Streaking a Plate (Ipswich Ale Yeast)

Today I’m going to give you a little explanation on streaking a plate of yeast.  I recently had the good fortune to get my hands on some Ipswich ale yeast from the Ipswich brewery.  I managed to streak some of this yeast on to a plate.  A plate is simply another term for a petri dish.  I use glass petri dishes which I bought online, and I make my own medium for the plates.  This medium is just malt extract, mixed with agar and yeast nutrients.  The agar solidifies the malt to form a solid surface area.  To streak a plate I have a tool called an inoculation loop seen in the picture below.

 

The small metal loop on the end is what transfers the yeast from a liquid sample to the actual plate.  I first run the loop over an open flame until it is red hot.  This sterilizes the loop.  I then cool the loop by submerging it into the medium on the plate.  After this I dip the loop into the liquid sample and use the loop like a pen or paint brush and rub the loop onto the surface area of the plate making several lines.  I then turn the plate half way and do this again.  The idea is to spread the yeast out over the plate to form individual colonies of yeast, which can be stored in the refrigerator for later use.  There are several reasons for doing this, but most important is that you can get pure strains of yeast from a plate and know that your beer hasn't been infected by wild yeasts which can cause off flavors.

This is Irish ale yeast.  As you can see, I used a little too much yeast and though you can see the streaks there are no individual colonies to speak of.  I can, and have used this for propagation purposes because I took this straight from a store bought vial so I know it is not infected.  However it is not good technique.

This is the Ipswich ale yeast.  It was taken from a rather old sample and so the yeast aren't as healthy as in the pure Irish ale yeast.  However I will be able to use this for propagation and will streak another plate soon.  Also note the brown spots underneath the yeast are just malt that became more solidified than normal and resulted in some chunks in the mixture.  This doesn't affect the yeast, it just looks a little strange.

This is Bavarian Weiss yeast.  This is a much better example of what a properly plated yeast looks like.  Notice the individual circles, each of those is an individual colony.

 So you might be asking yourself where do I do all this stuff?  Well the answer is quite simple...right in my living room!!!  That's right, I use my living room table for my lab space and use an alcohol lamp to create a germ free zone.  An open flame creates an updraft which prevents micro-organisms from landing in the area you are working in.  I make sure all the doors are shut and there are no drafts in the area when I work.  I then clean the table with whatever cleaning products I have available and I go to work.

By keeping the plate underneath the open flame I can prevent unwanted micro organisms from landing on the plate.

I try to get as wide of a surface area as possible so that I don't have interference from nearby objects.

It may sound a little crazy but I also brush my teeth and rinse with mouth wash before I begin.  Even your mouth can contain germs, so I hope by doing this I'm lowering the chances of spreading germs by breathing on the plate.  I have yet to get one of those doctors surgical masks but I think it would be a better solution.  I also where rubber gloves too.  

I am still learning a lot about this stuff but it's certainly a fun and exciting part of brewing that I've come to love.  It also helps me make better beer, which at the end of the day, is what it's all about!