Lime Jello, Yeast and Carbon Paper Fuel Cell

Step 2 Preparing the Microbial Media

Nutrient media is a fancy name for gelatin, sugar, yeast and some nutrients.

Grab a bowl and pour the Jello mix into it.

Measure out two cups of water and place them off to the side with some ice cubes to cool it down.

Bring two cups of water to a strong boil. Make sure you get the full two cup measure of boiling water. Add this to the gelatin mix and stir for about two minutes. Make sure that all the contents are fully dissolved.

When the candy thermometer shows that the temperature has cooled to around 100 degrees add one packet of yeast and stir to dissolve. Stir for several minutes allowing the media to cool naturally. After about 5 minutes pour into the pan or mold you are using. Use the cold water to rinse out any yeast bits stuck to the side and pour into the mold. Mix well and place in refrigerator or freezer to set.

Comments

[meekah]

i was trying a couple of variations and noticed something. is there a possibility that the effect of added nutrients (sugar) would not necessarily mean a higher voltage reading but a longer shelf life for the mfc because the yeast would thrive longer?

[egbertfitzwilly]

Absolutely. In that scenario I would expect that the yeast population has stablized at some level and survives for longer because of the additional nutrients. Possibly because the gelatin restricts mobility so there are little, yeasty slums surrounded by rich nutrient.

If you have a voltmeter I would be very interested in the power curve you get for your experiments. Just measure the voltage and current several times a day (whenever its convenient) and note the times and output over a week or so (or until the voltage drops below anything at all useful).

If you done a couple please publish an instructable and share your experiments. Even if "pure" scientific method isn't followed the results can be very informative and useful to others. Plus it will make you feel smarter, trust me....:-)

I have no good theory about how one might measure the yeast population, that's the really interesting bit.  A theoretical population can be guesstimated but doesn't really reflect the population growth curve.

[meekah]

when i  prepared the gelatin mix, it was kinda hardening as i was cooling it down. the yeast also floated at the top once added and did not really mix well. any suggestions? may i ask also if the yeast would die if the medium was too hot when the yeast was added?

[egbertfitzwilly]

You want the fluid to cool to about 100 degrees F ( 37C ). The gelatin mix is supposed to harden as it cools down and should be poured into the mold. It is okay to stir the mixture a bit as it cools to get a more uniform distribution of the yeast, however that does not seem to be particularly important since there is plenty of food and room to grow into. Remember that in a conventional MFC there is a much larger ratio of fluid to microbe than the gelatin MFC and no attempt is made to normaize the distribution, although it probably doesn't hurt anything.