Stir plate stir bar. . . What size?

Building a DIY stir plate and just received the stir bar I ordered - 1/2 x 1/8. Looks kind of small. Is this going to work with a 2000 ml flask? If not, what size do I need?

Thanx

IMO a 2 inch stir bar is the ideal size. The 1/2" bar you have will work, but a larger bar would work better. It's important to match the stir bar size to the magnet spacing on the stir plate if you are using two separate magnets. If you are using a single bar magnet or a salvaged hard drive magnet, the bar should center itself. Then, it's only important to have the magnet itself well centered and aligned on the fan.

1" stir bar w/ pivot ring works for me and is perfect for the length of the hard drive magnets.

This size works for 250 ml all the way up to 5000ml flasks I use. You don't need a huge vortex, just continuous agitation. 1.5" works ok too, but 1" is the sweet spot for me.

I have had ZERO luck on my DIY stir plate with the 2" stir bar. Maybe with a different magnet config it would work, but not with the 2-stacked hard drive crescent magnet config, IMO

Thanks for the info, I'll have to order another one. Any idea where to order from - some place that doesn't require ordering a dozen?

onlinesciencemall.com is pretty good for small orders...

You should try that 1/2 in stir bar before ordering another one. I've used 1/2 in the lab before in 2000 mL beakers and they worked just fine. As Randar said, you aren't looking to sink a container ship here, you just need a nice dimple. If you can get that bar to spin and stay centered in your flask then you should be set.

I've experimented with many different sizes and styles of stir bars including the cross shaped ones and the large barbell syles. I've settled on the pivot ring type 50 mm x 8 mm which is approximately a 2" x 5/16" size. IMO, the longer bars stir better at lower speeds than the short ones do. Obviously, this is of no value if your stir plate can't spin a larger bar without throwing it or if you can't run your stir plate at low rpms for some reason. A recent survey revealed that most female brewers prefer a longer rod. That explains a lot.

trigger said:

You should try that 1/2 in stir bar before ordering another one. I've used 1/2 in the lab before in 2000 mL beakers and they worked just fine. As Randar said, you aren't looking to sink a container ship here, you just need a nice dimple. If you can get that bar to spin and stay centered in your flask then you should be set.

Click to expand...

Good advice, I'll do that. That does raise the question of how much agitation we're going for. So, you're not trying to draw a vortex to the bottom of the flask? Sorry for my ignorance, but I've not used one of these before.

The objective is to keep the wort moving in order to continuously expose more of it to the surface where the gas exchange takes place. A gentle stirring is all that is needed. There is nothing to gain with faster stirring. The gases are trying to reach an equilibrium with the gases in the atmosphere. The faster the yeast produce CO2, the faster it will exit the flask and the same with the incoming O2. Some claim that high speed stirring can damage the yeast cells as the shearing forces are greater than at lower speeds. I have no way of verifying whether this is true or not, but I seriously doubt it. So, IMO faster stirring does no harm, but it also doesn't gain anything. Again, JMO, nothing more than that.

Randar said:

1" stir bar w/ pivot ring works for me and is perfect for the length of the hard drive magnets.

This size works for 250 ml all the way up to 5000ml flasks I use. You don't need a huge vortex, just continuous agitation. 1.5" works ok too, but 1" is the sweet spot for me.

I have had ZERO luck on my DIY stir plate with the 2" stir bar. Maybe with a different magnet config it would work, but not with the 2-stacked hard drive crescent magnet config, IMO

Click to expand...

I am going to be using hard drive magnets also. Please post a picture of the best way to mount the hard drive magnets with the 1" bar. Thanks!

Kai has a great article on speed for a stirplate. http://braukaiser.com/blog/blog/2013/03/25/stir-speed-and-yeast-growth/

Thanks for that info

I found these on Amazon through a recent link on HomeBrewFinds.


1" Stir bar


1 1/2" Stir bar

They come in different sizes, such as 1", 1.5" and 2". The picture shows them in "tan," but they are actually white, according to the reviews. I guess they didn't set the correct color temp on the camera .

The price ranges from $4.05-4.75 each, with free shipping right now. Beats the "sciencemall" pricewise by quite a bit. Sounds like a good deal as long as they work as expected. Does anyone have experience with these?

I just got 1" stir bars from amazon from scientific equipment of Houston and they work great. Hard to beat $4 and free shipping.

I use these. I love them.

\http://www.grainger.com/product/LAB-SAFETY-SUPPLY-Magnetic-Stir-Bar-21R593?s_pp=false

The nice thing is they won't shoot down the drain when you pour them out like the straight ones. I've lost a few that way.

They're less likely to get thrown.

A guy on E-Bay has them cheap every now and again.

Yea 1" seems to be the correct size for 1000-2000 flasks. I picked my auto stirer and 2k flask here:

https://bellsbeer.com/store/products/StirStarter-%2d-Yeast-Starter-Stir-Plate.html

https://bellsbeer.com/store/categories/Homebrewing-Supplies/

b-boy said:

I use these. I love them.

\http://www.grainger.com/product/LAB-SAFETY-SUPPLY-Magnetic-Stir-Bar-21R593?s_pp=false

The nice thing is they won't shoot down the drain when you pour them out like the straight ones. I've lost a few that way.

They're less likely to get thrown.

A guy on E-Bay has them cheap every now and again.

Click to expand...

GULP!........That's a pricey stir bar from Grainger there!!!!!

^ the funniest part is the compliance section for that product. Click the link and scroll down to the California compliance

I have been using a 1" stir bar in my 2000ml flask and homebuilt stir plate with a hard drive magnet and it has worked wonderfully. Mine does not have the center pivot on it though. Bought them off ebay. I use another magnet to get it out before I pour the yeast into the wort. I also have a 120ml fan in my stirplate setup as oppose to an 80ml fan. It was just something I have sitting around from an old computer. I just used a rat shack project box to set it up in.

Stealthcruiser said:

GULP!........That's a pricey stir bar from Grainger there!!!!!

Click to expand...

they are significantly cheaper on e-bay. I got a few for $24

My 2 cents.

1" stir bar works best in 2000ml or smaller flasks. It works fine most of the time in my 5000ml flask except with highly flocculent yeasts like wheat because the yeast will form large clumps and settle towards the outside of the flask where the liquid is not rotating much. When I turn up the speed all the way the wort is rotating very fast towards the center but is barely rotating towards the outside.

The 2" stir bar creates a wider column of rotating wort to help keep yeast clumps from settling towards the outsides of the flask, which also prevents larger clumps from forming I'm the first place. However, I do have a harder time keeping the 2" bar from being thrown but I can get it going fast enough to create a small vortex which is all you need. My 1" stir bar can hold on no matter how high I turn up the speed.

My stir plate uses cylindrical magnets. I recently replaced 1 of the failing drives in my NAS so I now have a couple of hard drive magnets waiting for me to try out to see if they work better for the 2" stir bar.

I use a 1.5 inch stir bar with a center ring. I have a 2000 ml beaker instead of a flask. I get great results with it, if I crank my plate all the way up my cone will stretch all the way down to the bar. From what I gather the point of the stir plate is to oxygenate and to keep everything in constant motion. You do not need an insane amount or agitation to properly aerate starter wort.
If you are concerned about not enough agitation you can always step up your stir plate motor. I have a second stir plate I built using the motor from a 10" fan and used a wall dimmer as my power control. That will get you a nice amount of agitation even with the smaller bar. I use that stir plate with my fermenters. I leave them running on that for a few hours to aerate my wort and I still use my little 1.5" bar.