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Q: How large of flask will your stir plate accommodate?

A: The stir plate is designed for use with a 1 or 2L flask but I have used a 1 gallon jug with a relatively flat bottom.  I have received feedback from customers that have said they are using a 4L flask with good results, but I have not done so myself.

Q: I bought a commercial stir plate off of eBay and it gets really hot even though it’s not a heated stir plate. Does this stir plate get hot?

A: No.  Running off of a 12 volt wall transformer, there just isn’t enough current to heat things up under normal operation.

Q: I don’t really use much liquid yeast, why do I need a stir plate?

A: Fermentis recommends “…Re-hydrate the dry yeast into yeast cream in a stirred vessel prior to pitching. Sprinkle the dry yeast in 10 times its own weight of sterile water or wort at 27C ± 3C. Once the expected weight of dry yeast is reconstituted into cream by this method (this takes about 15 to 30 minutes), maintain a gentle stirring for another 30 minutes. Then pitch the resultant cream into the fermentation vessel.”  A stir plate is perfect for this!

Q: How big of a vortex will this stir plate create?

A: It depends on the size of the flask, but the pictures you see (including my own!) of huge whirlpools to the bottom of the flask are misleading.  All you need is a gentle stirring motion to keep the yeast in suspension and drive-off CO2.  A large vortex to the bottom of the flask unnecessarily stresses the yeast, increases the risk that the stir bar will be thrown and doesn’t increase cell count.

Q: I just read about stir plates with a PWM control circuit. How is yours better than that one and why should I buy yours?

A: PWM stands for Pulse Width Modulation and rather than vary the amount of voltage to a load it varies the time the voltage is applied at a very fast rate. So for example, if you want a DC motor to turn at half its speed, you can either supply it half its required voltage or... you could supply it 100% of its required voltage for half the time. The latter choice is much more efficient and on a device like a cell phone where that technology is used to drive the LED backlight circuits it saves a tremendous amount of energy. However, for this application it's a really bad choice. Why? Because the modulation has to happen at a frequency we as humans can hear! So, you end up with a very annoying hum and/or whine. I tried several PWM circuits when I first started testing stir plate designs and while they will turn the motor with full torque at a low RPM they are just too annoying in most households and really, we don't need this application to turn at that low an RPM. Couple that with the fact that this isn't a battery powered device and you can see it's technology mis-applied.

If you're considering a PWM based stir plate, ask the manufacturer what frequency they operate at. If it's between 20hz or 20Khz, you're going to hear it.

Q: I already tried making my own stir plate and it just never worked right.  It would always stop or throw the stir bar.  How do I know yours will be any better?

A: Good question.  First, mine is built around the LM317 adjustable voltage regulator so it supplies very consistent voltage to the motor. Second, I align the drive magnet and test each stir plate with a 2L flask before shipping.  Third, I limit the top speed of the motor to help reduce thrown stir bars. I also encourage you to check out my eBay feedback rating and what others have said there and on the brewing forums.

Q: How do I ask you a question I don't see here?

A: Easy! Contact me!