Homebrew Beer Blog

Kind of basic, but a key component of the HERMS. In my post about the design, I discussed the decision on where to place the probe. A key point there was I decided to recalculate the mash continuously. Here I’ll detail how I set that up.

When doing research, and in my first HERMS design, I set the controller probe in the HERMS. My first design was a dedicated HERMS bath, but same idea if using the HLT. The trick here is to figure out how much hotter the HERMS needs to be to deliver the desired temp to the mash. If it’s too cold, the MASH will be a few degrees cooler than you want. If it’s too hot, just the opposite. I saw this as a potential issue since I mash out in my garage during sweltering heat and below freezing. I thought that it seemed likely the temp difference would change depending on a bunch of things.

So, an obvious solution seemed to instead measure the actual wort as it left the HERMS. The advantage here is if you want your mash at 150, and it drops to 149, the HERMS will just keep heating until it gets back up to 150. The HERMS water might be 150, or 160, it doesn’t matter. All that matters is the temp of the wort, which is the way it should be.

The key point of this whole system is the concept that if you deliver wort at a specific temp, that wort will heat the mash to that temp. I had all kinds of concerns about this, such as what would happen if I did a step and the burner ran for an extended time. Certainly the mash would lag behind the HLT in heat, would all that heat over heat the mash once it hit the set point? The answer is it surprisingly works well. The mass of the mash perfectly buffers the built up energy in the HLT post burner flameout. I think a key part of this is the heat exchanger and pump rate. Note my previous entry on my convoluted coil, while excessive, certainly gives a great exchange. I would probably recommend a 25-foot ½” coil to anyone, or certainly if one wanted to go all out, the convoluted coil.

I’m rambling here, but the point is I wanted the probe as the wort returned to the mash. So, I simply got a ½” threaded thermowell and a T fitting. Wort goes in one end, probe goes in the other, and the other side goes into the tun. When I had my MLT built, I had a ½ coupler welded on, but certainly a weldless fitting would be great too. I got my thermowell from Swagman/Martin since he was doing a bunch of other stuff for me. I see though that MoreBeer sells one that looks like it will work nicely. For me, I wanted the thermowell to extend a little past the T fitting. Part of the reason was to to be confident I was getting right in the flow for a good reading, but also it helps keep the probe from falling out.

So, some pix to illustrate.

Here's the whole deal put together. While not in the pic, the controller probe obviously goes in the left side there on the thermowell.

Here's a close up of the thermowell.

And why not... an obvious shot of the probe in the thermowell.