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I am researching about the impact of sugar on wine fermentation, so I am looking for the equation of that reaction. However, there are a few different versions from different sources, so I was wondering which one is the right one to use and what does each equation represent?

\begin{multline} \ce{Glucose + 2 NAD+ + 2 Pi + 2 ADP ->}\\ \ce{2 pyruvate + 2 NADH + 2 ATP + 2 H+ + 2 H2O + heat}\tag{1} \end{multline} \begin{gather} \ce{C6H12O6 -> 2CH3CH2OH + 2CO2 + ATP}\tag2\\ \ce{C6H12O6 -> 2C2H5OH + 2CO2}\tag3 \end{gather}

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Generally there are two types of fermentation in biochemical processes:

  • homolactic fermentation
  • alcoholic fermentation

Both these processes occur under anaerobic conditions to replenish NAD+ by the reduction of pyruvate in an extension of the glycolytic pathway.

  1. The overall reaction in muscles is: $$\ce{Glucose + 2ADP + 2Pi -> 2 lactate + 2ATP + 2H2O + 2H^+}$$

  2. For alcoholic fermentation:

    Glucose is first converted to pyruvate by glycolysis, and the pyruvate is converted to ethanol and $\ce{CO2}$ in a two step process:

    enter image description here Note: For the second one we just started with pyruvate (to show mechanism and enzymes involved)Otherwise, for alcoholic fermentation, the net reaction is:

    $$\ce{Glucose + 2ADP +2Pi + 2H+ -> 2CO2 + 2C2H5OH +2ATP +2H2O}$$

Both homolactic and alcoholic fermentation have the same function: the anaerobic regeneration of NAD+ for continued glycolysis. Their main difference is in their metabolic products

Having said that lets go back to experimental wine fermentation, it is essentially alcoholic fermentation (2).

Enzymes in yeast (zymase a mixture of enzymes) and cozymase a mixture of cofactors-coenzymes such as NAD+ , ATP, and ADP, as well as metal ions) help carry out the fermentation reactions.

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  • $\begingroup$ So pyruvate converts to acetaldehyde while giving out CO2, then converts to ethanol, while NADH converts to NAD+? What would be the equation for that reaction? Is this process within the Glucose⟶2CO2+2C2H5OH process? $\endgroup$ – lzy Jul 29 '17 at 15:51
  • $\begingroup$ @Izy instead I have put net equations (starting all the way from glycolysis) but I wanted to emphasize the conversion of pyruvate to ethanol and CO2 in alcoholic fermentation $\endgroup$ – xavier_fakerat Jul 29 '17 at 17:22

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