RIMS and HERMS - Recirculating 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 source to maintain a constant mash temperature during brewing. They also allow you to change the mash temperature in steps so much more complicated mash profiles can be used which can provide a more complex sugar profile and malt characters. Different mash profiles will be covered in separate blog post soon.

RIMS/HERMS versus Infusion Mashing

Most brewers start all grain brewing using a simple single step infusion mash – usually using a cooler with a filter screen to create an insulated mash tun. This involves mixing the grains with hot water to achieve a desired mash temperature then leaving to sit for around 90 mins.  Another all grain setup gaining popularity for first time brewers is BIAB (or boil in a bag). This method uses a bag to hold the grains in the vessel which are then removed allowing the resulting wort to be boiled without sparging. For most beer styles and applications these systems will provide adequate results. The cooler retains heat well over short time periods, and for BIAB you can apply heat directly to the pot if required. This system works well for smaller volumes, up to around 50 litres and for simple mash profiles.

Recirculating Mash Systems

For larger stainless steel mash tuns, issues with keeping a constant temperature for an average 90 minute mash can arise.  Most stainless vessels are not insulated and therefore they conduct heat.  The traditional technique of an infusion and letting it stand in the cooler might not work as well in a large stainless pot. Another problem is that the larger volume is more likely to develop hot and cool spots in the mash tun making it difficult to achieve a consistent temperature across the entire grain bed.

A recirculating mash system addresses these problems by pumping the wort.  Rather than infusing hot water and letting the mash tun slowly cool, a recirculating system uses a pump to constantly recirculate and heat the wort to maintain temperature.   A controller is used to turn on and off the heat source in the pump line to maintain a constant mash temperature or increase the temperature as required.

The temperature can be maintained very close to the target temperature even in an uninsulated vessel. Hot spots in the mash are minimized as there is a slow steady flow through the grain bed and the constant recirculation results in filtering through the grain which gives very clear wort. This system produces a mash which is more consistent and repeatable for large batches.  Repeatability is vital when working with that may serve as pilot batches for larger commercial systems.


A RIMS (Recirculating Infusion Mash System) system uses direct heat source to heat the wort as it is recirculated, usually via a tube.  The heat source may be electric or gas and the wort is heated as it passes by the heat source and is pumped back to the top of the grain bed during recirculation.  The pump keeps the wort moving at a steady rate to avoid scorching it which would burn the sugars and create colour. The heat itself is turn on and off to control temperature while the wort is constantly pumped passed it.  Scorching is a risk with a RIMS system if the pump rate is not quick enough, the pump fails or the heat source is too hot. The Braumeister by Speidel uses this type of technology to maintain a perfect mash temperature.

A HERMS system using a heat exchanger to maintain or change the temperature.  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 and the wort is pumped through the tubing. The water in the hot liquor tank is then heated as required to increase the temperature of the passing wort. There is not direct interaction between the wort and the heat source so this method eliminates the risk of scorching.

Both offer similar overall performance although RIMS systems are generally easier to construct.

We will cover different mash profiles and what actually happens during the mash process in forthcoming posts coming soon.