Stir Plate During Fermentation

I am doing a small experiment to see what effect keeping the yeast in suspension all the way through fermentation will have. I'll update as I get more data.

I did a simple Weissbier from extract. 1/4 lb Crystal 45 steeped until 170F, 3 lb Wheat DME, 1 lb Pilsner DME, 1/2 oz Hallertauer for 60min. My OG was 1.047 and was estimated to be 1.050.

I ended up with 3.50 gallons in the brew kettle and moved 1.5 gallons of wort into each of two 2 gallon buckets. I checked them by weight and each bucket had exactly the same amount of liquid. I then (by weight) divided up a packet of T-58 and sprinkled the yeast evenly over each batch.

I then put one of them on my stir plate and turned it up until the liquid was being noticeably swirled but no funnel was forming on the surface. I affixed lids fitted out to accept an air-lock and put a 3-piece in each. My basement has a relatively constant temperature of 65F. I didn't want to kick the Dunkelweizen out of the chest freezer / temperature controller just for this quick experiment and I'm satisfied that the fermentation temp is reasonable.

Here are my notes so far:


Control Batch:

DATE / TIME (hrs from start of fermentation) / GRAVITY/ NOTES

19 Sept 2012 / 19:00 (0) / 1.047 / Like an unfermented beer, malty and bitter.

20 Sept 2012 / 08:45 (13.75) / 1.036 / Still like a relatively unfermented beer, the bitterness has dropped off and there is a big round sticky sweetness to it. Banana is beginning to come through and just a trace of phenols when I burp afterward (band-aid flavor). Thick, creamy white krausen with some yeast on top.

20 Sept 2012 / 16:00 (21.00) / 1.026 / Tastes about the same as before, a little more banana and some spice. Some light phenols are coming through.

21 Sept 2012 / 01:15 (30.75) / 1.018 / The krausen has reduced but is still prominent on the top of the beer. The phenol odor and flavor has increased slightly but the banana flavors have leveled off. There is no clean malt profile, everything is smeared together. Acetaldehyde is noticeable now. The beer tastes green.

21 Sept 2012 / 09:45 (39.25) / 1.017 / The white topping has fallen in but there is still a noticeable layer of darker yeast coating the top of the beer. Only a trace of Acetaldehyde was detected. Phenols are decreased but still come through on the nose, in the flavor, and especially when I burp. Same as the stir-bar beer, I didn't notice the banana flavor anymore but a spiciness is developing. The malt flavor tending toward the wheat side of things is noticeable in this batch as well as the stir-bar beer.


Stir-Bar Batch:

19 Sept 2012 / 19:00 (0) / 1.047 / Like an unfermented beer, malty and bitter.

20 Sept 2012 / 08:45 (13.75) / 1.032 / Still like a relatively unfermented beer, the bitterness has dropped off and there is a sweetness to it. Phenols came through on the nose and heavily when I burped afterward. A little banana is forming as well. Thick, creamy white krausen with some yeast on top.

20 Sept 2012 / 16:00 (21.00) / 1.022 / Same changes as the control except the phenol smell and taste is more pronounced.

21 Sept 2012 / 01:15 (30.75) / 1.018 / All of the krausen has dropped back into the beer. The phenol odor and flavor is much more pronounced than in the control, as is a malty flavor I would associate with the pilsner malt. I detected almost no Acetaldehyde where the control still has a green flavor.

21 Sept 2012 / 09:45 (39.25) / 1.017 / Some carbonation looking bubbles on the top of the beer. Zero green flavors detected and the phenol odor, flavor, and aftertaste have all mellowed out. The banana I detected early on I can't sense anymore but there is an almost peppery spiciness which is coming through. Also, that Pilsner malty flavor wasn't pronounced anymore, it tastes more like a wheat beer now.


Notes:

This experiment is far from perfect. Also, a +/- 0.002 is assumed on all the gravity readings, which means that the two samples are fermenting at the same rate (within the measured error).

Holy crap, brewing is so much fun! And... Science!

Cheers!

-PhysicsBrew

PhysicsBrew said:

I am doing a small experiment to see what effect keeping the yeast in suspension all the way through fermentation will have. I'll update as I get more data.

I did a simple Weissbier from extract. 1/4 lb Crystal 45 steeped until 170F, 3 lb Wheat DME, 1 lb Pilsner DME, 1/2 oz Hallertauer for 60min. My OG was 1.047 and was estimated to be 1.050.

I ended up with 3.50 gallons in the brew kettle and moved 1.5 gallons of wort into each of two 2 gallon buckets. I checked them by weight and each bucket had exactly the same amount of liquid. I then (by weight) divided up a packet of T-58 and sprinkled the yeast evenly over each batch.

I then put one of them on my stir plate and turned it up until the liquid was being noticeably swirled but no funnel was forming on the surface. I affixed lids fitted out to accept an air-lock and put a 3-piece in each. My basement has a relatively constant temperature of 65F. I didn't want to kick the Dunkelweizen out of the chest freezer / temperature controller just for this quick experiment and I'm satisfied that the fermentation temp is reasonable.

Here are my notes so far:

Control Batch:

DATE / TIME (hrs from start of fermentation) / GRAVITY/ NOTES

19 Sept 2012 / 19:00 (0) / 1.047 / Like an unfermented beer, malty and bitter.

20 Sept 2012 / 08:45 (13.75) / 1.036 / Still like a relatively unfermented beer, the bitterness has dropped off and there is a big round sticky sweetness to it. Banana is beginning to come through and just a trace of phenols when I burp afterward (band-aid flavor). Thick, creamy white krausen with some yeast on top.

20 Sept 2012 / 16:00 (21.00) / 1.026 / Tastes about the same as before, a little more banana and some spice. Some light phenols are coming through.

21 Sept 2012 / 01:15 (30.75) / 1.018 / The krausen has reduced but is still prominent on the top of the beer. The phenol odor and flavor has increased slightly but the banana flavors have leveled off. There is no clean malt profile, everything is smeared together. Acedylhyde is noticable now. The beer tastes green.

Stir-Bar Batch:

19 Sept 2012 / 19:00 (0) / 1.047 / Like an unfermented beer, malty and bitter.

20 Sept 2012 / 08:45 (13.75) / 1.032 / Still like a relatively unfermented beer, the bitterness has dropped off and there is a sweetness to it. Phenols came through on the nose and heavily when I burped afterward. A little banana is forming as well. Thick, creamy white krausen with some yeast on top.

20 Sept 2012 / 16:00 (21.00) / 1.022 / Same changes as the control except the phenol smell and taste is more pronounced.

21 Sept 2012 / 01:15 (30.75) / 1.018 / All of the krausen has dropped back into the beer. The phenol odor and flavor is much more pronounced than in the control, as is a malty flavor I would associate with the pilsner malt. I detected almost no acedelhyde where the control still has a green flavor.

Notes:

This experiment is far from perfect. Also, a +/- 0.002 is assumed on all the gravity readings, which means that the two samples are fermenting at the same rate (within the measured error).

Holy crap, brewing is so much fun! And... Science!

Cheers!

-PhysicsBrew

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Subscribed. Good luck

Thanks for doing this and keep us posted.

Here is a tip for keeping track of the fermentation progress: determine the weight of the wort before shortly after adding the yeast. Weigh the complete flask on a regular basis (once or twice per day) and plot the weight loss in % of initial wort weight.

I have done this for a number of my fermentation experiments. (like this one http://braukaiser.com/blog/blog/2012/06/09/pitching-rate-experiment/). It keeps you from having to remove a sample and it is much faster. You still want to take a final gravity reading, though.

Kai

I don't know what T-58 is but if it is a wheat beer strain (and I assume it is as you mention bannana) I'd say that isn't a very good strain to do this experiment with because wheat beer strains are top croppers which, in a vigorous, healthy ferment, practically chase you out of the brewery. Thus I wouldn't expect much difference between stirred and unstirred beers made with such a strain unless the differences are due to effects that occur after flocculation. It would be, and this is, of course, no more than my opinion, much more interesting to do the experiment with a bottom fermenter such as a lager yeast. One of my brewing 'secrets' is that I keep lager yeasts in suspension throughout the fermentation and conditioning because of the design of my fermentors (not because I am so brilliant that I figured out that this is a good thing to do and no - I didn't design the fermentors so I can't claim credit for it that way either).

Thank you both for the feedback.

Kai, that is a wonderful idea and would definitely make this much easier. Nice experiment, by the way! I am looking forward to some brewing lab work. I've gotten so sick of reading forum posts where everyone seems to think something is true because enough people repeat whatever it is enough times. Besides... beer and science. What could be a more awesome combination? You'll get a kick out of this: I was going to put a temperature probe in my beer, one taped to the carboy, and the probe from the temperature controller in the chamber so I could see what the system looks like as the freezer gets turned on and off. I was at lunch with my former adviser (we both do computational physics) and he said "Why don't you program up a model?" Holy crap that will be fun! I'll make a post on that when it is completed.

Ajdelange, here is a link to information on the yeast: T-58.

Thanks again,

-PhysicsBrew

Based on the spec's I'd say this is not a wheat beer strain so I am a bit surprised at the amyl acetate production but then lots of yeast produce amyl acetate - just not at the levels one associates with wheat beer yeasts. I do not that it is a medium flocculator IOW it will tend to stay in suspension by itself. Thus I continue to think that you might get more interesting data with a more flocculent strain. But then all data is interesting data in the final analysis.

Stirred fermentation is something that may be worth looking into for lager fermentations since they tend to be sluggish towards the end. When I researched this topic I did find lots of papers out there since commercial brewing has had some interest in this.

One note of weighing the flasks to monitor stirred fermentation. Since a stirred beer will be less supersaturated with CO2 than the unstirred beer it may appear that the unstirred ferment takes longer to get started when you look at the weight loss. This is because the produced CO2 doesn't escape as quickly.

And yes, you can model this weight loss as well.

Kai