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Corcoran 's picture

Proofing the yeast

I just completed part II of this lab with my freshmen biology students. I recommend proofing the yeast a few days before working the experiment with students. You need to heat up warm water (35 C) and add a little sugar and yeast. Use the same proportions as listed in the procedures. If you see a significant amount of foam produced, the yeast is alive and will likely perform for your experiment.

Sometimes the yeast we buy is dead - that's why the author suggests using newer yeast.

Also I found it helpful to spend some time the day before the experiment explaining the procedure to my students. Even then it has a lot of moving parts and kids who daydream get very confused about what they are supposed to be doing. Just a FYI.

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