English

Yeast Fermentation

Middle schoolBiologySubstrate-limited virtual fermentation with stoichiometric ethanol and carbon dioxide production

Unlock this lab with a pass

A pass opens every simulation on the site, including Present mode for class. The teaching notes below stay free for everyone.

See passesI already have a pass

One-time payment, no subscription.

About this experiment

Use a virtual fermentation vessel and gas collector to investigate how sugar, yeast amount and temperature affect products. Divert new gas without erasing the amount already collected.

Learning goals

  • Relate sugar consumption to ethanol and carbon dioxide mass.
  • Distinguish generated gas from collected and vented gas.
  • Compare rate effects with the total amount possible from a sugar supply.

How to use it

  1. 1Run an 80 g/L sugar trial for eight hours and record its products.
  2. 2Divert new gas now, then continue the run and compare collected with vented carbon dioxide.
  3. 3Increase yeast concentration and compare equal-duration trials.
  4. 4Change the sugar concentration and compare the remaining substrate and alcohol fraction.

The model

Products follow the balanced fermentation reaction.
The consumption rate decreases as substrate is depleted.

Assumptions

  • The vessel is anaerobic, well mixed and at constant liquid volume with fixed active yeast biomass. Growth, respiration, death and inhibition are omitted.
  • Substrate use follows an illustrative saturating rate with a 5 g/L half-saturation concentration and a Gaussian temperature response centred on 30 °C.
  • Every mole of glucose consumed forms two moles of ethanol and two moles of carbon dioxide. The molar masses used sum exactly for mass accounting.
  • All captured carbon dioxide is treated as dry ideal gas at 298.15 K and 1 bar. Dissolution and headspace delay are omitted.
  • The displayed balloon radius uses logarithmic gas-volume scaling. Planned collection-cutoff edits recalculate collection history; the immediate diversion action retains collected products.

Try this in class

  1. Q1Why does ethanol continue increasing after gas diversion?
  2. Q2How does raising yeast concentration differ from adding more sugar?

Frequently asked questions

Does the balloon show the actual vessel pressure?

No. Gas is reported at a fixed reference temperature and pressure; the balloon is a volume symbol with compressed visual scaling.

Does hotter always mean faster?

No. This illustrative rate peaks at 30 °C, and the model does not represent all yeast strains or predict a real fermentation.