Fermentation & Heat



I am a student at the University of Iowa and I am trying to finish up a major project that is due in two days.

 

My focus is on the wine production process and I was wondering if you could give me that formula for fermentation in relation to wine production. I need this to perform a heat of reaction around the fermentation process and I need to know more than: sugar + yeast = alcohol + CO2.

 

I need metabolic pathways for yeast and other side products that may be occurring. Any help you may offer would be greatly appreciated.



Volumes have been written on the subject. Most important wine yeast are Saccharomyces cerevisiae and S. bayanus.

 

There are many strains of both cerevisiae and bayanus used in making wines. Each produces the alcohol and CO2 that you refer to. Each is selected for other particular by-products that contribute to wine flavor and aroma. There are over 1000 organic compounds produced during wine fermentation that are present in subtle amounts contributing to the complexities of wine.

 

The amounts of these by-products that are produced depend on the yeast strain, fermentation temperature, pH and grape condition and variety.

 

The following may be of help regarding heat production:

 

Oxidation: C6H12O2 + 6O2 + yeast = 6CO2 + H2O + yeast cell mass + 686 kcal.

 

Fermentation: C6H12O2 + yeast = 2C2H5OH + 2 CO2 + >1000 organic compounds + 54 kcal.

 

You will note that in the oxidation process (presence of air), there is a more efficient combustion of the sugar to give the yeast more energy for reproduction. One very important fact to remember in the oxidation process is the Crabtree effect. When the sugar is over 0.02%, the mitochondria bodies are damaged to the point the yeast will produce alcohol instead of cell mass no matter how much oxygen is present.

 

You will have to get a flow chart on the metabolic pathways, from your biochemistry department, to begin to get an idea of all the possible organic by-product compounds produced from sugars and the other yeast nutrients required for yeast growth and alcohol production. Hope that this points you in the right direction.



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