I resently discovered how to " catch " a yeast using a carved stick made of Maple. I use pieces that are about as thick as my finger and about 5 inches long. You can use Birch and Alder too. When you do this trick, make sure you already have an active primary fermentation going with the yeast you want to catch. A healthy froth is the best ! I find that Trappist style yeasts work the best for this but it will work on any of them.

In a small pot I have some honey and water ( 50/50 ratio ) at a rolling boil.

I carved runes all over the stick, this makes lots of nuck and crannies for the yeast to hide in. I then place the stick over a fire, paying attention the cut end and lightly cooking it ( about 5min ) I then throw the stick into the boiling honey water while still hot and let in soak in that for about 5 min.

While it's still hot out of the pot of honey water, carefully place the stick into the fermenter and let it stay there til primary fermentation is over. After you rack the brew, carefully fish out the stick from the yeast sediment and hang it somewhere cool, dark and dry to " cure ". The yeast will have colonized the stick and remain dormant til you place it in some fresh wort where it will then reactivate. Saves me money.