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Home Brew Stir Plate

Home Brew Stir Plate

To make a stir plate for growing larger numbers of yeast organisms.

Yeast cultures are expensive. Often the culture does not contain adequate numbers of active cells for inoculating (pitching) a certain batch of home brew.

the good news is that yeast multiplies like crazy! Given the proper conditions, yeast is like a copy machine on steroids.

Yeast Stir Plate Project

This is how I made a simple stir plate out of spare parts and a couple inexpensive purchases.  Stir plates use a magnet in the plate to spin another teflon coated stir bar in the yeast culture. I got my magnet from an old hard drive. It was fairly easy to take apart and harvest the two magnets. (Too bad I threw away about 10 loder hard drives last month. the real old ones had better magnets!)

Mini Fridge

I used one of the many old 12 volt computer case fans I had lying around. You can use case fans, opwer supply fans, or just buy one for about $4 online. I also build a small pine project box. I just glued it together with Tight Bond II. This wood glue is waterproof. People have used old cigar boxes, plastic project boxes, etc for housings.

Door and Freezer

I used some CA glue to add small motor mounts to the inside of the box. These had threaded wood nuts CA glued to the underside. A few spare machine screws and it was mounted.

5 Gal. Better Bottle

I painted the wooden box with Rustoleum white paint. A couple of coats did the trick! I have many ole power supplies from now dead computer items, like zip drives, routers. old laptops, etc. I selected a 12v 1 amp supply. I ordered five stir bars on eBay for about $5. I used 5 minute epoxy to glue the HDD magnet to the top of the fan.

I drilled a few holes in the wooden box to mount the power indicator LED, the speed adjustment knob, and the power connector. Since my power supply had an M type power jack, I mounted n M type panel connector. This and the LED were from Radio Shack.

Mini Fridge

I ordered a small PWM motor speed control on E-Bay. It was $8 shipped. It included the knob, pot, and IC board with another LED. Wire the 12 volt leads from the power jack to the board. Make sure to place + to +! It is marked on the board. The panel LED was wired in with the 12V supply lines.

Then the fan is wired to the output. these are simple screw on connections.

5 Gal. Better Bottle

The power can then be connected easily.


I got two 2L Erlenmeyer flasks at the Bargain Barn at UC Davis. They also had 12 volt power supplies for $1 if you need one.


I plugged it in… It works! Speed control is good.

Check eBay for “12-24V 3A DC brushed Motors Speed Control PWM Controller”