Types of HERMS

Last time, I discussed my reasons for wanting to build a Heat Exchange Recirculating Mash Systems (HERMS). This time, I'd like to discuss the types of HERMS. They seem to boil down to two types: automated and manual. Both are outlined below.

The automated HERMS has a temperature probe in the mash tun's inlet hose that controls the heat to the hot liquor tank (HLT). The flame is controlled by a pilot lit, propane burner with a solenoid to turn on and off the gas. With that, some systems use an elaborate temperature controller called a PID, which performs calculus on the fly to correctly control the temperature.

The advantage to this type of HERMS is that you have exact control over the temperature of the liquid reentering the mash. Well made systems can keep the mash to within one degree of accuracy. The drawback to these types of systems is that they are complicated to build. It requires knowledge of propane gas plumbing, electrical wiring, and so on. This is all in addition to the plumbing required to have the mash liquid to recirculate properly.

The manual system is a lot simpler. All you have to do is hook up the hoses, copper coil, ball valves, and pump. However, the accuracy is not as good. When adding heat to HLT, you have to know the temperature differential between that and the mash tun. The temperature of the HLT needs to be several degrees higher than the mash tun, as the mash liquid will cool off when it is pumped out of the copper coil and returned to the mash tun. This can be a delicate balance that is easily screwed up, causing you to overheat or underheat the mash. You have to watch the temperature gages on both the mash tun and HLT and turn on and off the heat to the HLT by hand. Even doing that, there is often a latency between turning off the heat, and having the temperature of the mash still rise a couple of degrees. In fact, the mash can have a gradation of temperature where the top is warmer than the bottom.

I found examples of both types of systems out of the web. First, this blog outlines in great details his automated HERMS. I was extremely impressed. On the other hand, this YouTube video shows a manual system:



While the video is a little too rednecky for me, it does show someone measuring the temperature, and turning on and off the heat by hand. I was impressed on how simple his equipment was.

I am opting for the manual system for now. The reason for this is that I brew on the stove top in the kitchen, rather than outside on propane. I do not have the option of automatically turning on and off the heat. I do have plans to eventually move outside, which I blogged about previously.

I actually have given serious thought about a hybrid system, that basically has the temperature probe on the inlet hose, but instead of turning on and off the heat, it would simply turn on and off a light, indicating when I should turn on and off the heat by hand. It would be a very hands on operation, but still give me greater control.

In my next HERMS post, I plan to discuss the first pieces of equipment for my system.