Lab Report: GEN2, Yeast for homebrewers

Our second Group Experiment Night was delightfully bubbly.  We worked on isolating yeast strains from an assortment of commercial beers.  The goal was to isolate yeast strains and determine if we could grow viable yeast for use in further beer fermentations.

The first step in the process was to make growth media from such varied ingredients as potato starch, sugar, body builder mix, and agar agar (for fermentation in petri dishes).  We sterilized the media in our pressure cooker for 20 minutes and then allowed it to cool.

Meanwhile, we had acquired an assortment of beers.  Because the yeast sinks to the bottom, it was necessary to drink all of the beers down to the last quarter to get a good yeast sample.  This was highly enjoyable, and someone took tasting notes.  The beers  sampled were a variety of unfiltered bottled beers, from both wild fermentations and specific strains.  We included Belgian style ales to see if we could isolate the yeast strains which give their distinctive flavors.  We also included beers which were fermented with brettanomyces, a unique yeast species.

Once the beer was mostly drunk, we poured out the media into petri dishes and allowed it to cool.  We practiced our sterile technique and streaked the plates with samples of the different beers, and set them at 30C for a week.

Here are some of the plates we produced, two weeks from the night of the experiment:


There was quite a lot of contamination in most plates due to many factors BUT there were also some clean plates that featured happily budding yeast cells as can be seen here:

yeast cell


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