I came across this article on HomeBrew Talk. http://www.homebrewtalk.com/freezing-yeast.html
I was used to using 50% glycerin final concentration, but this article states that 10% works better.
Any suggestions? Any experience with doing this?
Back when I was in grad school, we added equal volumes of saturated yeast culture to sterile 30% glycerol, for a final concentration of 15% glycerol. We kept our glycerol stocks at -80C. I'm sure -20C works too, but you'd probably want to remake your stock yearly or something. At -80C it will last a lifetime.
Alternatively, if you have YPD plates, you can grow your cells on the plate, then scrape as many as possible off with a sterile toothpick or something, and inoculate your 15% glycerol that way.
If you can store bacteria, you can store yeast.
That said, repitching slurries is easier. Even if you let it go months in your fridge, lots of cells will be alive. Yeast are not as delicate as you may have been led to believe.