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Home Made Stir Plate - Enough Whirlpool?

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Mr. No-Tip

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Hey Brewers,

I've been building a home made stir plate this weekend:

-12v PC fan
-12v 500ma PSU
- eBay purchased 'rare earth' magnets
-70mm stirrer bar without pivot
-2l flask

Having a few problems...

The magnets aren't place entirely evenly - they got kind of sucked in by the fan's central magnet while the araldyte was drying. Not perfect now, but still pretty close. I initially found that the bar was throwing no matter what distance I picked. I think I have that figured out - maybe the chinese magnets aren't all they're cracked up to be - stack four of them, and we get a stir.

So now I have my stir, but this is the best whirlpool I can get (starts at 1.5l, topped up to 1.75l before the end...ignore dog and masterchef)


That's nowhere near what I have seen in demo videos. Now I can see the problem - not enough fan torque. As soon as I lift the flask off, the fan goes visibly faster a second later. I suspect the weight of the four magnets and the less than perfect positioning may also contribute.

I did try it with a 1a power supply, but the difference was pretty negligble.

Is that whirlpool sufficient for a 1-2l starter? If not, any suggestions on how to fix?

Thanks!
 
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Rob S

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I get a tiny little vortex at the top. I see the whole surface of the top turning slowly. It gets there. I don't think you need some violent tornado. Just a nice steady swirl is sufficient.
 

bullsneck

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I find that the 35mm bar is not as good as my 20mm or 25mm.
 

mmmyummybeer

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In Jamils yeast book he states that it doesn't need to be a big vortex type spin. the idea is more to keep the starter moving so more of the starter is exposed to the air for oxygen absorption. others can probable help you pimp it to spin faster but if not it will still do the job as is.
 

Mr. No-Tip

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Quick replies, and exactly what I wanted to hear! Thanks guys. :)
 

mkj

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A 12v fan with 5v power supply (old nokia charger) limited by a ~15 ohm resistor (3x 47ohms in parallel) works fine for me, draws about 100mA. Using the full 5v was too noisy and often threw the bar off.

I'm not sure whether the bigger factor in improved growth is aeration or just keeping in in suspension?
 

beerdrinkingbob

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that's plenty to get airation, you've done well, relax and have a home brew!! :icon_cheers:
 

lachc88

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yes; (having seen vid) that's more than sufficient.
 

Lurks

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I reckon that aeration stuff is a load of old bunk. Yer flask is full of CO2 eh? More likely to be keeping yeast in suspension and offgassing CO2 which helps yeast activity. I did, however, just pull this out of my ass rather than having any evidence.
 

jaypes

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you only need a small dimple in the top not a raging tornado type vortex.

moving the surface of the liquid will enable gasseous transfer - same principle for my fishtank
 

Mr. No-Tip

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Lurks

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That's interesting. Not surprising to see cell count boosts based on uncovered and air injection but surprising there's a difference between foil and an airlock. I mean O2 + yeast isn't in doubt, hence people bothering with O2 injection and all.

That said, my intuition would have been that with any sort of cover on a flask, the off gassing CO2 will displace all air but this suggests not. Still a bit dubious really.
 

djar007

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Does this mean that I need to aerate my starter as well. Oh god. I started with pouring a couple of cans into a container. I got fancy by heating them in a boiling pot of water to make it easier to pour. I am now , as swmbo puts it, out of control. But still open to new methods. :ph34r:
 

Yob

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djar... there is no end to it, only the limitations (and rightly so) of what you NEED..

I started much the same way.. my wife (who rolls her eyes when I remind her) bought me the time old coopers kit.. and now calls herself a 'brew widow' :lol:

..of course, what you need is rather subjective and Im pretty sure I didnt need those last 3 kegs I bought.. or that pressure cooker.. or that.... etc.. etc..

:beerbang:
 

MaltyHops

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djar007 said:
Does this mean that I need to aerate my starter as well.
Not if you have a stirplate - the stirring does the job of aerating your starter. Well, you could aerate your starter with O2 but that's moon mission scale.

djar007 said:
Oh god. I started with pouring a couple of cans into a container. I got fancy by heating them in a boiling pot of water to make it easier to pour. ... :ph34r:
Hee hee, well, don't really want to waste any of that sugaz now, do we?


Chinamat said:
That's interesting. Not surprising to see cell count boosts based on uncovered and air injection but surprising there's a difference between foil and an airlock.
Actually Kai didn't inject air into the starter, just about 5mm above the wort. Using an airlock on a starter was a mistake I made on my first few - loose foil is what I use now and it makes a big difference. Infection worry is dealt by tasting the spent wort as they're poured off to check for anything suspect.
 

Edak

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Does anyone actually trust the numbers on the side of their flash? I find that the numbers on both my 2L and 3L flasks are WAAAAY off... 1L in comes up as 800ml on the side of the flask. I verified it by weighing the amount of water.

why is this crap 20% off?
 

Lurks

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By jove you're right, mine is 1850ml at the 2L mark!
 

markxbeesley

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Just wondering as these flasks are sometimes used for boiling things does the scale allow for expansion of the water at boiling point. Is there that much difference in water volumm between 20c and 100c?
 

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