Expert: Dana Krempels, Ph.D. - 2/17/2008

Question
Dear Dr. Krempels

Thank you very much for reading this message. I am planning an experiment into the rates of fermentation by yeast using different concentrations of the same substrate in my college and I was wondering if you could offer any advice to aid my investigation.

I understand the basics of how yeast ferments sugars but I'm getting a bit confused into the more in-depth explanation as to how this happens (i.e. pyruvate converted to ethanal and then reduced etc). If you could put the explanations into steps of how fermentation actually happens it would be hugely appreciated!

secondly, my experiment at the moment is to measure the levels of carbon dioxide evolved from the reaction at regular intervals, with different concentration substrates being fermented. it's a basic experiment and i am hoping you could think of a more scientifically accurate way of measuring rates of fermentation by yeast.

Thank you so much for any advice you can offer, it will be massively helpful!

Thanks again,
Adam Shellard

Answer
Dear Adam,

You can review the chemical steps of fermentation here:

http://www.meadmadecomplicated.org/science/fermentation.html

(and then make some mead when you're in the mood.)

To quantify the levels of carbon dioxide being produced by your yeast, you will need a pretty sophisticated sensor that detects CO2 in solution, and use a closed system to anaerobically incubate your yeast and substrate.  If you college lab doesn't have such a sensor, I doubt you'd want to invest in one for just this experiment, since they are pricey.  (You know you're in deep water when they won't even list the price on the web site:

http://www.vaisala.com/instruments/products/carbondioxide/gmp343

)

An alternative would be to incubate in sealed fermentation tubes and measure the *relative* generation of gas.  Ferm tubes are expensive, too.  So if you don't have those, you might have to devise some type of glass chamber that will allow you to measure the displacement of liquid suspension by the CO2 gas.

Hope this helps.

Dana