A Craft Beer & Brewing Magazine reader recently asked us the following question:
What’s the difference between RIMS and HERMS systems for all-grain brewing?
Recirculating Infusion Mash System (RIMS) and Heat Exchanged Recirculating Mash System (HERMS) brewing systems are both recirculating mash brewing systems. Once your brewing system gets to about a 10-gallon (38 l) size, it becomes difficult to move large (100 lb/45 kg) pots full of hot wort around, so most brewers incorporate a brew pump to transfer wort. Once you have a pump available, you can also use that pump to recirculate wort through the mash.
Recirculating wort through the mash lets you control the temperature of the mash. It also reduces hot spots in the grain bed and aids in wort clarity. RIMS and HERMS systems both use a recirculation pump to help control the temperature of the mash and vary only in how they heat the wort and control the temperature. Since both systems also incorporate a heat source, they can be operated without an insulated mash tun.
In a RIMS system, the heating pump runs continuously, recirculating the wort from the bottom of the mash tun to the top. The heating element, whether gas or electric, directly heats the pipe through which the wort flows. Temperature control is achieved by turning the heating element on and off as the wort continuously recirculates. Typically, a simple electronic controller and temperature probe are used to turn the heat on and off.
In a HERMS system, the mash is also recirculated from bottom to top, but in this case the pipe passes through a heat exchanger or coil that is usually immersed in the hot-liquor tun (HLT). The temperature is controlled by turning the pump, rather than the heating element, on and off. Heat is drawn from the HLT, and again a simple controller is used to cycle the pump to maintain temperature.
In addition to RIMS and HERMS, there are a few other variants. Some two-vessel systems, such as the Blichmann BrewEasy, use a Kettle-RIMS (K-RIMS), which recirculates wort through the boil pot to heat it. However the basic concepts are the same—RIMS systems run the pump continuously and vary the heat source, while HERMS systems turn the pump on and off to control the temperature, drawing heat from a fixed source such as the HLT.
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