For my next batch of saison I am going to be culturing the yeast from a bottle of Saison Dupont. It is not very complicated, if you have experience with starters than you should have no problem. I think the only issue you may run into is yeast viability. Choose a fresh, bottle conditioned beer and hope that it has been treated with care on its way to your local bottle shop.
Some bottle conditioned beers use a bottling strain instead of the primary fermentation strain so do some research and find out if the yeast in the bottle is indeed the yeast you want to culture.
Before opening the bottle, wipe down the neck with some rubbing alcohol and/or flame the top of the bottle to kill any bacteria that could infect your culture. Decant the beer into a glass, trying not to disturb the sediment, cover with sanitized foil and allow it to come up to room temperature. Make a small amount of starter wort, keeping the specific gravity around 1.015-1.020, cool to room temp and pour in just enough wort to suspend the yeast (approx. 3-6 mL). Allow to incubate for a period of 1-3 days while watching for signs of fermentation. If you see activity or 3 days have passed add the yeast to some fresh starter wort (approx. 15 mL) and allow to incubate another 1-3 days.
Hopefully you notice some activity, if so, start to step up your culture just like you would your starter until you have enough viable yeast to pitch. Check back soon for steps on building your own magnetic stir plate.
