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Caffeine inhibition

Success Goal

Use caffeine-containing liquids to inhibit the growth of your culture.



  • At least two available Pioreactors
  • Dry baker's yeast
  • YPD broth mix, or any other media mix
  • Caffeine-containing liquids (tea, coffee)


Yeasts are versatile eukaryotes that have biological systems synonymous to those found in humans. Substances that affect us are likely to affect yeast as well, so yeasts are commonly used in research to study certain behaviours. Let's take a look at yeast reactions to caffeine, and model these behaviours using our Pioreactor!

Caffeine is the most common stimulant in the world, and is found in many consumed items such as coffees, teas, chocolates, and even within certain medication. Ponder this: what do you expect to happen when caffeine is added to yeast cultures? We know that we feel more awake and focused after consumption, but have your students think about why this happens. Think about both the positives and negatives of consuming coffee and form a hypothesis on how yeast cultures will react to caffeine addition. Also consider the other components of black tea


We used two Pioreactors and two vials containing 15 mL of YPD media. We added 1 mL DI water to one vial and 1 mL steeped black tea to another. For the steeped black tea, a teabag was steeped in 250 mL hot water for 5 minutes before inoculation. Finally, we inoculated with 100 uL yeast slurry using a micropipette.


The growth rate chart clearly demonstrates an inhibition of growth occuring in the sample containing tea:


We recommend trying different amounts of tea, coffee, or other caffeine containing liquids to evaluate effects of caffeine concentrations. For example, how does adding one drop of black coffee compare to one drop of black tea? For a larger study, also consider giving your students a collection of common substances (vinegar, teas, salt, sugars) and see how these can boost or reduce growth rates.

Detailed procedure

  1. Prepare identical sterile stocks in vials with your media of choice.
  2. Add some amount (a few drops to 1 mL) of a liquid containing caffeine to a vial. Add the same amount of DI water to another vial.
    • If the media appears different before inoculation, we recommend you blank your vials before adding your culture.
  3. Inoculate each vial with a very small amount of your microorganism, using best practices to avoid other contamination.
    • In our example, a yeast stock solution can be made by diluting a small amount of yeast in 15mL of YPD stock media, then a drop of this stock solution can be added to your vials.
  4. Wipe the vials and place them in the Pioreactors.
  5. Visit pioreactor.local and start a new experiment.
  6. On the left menu, select the Pioreactors page. Add any additional Pioreactors that you would like to use (more information here).
  7. Select Manage all Pioreactors, and start Stirring activity, Temperature automation activity (set to an optimal temperature; ex. 30°C) and OD reading activity.
  8. Confirm that everything looks normal (ex: receiving optical density signal).
  9. Back on the Pioreactors page, select Manage all Pioreactors and start Growth rate. It will take a minute for results to begin showing up.
  10. Watch growth progress on the Overview page.