Why Can't Yeast Survive High Concentrations of Ethanol in Fermentation?

[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 tendency 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,

why Yeast can't survive too high concentrations of ethanol?
Something to do with the denaturation of proteins?

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 tendency 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.

 

[LudusRex]

Thank you for your question. The survivability of yeast during fermentation is indeed a crucial factor in the yield of ethanol production. Yeast is a type of microorganism that plays a central role in the fermentation process by converting sugar into ethanol and carbon dioxide. However, as you mentioned, yeast has a limited tolerance for high concentrations of ethanol, and this can significantly impact its survival and ability to produce ethanol.

The main reason for this is the denaturation of proteins. Ethanol is a solvent that can disrupt the structure and function of proteins, which are essential for the yeast's survival and fermentation activity. As the concentration of ethanol increases, it can cause the proteins to unfold and lose their shape, rendering them unable to carry out their biological functions effectively.

Additionally, high concentrations of ethanol can also lead to changes in the cell membrane of the yeast, making it more permeable and disrupting its ability to maintain proper internal conditions. This can further impact the yeast's survival and ability to produce ethanol.

To ensure the survival of yeast during fermentation, it is essential to maintain a suitable environment with optimal levels of ethanol and other nutrients. This can be achieved by carefully monitoring and controlling the fermentation process, allowing for the yeast to thrive and produce the desired amount of ethanol.

I hope this helps to answer your question. If you have any further inquiries, please do not hesitate to reach out. Thank you.