how long do you leave yeast starter on stir plate

I am making my first yeast starter and am using a stirring plate. Do you leave the yeast starter mixing on a stir plate throughout the process until you are ready to pitch?

You can. I usually turn mine off when it's done and let the yeast settle. Decant and pitch only the yeast slurry. It will change color and look more milky when it's done. Shouldn't take any longer than 24 hours, if that.

Thank you!

I make the starter, get it going, let it run until 100% complete then chill for 12-24 hours to get the yeast to settle. I then decant the spent starter wort (leaving no more than 1/4" on top of the yeast cake IF it's the final starter step) and make it up into a slurry to pitch into the oxygenated wort.

I've been making two, and three, step starters lately. Just means I plan my starters a bit further out from the brew day. This has allowed me to use some older yeast packs/vials. Some were almost a year old when I made the first starter step. Gotten the cell count up to where needed and rock solid fermentation too. Depending on how old your original yeast is, the first starter (if doing more than one step) can take 36-48 hours, or more, to finish.

I'd also advise using the calculator on the yeastcalc.com site to figure out starter sizes. IMO, it's better than Mr. Malty if you want to use older yeast and don't want to make 20L+ sized starters (Mr. Malty only has one step).

I've not made a starter yet, and I haven't done a ton of reading on starters yet, but I did just make a stirplate and plan to make a starter for a Pliny clone. How do you know when the starter is done?

See what BBL_Brewer posted. It's pretty easy to tell when the starter is finished. You'll also know when the yeast is really going due to the foam on top of the swirling starter wort.

I highly recommend using the tool on the yeastcalc.com site. You can do two, or three, steps and get the cell count needed that would otherwise take upwards of a 20L (or larger) starter.

My starter took 23 hours and looks milky. No more foaming so into the fridge it went. Plan on brewing in two days. Homemade stir plate works great. I used a variable volt output power supply. I found the best output voltage was 6 volts. 7.5 was good also. The 9 and 12 volt output settings did not allow me to slow the spin rate enough resulting in less control of the mixing rate. So if you can find a 6 or 7. Volt power supply laying around from and old device I recommend building a stir plate. I made a 800 ml starter. My neighbor is going to use it to make a 1500 ml starter. It will be interesting to see if the output voltage will need to be increased. Who knew brewing beer would be this much fun! And the beer tastes so much better than what you buy in bottles. Thanks for the help on the starter everyone. This will be my third batch, first starter.