RIMS and HERMS – Recirculating Infusion Mash Systems for Beer

Recirculating mash systems such as RIMS (Recirculating Infusion Mash System) and HERMS (Heat Exchanged Recirculating Mash Systems) are advanced beer brewing systems that use a pump and heating element to maintain a stable mash temperature during brewing. RIMS and HERMS are the two most popular, though many other systems exist. So this week, we take a look at these more brewing systems and how they differ from simple infusion mashing.

Infusion Mashing vs RIMS/HERMS

Most brewers switching to all grain start with a simple infusion mash system – made of some kind of cooler with a filter screen or tubes added to create an insulated mash tun. Another all grain setup gaining in popularity for first time brewers is Brew-in-a-Bag (BIAB) (podcast). Both of these systems offer simplicity at a reasonable cost, and both give you a method to maintain a steady temperature during the mashing process. The cooler retains heat, and for BIAB you can apply heat directly to the kettle.

The limitations of the simple cooler or BIAB setup become apparent when you try to work with much larger home brew systems. While its relatively easy to transfer 5-6 gallons of hot wort by dumping or siphoning it, or manage 10 lbs of grain in a bag, brewing at larger scales of 10, 15 or 20 gallons starts to make transferring large quantities of hot wort and grain by lifting very difficult. Also its difficult to find coolers large enough to support these batches.

As one scales up to larger brewing systems, pumping wort and water around becomes a necessity for most brewers, and most sophisticated all grain setups use three large vessels – one for the mash, one for the boil and one for hot water used during the infusion and lauter. Large converted Sanke kegs with the tops cut off are common, though many also use high end stainless steel pots. Pumps are used to transfer wort and water between the various components.

Recirculating Mash Systems

If we consider the problem of keeping a large 15-20 gallon stainless steel mash tun at a constant temperature for the an average 60 minute mash, other problems arise. First, most stainless vessels are not insulated, and conduct heat relatively well. The old technique of heating an infusion and letting it sit in the cooler we used for smaller batches might not work as well in our large stainless pot or converted keg. A second problem is that the larger volume is more likely to develop hot and cool spots in the mash tun over time – again making it difficult to achieve a consistent temperature across the entire grain bed.

A recirculating mash system addresses both of these problems using the pump mentioned earlier. Rather than infusing hot water and letting the mash tun slowly cool, a recirculating system uses a pump to constantly recirculate and heat the water to maintain temperature and also avoid hot spots. Typically a controller is used to turn on and off the heat source in the pump line to maintain a constant mash temperature.

This provides the following benefits:

• The temperature can be maintained very close to the target temperature even in an uninsulated metal mash tun – particularly if you use an electronic controller. Often the mash temperature can be controlled much more precisely than a typical infusion cooler.
• Hot spots in the mash are minimized as there is a slow steady flow through the tun
• The constant recirculation of the mash results in very clean wort during the lauter
• Overall the mash is more consistent and repeatable for large batches than a non-recirculating infusion. Repeatability is important when working with large home brewing systems or advanced systems that may serve as pilot batches for commercial microbrewers.

The recirculating mash systems (RIMS/HERMS) vary in how they heat the recirculating wort.

• A RIMS system uses direct heat on the tube to heat the wort as it is recirculated. The heat source may be electric or gas, but the wort is heated as it passes through the tube and is pumped during recirculation. The pump keeps the wort moving through the tube at a steady rate to avoid scorching it. The pump must run continuously during the mash when heating, though the heater itself is often cycled on and off to control temperature. A risk with the RIMS system is scorching the wort if the pump fails for some reason.
• In a HERMS system the wort is passed through a heat exchanger. The most common type of heat exchanger is an immersion setup (much like an immersion chiller) where a coil of copper tubing is immersed in a hot liquor tun. In this type of setup the hot liquor tun is often kept at a constant temperature slightly above the target mash temperature and the pump is cycled on and off to maintain the temperature of the mash.

Which one best fits your needs is up to you. Often a RIMS system is easier to physically construct, but you need a variable heat source (one that can be turned on and off). A HERMS system requires more equipment (often a coil immersed in a large pot) but can be regulated by simply turning the pump on and off. Both offer similar overall performance for the advanced brewer.

If you want to build a RIMS or HERMS system of your own, More Beer (a BeerSmith sponsor) has a wide selection of pumps, kettles, and brewing sculptures to help you assemble your ideal system.

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