Alternatives to stirplates

Okay, so I built a stirplate for my yeast harvesting. It worked spectacularly for the first 10 or so generations of yeast when it magically began throwing the stirbar (both pre-fab and homemade) 100% of the time.

There's criticism of mechanical stirring mechanisms because of the contact which could open up infection.

I've tought of another idea, and wanted to float it by you guys. I'm still going to do it but perhaps tossing this out can help me avoid mistakes in the process.

Invision an inverted cone, perhaps an upside-down Mt. Dew bottle. In place of the cap there's a drilled rubber stopper with an infusion stone on the inside of the bottle. Connected to the infusion stone is an aeration pump with HEPA filter.

The incoming air bubbles would agitate the yeast continuously while providing the oxygen they need. I'd get the conical effect of channeling the yeast back towards that center where the air was coming in.

I'd deal with pressure by either an airlock, a blow off tube or a drilled (and covered) outlet.

Any thoughts on this?

Kevin Dean said:

There's criticism of mechanical stirring mechanisms because of the contact which could open up infection.

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Are you not sterilizing your equipment? The flask? The stir bar?

And how is an aeration stone, with millions of little hiding places for bacteria, any safer than a teflon coated stir bar?

I am really confused. You know from your own experience, and the experience of others, that the stir plate method works, why try to create a system that seems even more complicated?

Or you could use one of those mechanical stir plates where the entire platform the flask is on gently rotates, sloshing the contents. Maybe try looking on ebay.

I would worry about the air stone getting infected before I would worry about a stir bar that I boil.

They sell premium stir bars in Scientific supply houses. Some of these are oblong and have awesome magnets. Don't think there are any yeast that can throw these if you keep the slurry moving.

I think that is a neat idea. I have done a couple of 10 gal batches lately where I used two different yeasts and seperated the batch. I only have one stirplate and have had to make two starters and alternate them on and off. The only thing is you would want to decant the wort and pitch only yeast since it would obviously be highly oxidized beer. I am interested to see this in action, keep us updated.

rabidgerbil said:

Are you not sterilizing your equipment? The flask? The stir bar?

And how is an aeration stone, with millions of little hiding places for bacteria, any safer than a teflon coated stir bar?

I am really confused. You know from your own experience, and the experience of others, that the stir plate method works, why try to create a system that seems even more complicated?

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I think Kevin is saying that ALTERNATIVES to stir plates are criticized as introducing opportunities for infection. For example, a "device" that you might attach to the top of a flask, with a long shaft and tiny "paddles" at the bottom. That would agitate the yeast similarly to a stir plate, but you would be sticking something into your sterile solution that is not sterile.

I think Kevin is suggesting the aeration stone + upside down conical device as a possibility for a NON-infecting device.

That being said, are you sure that either your homemade stir plate, or maybe your stir bar(s) somehow got demagnetized? Perhaps the beaker is off-center? In a perfect world, a stir plate shouldn't throw a stir bar because their circles are perfectly concentric.

There is no reason that a stir plate should throw the stir bar unless something is off-center, or you are trying to spin it too fast (or accelerate it too fast)...
If the magnet on the rotor is centered, and the stir bar is properly centered in the container (especially important if your container does not have a very flat bottom) and you don't try to ramp up the speed too quickly and don't try to run it at way too high of a speed, you shouldn't have a problem - and none of these possible problems are at ALL hard to avoid.

On mine, I put the flask with stir bar on the plate, make sure the bar has been grabbed by the stirrer magnet, center the flask, and gradually ramp up the stir speed from zero to wherever I want it. Takes less than a minute and it never throws the stir bar - and I am quite certain that the magnet on the stir plate is not perfectly centered, yet it's never been a problem.

I have been thinking of building a stir plate and was looking at stir bars when I ran across this

http://boreal.cm/product.asp_Q_pn_E_IG0024796
They are a bit more expensive then the standard one you see but might be worth it

BeerCanuck

Yep thats what I was talking about. They also have off center stir bars

I would think that continuous infusion of oxygen during the fermentation process of a starter would be far more likely to induce an infection, much as it would if you did that while fermenting a batch of beer.

I had the same problem only in reverse w/ my homemade stir plate. When I first built it, I couldn't get the stir bar going. It'd fly off before it spun 10 times. One night after several futile adjustments and magnet repositions I gave up and threw the stir bar on top of the stir plate without the flask and went to bed. In the morning it worked fine and never has never stopped. Maybe stir bars need to be "trained". Maybe they work better after being magnetized slightly by another magnet. I don't know. Just letting you know my experiences.
I'm no rocket scientist, just a home brewer.......

Bernie Brewer said:

I would think that continuous infusion of oxygen during the fermentation process of a starter would be far more likely to induce an infection, much as it would if you did that while fermenting a batch of beer.

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That is why many people use foam stoppers so that they get filtered air into the flask, and further reduce the risk of contamination. All I can tell you is that I have not had a problem yet with a starter.

rabidgerbil said:

That is why many people use foam stoppers so that they get filtered air into the flask, and further reduce the risk of contamination. All I can tell you is that I have not had a problem yet with a starter.

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how do you sterilize the foam stoppers? I would think they would trap and house more bacteria than the plain old foil cap (which I can heat sterilize with a torch)

Seabee John said:

how do you sterilize the foam stoppers? I would think they would trap and house more bacteria than the plain old foil cap (which I can heat sterilize with a torch)

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They are autoclavable.

Another alternative, to answer the main poster's question, is to use an orbital shaker instead of a stirplate....but these are much, much more expensive.

Really, a good teflon coated stirbar that is bleached won't be contaminating your yeast, and should be able to turn some pretty thick slurries (as in i've gotten cell cultures with the consistency of snot stirring). One thing you might try is slowly ramping up the speed rather than just cranking 'er on.