Science Buddies: "Ask an Expert"

I am working on a science fair project about yeast fermentation in different liquids. I have done plenty of research and am working on my Experiment Plan. I was just wondering if you knew of any good sites to use. Also, what kind of yeast should i use for my experiment? Lastly, i am measuring the most active fermentation by the CO2 produced which i will measure with water displacement. Is there a formula to convert the water displacement to an actual air measurement?

Hi Jordan!

Here are some sites that should help you out with some specifics for your project:

http://www.selah.k12.wa.us/SOAR/SciProj ... iProj.html
http://www.all-science-fair-projects.co ... 9af5f.html

Putting "Yeast science fair projects" or some variation into any search engine will give you lots of results.

As for yeast, I would think that rapid-rise yeast from the grocery store would be fine and as long as you make sure that all yeast in the experiment is the same, there shouldn't be a problem. I don't know of a formula for making that conversion, but maybe someone else will. Try doing some good old fashioned book research and you might get more complete answers to your questions, but you're off to a great start! Hope to hear back from you with any progress you make.


-Susan

Hi Jordan,

Here's the equation you need to know for your experiment:

C6H12O6( glucose or sugar in solution aqueous) + 6 O2(gas) + 6 H2O(liquid)→ 6 CO2(gas) + 12 H2O (liquid)
glucose + oxygen → carbon dioxide + water

It sounds like you will be collecting the carbon dioxide from your fermentation sample. If you measure the volume of carbon dioxide produced in your experiment, you can calculate the exact amount of sugar used and the amount of carbon dioxide produced. Here's how to measure the amount of carbon dioxide produced:

1 mole of carbon dioxide = 22.4 liters at standard conditions.

To understand this better, you will need to learn about the ideal gas laws. Here's a good website for this subject:

http://www.chemistry.ohio-state.edu/betha/nealGasLaw/

If you have taken chemistry, this will be familiar, but if you haven't you will need to study this subject and make sure you can explain it in your background research. You will also need to show the calculations you used to convert the volume of carbon dioxide to moles or grams.

Your question about the source of yeast is a good one. Ideally, you would want to use a pure culture of yeast, grown to the same growth stage, and used in the same concentration in each experiment. If this is not possible, (and it probably won't be unless you have access to a microbiology laboratory), then you can buy enough bakers yeast from one lot of one brand (purchased at the same time) and use the same amount of this yeast for each experiment. The idea is to keep all parameters of the experiment identical, except the variable, which is the liquid you are using to grow the yeast.

I don't know what grade you are in, but do let us know if you need help understanding the equations or the gas laws.


Donna Hardy