Fermentation – lactic acid and ethanol pathways
BiologyMicrobiology & VirusesAges 15–16Virtual lab
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Microbiology & Viruses
Incubate a batch culture with microorganisms: choose the strain, temperature, initial sugar level and whether oxygen is present, and track cell density, remaining sugar, product and pH. A second screen makes tempeh and tape: vary the temperature, wrapping and time and watch mould mycelium bind soybeans into a cake, or moulds turn starch into sugar and yeasts turn it into alcohol, with red oncom and yoghurt for comparison.
Lesson: Microbial fermentation and its applications
What it shows
Fermentation lets microorganisms release energy from sugar without oxygen. Lactic acid bacteria turn glucose into lactic acid, which lowers the pH and stops spoilage microbes; yeast makes ethanol and carbon dioxide but switches to aerobic respiration when oxygen is present. Moulds ferment solid foods. In tempeh, Rhizopus hyphae grow through cooked soybeans, bind them into a firm cake and partly break down their protein; the mould needs warmth, moisture and some air. In tape, mould enzymes turn starch into sugar, then yeasts turn the sugar into ethanol. The model is simplified, with typical values.
How to use
On Lactic acid and ethanol, choose the Strain, set Temperature and Sugar, and compare a sealed jar with Lid open (O₂ present). On Tempeh and tape, choose the Food, Incubation temperature, Wrapping and Harvest after, then press Start incubation. Each harvested batch adds a row to the table; try the three tasks below it.
Parameters you can change
- Microorganism strain Lactic acid bacteria (sauerkraut, yogurt), Yeast (wine, bread)
- Incubation temperature 5–50 °C
- Initial sugar content 10–200 g/L
- Oxygen present (lid open)
- Screen Lactic acid and ethanol, Tempeh and tape
- Food (Tempeh and tape screen) Tempeh (soybeans + tempeh starter), Tape (starchy food + tape starter), Red oncom (for comparison), Yoghurt (for comparison)
- Starchy food for tape Steamed cassava, Steamed glutinous rice
- Incubation temperature (Tempeh and tape screen) 15–50 °C
- Wrapping Banana leaf, Plastic with air holes, Sealed plastic, Uncovered tray
- Harvest time 2–96 h
Questions to explore
- Why must a sauerkraut jar be sealed with the vegetables kept below the liquid?
- With 200 g/L of sugar, does the yeast use all of it? What stops the fermentation?
- Why does tempeh in sealed plastic spoil instead of becoming a firm white cake?
