Fermentation of ethanol

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Fermentation is a generic process for using yeast to convert sugars into dilute ethanol.


  • During the first (sealed) phase of fermentation, pressure can build rapidly if the yeast is particularly vigorous or the temperature is high. Prevent structural failure of vessels.
  • Potable ethanol can be a problem for some humans, both short and long term.


Fermentations are usually differentiated by the sugar feedstock:

Sugar Source Result
Honey Mead
Apples Cider
Molasses Rum
Malted grain Lager
malted grain stabilized with hops Beer
Mixed fruits / grains / sugars Moonshine

Alcohol content

The alcohol (ethanol) content of most undistilled (dilute) ethanol will range from 1.5% v/v to 8% v/v, mostly in the 4% range, depending on the particular breed of yeast.

Breeding more alcohol tolerant yeast is a matter of adding a bit (0.5-2.0%) of purified/concentrated ethanol to the brew (cooler, larger) sugar mixture before the started yeast is added. This will cause the reaction to proceed more slowly, but only the yeast that survives in the higher alcohol solution will reproduce and survive. Toward the end of the fermentation, periodically extract some of the (still viable) yeast and give it an alcohol-free water/flour/sugar mixture to thrive in. Retain the last yeast surviving, and use that as your next yeast starter.


  1. Gather 3 ubm of yeast
  2. Gather 225 ubm of sugar
  3. Gather 150 ubm of warm water
  4. Gather 600 ubm of cool/cold water
  5. Thoroughly mix the sugar with the warm water
  6. Separate 1/10th of the sugar/water mixture into a new container (called the yeast feed)
  7. Mix the cool water into the large sugar/water mixture (called the brew)
  8. Mix all of the yeast into the yeast feed
  9. Wait for 10 minutes
    Check: The yeast should have doubled in size, including the head
  10. Discard the yeast head
  11. Mix the yeast feed into the brew vigorously - bring lots of air into the mix.
  12. Place the brew into a container, filling the container to 3/4 full. (The rest is air)
  13. Seal the container.
  14. Shake the container if possible, to mix the air into the brew thoroughly.
  15. Wait one day
  16. If unsealing the container does not release pressure, repeat the seal/shake/wait.
  17. Seal the airlock onto the container
  18. Wait until the bubbling stops, typically several days to several weeks
  19. Filter
  20. Discard residue
  21. Retain the filtrate. It contains water and 3-8% ethanol.


  • This process works most efficiently when the temperature of the brew remains between 18°C and 23°C.
  • Almost any temperature between 10°C and 38°C will produce some ethanol.