Sulaiman
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KOH made my ethanol turn yellow ?
I made several batches of fermented sugar using various sugar concentrations and nutrient mixes,
multiple distillations (with a Vigreux column) were performed to ultimately give 3.6 litres of crystal clear 83%ABV with pH of about 4.
which I stored in a 5 litre PET water bottle.
While waiting for a fractionating column to arrive I neutralised the solution to pH near 7 using a little KOH.
A few days later I used more KOH to raise the pH to 10,
the next morning my ethanol solution was yellow !
I re-distilled the ethanol solution into five jars of 90 to 87 %ABV, the distillate in each jar is colourless with pH near 4.
I discarded c400ml of dark amber liquid left in the pot of pH near 13.
Q1) What caused the yellow colour ? (KOH + EtOH or KOH + PET bottle)
Q2) Why do the distillates have pH near 4 given that ethanol should be very slightly basic ?
CAUTION : Hobby Chemist, not Professional or even Amateur
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SWIM
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The yellow color could be from acetaldehyde polymerizing perhaps?
The initial low pH could be acetic acid.
Not sure how you'd be getting acetic acid in the second instance with all that KOH in there though.
Did you check the pH of the mash before you distilled it?
EDIT: I have distilled old soured wine a few times to reclaim the alcohol.
When I did this, I'd add some bicarbonate of soda to each batch to fix the acetic acid.
Boiling White wines with bicarbonate left a brown residue that looked like wine spiked with pine tar.
[Edited on 29-5-2020 by SWIM]
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OldNubbins
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From my experience making a whiskey-like drink from straight sugar, especially with turbo yeast which contains nutrients, there are a fair amount of
congeners both in the heads and tails of the distillate that I would imagine can contribute to the pH and color.
[Edited on 5-29-2020 by OldNubbins]
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draculic acid69
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Turbo yeast does indeed lead to a dirty harsh product.apparently it makes lots of acetone methanol and fusels
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Sulaiman
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The fermentations finished with pH from 3 to 4 depending upon starting conditions.
One batch finished with pH near 5 due to added oyster shells.
The fermentations finished with ABV from 5% to 15% depending upon the quantity of sugar used.
All fermentations used dried bakers yeast.
c100ml of foreshots were saved from the final 3.6 litre distillation for misc. usage.(Jar#1)
Near the end of the final distillation, after the 5 'cuts' were saved, I added some lower %ABV from earlier distillations to get a sixth jar of c400ml
83%ABV.(Jar #7)
All distillates are water clear and colourless.
The final 400ml in the pot were discarded due to the high pH.
As the distillation proceeded the yellow colour intensified, mainly I think due to concentration.
Various online resources indicate that PET is not compatible with KOH which is why I wonder if the yellow came from the EtOH or the PET.
P. S. SM was only down for 36 hours?... It seemed much longer... I was experiencing withdrawal symptoms 
[Edited on 29-5-2020 by Sulaiman]
CAUTION : Hobby Chemist, not Professional or even Amateur
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Ubya
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PET is not compatible with KOH because it hydrolizes the polymer, but the products are potassium terephtalate and ethylen glycol, both transparent in
solution. you probably distilled some aldehydes or chetones that polymerized in the highly basic solution. distilled liquors have a different taste
from pure ethanol for a reason
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OldNubbins
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Try diluting to 40-50% and freezing. The fusel oils should start to separate and float to the surface. Filter through activated carbon then redistill.
Low fermentation pH can increase fusel oil formation as well as certain nutrient combinations. The oyster shells may have carried some unknown
variables into the fermentation.
Too bad you can't drink - I always went by tasting the distillate to tell when to take the foreshots and tails. Once it started tasting like an old
dishrag it was time to stop 
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