For years I have used liquid yeast in a vial and have always had trouble getting the final gravities I was after. In the last few batches of home brew I have also noticed a few off flavors. I decided to start using a yeast starter. A five gallon wort should have about 200 billion cells pitched. This is much less than what is in the vials or smack packs. My first starter was made in an 1000ml Erlenmeyer Flask using White Labs California Ale Yeast WLP001, without a stir plate. I boiled 2 cups of water with ½ cup DME for 10 minutes, cooled, and pitched the yeast. It worked fine but didn’t seem like the yeast was as active as it should have been. I noticed a lot of the yeast was settling on the bottom of the flask.
I decided to build a stir plate. A stir plate keeps the yeast in suspension and in contact with the nutrients. It will aerate the small batch of wort and this oxygen is essential for yeast propagation. The constant moving of the wort will also knock the carbon dioxide out of suspension, you don’t want that in your solution as it inhibits yeast growth.
I was able to make the stir plate from parts lying around my house, mostly a computer.
Parts For Stir Plate
- Computer Fan
- AC/DC Adapter, that matches the volts of the fan
- Box to hold everything
- Switch (I had an extra)
- Rare Earth Magnet from a hard drive
- Stir bar, I used the middle of CD-Rom drive
- Nuts and bolts to hold the fan in place
- Rheostat, also called a Potentiometer (I didn’t use one of these but hope to add one soon)