State of carbon dioxide during fermentation

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Discussion Overview

The discussion centers on the state of carbon dioxide during the fermentation process, specifically whether it is expelled as a gas or remains in an aqueous state. The scope includes theoretical aspects of fermentation chemistry and practical implications observed in brewing.

Discussion Character

  • Homework-related
  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant suggests that carbon dioxide is initially in an aqueous state and then escapes as gas as the solution settles.
  • Another participant proposes that carbon dioxide forms aqueous carbonic acid during fermentation.
  • A later reply emphasizes that carbon dioxide will be dissolved in the liquid but can escape as gas, depending on solubility and the amount produced during fermentation.
  • It is noted that the solubility of carbon dioxide in water and the moles produced are critical factors in determining how much remains dissolved versus how much escapes.
  • One participant mentions that the vapor pressure above the liquid influences the amount of dissolved carbon dioxide, highlighting that brewing under pressure increases solubility.

Areas of Agreement / Disagreement

Participants generally agree that carbon dioxide is both dissolved in the liquid and can escape as gas, but there is no consensus on the exact dynamics of this process, including the influence of solubility and pressure.

Contextual Notes

The discussion does not resolve the specific conditions under which carbon dioxide remains dissolved versus when it escapes, nor does it clarify the exact solubility limits in the context of fermentation.

miniradman
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Homework Statement


I know that the process of fermentation occurs in two steps, however, in the second step where glucose/sucrose is broken down into ethanol and carbon dioxide, is the carbon dioxide expelled as a gas or in an aqueous state? (I'm assuming water is involved here)

Homework Equations


C_6 H_12 O_6 <sub>(aq)</sub> \rightarrow 2C_2 H_5 OH <sub>(l)</sub> + 2CO_2 <sub>(?)</sub>

The Attempt at a Solution


Well, I'm going to take a stab in the dark and say its in an aqueous state, then escapes as gas as the solution settles down.
 
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Yep. Aqueous carbonic acid.
 
Try to take a trip round a brewery one day. Then you'll see. :smile:

Don't fall into the fermentation vat though, it might sound nice but without immediate trained rescue you would soon suffocate. Don't even fall into it after they have opened the plug and taken the beer away. :wink:
 
Last edited:
Both chemisttree and epenguin are correct, the CO2 will be dissolved aqueously and then potentially escape out as gas. If you wanted to know exactly how much CO2 will remain dissolved vs. how much will escape, you would have to know the solubility of CO2 gas in the liquid (say, water), and the moles of CO2 that are being created. In the case of fermentation, typically the amount of moles of CO2 created are very high, and easily overpower the solubility of H2O, thus resulting in large amounts of CO2 gas being released. However, the water that the fermentation is taking place in will also be heavily saturated with dissolved CO2. That is why when you open the top off of a soda or beer the dissolved CO2 begins escaping.

EDIT: I should have added that the vapor pressure on top of the liquid will also affect how much CO2 is dissolved vs. escapes as a gas. This is why beer is typically brewed under pressure, increasing the amount of CO2 that is dissolved.
 

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