Only real world testing will tell. Once I get my repaired sanke fermentation kit back next week, I should have an opportunity to test the idea.

What were the results of your experiment?
 
The experiment was from 4 years ago and the poster you quoted hasn't posted anything here in more than a year and a half, so he may not get back to you on this one ;)
 
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

Yes I aswell appreciate the question. We are taught that agitation, heat etc naturally speed up reactions.
I mean would you just add a few teaspoons of sugar to a glass of water and wait 30 years for it to dissolve.
Also, what effect would this have on the end product is as good a question.
 
Just another point of reference......about 35 years ago I bought a keg off a guy who turned our to be the recently retired head brewer of one of the biggest breweries in New Zealand. He had just built a fermentation system for his home brew that incorporated a recirculation system during fermentation. He told me it was very important to keep everything stirred up. Oxygen would not be a problem as it was a closed system. Just an fyi FWIW. Cheers.
 
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