I'd like to stop buying yeast all the time, especially when I use the same strain repeatedly.
This is especially a problem when it comes to seasonal strains. I'd like to brew with WLP351 Bavarian Weizen Yeast whenever I'd like, but it's only available around March and April.
It would also be nice for our brewing friends in the southern hemisphere that would like to brew with the seasons, but can't because the current seasonals are in sync with the northern hemisphere seasons.
Clarification: I'm looking for a way to keep the strain indefinitely without potentially changing the strain due to factors like contamination and genetic drift. More of a solution where it would be a one-to-many situation. I'm looking for steps that would show me how to keep a culture from changing over time. Be that using petri dishes or test tubes with agar or whatever.