While I am bored over Christmas break I thought I would add to the brewery by making a stir plate. Earlier I think I have posted something about making starters in which the goal is to grow yeast. Higher alcohol beers require more yeast (>300 billion cells) compared to lower alcohol beers (~150 bill), but yeast is only sold in packs with 100 billion cells. When we make starters we would constantly have to agitate, swirl, and shake the solution up while it was going to increase oxygen concentrations in the starter. Yeast can create energy both aerobically and anaerobically (i.e., with and without oxgen). As a brewer, we like the anaerobic phase as the by products created are alcohol and CO2. However, intitially into a fermentation, the yeast are aerobic and use the oxygen to reproduce which is why we oxygenate before fermentation has started (e.g., shaking, or injecting pure oxygen, more on that later). Starters are no different and we want high oxygen levels to promote maximal yeast growth. By using a stir plate, the solution is in constant agitation and with the vortex created, a constant supply of oxygen is provided to the yeast. The end result: smaller volume starters that create more yeast. Instead of making 3.5 L starters, we'll be closer to 1.75-2 L. Commercial stir plates sell for ~$160, so I decided to make one myself.
I went to Radio Shack and bought a nob, a rheostat, and a switch. The rheostat is a device that used to toggle the amount of resistance through an electrical circuit, in our case the fan.
The fan was taken from our old desktop hard drive as well as the curved magnet. I wired everything together and suprisingly, the fan spun the first time I turned the swtich. By spinning the fan, and the magnet on top, the magnetic field will turn a stir bar in our starter flask. The stir bar is basically another plastic-coated magnet that when spun in a liquid will constantly stir the liquid and create a vortex down into the solution. The rheostat can control the speed of the fan and in turn the speed of the stir bar.
I used a cigar box for the base of the stir plate and mounted the knob and switch to the front. The hardest part encountered was getting the stir bar to spin constantly. Initially, it would spin momentarily and then would be "thrown" off the magents below and jitterbug around in the flask. We figured out we were spinning the fan too fast for the power of the magnet and after digging through the house were able to find a smaller (5V compared to 9V AC/DC power cord) that effectively slowed the fan enough to allow the sitr bar to remain in place.
Here is a close up of our 2L flask with the stir bar (white pill). You can see that the stir bar is spinning quickly enough to pull the vortex from the surface down. Although I think a 6V power supply would work a little better as the vortex is not constantly this far down with the current set up, a vortex is created nonetheless. When we do actually have a starter going, there will be more resistance as the solution is more viscous due the yeast and sugar in suspension. Hopefully this stir plate will be strong enough to maintain a vortex similar to this, but in the very least a small one will be created to provide enough oxygen for the yeast. All in all I spent about $26 making this stir plate and another $23 on the 2L flask; much cheaper than from the store, and cooler because it is totally unique.
I went to Radio Shack and bought a nob, a rheostat, and a switch. The rheostat is a device that used to toggle the amount of resistance through an electrical circuit, in our case the fan.
The fan was taken from our old desktop hard drive as well as the curved magnet. I wired everything together and suprisingly, the fan spun the first time I turned the swtich. By spinning the fan, and the magnet on top, the magnetic field will turn a stir bar in our starter flask. The stir bar is basically another plastic-coated magnet that when spun in a liquid will constantly stir the liquid and create a vortex down into the solution. The rheostat can control the speed of the fan and in turn the speed of the stir bar.
I used a cigar box for the base of the stir plate and mounted the knob and switch to the front. The hardest part encountered was getting the stir bar to spin constantly. Initially, it would spin momentarily and then would be "thrown" off the magents below and jitterbug around in the flask. We figured out we were spinning the fan too fast for the power of the magnet and after digging through the house were able to find a smaller (5V compared to 9V AC/DC power cord) that effectively slowed the fan enough to allow the sitr bar to remain in place.
Here is a close up of our 2L flask with the stir bar (white pill). You can see that the stir bar is spinning quickly enough to pull the vortex from the surface down. Although I think a 6V power supply would work a little better as the vortex is not constantly this far down with the current set up, a vortex is created nonetheless. When we do actually have a starter going, there will be more resistance as the solution is more viscous due the yeast and sugar in suspension. Hopefully this stir plate will be strong enough to maintain a vortex similar to this, but in the very least a small one will be created to provide enough oxygen for the yeast. All in all I spent about $26 making this stir plate and another $23 on the 2L flask; much cheaper than from the store, and cooler because it is totally unique.
I write this as I'm brewing our Anniversary Barleywine 2012, and I'll post later on that.
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