Author Topic: Stir plate issue  (Read 8636 times)

Offline motox215

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Stir plate issue
« on: September 12, 2012, 09:08:54 AM »
I hope I put this in the right forum...

I have a stir plate that i purchased at I have made one yeast starter with it for a ALE style beer and used a 1000 milliliters flask and 1 inch stir bar. Everything worked great and I had it running for 3 days until i pitched it.

Now I'm doing a Lager and I have to make a BIGGER yeast starter, so i purchased a 2000 milliliter flask with a 2 inch stir bar (yellow one from Northern brewery)  and the stir bar continues to fly off to the side of the flask as soon as it speeds up.... The 1 inch bar works from time to time, but i have noticed it does fly off to the side every now and again.... Also the 1 inch bar doesn't seems to vortex the bigger start enough.

Any ideas to make this accept the 2 inch stir bar, or to make the stir plate work with the 2000 milliliter flask? Frustrated

Offline Humble Brewer

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Re: Stir plate issue
« Reply #1 on: September 12, 2012, 09:33:33 AM »
My first thought would be to ask if you have variable speed control and are you slowly increasing the speed?  Moving the extra mass is a bit more difficult and if resistance from the fluid overcomes the speed of the magnet rotation it will fling the magnet because it can't keep up.  If you have variable speed control start it really slow and then increase it over time as the water begins to move.  That might help.
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Offline jomebrew

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Re: Stir plate issue
« Reply #2 on: September 12, 2012, 09:55:49 AM »
I use a 1" stir bar on my 200ML flask all the time.   Looks like we have the same stir plate too.

keep in mind you do not need to create a giant vortex in the starter.  You just need to move the surface.  This will keep the yeast in suspension and picking up oxygen into the starter. 

The vortex looks cool though. I might be guilty of putting a couple drops of food coloring in my PBW to watch it spin around while it cleans my Erlenmeyer.
« Last Edit: September 13, 2012, 08:26:33 AM by jomebrew »

Offline dharalson

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Re: Stir plate issue
« Reply #3 on: September 12, 2012, 09:37:48 PM »
A couple of things to watch
1) Make sure the flask is centered on the stir plate, if not the stir bar will be thrown out to the side (centrifigal force) instead of spinning about itself.
2) When you put the flask on the stir plate tilt it slightly to get the bar to slide to one side; allow the stir plate magnet to "grab" the stir bar, then position the flask in the center.
3) Start slowly
4) I use a 1" bar on all of my starters.  I have used a number of containers, a 300 ml jars, qt. mason jars and 1000 & 2000 ml Erlenmeyer flasks.

Good Luck. David

Offline Wingeezer

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Re: Stir plate issue
« Reply #4 on: September 14, 2012, 06:13:56 PM »
I have a home made stir plate.   I started with a 1" stir bar  and one litre flask and it worked fine.  I then moved to a 2 litre flask and bought a 2" stir bar to use.

I had the same problem that you have encountered when using the 2" bar even when increasing speed gradually.

So I switched back to using the 1" bar with the 2L flask.  I usually make starters around 1.5L.

That combination works fine.  I don't get a big vortex on thd surface but from what I have read a small dimple in the surface is fine, and i do get that.


Offline rocaegis

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Re: Stir plate issue
« Reply #5 on: September 18, 2012, 09:45:10 AM »
Check the quality of your flask. I have had several flasks come into the lab where the bottom of the flask had a dome shape which caused the stir bar to fly to the side