I recently emptied a wonderful bottle of Brewer's Art Resurrection Ale the other night in hopes of propagating the yeast for a batch I'm going to make this weekend.
I prepared the starter wort, drank the beer, and swirled/pitched the remaining yeast into my flask and popped it on the stir-plate. It's been about 20-ish hours, and the wort is appearing cloudy, but with the stir-plate going I'm not getting a krausen or anything that would indicate active fermentation other than some bubbles in the middle. (But could those just be from stirring?)
Anyway... I searched a bit and didn't come up with a solid answer, so how the hell do you know if your starter is active on a stir plate?