Homebrew Beer Blog

Some thoughts on my HERMS design. There are many ways of doing this, and believe it or not, I actually had a plan from the beginning and stuck to it.

When I first started, I had one main goal – I wanted to repeat my mash every time. I set out to build what I thought would be an ideal system, even if some concerns weren’t practically all that relevant. I identified my main concerns as:

1 - A more homogeneous mash temp, meaning the side of the tun facing the wind wouldn’t be all that much cooler than the side not.

2 - Accurate temp of my entire mash, not just the area around a thermometer. This is critical, obviously, because if I can’t get a good reading, this is all for not. Garbage in, garbage out.

3 - I didn’t want to expose the mash or wort to any temps much higher than my set mash temp. This tosses out direct fired mash-tun, and to a lesser extent, a RIMS. RIMS is cool, but for reasons below, electric wasn’t going to work for me. This is basically directed at intermittently running wort through a coil in a rather hot water bath.

4 - Initially, I wanted to just maintain set temps, but then wanted to do steps with it. This meant I would need significant heat to do a step in a timely fashion. Without adding a new breaker box to the house and a dedicated circuit, maybe even 240, I would have to use gas.

So, that was what I determined would be important in my goal of repeatability. To do this, I felt the best approach was to recirculate the wort continuously throughout the entire mash. This posed two problems: One I needed to make sure I wouldn’t compact the grainbed, and two, how to maintain the temps in my HLT. To address the grain bed, there really is only one solution, and that’s a false bottom. The false bottom has the surface area needed to keep the grain bed from getting stuck or excessive channeling, and being raised lets the pump run without applying suction to the grain bed. As an added bonus here, recirculating the wort makes for crystal clear run off come sparge time. This, by the way, is when I became a fly sparger. For the hot liquor tank, it must be held at a specific temp to deliver the right wort temp to the mash. This is where the gas solenoid valve comes in. To try and maintain the HLT temp manually would require an enormous amount of attention.
N
ext, how do you decide how much heat you need, and when you need more? A popular approach is to set the HLT to X-degrees above whatever you guess it will take to heat your wort. This is rather problematic, mainly because that X can change. Instead, I just put my temp probe on the MLT as the wort reenters. This is a great solution, because HLT temp no longer matters. If the HLT is 152, and the mash needs to be 152, but the wort coming out is 150, the controller will just keep heating the HLT until the wort reaches 152. If it’s really cold outside, and the the HLT needs to be warmer to deliver the same 152, it doesn’t matter. The controller will just heat the HLT as hot as it needs to get to 152. The temp of the HLT is of no consequence. To make this work, I use a thermowell with a 1/2-inch male fitting, and run it through a T-fitting between the return hose and the MLT.

As a check on the whole system, I’ve got a calibrated probe thermometer in the mash. I use this to verify everything is working as intended, and when doing steps, there’s a delay between the temp of the wort entering the tun and the actual mash. The thermometer lets me monitor how things are going, more specifically, lets me know when to start the clock for the next step.

I’ve brewed as cold as 15 degree weather and this baby kept my uninsulated stainless tun perfectly set for an entire hour. It also heats the mash at a rate of about 1.5 to 2.0 degrees per minute for typical 5 gallon batches and 1.0 to 1.5 for 10 gallon.

So, there it is. A continuously recirculating HERMS that gives good even temps across the entire mash, accurate reading of the mash, doesn’t expose the mash to temps beyond the mash temp, and can efficiently execute steps of any size grain bill.