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Old 12-14-2011, 11:09 PM   #1
tCan
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Default Anyone measure their rate of fermentation?

I ferment with a balloon as my airlock. The fun advantage of this is it allows you to roughly measure the rate of fermentation. If it takes roughly twenty seconds to fill a ~75ml balloon with CO2, then you can crunch the numbers and figure out that roughly 93.3 Quintilian (9.33x10^19) molecules of CO2* are being produced every second.

We also know that 2 molecules of CO2* are made from every sugar molecule. If the population size is known, you can then calculate the rate of fermentation per cell (since yeast are unicellular organisms). The hard part is counting them all.

If you also know the maximum alcohol tolerance of the specific yeast you are using, then you can estimate the appropriate amount of sugar to add to achieve a desired result, be it dry or sweet. This would be useful for recipies you've not yet tried before. Tracking the rate of fermentation at several hour intervals also offers insight into the alcohol tolerance of certain yeasts, assuming abundant sugar and appropriate temperature.

Footnotes:
* - and ethanol


EDIT: DATA POSTED! Click to go to post





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Old 12-16-2011, 12:01 AM   #2
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We also know that 2 molecules of CO2* are made from every sugar molecule. Footnotes:
* - and ethanol
Is that true for every yeast strain?
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Old 12-16-2011, 01:33 AM   #3
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tCAN, I guess you are new to this infatuation. What's the point. Brew it, check it's fermenting, go drink and come back 2 weeks later. Watching is is not going to make it go quicker, or change how the beer is going to turn out.

Have fun with it.

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Old 12-16-2011, 01:44 AM   #4
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Ehh I'm a geek for science and all. But use a hydrometer...

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Old 12-16-2011, 01:48 AM   #5
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What happens when the balloon fills up all the way? Does it fly off your carboy and make farty noises as it flies through the air or does it pop?

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Old 12-16-2011, 05:45 AM   #6
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Originally Posted by maltoftheearth View Post
Is that true for every yeast strain?
As far as I know, it holds true for every 6 carbon sugar converted to ethanol.

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Originally Posted by Calder View Post
tCAN, I guess you are new to this infatuation. What's the point. Brew it, check it's fermenting, go drink and come back 2 weeks later. Watching is is not going to make it go quicker, or change how the beer is going to turn out.

Have fun with it.
The point? FOR SCIENCE!

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Ehh I'm a geek for science and all. But use a hydrometer...
Less awesome, and less informative. Also, I thought this was the science sub-forum?

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What happens when the balloon fills up all the way? Does it fly off your carboy and make farty noises as it flies through the air or does it pop?
I've poked some tiny pinholes in the balloon which bleed the excess pressure.
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Old 12-16-2011, 12:14 PM   #7
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Is that true for every yeast strain?
It's approximately true for any strain that ferments (as opposes to respires) for the portion of the hexoses that are fermented.

C6H12O6----> 2 CH3CHOCOOH --> 2 CO2 + 2 CH3CHO --> 2 CH3CH2OH

As written many reactants, products and intermediate products (ADP, ATP, NAD, NAD+, H+, H2O) are left out here - that's why it doesn't balance WRT hydrogen)

But not all sugar goes down this pathway. Some is diverted for the formation of amino acids, some for sterol synthesis, some winds up in esters etc.

Balling found that 2.0665 grams of "extract" produce 1.0000 gram of alcohol, 0.9565 grams of CO2 and 0.11 grams of yeast biomass. This finding is the basis for the formulas we use to calculate alcohol production based on specific gravity change (extract consumption) but one could, of course, also use Balling's findings to estimate it based on production of CO2. Getting the weight of CO2 is a bit tricky. First off, all the CO2 that the yeast produce are not evolved. One could use the temperature tables to estimate the number of volumes of CO2 contained in each volume of beer and convert that to mass. The gas evolved would be tricky to measure too. Obviously the mass contained in a given volume is strongly dependent on pressure so you would need to know the pressure inside the balloon to determine the mass of CO2 in its known volume. You could tare the balloon and then weigh it when full but don't forget to correct the weighing for buoyancy - it would be a big factor here. Also don't forget to correct the weighing for the water vapor content.

Every brewer monitors his rate of fermentation first by the rate of CO2 production. If the CO2 is running steadily then its going full bore. When it slows to blurp.......blurp.......blurp then it's time for a hydrometer reading.
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Old 12-16-2011, 03:53 PM   #8
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Thanks for typing that up! I just thought I'd add that some species, humans for example, will ferment with different products entirely. When humans ferment (as during vigorous physical activity) pyruvate is reduced to lactic acid. Lactic acid is a waste product and must be eliminated. In the presence of abundant oxygen, the pyruvate is instead converted to Acetyl-Coa which can be used in further energy production.

Other products of fermentation can include lactate, CO2, hydrogen gas, and methane. Of course, there also exists other types of energy production, anaerobic respiration results in a myriad of end products, but that's another topic.

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Old 12-16-2011, 04:16 PM   #9
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Would this work?

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Old 12-16-2011, 05:23 PM   #10
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Quote:
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will ferment with different products entirely.
I should have said "ferments to ethanol". When making sauermalz, for example, we rely on L delbrukii to ferment sugars to lactate.
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