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How much vortex on a stir plate?

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Alemental

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I am currently playing around with a homemade stirplate. I've been trying different spacings of 3/8" rare earth magnets using double sided tape on a fan. The problem is that the stir bar gets thrown too easily. I can get a vortex that extends down to 1/2" to 3/4" and be fairly stable, but if I increase the RPMs any faster, it gets thrown. The problem is much worse in my 2 liter Erlenmeyer flask than it is in the 1 liter one.
How much of a vortex is really necessary? Spinning the wort will certainly keep the yeast in suspension, but it doesn't seem like it would aerate as well. I've seen plenty of pics posted that show the vortex extending nearly to the bottom, but that seems a bit much.
 
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I like to get as big a vortex as possible, and I find that if I'm careful, I can get the vortex almost down to the stir bar. If I allow the vortex to actually touch the stir bar, it gets thrown pretty shortly thereafter.

I use 5/8" neodymium magnets that are at least 1/8" thick. The hard drive magnets that some people use are probably even more powerful. I think you need to get some stronger magnets. Also, try to minimize the space between the bottom of the flask and the magnets.
 

raceskier

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I used two 1/2 inch diameter by 1/8 inch thick round neodymium magnets on my stirplate. I can't get the vortex down to the bottom of my 2l flask without throwing. I started with four really small magnets and they would not hold the stirbar at all. More magnet and closer spacing as Yuri suggested are the keys.
 

Desert_Sky

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I have one of Yuri's stir plates and love it. Like he said I like to have the vortex as big as possible, but can't go too much or the stir bar gets thrown off to the side.
 

Scimmia

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First thing to check is that your magnets aren't off center, that'll throw the bar quicker than anything. Then make sure that they're spaced right, having them directly below the ends of the stirbar seems to be about right for me. I've got 4 ~1/2 x 1/8 magnets (stacked 2 high), and with my 1 5/8 stirbar, I can easily pull the vortex down to the stirbar in a 2L flask. In fact, I was trying some things with water, and was able to hold the vortex all the way to the bottom for hours without throwing the bar. I just run it with the vortex most of the way down, though.
 

Kaiser

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I'm seeing a similar thing with my stirplate.

The vortex is nice, but not necessary. You wan't to have a vortex when the amount of starter is small and the starter level is shallow. But as soon as the starter gets larger and/or starts fermenting there won't be much of a vortex or aeration anyway. At this point the big benefit of the stirplate is to keep the yeast in suspension so all the cells can take part in multiplying. I hold the O2 wand into the starter once in a while to add some more O2. Watch out it when it foams up.

Once I have an aquarium pump set-up I'd like to automate intermittend air injection.

Kai
 

foxtrot

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I've been using a stirplate for the last 2 brews and have a 1" vortex at best, using a 2 liter flask. Although I don't have a means of cell counting, both worts (a 1.060 OG lager and a 1.072 Belgian) fermented out within 2 weeks, so I'm confident that plenty of healthy yeast was produced!

I believe the big advantage of a stirplate is to keep the yeast in constant contact with nutrients and to drive off CO2, which supresses growth. Try stopping the stir bar for about an hour during the growth phase, then turn it back on and watch the huge evolution of CO2! (its pretty cool to watch and proves the point). Since the wort is constantly turning over at the surface, I think this alone is enough aeration. Just my thoughts.
 

ebeer

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The vortex is immaterial to me. When I pitch the yeast in my starter I aerate with O2 just as I would the wort. I let the stir plate spin enough to keep the beasties in suspension. Any more is probably not necessary, though probably not harmful.
 
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Alemental

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Good replies, all. While I could probably get by with the slower spin, I am bothered by the inherent instability. I decided to take Yuri's advice. I went to allelectronics.com and ordered bigger magnets. They had 2 sizes of the hard drive type, with the larger size at $1.35 each. Can't wait to get them.
Thanks everybody.
 
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Alemental said:
Good replies, all. While I could probably get by with the slower spin, I am bothered by the inherent instability. I decided to take Yuri's advice. I went to allelectronics.com and ordered bigger magnets. They had 2 sizes of the hard drive type, with the larger size at $1.35 each. Can't wait to get them.
I was just in All Electronics the other day, buying a voltage regulator for my stirplate, and I saw those very magnets on the shelf! Small world.

For anybody who's never been there, All Electronics is a geek's delight! They come across some very unusual surplus items, not all of which make it into their catalog or website. I've been shopping there for over twenty years.
 

seawort

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as long as you are getting a good stir action there should be no problem getting the kind of yeast propagation you need. I get a good vortex going on mine most of the time but have found that if it just stays in motion it is just as good looking a starter. YMMV
 

Desert_Sky

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honestly I love having a vortex going just so people have to do a double take just to see whats going on
 

DRAGGER

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I used a hard drive magnet on my homebrewed stir plate with a 1-3/8" bar.... I have a varible speed fan and can get the vortex and hold it to the stir bar.... However I have just a little speed control left and if I turn it all the way up the bar starts to cavitate and is thrown.....

DRAGGER.....



 

stevecaaster

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Chimone said:
honestly I love having a vortex going just so people have to do a double take just to see whats going on

LOL I do the same thing, with water i presume? also I spent so much damn energy, money, and time building the thing, so its my way of appreciating it. I just run her with some water while im doing other things like bottling or brewing.
 

Vels

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I run mine with a vortex half way down the liquid, more than enough to drive off co2 and pick up oxygen.
I also run a hose in to the flask from an aquaruim pump with hepa filter (wort areator) which will supply fresh air in to the flask. Do not submerge hose if you want to try this, bubbles will cause excessive foaming.
I made a huge starter this way for me brew session on Sunday, Monday evening i had lost a couple of liters/quarts through the airlock due to insane fermentation.
Plan for more headroom with huge starters
Night before brewday i put the flask in fridge, pour off oxygenated beer next morning, and pour on ½quart of wort to wake up the yeast again. Its ready to pitch within 2-3 hours.

Cheers
Jakob
 

pjj2ba

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In the lab when we grow yeast or bacteria we typically use a platform shaker set at around 200 rpm. That's all you really need. You just want the critters in suspension. Remember oxygen will always want to be at equilibrium between the air and your culture media. Assuming you're using a foil cap or a foam plug (you don't want to use an airlock unless you are pumping in air or O2) as the yeasties consume O2 from the liquid it is replaced with O2 from the air. The faster they use up the O2, the faster more will diffuse in to the liquid to replace it. This happens pretty quick for such small volumes (under 1000 ml). Stirring will help speed up the diffusion into the liquid, but I don't think the yeast are consuming O2 so fast that a vigorous stir is needed. That is certainly not what we do in the lab.
 
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