Update! The original N52 magnets used, and seen in pictures here, are no longer available readily. I have updated the magnet holder for the more common 1.25″ N52 disc magnets (Link is updated too).
For anyone who brews beer, eventually you end up down the path of yeast propagation, to start out your fermentation with a nice strong, active yeast starter. Managing yeast can get quite complex, but in its’ most simple form, you are simply waking up your dormant yeast, and increasing the cell count. This is done by introducing the yeast to a low-gravity maltose solution; most brewers aim for about 1.040 Specific Gravity, in a volume of around 200mL per gallon of your target wort.
The only tool you need in this, besides the obvious 2L Erlinmeyer Flask, is a stir plate which we’ll be 3D printing, and a magnetic stir bar. It’s job is to keep the yeast cells constantly circulating and in suspension in the liquid maltose solution so the yeast can have maximum opportunity to gobble up those sugars, as well as additional oxygen, which helps build strong cell walls, increasing overall attenuation once the yeast hit your actual wort.
Beyond the 3D printed parts, the Erlinmeyer flask and stir bar mentioned above, you’ll need just a couple components: a 120mm fan, a PWM speed controller, a pair of strong N52 magnets, a basic 12v DC wall wort for power, and a DC barrel jack. You’ll also need four #4 wood screws for the base, some rubber stand-off feet, and about a foot of light-gauge wire to hook it all up. Here’s some links to make it easy:
I’m assuming anyone making something like this is going to have everything else: a drawer full of 12v wall warts, take your pick. Wire, basic soldering skills, some rubber feet and random screws (#4 wood screws about 1/2″ long is ideal) and, oh yeah! A 3D printer!
Here’s the link to download 3D printed files. Have at it 🙂
The whole unit consists of only three 3D printed parts: The main shell, the bottom plate, and the magnet mount. I designed these to be as simple as possible, giving you a very clean, minimalist design. Just one knob, and the power input. No extra buttons, switches or lights. I like simple.
Print the main body, bottom plate, and magnet mount with no supports needed. I printed all at 30% infill. Mount the 120mm fan to the bottom plate with standard PC fan course screws, install the DC barrel jack, and speed controller. I recommend using a couple spots of hot glue to secure the wire running between the DC jack and the speed controller, to keep it from getting anywhere near the fan blades. Insert the N52 magnets in to the magnet holder part, with the North pole of one facing up, and the other facing down. Be careful when handling these magnets; they’re extremely powerful, and can cause injury if they were to snap against your fingers, and are powerful enough to shatter themselves if you allow them to snap together!
Use a few dabs of epoxy on the underside of the magnets to hold them in to the housing, then use a generous amount of epoxy to secure the magnet holder to the center of the 120mm fan hub, as pictured. I recommend gently spinning the fan before the epoxy sets up, to be sure you have the magnet holder centered as well as possible, to prevent any unnecessary vibration when it spins.
Once assembled and the epoxy dries, you can fit the main housing over the fan assembly, flip it over and screw the lid in place with four screws.
Now it’s time plug it in and test it out! If everything went to plan and you assembled it well, you should be able to spin a very powerful vortex in your flask. Next time you do a yeast starter, you’ll be helping to produce a healthier, higher cell count pitch, which will in turn give you better beer! Drop me a line if you have questions or comments, and please let me know how your stir plate turned out!