Now that I've discovered (thanks to jsled and Google) what a stir plate is and why I need to make one, I'm curious to know how far they can be pushed.

Being a lazy brewer with a fairly well-equipped workshop, limited bench space, a hearty appetite for beer and a recurring case of gout, I prefer to make big batches of full-bodied but low-alcohol ales. Lack of time and near-absence of temperature control rule out lagers and lagering, at least for now, so I'm mostly interested in producing the best beer I can with the least time & effort necessary.

Looking at various homemade stir plates, I see they all use flat-bottomed lab beakers, they're all too small for the 100-litre batches I like to make, and they generally use 12V muffin fans to run the pellet around. I'm wondering if anyone has built a hairy-chested (say, gallon-jug-size) stir plate using a stronger DC motor, stronger rare-earth magnets, and a big honking swirl pellet that will do the job.

The power supply isn't an issue, since I have an adjustable Mastech digital monster that weighs about 20 pounds, but I don't know about the other components. Supposing I could get a suitable DC fan or other motor, and an appropriately sized stirring pellet (or perhaps two?) I can easily picture them losing contact with the magnets or wearing grooves in my proposed gallon-jug starter.

Sorry to be so long-winded, but I want to explain what I have in mind, and why. Any suggestions or comments will be much appreciated, as always.

1 Answer 1


I don't think you need something so heavy duty for the batch sizes you're talking about.

The "standard" homebrew stir plates are generally built with hard-drive magnets and computer case fans. These can readily move wort in flasks from 2-4L, and probably up to 6L, as well, with just a bigger stir-bar.

Looking at yeast-starter calculators, for 100L of low-gravity ale wort, you'll want about 750bn cells. You can get this with a single 5L stir-plate starter (for which I'd recommend at least a 6L flask), or by doing two 2.5L steps (for which I'd recommend a 4L flask). Using anti-foam agents in smaller flasks can work very well, though definitely not 2.5L in a 2L flask ;)

The other option, of course, is to use multiple packets of dried yeast, which have a higher cell count (when properly rehydrated) and are much cheaper than liquid yeast, even after doubling and tripling up.

  • I've never had a stir plate at my mercy, so until I build one I can only guess what to expect. But I do want to try various liquid yeasts at the recommended pitching rates & see how those compare with dry yeasts. Luckily, my local homebrew supplier carries a good stock of Wyeast and other brands, and professional-grade equipment (not that I can afford it). Anyway it's good to know I'm not dreaming the impossible dream! Thanks again, eh?
    – Glasseyed
    May 7, 2014 at 17:59

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