Because our batch sizes are typically small compared to commercial brews, one problem many all-grain homebrewers have is maintaining their mash temperature. Ideally, mash temperature should remain relatively constant throughout each rest. Maintaining a specific temperature helps to control the fermentability of a beer, which in turn affects such qualities as body, finish and residual sweetness. However, even in a relatively well-insulated mash tun, is not uncommon to experience a drop of 4–5 degrees Fahrenheit (2–3 °C) during the 45–90 minutes of mashing.
   
One solution to this problem is provided by two types of advanced all-grain systems — RIMS (Recirculating Infusion Mash System) and HERMS (Heat Exchanger Recirculating Mash System). In both systems, mash liquid is drawn off the grain bed, pumped past a heating element or heat exchanger, and returned to the mash.       

Other benefits
In addition to maintaining mash temperatures, a RIMS or HERMS can also be employed for raising the temperature of a mash in a step mashing program. Likewise, once starch conversion is complete, a RIMS or HERMS can facilitate the “mashout,” in which temperature of the mash is raised to 168–170 °F (75–76 °C) and held for 5–10 minutes before sparging. In both these cases, the temperature is raised without diluting the mash, as when boiling water is added to raise the temperature of the mash.
   
Recirculating the liquid portion of the mash also helps to minimize the temperature differences during mashing. As the liquid diffuses throughout the grain, it equalizes the temperature. The recirculation and the heating of the mash liquid are therefore the basic principles behind all recirculating mashing systems.
   
In a RIMS, the heat source is an electric element placed in the recirculation loop to heat the mash liquid. A HERMS uses hot water as the heat source, usually incorporating a copper coil as a heat exchanger. The coil placed in the hot liquor tank (HLT) is used to heat hot water for sparging the mash. Both types of systems require a pump to move and return the mash liquid from the mash tun through the heat source and back again.

RIMS: Electric breweryland
The key to a RIMS is the heating element, which is placed in the recirculation loop. This requires building an enclosed chamber for the element, most commonly from copper or brass pipe and fittings available at hardware stores and home centers. Some plumbing skills are required, but someone who has experience with basic home plumbing projects should be up to the task. The element itself is one used for electric water heating. A variety of replacement water heater elements are available in various lengths, sizes and wattage ratings.
   
Three factors are important in the selection of the heating element. The element voltage (120 or 240 volts) must be compatible with the electric service and wiring available in the brewing area. The element density (typically expressed in watts per inch or centimeter of length) must not be so high as to easily scorch the mash liquid. And the heat output (expressed in watts) must be sufficient to maintain or raise the temperature of the liquid. Heating elements rated for 240 volts may be used with 120 volts with a 75 percent reduction in output (to calculate the watts at 120 volts, divide the 240 volt rating by four).
   
To maintain the mash temperature in a RIMS, 1,500 watts is sufficient for 5–10 gallon (19–38 L) batch sizes. For step mashing, more power is required to raise the temperature quickly enough; 4,000–5,000 watts is not unreasonable. This almost certainly requires 240 volt electrical service and the appropriate wiring. A home dryer outlet, for example, is typically rated for 30 amps at 240 volts, for a total capacity of 7,200 watts (actually somewhat less to allow for overload).
   
Safety is very important when working with electricity in the presence of liquids. The heating element and brewing system must be well grounded to avoid electrical shock and consequences that can be fatal in the wrong circumstances. If you have little experience in this area, I strongly recommend having a professional electrician review the plans and construction.
   
A potential drawback of a RIMS is scorching of the mash liquid. This occurs at a temperature of about 480 °F (250 °C) as the sugars begin to break down. Caramelization, which darkens the sugars and alters their flavor, occurs at a lower temperature that can be produced rather easily by electric elements. It is important to maintain an adequate flow of liquid past the heating element while it is on, so that scorching and excessive caramelizing do not occur. A little darkening is inevitable, but is not considered a major problem if kept to a minimum.
   
There is also some concern about denaturing of the mash enzymes. Alpha amylase, the primary enzyme in conversion of the malt starches to sugars, begins to break down at temperatures above about 160 °F (61 °C). However, the evidence is that it takes a considerable period of time before a significant portion of the enzymes are compromised. As a practical matter, the relatively short period of time the liquid is at a high temperature (it is quickly cooled as it is returned to the mash) does not cause a problem.

HERMS: Let water do the work
The possibility of scorching is eliminated in a HERMS because the temperature of the hot water in the hot liquor tank recirculation coil is far less than that of an electric heating element. There are also no electrical requirements for heating the mash liquid. However, there are other design concerns, such as maintaining efficient heat transfer between the hot water and the coil, and incorporating the coil into the HLT. Many HERMS also use a bypass loop to route the flow of the mash liquid around the coil when it is at or above the desired temperature. This requires a three-way valve, or two valves and plumbing tees so that the flow can be directed either through or around the coil.
   
The recirculation coil in a rudimentary HERMS can be merely an immersion chiller lowered into and removed from the HLT as needed. This has the advantage of simplicity; no drilling of the HLT and expensive bulkhead plumbing fittings are required. However, this is less permanent and somewhat less graceful for those who place a priority on elegant design.
   
The diameter of the tubing used for the coil is important to maintain an adequate flow rate and not stress the recirculation pump. Typically this requires a tubing diameter of approximately one-half inch (13 mm). As for the length of the coil, most homebrew HERMS use between 25 and 50 feet (7.5–15 meters). Incidentally, it is worth noting that soft copper tubing is usually measured by the outside diameter, as opposed to rigid copper pipe where the nominal size is the inside diameter. The builder needs to keep this in mind when selecting plumbing fittings and adapters.
   
The temperature of the water in the HLT should be hot enough to transfer heat to the mash liquid in the recirculation coil. Assuming typical heat losses, this is approximately the same as the requirement for the sparge water, about 180 °F (82 °C). Stirring of the water during recirculation greatly increases the efficiency of the heat transfer. A few HERMS incorporate an electric motor and stirrer to accomplish this; other homebrewers stir the water manually with a long spoon or paddle. There is also convoluted copper tubing with interior ridges or fins that increase the turbulence of the mash liquid flow and facilitate the transfer of heat. Recirculation will gradually lower the temperature of the water in the hot liquor tank, very likely making it necessary to apply additional heat to the HLT occasionally during the process.

System design considerations
If a RIMS or HERMS is used for step mashing or mashout, it is important to design the system so that the flow rate and temperature increase are sufficient to accomplish the steps in a reasonable time period. Too slow a temperature rise between steps (less than 2 °F or 1 °C per minute) can adversely affect head retention of the beer, especially over the temperature range of 122–148 °F (50–65 °C). Avoiding this problem typically requires a flow rate of approximately one gallon (3.8 L) per minute. However, too high a flow rate creates suction on the mash and can compact it, causing a reduction in the flow or even stopping it altogether. This can be minimized by careful mash tun design-whether using a false bottom, manifold or hose braid — as well as by closely regulating the recirculation flow with a valve at the pump outlet. But it can make for problems if not considered and addressed.
   
One solution to mash compaction is to use a lauter grant. This is common in commercial brewing systems and consists of a smaller vessel placed below the mash tun outlet and before the recirculation pump. The grant is filled by gravity and the pump creates suction only on the grant rather than on the mash itself. For a 10–15 gallon (38–57 L) homebrew system, the grant can be a 4-quart (4-L) pot with inlet and outlet fittings attached. In automated systems, liquid level switches in the grant turn the pump on and off so that the grant neither overflows nor runs dry; manual systems require adjustment via valves regulating the flow to and from the grant.
   
Both RIMS and HERMS lend themselves to automated control systems. The subject of electronic controls is beyond the scope of this article, but see Marlon Lang’s article, “Brewing on Autopilot,” on programming digital controllers in the November 2003 issue of BYO.

Pumping it up
As has been mentioned, both RIMS and HERMS require a pump to recirculate the mash liquid. A variety of pump types can be used (the November 2003 issue of BYO also contained an article on pumps, by Thom Cannell); one of the most common for homebrewing applications uses magnetic coupling. In these pumps, the motor shaft is not directly connected to the impeller. Instead, a magnet attached to the motor shaft causes a corresponding magnet on the impeller to rotate as well. The advantage of such a pump is that it does not require a seal on the motor shaft and is relatively easy to keep sanitary. These pumps also are less prone to motor burnout because a disruption of the flow will not cause the motor to seize. Nor is a small amount of grain solids in the mash liquid
a problem.
   
The primary disadvantage of magnetic drive pumps is that they are not self-priming. As a consequence, the pump should be located at the lowest point in the system so that it always has liquid in it and does not draw air. It is strongly recommended to use a pump rated for the temperatures involved, at least 180 °F (82 °C) for the recirculating mash liquid. The cost of such pumps is in the range of $100–$150 and they are available from some of the larger home-brew suppliers.
   
Other considerations with a RIMS/HERMS include piping, hoses and connectors. Some systems are plumbed with copper, brass or stainless pipe, while others use reinforced food grade vinyl hoses. One is not necessarily better than another: Pipe is rigid and relatively permanent, while hoses allow greater portability and flexibility. In general, a diameter of one-half inch (13 mm) is best for homebrew systems. Plumbing with smaller diameter pipe, tubing or hose can cause flow and pump problems.
   
Quick disconnects can be used to facilitate frequent attachment and removal of hoses. Food grade plastic disconnects that are rated for the temperatures involved are usually available from larger homebrew suppliers and industrial distributors.
   
These types of disconnects are somewhat expensive but extremely convenient. I don’t recommend cheaper plastic or brass fittings intended for garden hose. These can either cause burns or are not rated for food or beverage applications.

Taking it out for a test drive
Any system as complex as a RIMS or HERMS will likely require some modification for maximum performance. For those who relish such projects, tweaking and fine tuning are part of the challenge and the fun. Build and install the system in place and conduct a test using only water. This will not produce identical conditions to those with a mash (for example, water heats and mixes more evenly and easily), but it will allow you to detect many potential problems and provide a very good idea of what it will be like to brew with the system. Make notes and consider the changes that may be necessary for the sake of both effectiveness and convenience. You should also take detailed notes during your first several brewing sessions. It takes time and experience to achieve a brewing system that  accomplishes your desired results.
   
As you can see, there are a host of design, construction and operational issues to consider and address, as well as a huge variety of means to accomplish them. In most cases there is neither a single right answer nor a single best method. Hundreds of homebrewers have pondered the questions and built their own systems. One of the joys of homebrewing is being able to do it your own way. You may well wish to consult with others who have done this, each of whom has approached the subject in a unique manner. Many of them have shared their thoughts and methods in considerable detail. Browsing the Internet using the search terms “RIMS” and “HERMS” should provide hours of interesting and valuable insights, some of them quite ingenious and specific.
    
Bill Pierce completed Siebel’s Craft Brewers Certification program and recently began writing “Advanced Homebrewing,” for BYO magazine.