Freezing Yeast Cultures
Noonan's book does
mention freezing as a viable way of culture storage. It seems that yeast
cultures that have been refrigerated are allowed to warm up to around
50F/10C for about a week. This causes a sedimentation and the liquid
above the yeast layer is decanted off and the bottom layer is harvested.
This layer is squeezed of excess water and then tightly rolled into a
ball, stored in plastic wrap and then moved to a freezer. It apparently
can be stored for several months. To re-animate this yeast, it needs to
be thrown into a starter culture of aerated wort before pitching.