Frozen yeast viability

[ojaason]

I owe everyone here a huge thanks for all the valuable information I've learned over the years... figured it's time to emerge from the shadows.

I've been maintaining a frozen yeast bank over the past couple years with fairly good results. Occasionally I have issues with under pitching, so it's been kinda trial and error. Any idea on the viability over time? What's everyone's procedure from going from a frozen vial to an adequate pitch?

 

[Mer-man]

Are you freezing it with some sort of freeze buffer, like a glycerol solution?

Either way, start very small and work up.

 

[Queequeg]

Depends on freezer temperature. A normal -20C freezer you are going to see a decline in viability over time. The rule of thumb in most micro labs who cheap skate out and use a -20C freezer is after a year viability starts to drop off. However ime it lasts a lot longer, though I do remember some candida parapsilosis eventually becoming non-viable after a few years.

If you can somehow get your hands on a -70C freezer then you are looking at indefinite storage.

Standard industry practice is to use a sterile porous bead soaked in a cryo-preservative. Others will probably be bale to help you how to replicate this on the homebrew scale.