Science Buddies: "Ask an Expert"

Does temperature really matter in the production of co2? i've experimented with different degrees of water temperature mixing with yeast and sugar (temps ranging from 80 to 140f) and my results have varied but each degree has produced a different amount of co2. I thought the hotter the temperature the yeast would be killed and not produce co2 but i'm not seeing this! I'm also wondering even though my initial temperature may have read 140f that by the time it shows a reaction the 140f is no longer the temperature but is more room temperature . So are my findings inaccurate? Im confused is there a better way to proceed? Will there be a different reaction if I use a fast acting yeast or not or is the change only in how fast it will react? Also will the fast acting yeast produce more co2 or does it really matter? How long should I run a trial? I've had some where I have waited a day, so is the fermentation process still going on ? Or is it pretty much finished within the first five to ten hours? Does the fermentation process go through stages of co2 production? I'm using balloons and I have had trials where the balloon goes up and down is this normal or is my trial contaminated? I must present my project by the end of the week but I have so many questions and I really want to understand so i look like I know what I'm doing? Please help!

Hi Scimon.

Temperature does affect the production of carbon dioxide by yeast and so does the growth phase, number of viable yeast cells, nutrient composition, pH, and other factors. If you are used different sources of yeast, you would expect to see differences in the production of carbon dioxide because of the difference in the yeast cells. With a science fair project you want to design an experiment with just one variable; all other experimental parameters should be controlled. To compare the effect of temperature, you could use multiple packages of the same brand and lot number of yeast, and measure carbon dioxide production at different temperatures. It would be best to maintain the temperature of the test sample from the beginning to the end of the measurement if it is possible. If the test temperature drops to ambient temperature within a few minutes, you may not see a difference in results.

Since you have finished your experiment and the project is due on Tuesday, you should explain what may have happened and what you would do differently if the project were done again.

Here are a couple of websites that provide more background information about carbon dioxide production and a typical experimental design.

http://growthrate.princeton.edu/transcr ... ndex.shtml

http://www.hartnell.edu/faculty/awright ... 20temp.doc

Something else to consider is the inherent variability of results of an experiment. What was the difference in the amount of carbon dioxide produced in your samples? If you can did multiple measurements at the same temperature, your student can calculate the standard deviation of the results and use the student’s t test to determine if there is a statistically significant difference in results.

http://en.wikipedia.org/wiki/Student's_t-test

For a science fair project, your temperatures should be converted to degrees Celsius.

http://www.csgnetwork.com/tempconvjava.html

I hope this helps. Please let me know if you have any other questions. This is a really great science project.


Donna Hardy