Plating Yeast & Selecting Colonies
Posted Feb 27th 2013 | By:
I've seen several articles on this site about the proper way to slant yeast but haven't found one that shows the process of streaking yeast onto a plate and selecting individual colonies. This is the method I use. It's not flawless and it certainly has room for improvement but it's cheap and works well for me.
What you'll need to do this:
- yeast source (bottle dregs, old washed yeast)
- Petri dishes (ideally ones made of tempered glass that can be boiled but I used sterile disposable ones)
- inoculationloop (I use a paper clip because it's practically free andI'veseen others use it online)
- aluminum foil
- small pot or flask
The first thing you'll need to do is create the growth medium. I use the same recipe that Saccharomycesuses in his slanting tutorial: http://www.homebrewtalk.com/f163/slanting-yeast-133103/
It is 35g DME, 400ml water, 2.5g agar
When I first did this I used those exact numbers and filled 8 plates. That left me with way too much growth medium. So either fill more plates or cut back on the recipe.
Mix all the ingredients for the growth medium into a 1L flask and get it boiling.
While the medium is cooking away, lay out some sterile aluminum foil to set the plates on for when you pour them.
Once the growth medium has boiled long enough to sterilize it, take off the heat and pour right from the flask and into the Petri dishes. The hot liquid helps to sterilize them again, just in case. They need time to cool and solidify after they're poured. This is where the highest risk for infection is, so what I do is keep a steady updraft going right next to them so anything floating in the air doesn't have a chance to land. This was achieved by putting the plates on one side of my stove, turning the burners on on the opposite side of the stove, and also turning on the exhaust fan.
After the plates have cooled and solidified you'll need to streak the yeast onto the plate. Give them some extra time if you're not sure. If they're still too hot you'll kill the yeast and if they're just a little watery you'll make a mess. Illustrated below in my awesome Microsoft Paint drawing is the pattern that you want to use when streaking the plate.
When you streak the plate all you're doing is trying to spread out the yeast so when it begins to grow you can identify a healthy, single, uniform yeast colony to eventually start some delicious beer from. This is where you'll need your yeast source (mine is some rinsed Pacman yeast that was on its last leg in a mason jar) and your paper clip. Straighten your paper clip out. You'll need to sterilize your paper clip somehow. I've found it's easiest to just crank the gas burners up and heat it up that way.
After its good and hot let it cool back down so you don't kill the yeast. Then you want to stick your freshly sterilized paper clip into your yeast source. Make sure to keep the paper clip fairly dry after you bring it back out of the yeast, I give it a little shake or tap otherwise the plate will get watery and messy. There will be plenty of yeast left on it, don't worry.
After your paper clip has some lovely yeast on it you need to streak the plate by rubbing the paper clip across the growth medium in the pattern illustrated above.
Now you need to put the lid on the plate, seal it up either in aZiplocbag or plastic wrap, put it in a dry place between 60-70 degrees F and wait. After a a day or two you'll start to see yeast growth.
From this point you can either put the individual colonies into a small starter and begin to step it up to a pitchable volume (I do steps of 10ml, 100ml, 1L) or you can slant the yeast and save it for later. To get them off the plate use the same method as before for handling the yeast. Sterilize the paper clip, let it cool, scrape the colonies off the plate, and move them onto their next step. I circled some of the ideal colonies that you would want to select.
And following the Saccharomyces' guide to slanting, I put several of those colonies into slants for later use.
and Tagged with
diy, tutorial, how to, homebrew, brew, brewing, homebrewing, yeast, plating, plating yeast, yeast colony, yeast colonies, slanting, slanting yeast, petri dish, dme, agar, flask, growth medium