World's cheapest stir plate NEEDS MOR POW-RRR!

[hardrain]

I'm looking for some cheap DIY tips -- I've built (as you can see below) what you might call a stir plate, thrown together from some cheap parts. But hey it (mostly) works!

At first I had a hard time keeping the stir bar from spinning out of control, and went from one magnet per side to three. I've since been doing some 2L size starters for lagers (in the past I'd been doing .8L-1.5L starters with fresher yeast, which based on calculators was more than enough to get to the ~200B or so cells I shoot for in most of my low gravity ales).

The problem: I'm not able to get much of a funnel at the 2L+ size without throwing my stir bar off the magnets. The starter is controlled by a fan speed nob below the fan, not pictured, and I can only get up to about half speed. I can actually get it going with just the wort, but once the yeast had a chance to establish itself, the liquid appears to somewhat thicken, and my stir plate can't keep up.

I'm wondering if anyone else has souped up their cheap homemade stir plate. I don't know much about magnets, should I be trying to find stronger ones (if so, what are those called?)...or is there a problem with my stir bar? I've had trouble keeping large bars on center even at low volumes, probably because of the magnet spacing...

...curious anyone else's experience. Thanks!

 

[beskone]

I have the exact same DIY stir plate, using a pair of disk magnets attached to the fan. I found that using a 1" stir bar I'd throw it all the time with a 2L starter. Once I went up to a 1.5" stir bar It's been fine ever since.

How big is your stir bar? Might be an easy fix.

 

[Newsman]

Also, might try picking up some rare earth magnets. They are stronger than "regular" magnets

 

[hardrain]

I have the exact same DIY stir plate, using a pair of disk magnets attached to the fan. I found that using a 1" stir bar I'd throw it all the time with a 2L starter. Once I went up to a 1.5" stir bar It's been fine ever since.

How big is your stir bar? Might be an easy fix.

Interesting. In a flask so I can't remember exactly but I think ~1/2". Do you worry about the spacing of the magnets on the fan when going all the way up to 1.5", or was that not an issue for you?

 

[NTexBrewer]

I think I have you beat for cheapest and simplest stir plate. Tupperware container works perfect and keeps the fan safe from splashes. I have a very small fan and never get a vortex with large starters but it really is not necessary in my opinion.

Getting a rare earth magnet will also help, I dug mine out of an old backup hard drive that died.

 

[MagicMatt]

I have a very small fan and never get a vortex with large starters but it really is not necessary in my opinion.

If it's not necessary, then what's the purpose of the stirplate in this context? The goal here isn't to simply stir or mix the wort, it's purely for gas exchange (getting fresh oxygen to the yeast). If you're not spinning fast enough to even create a vortex (much less get the vortex to the stirbar), then what is the benefit of using a stir plate at all?

There have been several experiments that show that the faster and larger the vortex, the higher the yeast count in the end. With a minimal stir and vortex, there was little-to-no difference when compared to the control of no stir plate whatsoever.

 

[501irishred]

Trying a new stir bar is a good idea even if its the same size as the one you have. My first bar wouldn't even spin at low speeds without throwing, no matter what magnets I used.....or magnet spacing....or distance from flask.....(weeks of tinkering later......). A new stir bar later (same size, but different brand) and I can drag a vortex to the bottom of a 2 liter flask with no problems.

 

[SanPancho]

the other thing that helps with stir bar throwing is to get some silicon orings. i put them on the ends of the stir bar and it helps it not get thrown, also quiets down the rattle from the flask not being 100% flat on its bottom. the red ones are food grade and hi temp. i put bar in the flask when i boil starter to get it sanitized, then just plop it on stir plate.

got them on amazon, few bucks for a 10 pack. wont help you with power, but should help throw less. you may want to get some rare earth magnets, it looks like you're weighing down that fan quite a bit with all the magnets.

 

[WrQth]

A vortex isn't necessary, a dimple on the surface is sufficient. The stirring a does few things: keeps the yeast in suspension, releases CO2 from the wort which can inhibit yeast growth, and helps with oxygenation which the yeast use to reproduce. Too strong of a stirring action could damage the yeasts cellular walls that come into contact between the stir bar and the bottom of the vessel.

 

[Qhrumphf]

A vortex isn't necessary, a dimple on the surface is sufficient. The stirring a does few things: keeps the yeast in suspension, releases CO2 from the wort which can inhibit yeast growth, and helps with oxygenation which the yeast use to reproduce. Too strong of a stirring action could damage the yeasts cellular walls that come into contact between the stir bar and the bottom of the vessel.

Not inherently true.

http://braukaiser.com/blog/blog/2013/03/25/stir-speed-and-yeast-growth/

Experiment confirms that faster vortex = more growth.

 

[WrQth]

Not inherently true.

http://braukaiser.com/blog/blog/2013/03/25/stir-speed-and-yeast-growth/

Experiment confirms that faster vortex = more growth.

In his scenario sure but can it be said it would be the same for larger volumes like a 1L or 2L starter that is covered (his were uncovered which would promote greater air exchange) which would be more like the scenario for a homebrewer, I agree that probably it would be but only one way to find out.

 

[Baja_Brewer]

I just built this last night - not sure what grade Neodymium they are, but they're strong! I'd look for some of those if you want more strength. Maybe check out some N52 ones: https://www.kjmagnetics.com/products.asp?cat=168 Look at the N52-DA1 (5lbs) or similar... even at $5 shipping, you'll greatly improve your cheap stir plate for under $10.

Don't mind the hot glue on the fender washer - I was out of super glue.

 

[RM-MN]

If it's not necessary, then what's the purpose of the stirplate in this context? The goal here isn't to simply stir or mix the wort, it's purely for gas exchange (getting fresh oxygen to the yeast). If you're not spinning fast enough to even create a vortex (much less get the vortex to the stirbar), then what is the benefit of using a stir plate at all?

There have been several experiments that show that the faster and larger the vortex, the higher the yeast count in the end. With a minimal stir and vortex, there was little-to-no difference when compared to the control of no stir plate whatsoever.

The stir plate accelerate the yeast growth but do little more than that. You can get the same amount of yeast cells by shaking the starter when you walk by as you can with a stir plate but it will take longer. http://www.woodlandbrew.com/2015/02/yeast-starters-stirred-vs-not.html

 

[DurtyChemist]

The stir plate accelerate the yeast growth but do little more than that. You can get the same amount of yeast cells by shaking the starter when you walk by as you can with a stir plate but it will take longer. http://www.woodlandbrew.com/2015/02/yeast-starters-stirred-vs-not.html

I can also run 26 miles but it's much easier in a car. Yes the car is expensive but it takes a lot less effort than running and it's much more efficient.

I run my stir plate http://www.brewchatter.com/index.php?main_page=product_info&cPath=58_112&products_id=451 at half to 3/4 speed and get a dimple on the top. I've tested it with water and this pulls a vortex all the way down. Yes it will pull more but it annoys me hearing the stir bar rattle and sometimes the gas exchange is too much for my 2L flask and 1.5L starters and yeast come out the top. I've never calculated a difference but it seems to do just fine at either speed.

 

[hardrain]

I think I have you beat for cheapest and simplest stir plate.

I knew this would be controversial

Maybe check out some N52 ones: https://www.kjmagnetics.com/products.asp?cat=168 Look at the N52-DA1 (5lbs) or similar... even at $5 shipping, you'll greatly improve your cheap stir plate for under $10.

Excellent, thanks! Also -- I've always wondered this: what's the function of adding the washer like you did in yours? Is it a spacing thing?

And I'm going to try the 1.5" stir bar first, before the magnets. I'm already using the rubber rings which have been a godsend on noise alone, haven't seen the red ones though, I'll check them out b/c would be nice to just boil the whole thing (currently I sit in starsan and add after cooling).

On the digression (don't all yeast posts do this?)

The stir plate accelerate the yeast growth but do little more than that. You can get the same amount of yeast cells by shaking the starter when you walk by as you can with a stir plate but it will take longer. http://www.woodlandbrew.com/2015/02/yeast-starters-stirred-vs-not.html

I find that article very confusing. I've previously subscribed to the tests I've seen online that stirplate speed matters to a point, and that makes intuitive sense to me as well. In the link above, it seems to go:
-o2 is absolutely critical to yeast growth (good so far)
-But then: "The lack of aeration make Chris White's experiments questionable when used to predict growth on a stir plate. Oxygen is critical for sterol production in yeast. Without aeration an the onset of fermentation the yeast membranes will lack the pliability they need to bud new cells."
-Followed by: "Using a stir plate oxygen is constantly introduced."...okay so we didn't add o2 with a stone before pitching yeast, but we have it constantly introduced because of the stir plate...
-And then the kicker: "[The stir plate is note effective] due to the Crab Tree Effect."

...he doesn't elaborate. What he doesn't explain is why the crab tree effect only discounts the o2 from the stir plate and not the pre-pitch o2. Based on my layman's understanding, the crab tree effect is simply what yeast does in the absence of o2, with the stir plate entirely designed to prevent that. If anything my (potentially warped) understanding of that post is that I should be spinning the damn thing as fast as possible to prevent crab tree. How can he say White's study has a "lack of oxygen" when in fact he's using a stir plate specifically to introduce constant oxygen?

 

[Qhrumphf]

I knew this would be controversial



Excellent, thanks! Also -- I've always wondered this: what's the function of adding the washer like you did in yours? Is it a spacing thing?

And I'm going to try the 1.5" stir bar first, before the magnets. I'm already using the rubber rings which have been a godsend on noise alone, haven't seen the red ones though, I'll check them out b/c would be nice to just boil the whole thing (currently I sit in starsan and add after cooling).

On the digression (don't all yeast posts do this?)



I find that article very confusing. I've previously subscribed to the tests I've seen online that stirplate speed matters to a point, and that makes intuitive sense to me as well. In the link above, it seems to go:
-o2 is absolutely critical to yeast growth (good so far)
-But then: "The lack of aeration make Chris White's experiments questionable when used to predict growth on a stir plate. Oxygen is critical for sterol production in yeast. Without aeration an the onset of fermentation the yeast membranes will lack the pliability they need to bud new cells."
-Followed by: "Using a stir plate oxygen is constantly introduced."...okay so we didn't add o2 with a stone before pitching yeast, but we have it constantly introduced because of the stir plate...
-And then the kicker: "[The stir plate is note effective] due to the Crab Tree Effect."

...he doesn't elaborate. What he doesn't explain is why the crab tree effect only discounts the o2 from the stir plate and not the pre-pitch o2. Based on my layman's understanding, the crab tree effect is simply what yeast does in the absence of o2, with the stir plate entirely designed to prevent that. If anything my (potentially warped) understanding of that post is that I should be spinning the damn thing as fast as possible to prevent crab tree. How can he say White's study has a "lack of oxygen" when in fact he's using a stir plate specifically to introduce constant oxygen?

Crabtree is what happens in the presence of glucose irrespective of oxygen.

However this Woodland site is the only place I recall seeing that a stir plate creates no added growth. And his source for that claim is his own site.

Where Kai and others have done data and cell counts showing otherwise.

I need to dig into his claim further but as of now I don't buy it.

 

[RTL]

Just to jump on the new stir bar bandwagon. I found that some of the stir bars have weaker internal magnets that others. My litmus test for them is if they can't hold themselves to the side of my fridge they go in the trash. Sounds like everything else have been covered. Good luck.

 

[MagicMatt]

I just built this last night - not sure what grade Neodymium they are, but they're strong! I'd look for some of those if you want more strength. Maybe check out some N52 ones: https://www.kjmagnetics.com/products.asp?cat=168 Look at the N52-DA1 (5lbs) or similar... even at $5 shipping, you'll greatly improve your cheap stir plate for under $10.

Don't mind the hot glue on the fender washer - I was out of super glue.

Get yourself a project box and make that thing look good! That's the same fan I used (black model though) and added a lighted rocker switch:

 

[Baja_Brewer]

Get yourself a project box and make that thing look good! That's the same fan I used (black model though) and added a lighted rocker switch:

Its on the to-do list. I actually know where I can snag a good NEMA enclosure for free. I just wanted to get it up and running.

 

[WrQth]

Crabtree is what happens in the presence of glucose irrespective of oxygen.

However this Woodland site is the only place I recall seeing that a stir plate creates no added growth. And his source for that claim is his own site.

Where Kai and others have done data and cell counts showing otherwise.

I need to dig into his claim further but as of now I don't buy it.

A stirplate increases the rate of growth seems to be agreeded upon. Noted in the comments of the Woodland articles there were observations the biomass varied between stirred and not stirred and may even indicate healthier yeast

 

[mappler]

I have used cigar boxes successfully as enclosures. They are a nice size, usually pretty sturdy, and easy to drill some holes in.