Stir Plates for Yeast Starters

Michigander Dan Jeska's Stir Starter for boosting yeast procreation.

Once you have precise control of the grain crush through a homebrew mill, the next gadget to think about is a stir plate. Actually, now that I have used a stir plate on just one batch, I wish I had bought or made one at the very beginning of my brewing hobby. The yeast on my current batch, a double IPA, were the happiest of any I've worked with. Within ten hours of pitching, the CO2 foam in my 6.5 gallon carboy was a 4" thick white mouse. I dialed the ambient temperature down to 58 ºF for the first 36 hours, until the initial activity seemed to slow, then raised the temp to 68 ºF for the remainder. The temperature rise gave way to still more vigorous fermentation activity, practically reaching the vessel's blow-off tube.

Most bigger homebrew supply web sites offer at least one, and maybe a couple of stir plates. Typical examples are the Fermtap Magnetic Stir Plate from More Beer ($69.95 shipping included), and the Northern Brewer Stir Plate ($79.95 plus $7.99 shipping). I chose the Stir Starter Stir Plate ($42 shipping included), not just because the price was very competitive, but mainly because the designer, Dan Jeska, solved the problem of losing the Teflon coated rotator bar into the fermenter at pitching time. He includes a second small "keeper" magnet in the kit which you use to stick to the bar magnetically through the bottom of the starter flask. This keeps the stir bar from pitching right along with the yeast. During the starter growth phase, you can kept the stir plate and flask wrapped in towels, set into a decent sized kettle to stabilize the rig, or to allow for easy relocation if needed.

Dan links to a must-read article by M. B. Raines-Casselman, "Yeast Propagation and Maintenance: Principles and Practices". Raines-Casselman has some insightful techniques for optimizing a yeast starter, and explains how starter wort needs to be treated differently than the final batch of beer. Your basic goal with a starter is to make it possible for the yeast to expend most of their procreation energy in the starter. You want to keep oxygen flowing in with a loose tinfoil seal over the flask, which is maybe a little counter-intuitive to the rest of the fermenting process. The stir plate's vortex continually draws in oxygen that the yeast needs for creating more yeast. Alternately, you could use a rubber stopper, but attach a sanitary filter to it instead of an airlock. Then, when you pitch the yeast into the final wort, they are healthy and plentiful enough to immediately start the desired activity of full fermentation.