stir bar won't stay in middle of my flask

[gkeusch]

Maybe someone can help me with this. I finally popped for a 2L Erlenmeyer flask for yeast starters. I got it at the homebrew shop. I've never had a problem with my 1L flask, but with the 2L the stir bar will fly off to the side of the bottom instead of spinning in the middle. I guess there must be a slight crown in the bottom, but I can't believe mine is much different than others. I have tried centering the bar on the bottom with my magnet and then carefully setting it on the plate and then turning it on - this has worked sporadically but more often than not the bar still flips off to the side and remains stationary.

Any ideas? I really don't want to buy yet another one.

 

[Konadog]

What stir plate are you using? If it's a home made one, maybe your magnets aren't strong enough as the glass may be a bit thicker. If you think your 2L flask is domed, sometimes if you use the stir bar that has a little ridge in the middle, they will spin better on a dome than a non-ridged stir bar, but they are noisier.

 

[Jaybird]

A crown will cause you issues for sure. I have a 5000 ML I got from B3 YEARS ago and it has a crown and I cant use it at all for my plate. You can try using a smaller stir bar. Or adding 2 small O Rings (the kegging O Rings seem to be a good size) to it that might help a little also. What is the size of the bar you are using? What speed are you trying to spin?

Cheers
Jay

 

[TennBrewer]

I've had this happen when I was a using a stir bar that was too long. The stir bar should not be longer than the distance between the two magnets that make it spin. Also, Konadog sez to use a ridged stir bar if the bottom is not really flat, this does indeed work but it is very noisy. I have had success getting the spinning started by first keeping the stir bar near the outer edge and just turn up the speed slowly until the bar starts spinning. Then I can slide the flask toward the center and increase the speed. You don't need to spin at top speed, creating the vortex is fun to watch and it does help to oxygenate the wort, but you don't need it to reach all the way to the bottom, just a little bit is fine.

 

[day_trippr]

I've had this happen when I was a using a stir bar that was too long. The stir bar should not be longer than the distance between the two magnets that make it spin.[...]

I'd say the bar should be as long as the magnet span measured at the outside edges...

Cheers!

 

[mwmcal]

How about moving the flask a little so that the bar is not dead center of the flask? Worked like a charm on mine.

 

[paulshe]

what has worked for me on my ghetto stir plates. https://www.amazon.com/dp/B00080G0BK/?tag=skimlinks_replacement-20
I just use the fan itself without a box. The nice think on this is the screws work as standoffs and can be adjusted. So the other variable to look at is the distance from magnet to bar. If you have a box then you're sorta screwed. Odd think for me is sometimes the bar is thrown when i reduce the distance so i just tweak it up.
As an aside total cost for the ghetto stir plate is 12 bucks fan, 5 bucks bar (actually a set), a left over USB plug and a magnet scavenged from a old hard drive (I also use the magnets that they have at home depot which are like 7 or 8 bucks for 6. And it's speed adjustable.

So your variables that effect the throwing of the bar. Speed of stir, length/geometry of the bar (for some reason the ones with the little ridge in the middle work best for me), distance from magnets, strength of magnets.

My fist recommendation would be like others have said. Try a different sized bar since it's unlikely you can adjust all the other variables.

 

[trav77]

Or... Just slow it down? They hop off centre a lot more often when sped up and you don't really need it spinning fast at all.

 

[RM-MN]

Or... Just slow it down? They hop off centre a lot more often when sped up and you don't really need it spinning fast at all.

If you believe this research you may find you don't need the stir bar at all.

http://www.woodlandbrew.com/2015/02/yeast-starters-stirred-vs-not.html

Note that it does take more time without stirring.:rockin:

 

[imasickboy]

I use a small, ridged bar, my magnets are about the same distance apart as the bar is long, and I have zero trouble. I can even use a screw top growler, (with the domed bottom), on my plate.

 

[gkeusch]

Thank you all for your replies. My plate is a purchased one so I don't know the technical details. I will take the top off tonight and learn something about magnet spacing, etc.