Is Yeast Alive? First Lab of the New Semester

I almost messed up today!  Tomorrow is the first lab of the new fall semester--a lab titled Is Yeast Alive?  I got this lab on the internet a couple of years ago and have used it as the first lab every semester since, but I almost had an epic "fail" on my hands tomorrow which would not have been a great way to start a semester! There are two parts to this lab, one a test for metabolism (cellular respiration producing carbon dioxide gas that will fill up balloons) and the second a test for growth.  I remembered to buy balloons yesterday, although I only found 9" balloons, not 7" which I think is what I have used in previous semesters.  I hope those will be OK.  Today when I went to make copies of the lab for my students, I remembered that I also needed Petri dishes of nutrient agar for the second part.  I had not planned on making agar today, but frantically got everything mixed up and into the autoclave in time to get it processed and hopefully poured without staying too late.

My autoclave is a highly manual (as opposed to automated) version that is really just an overgrown electric pressure cooker and the entire process takes approximately 2 1/2 hours to complete.  There is no thermostat which regulates itself--someone must stay with the autoclave at all times once it comes up to pressure to be sure that it doesn't overheat.  If you are lucky, you can get the gauge set to where it will toggle on and off within the appropriate range, but I still will not leave it unattended.

Anyway, I mixed up 1600 mL of nutrient agar in two 1000 mL Erlenmeyer flasks (18.4 g of nutrient agar powder to 800 mL water in each to avoid boiling over), let the mixture stir and then placed both flasks with lids loosely screwed on into the autoclave to sterilize.  I had a new lab tech student helping me today, so even with teaching her how to pour plates, I was able to pour 74 plates from the agar I made.  

I did  finally have to buy new yeast this time.  I had my lab tech check the viability of the yeast that had an expiration date of October 2011 on it.  And, as expected, the foaming action was not what I had hoped.  New yeast this semester!  I'll be going to Publix after school today to try to buy another container of yeast.  I don't want to use the packets, but I may have to.  I need 4 grams per lab station, so I will need at least 56 grams.  Well at least that's an excuse to go visit our new Publix grocery that just opened up here in Knoxville.  LOVE that store!  I also had the lab tech place four balloons in each of the white baskets that hold student supplies for lab.  I'll just have to replenish them between 1st and 2nd block.

I am going to try to revisit and update this blog with each lab this semester.  I hope it will be beneficial to others and especially to someone here at my school if I end up somewhere else sometime in the future.  At that point, someone else would have to step in and teach Microbiology.  This blog should be a big help to them if that should happen.