Stir Bar Size for Maelstrom Stir Plate

[Nagorg]

Hey there HBT! I've had my Maelstrom for a few years and it works great. I typically make 3L+ starters using my 5L Erlenmeyer Flask and a 50mm (~2") stir bar. Sometimes I have to fiddle with it to get things spinning without the bar throwing but this not typically a big problem.

But recently I needed to make a 2L starter. I did this in my 5L flask since that's all I had. But I found that the shallower depth of the wort in that 5L flask allowed the vortex to dip down and cause the stir bar to be thrown. No matter what I tried, or how many times, it would always get thrown.
I now have a 3L flask which should prevent this problem since 2L of wort will have more depth in the smaller flask. But, this got me looking into stir bar sizing.

Its hard to find "authoritative" information on the topic of stir bar sizing but I have found info that suggests the stir bar should be "about equal to the magnet size to avoid spinout".

https://www.fishersci.fi/fi/en/scie...gnetic-stirrers/stir-bar-selection-guide.html
I think the Maelstrom comes with a 50mm stir bar if you buy one new today. That's what I have and maybe its the one that came with it. But if I measure from outside to outside of the magnets, its 3" which is ~76mm. However the Maelstrom actually has 2 smaller magnets that are places at opposite ends of a bar that spins. So I'm not sure how to apply this sizing "rule of thumb" in this case.

I have found 76mm stir bars and 70mm that seems more common. Both sizes are more expensive than the much more common 50mm stir bars. I don't mind buying a larger one but also don't want to waste money. So I thought I'd see if anyone on this forum had any insight on this topic.

Should a longer stir bar "hold" better on the Maelstrom or would this be a waste of money?

 

[marc1]

Does the maelstrom allow you to turn down the speed?
With my non maelstrom stirplate, I can do 1L in a 5L flask by stirring slower.

 

[Chorgey]

The

Does the maelstrom allow you to turn down the speed?
With my non maelstrom stirplate, I can do 1L in a 5L flask by stirring slower.

The Maelstrom has 5 speeds

 

[Nagorg]

Does the maelstrom allow you to turn down the speed?
With my non maelstrom stirplate, I can do 1L in a 5L flask by stirring slower.

I should have mentioned that this is on the lowest speed of 1. Any higher is too fast, even on 4L starters. This thing is a beast...

 

[Chorgey]

Should a longer stir bar "hold" better on the Maelstrom or would this be a waste of money?

I lost the stir bar that came with the Maelstrom (accidentally dumped it). I reached out to Northern Brewer and they sent me two sizes, 25mm and 50mm.
I never use the 50mm

The 25mm works great but I only use 2L starters. Works great at different speeds.

 

[Nagorg]

The 25mm works great but I only use 2L starters. Works great at different speeds.

I ordered a 70mm stir bar. I have a 25mm too so I'll have to do a stir test using different bars with different volumes... in water so that I can see the bar and its position in relation to the magnets.

 

[Mac's Brew]

I typically make 4 - 5L starters. Even with these large starters, the Maelstrom is difficult to dial in - it's prone to throwing off the 50mm bar. I almost always use the 25mm bar and have no problem, even at higher speeds.

BTW, I recently switched from White Labs Pure Pitch to Pure Pitch Next Generation and no longer make starters (for 1-bbl batches). I'm getting great results.

 

[Nagorg]

it's prone to throwing off the 50mm bar.

Glad to know I'm not the only one that's had that experience... This is contrary to the marketing verbiage on the Northern Brewer website. Maybe I've got a dud... lol

 

[Nagorg]

Alright, my 70mm stir bar came in and I've conducted my tests of 3 sizes on my Maelstrom; 70mm, 50mm and 25mm.

The clear and indisputable winner is hands-down the 25mm stir bar. It performed solidly in both my 3L and 5L Erlenmeyer flasks in volumes from 2L to 5L.

Guess it was a waste of money to buy the 70mm stir bar. Good thing I can return it. I'd almost say the same about my 3L flask since it turns out that I didn't really need it for a 2L starter. But, I'm sure it will come in handy so I'm keeping it.

Simple results.
25mm:
It was quickly "grabbed" and centered by the magnets on the Maelstrom. This was true for either flask regardless of water volume. It easily spun in 2L of water in my 5L flask and had no problems at all in the 5L volume test. It even produced a small dimple at speed 1. I was also able to kick the speed up all the way to 5 in either flask, including 2L in the 5L flask, and the bar did not throw.

50mm:
Sometimes had trouble being "grabbed" and centered by the magnets on the Maelstrom. Sometimes it would even stick to the outer end of one of the magnets. It was finicky to get spinning on the lowest speed and would throw fairly easily in the 5L flask. I could eventually get it going after 2-3 attempts though. But in the 3L flask, I could never get it to spin without being thrown. This could have something to do with the glass thickness of this flask. Its a cheaper one I got from my LHBS instead of from a science/lab supply and noticeably thicker and heavier than my 5L. Regardless, this was a non-starter; pun intended.

70mm:
The shortest of all tests. While it seemed to be "grabbed" and centered okay in either flask, it simply wouldn't spin. I could see the spinner spinning in the Maelstrom but the stir bar wouldn't spin with it. It would just sit there and kinda jiggle a little with each pass of the magnets spinning beneath it.
I cant say I understand this outcome. Maybe it's a bad stir bar. It was cheaper (~$8.00 from Amazon) than others I found from science/lab supply shops. Those are easily ~$15 each and up. Whatever the cause, it was a hard FAIL.

So to answer the question I posed, it looks like a 25mm stir bar is the best size for the Maelstrom. At least it has been for my tests, YMMV...

Thanks to @Mac's Brew for the suggestion and confirmation from personal trials!

 

[JohnDBrewer]

Only ever used a 50mm and never had an issue. I have another lab model stir plate and it always throws the bar. Think I'll try a 25mm or smaller on that.

What direction does your maelstrom spin? I have a different power supply, not the original, and it spins counter clockwise. The lab plate is clockwise.

 

[Nagorg]

What direction does your maelstrom spin? I have a different power supply, not the original, and it spins counter clockwise.

My Maelstrom spins counter clockwise, just like yours.

Only ever used a 50mm and never had an issue.

That's all I've used in the past. And its not been a problem in my 5L flask with 3L+ starter sizes. I didn't have an issue until I tried a 2L volume in my 5L flask.

Like I stated, the 25mm bar worked perfectly at this volume and all the way to 5L. I could even speed the spinning up to level 5 in 2L of water without throwing the bar. It was churning a lot of bubbles and splashing up to the top of the flask neck [EDIT: NOT WHAT YOU WANT WITH A STARTER!] but the bar held!

I'll be using this size bar (25mm) on all my starter sizes from this point forward.

 

[wepeeler]

I typically make 4 - 5L starters. Even with these large starters, the Maelstrom is difficult to dial in - it's prone to throwing off the 50mm bar. I almost always use the 25mm bar and have no problem, even at higher speeds.

BTW, I recently switched from White Labs Pure Pitch to Pure Pitch Next Generation and no longer make starters (for 1-bbl batches). I'm getting great results.

You're doing 31 gallon batches with 1 pack of Next Gen? That's severely under-pitching. The Next Gen pouches are only 150 bil cells. Their claim is more cells to start and longer lasting, not no starters for big batches.

As for the stir bar size, not sure about the Maelstrom plate, but I find smaller stir bars work better and don't get thrown as often. Don't try for a vortex, just enough spin to keep everything in suspension.

 

[Nagorg]

Don't try for a vortex, just enough spin to keep everything in suspension.

Understood... Vortex was not the goal. Spinning on the lowest speed while not being thrown was the initial objective.

But on topic, with my 50mm bar I couldn't turn the Maelstrom up higher than 1 without it getting thrown. With the 25mm, I can go all the way to 5 and it stays put. Not that I'd spin an actual starter at that speed but that it will stay put at that speed.

Larger starters will require a higher speed than 1 with the 25mm bar to even get a "dimple" at the surface though. But the highest speed does produce a full height vortex if anyone was wondering...

 

[wepeeler]

Understood... Vortex was not the goal. Spinning on the lowest speed while not being thrown was the initial objective.

But on topic, with my 50mm bar, I couldn't turn the Maelstrom up higher than 1 without it getting thrown. With the 25mm, I can go all the way to 5 and it stays put. Not that I'd spin an actual starter at that speed but that it will stay put at that speed.

Larger starters will require a higher speed than 1 with the 25mm bar to even get a "dimple" at the surface though. But the highest speed does produce a full height vortex if anyone was wondering...

All good. Just figured someone else reading might not know a vortex isn't the goal.

 

[balrog]

the longer the stir bar, the further from center are the magnets in them (sometimes, ymmv, manufacturers are different, etc). That meshes with your observations. The maelstrom's magnets are a certain spread from center and ideally you want the stir bar magnets to exactly match.

I had the same issue when I built mine on a fan. The right sized stir bar was the size where the magnets matched up, regardless of stirring large or small volume. I use a gallon jug. But not *that* gallon jug because the bottom's too curved. Use **That** gallon jug. And don't mix them up. And insert your best "bottom too curved" snide remarks here.

[Edit: +1 to what @wepeeler says about simple movement over raging At World's End movie type vortex]

 

[Nagorg]

Come on guys... I didn't mean to imply that I was going for a Sharknado style Yeast starter...

Hopefully folks don't get that impression from this thread. But you DO want your stir bar to not get thrown...

 

[Mac's Brew]

You're doing 31 gallon batches with 1 pack of Next Gen? That's severely under-pitching. The Next Gen pouches are only 150 bil cells. Their claim is more cells to start and longer lasting, not no starters for big batches.

As for the stir bar size, not sure about the Maelstrom plate, but I find smaller stir bars work better and don't get thrown as often. Don't try for a vortex, just enough spin to keep everything in suspension.

I use one Nano Bundle for 1-bbl batches. That's five packs. It's the recommended pitch rate per White Labs (for OG up to 1.070).

 

[wepeeler]

I use one Nano Bundle for 1-bbl batches. That's five packs. It's the recommended pitch rate per White Labs (for OG up to 1.070).

Gotcha. I was like damn son, that's not a lot of yeast!