Warning! This post has some numbers, and some technical beer words. Because I’m a nerd for beer.
I’ve had this problem on brew days. I want to maintain a steady mash temperature for long periods of time, but my gas heat source is either too high and the temperature rises, or too low and a breeze blows the flame out. As a result I end up staring at the stove for 60-90 minutes, constantly adjusting a gas valve and re-lighting the stove. It’s a tedious process, but my real concern is recipes are really, really hard to repeat with this method – and I want repeatability.
I saw two solutions: buy some really expensive pre-made controller, or build my own. I chose the latter, and recruited my dad for help. After lots of very confused discussions about the concept of the controller (electric or gas? HERMS or RIMS? how do you convert 3/4″ pipe thread to 5/16″ compression thread? what the #$@# are we doing? that sort of thing), we settled on keeping the RIMS system I had (heated with natural gas), and adding an electrically actuated gas valve controlled by an Arduino processor. When the temperature is too low, the Arduino commands the valve to open, the stove is lit by the pilot light, and it heats up. When the temperature hits the target temperature, the Arduino closes the valve. It’s a simple concept, and took us a painfully long time to iron out. But it’s done!
Last night was the first test run. It’s not exactly pretty… but the result is amazing. I programmed in a 4-stage mash and hit “go”, and it held the temperature within a degree of my targets for 90 minutes. Absolutely repeatable!
Oh, and side-note, last night’s mash gave me 90% conversion efficiency. If that’s not hot, I don’t know what is.