How long can yeast sit on a stirplate and still be usable?

So I meant to brew last week, and had a Conan starter on my stirplate. I ended up having to go out of town for work, and it's now been on the plate for at least a week, covered with foil and constant movement.

Should I even consider this yeast viable any longer, or should I dump it and start over (which would mean pushing my brewday back 5 days to build up a starter from a slant)?

i'd start over. being warm and stirred for that long they probably used up all the energy a week ago, and are dead/unhealthy now.

It should be fine. Yeast are not stupid and realize when they are running out of food. The yeast will exit growth phase, put down energy stores, and then enter dormancy as they run out of food. The only real concern is that there may be some loss due to physical damage from being stirred while dormant. I'd sediment the yeast in the fridge overnight, pour off the spent wort, and then grow it for 24 hours or so in fresh wort before pitching. That should get your numbers back up, and make the critters happy.

Bryan

It'll be fine. Just let it settle, decant and use it.