Stirred Fermentation

[Sulli]

Also found this. Thoughts?

 

[GNBrews]

I just did a pretty thorough search of the web, and I can't find any information on the effects of c02 on the refractive index. I did find this website. Which says A refractometer with ATC (Auto Thermal Compensation) is unaffected by temperature or fermentation gases. Where did you get your information? Can you site some sources?

It's something that a few of the guys mention when people complain about the discrepancy between the logarithm-compensated refractometer reading vs. what they measure with a hydrometer. For both measurements, you need to have a degassed sample in order to get an accurate reading. I'll search around and see if I can find some specific examples for you.

In the mean time, if you've got a small container like a clean film canister or something (I know...what's this "film" thing I speak of?), take a small sample, and measure the difference between right out of the fermenter and after it's been shaken for a few seconds. If there's no difference, no harm done.

 

[GNBrews]

Also found this. Thoughts?

I'm not as well versed in physics as I'd like to be, so I'm not sure how to interpret that paper. It seems that they are looking more at the discrepancies in air densities, factoring in pressure, CO2, and moisture content. I'm not sure that it would necessarily apply to gases dissolved in a liquid medium, but I honestly have no idea.

 

[Sulli]

It's something that a few of the guys mention when people complain about the discrepancy between the logarithm-compensated refractometer reading vs. what they measure with a hydrometer. For both measurements, you need to have a degassed sample in order to get an accurate reading. I'll search around and see if I can find some specific examples for you.

In the mean time, if you've got a small container like a clean film canister or something (I know...what's this "film" thing I speak of?), take a small sample, and measure the difference between right out of the fermenter and after it's been shaken for a few seconds. If there's no difference, no harm done.

Will do. Thanks.
BTW, I still have a circa 1970's Olympus OM-1; makes a nice paper weight.

 

[WortMonger]

Any more updates? I have been anxiously awaiting more taste tests and information about the batches.

 

[jammin]

x2 - I was excited to read an update when i checked my CP.

 

[Basevol]

I'm interested in this as well, I wonder how it would effect a lager fermentation.

 

[WortMonger]

My thinking on lagers is that stirring during the lagering period would increase the yeast to beer surface area, hence doing the same thing Budweiser does with the beechwood chips. What I love about this thread is how the OP is using it during primary. I am excited to even think about the additions that could occur during my pressurized fermentation. Sorry for the plug, but I think it could be discussed. When I do a P-ferment in a Sanke, I am alleviating some of the krausen height due to pressure anyway. With a stir going on, and the addition of Fermcap in conjunction with the benefits of pressure, I am seeing the possibility of even more volume in the primary fermentor. Now, take the fact that I am naturally carbonated before I transfer (all in a atmosphere free environment), and I should leave the bulk of primary yeast behind. If I were to put a stir-bar in my secondary/lagering keg, I should have plenty of yeasties swirling about to clean up the lager very quickly. Can you tell how pumped I am from this dude's thread? Can you? LOL

 

[Sulli]

Any more updates? I have been anxiously awaiting more taste tests and information about the batches.

As a matter of fact...I had another tasting party Friday night, and I got to taste a Sierra Nevada beer I've never even heard of; it was called Ruthless Rye, and it was quite delicious. [In fact it's the first rye beer I've tasted; I definitely see a homebrewed rye beer in my future]
The Stone Clones are now residing happily in their kegs; this time around each one had it's own distinct flavor profile. Of the two that were in unstirred carboys, one of them had a hint of diacetyl and tasted just a little off, I'm hoping it will still clean up some in the keg; the other tasted clean and had great hop aroma.
The carboy that was stirred, was excellent; clean as could be, with a nice smooth bitterness, a very balanced profile, and a great nose.
The conical, tasted very dry, and the bitterness was a little harsh, but I couldn't detect any off flavors, it was quite good.
All the carboys had a final gravity of 1.014; interestingly though, the conical finished out at 1.011, this is probably one of the reasons the bitterness tastes a little harsher.
To sum up, the stirred ferment is the clear winner here, in fact it I would say all it needs is some CO2 and 24 hrs in the kegerator, and it's good to go.
The others would do better with a couple more weeks of aging.
I'm extremely pleased with the result of this experiment, and plan on doing more stirred fermentations.
@Wortmonger: I look forward to hearing about your future experimentation with pressure-stirred-fermentation, good luck.

 

[mightynintendo]

So you had two unstirred carboys with exactly the same everything and they turned out differently?

 

[Basevol]

Reading about this experiment, I just get more and more questions. I see your keeping the yeast in suspension longer, and you are degassing all the time(stirring) so less co2 in suspension. Now add stirred fermentation under pressure to the mix.
Hope you both keep great notes and Post them.

 

[Sulli]

So you had two unstirred carboys with exactly the same everything and they turned out differently?

The only real difference was one of them had a slight buttery [diacetyl] flavor, but essentially, yeah.

 

[WortMonger]

Did you do a D-rest? I think slightly higher than fermentation temp would have taken care of cleaning up the diacetyl.

 

[Sulli]

Did you do a D-rest? I think slightly higher than fermentation temp would have taken care of cleaning up the diacetyl.

I did. After the first week of fermentation, I bumped the temp up to 74 degrees which they sat at for another week. Then I dry hopped them at that temp for an additional week. For some reason just that one carboy wasn't quite cleaned up. I'm going to leave it in the keg at room temp for a couple more weeks, it should clean up just fine.

 

[Satisfaction]

This thread inspired me to try this.. was thinking about it but just have not gotten around to doing it.

My stir setup with a 1.5" bar and 5 gallons of water. Quite surprised a vortex of this size shows up!

 

[Sulli]

This thread inspired me to try this.. was thinking about it but just have not gotten around to doing it.

My stir setup with a 1.5" bar and 5 gallons of water. Quite surprised a vortex of this size shows up!

Excellent! Let us know how it turns out.

 

[Satisfaction]

How long did you run the stir plate during the fermentation process?

 

[Sulli]

How long did you run the stir plate during the fermentation process?

I only ran it for about 4 days, but I had an extremely vigorous ferment. In retrospect, I think next time I will run the stir plate for at least a week.

 

[mightynintendo]

The only real difference was one of them had a slight buttery [diacetyl] flavor, but essentially, yeah.

I just don't understand how two carboys containing exactly the same everything could come out differently unless you did something different. I think you said before that you pitched the yeast after you moved the wort to the fermentation containers. Is this right?

If so, there must be a discrepancy in your pitch rates. I can't think of anything else that would cause the two unstirred carboys to come out tasting different.

 

[Sulli]

Yeah, I agree, it's weird. I was very careful in measuring my slurry; the entire slurry was contained in a 1000 ml Nalgene bottle, I just poured 200 ml into each 5 gallon volume, shaking it well between pours, of course.

The diacetyl is pretty subtle though, it's not like it's a butter bomb or anything like that.

 

[mightynintendo]

I guess it could also be there was some settling as you were transferring the wort to the respective containers. Do you use a hopback? just trying to think of other things that may have contributed to a different wort profile in different containers.

 

[Sulli]

I guess it could also be there was some settling as you were transferring the wort to the respective containers. Do you use a hopback? just trying to think of other things that may have contributed to a different wort profile in different containers.

Nope, no hopback.
Thinking back now though, I remember one of the unstirred carboys had a longer lag time than the other; maybe it had something to do with a difference in oxygen levels. The two unstirred carboys were just shaken for a few minutes each. I wasn't the one who did the shaking though, so maybe one got less time than the other.

 

[mightynintendo]

was the carboy with the diacetyl flavors the one that lagged longer?

I think we may be on to something with the oxygen levels.

 

[Sulli]

was the carboy with the diacetyl flavors the one that lagged longer?

I think we may be on to something with the oxygen levels.

At this point, unfortunately, I can't say with certainty which one it was.

 

[Hermit]

At this point, unfortunately, I can't say with certainty which one it was.

Bottom line is you didn't get the oxidation flavors the naysayers always said would happen even though the brew was airlocked? Never understood that reaction.

 

[mightynintendo]

Bottom line is you didn't get the oxidation flavors the naysayers always said would happen even though the brew was airlocked? Never understood that reaction.

He also only kept it under stirred fermentation for four days.

Keeping it stirred beyond some arbitrary fermentation activity level would increase the risk of oxygenation if you were opening the container for reasons like checking gravity and what-not.

I agree that there should be little reason for concern as long as there is active fermentation going on and there is no chance outside air is getting inside the container.

 

[Hermit]

He also only kept it under stirred fermentation for four days.

Keeping it stirred beyond some arbitrary fermentation activity level would increase the risk of oxygenation if you were opening the container for reasons like checking gravity and what-not.

I agree that there should be little reason for concern as long as there is active fermentation going on and there is no chance outside air is getting inside the container.

Letting air in shouldn't be any different, stirred or not. But, yeah. For purposes of this experiment I can see where it would be a problem.

 

[mightynintendo]

Letting air in shouldn't be any different, stirred or not. But, yeah. For purposes of this experiment I can see where it would be a problem.

Why wouldn't it be different? A stirred fermentation would have a higher gas exchange rate and would result in increased oxidization if there wasn't adequate yeast activity to consume any oxygen that wandered into the beer.

 

[Hermit]

Why wouldn't it be different? A stirred fermentation would have a higher gas exchange rate and would result in increased oxidization if there wasn't adequate yeast activity to consume any oxygen that wandered into the beer.

That's another thing I've wondered about. As long as you have active yeast, how much do you have to worry about oxidation anyhow? I bottle condition, generally after three weeks in the primary, and it isn't an issue then. I have some beers over a year old. Chris White seems to think the yeast scavenge available oxygen pretty rapidly.

 

[mightynintendo]

That's another thing I've wondered about. As long as you have active yeast, how much do you have to worry about oxidation anyhow? I bottle condition, generally after three weeks in the primary, and it isn't an issue then. I have some beers over a year old. Chris White seems to think the yeast scavenge available oxygen pretty rapidly.

As long as the yeast is active I think the risks of oxygenation are low. I can't speak with too much authority here as I am by no means a mycologist. However, you really don't want to introduce oxygen to your beer at any point after you pitch yeast early on. Alcohol is only created under anaerobic conditions. Like I said before with an active fermentation I don't think oxygen would have the ability to get into a well-sealed container with or without a stir bar. Once the activity level decreases and the yeast stop producing as much CO2, the chances of introducing oxygen to a stirred fermentation, especially after breaking the seal to check gravity, are probably higher than if it was not being stirred due to the increased gas exchange capacity.

Bottle conditioning has no problems with oxygenation if you're careful not to splash or otherwise aerate the beer.