fermentation question

[pippo]

wasnt sure if this should be in Biochem, or inorganic, so here it goes:

 

In fermentation, I heard that when yeast "digests" the sugar to create ethanol and CO2, a small amt of methanol also is produced, and stays in the solution. Its kind of an equilibrium. I heard the amt of Methanol is 0.5%. Then I said "wow- 0.5%" ?? Then the guy said "maybe it was 0.05%" (a doctor).

 

Man, 0.5% is high. I make my own beer, and dont want to go blind, people! Is there an equilibrium of methanol and ethanol in this reaction?

 

Thanks

[CharonY]

The actual fermentation pathway to ethanol using sugars as starting material does not yield methanol. So there is no equilibrium reaction between those two constituents.

However, during fermentation of beverages the starting material is more complicated (e.g. grapes for wine). Methanol can then be released during the breakdown mostly from pectin, I think. During pectin degradation a methyl residue is removed from a methylesterified galacturonosyl yielding methanol and a homogalacturonan, I think.

So again, it is mostly decoupled from the ethanol fermentation pathway.

 

However, many plants (especially the fruit) for fermentation are not terribly high in pectin and for wine I found concentrations between 0.1-0.2 g/L (or 0.01-0.02 % w/v).

[pippo]

The actual fermentation pathway to ethanol using sugars as starting material does not yield methanol. So there is no equilibrium reaction between those two constituents.

However, during fermentation of beverages the starting material is more complicated (e.g. grapes for wine). Methanol can then be released during the breakdown mostly from pectin, I think. During pectin degradation a methyl residue is removed from a methylesterified galacturonosyl yielding methanol and a homogalacturonan, I think.

So again, it is mostly decoupled from the ethanol fermentation pathway.

 

However, many plants (especially the fruit) for fermentation are not terribly high in pectin and for wine I found concentrations between 0.1-0.2 g/L (or 0.01-0.02 % w/v).

 

Big thanks, charion. I suspected that methanol equilibreum was malarchy (to borrow from Biden's debate last night....LOL). Just for the record, how did the back woods brewers in the mountains get methanol contamination in their booze?

[spider87]

I'm sorry to revive an old thread like this but I found it and I saw his last question and I know I used to wonder the same thing and figured I could help out someone else with my understanding of it at the same time.

 

My understanding is that the methanol was actually added to ethanol (moonshine) to denature it so that people couldn't drink it. That then perpetuated to "all moonshine has methanol" by way of people not being completely informed and gossiping, etc. The other possibility was, in some cases, moonshiners DID add nasty ingredients to their shines such as brake fluids and stuff. Some of those could be the reason for blindness back in the day.

 

Also, methanol is sometimes called wood alcohol or wood spirit because it was a byproduct of destructive distillation of woods. (This last bit is from the Wiki page because I remembered part of it but didn't want to fly off and miss something)

 

Lastly, do note that there sometimes are small amounts of methanol in fermented wines and beers (as Charon said) but, as far as my understanding of it goes, these are nowhere near enough to harm you.