Yeast in Fermentation Process

dazza95

Yield of ethanol is mostly about survivability of the yeast.

We were wondering why Yeast can't survive too high concentrations of ethanol?
Something to do with the denaturation of proteins?
Not really sure on this, any help is appreciated
Thanks

Dadface

I don't know much about this but your answer seems to make sense.As time passes the rate of fermentation seems to die down due to, I'm guesssing,the enzyme proteins becoming less active and tending towards denaturing.Enzymes can be sensitive to temperature and PH and in this case,I assume to ethanol concentration as well.

dazza95

Here are some notes we gathered, does any of it make sense. Or is any of it a reasonable explanation?

A 62% ethanol solution is used as a disinfectant on the skin. This concentration of alcohol is able to penetrate the bacterial cell wall and denature the proteins and enzymes inside of the cell. A 95% alcohol solution merely coagulates the protein on the outside of the cell wall and prevents any alcohol from entering the cell. Alcohol denatures proteins by disrupting the side chain intramolecular hydrogen bonding. New hydrogen bonds are formed instead between the new alcohol molecule and the protein side chains.

Proteins depend heavily on "hydrophobic" interactions
Water molecules like to form strong hydrogen bonds with each other, if there's a large surface area of protein in the solution, these interactions are disrupted. In order to minimise exposed surface area, the bits of the protein which aren't able to interact with each other tend to fold over themselves to minimise exposed surface area.

It's basically the same reason oil and water don't mix.

In ethanol, however, the tendancy for non-interacting regions to stick together is much weaker so proteins tend to unfold.

The more water that is added, the more pure the ethanol is because it denatures protein too quickly and forms a thin outer layer of denaturated protein beyond which the cell lives on.

dazza95

Don't worry about the above post,
we have refined it down to this explanation, not sure if it is entirely correct,
Alcohol denatures proteins by disrupting the side chain intramolecular hydrogen bonding. New hydrogen bonds are formed instead between the new alcohol molecule and the protein side chains.

Proteins depend heavily on "hydrophobic" interactions
Water molecules like to form strong hydrogen bonds with each other, if there's a large surface area of protein in the solution, these interactions are disrupted. In order to minimise exposed surface area, the bits of the protein which aren't able to interact with each other tend to fold over themselves to minimise exposed surface area. In like a ball or coil.
The more pure the ethanol is, the tendancy for non-interacting regions to stick together is much weaker so proteins tend to unfold.

The more water that is added, the more pure the ethanol is because it denatures protein too quickly and forms a thin outer layer of denaturated protein beyond which the cell lives on.
Too much alcohol = dead yeast.
Hydrogen bonds cause the tertiary structure (ethanol) to stuff up. Only one hydrogen bond needs to stuff up and the whole process is over and the yeast dies.