Introduction to RIMS and HERMS - Brewer's Friend
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Introduction to RIMS and HERMS

Sunday, February 22nd, 2009

This article explains the basic difference between RIMS and HERMS systems. Both are advanced setups for home brewers where mash water (wort) is circulated through a heating system. The benefits include clearer wort, higher efficiency, and an impressive looking setup that helps automate the brewing process and leads to consistency.

The difference between RIMS and HERMS comes from the method of heating in order to maintain or change the mash temperature. This is very different from the basic style of mashing, where hot water is infused to raise temperature. With RIMS and HERMS heat is directly applied to the mash water.

We can begin with de-constructing the acronyms RIMS and HERMS.

RIMS is short for Recirculating Infusion Mash System.
HERMS is short for Heat Exchange Recirculating Mash System.

We also need to introduce two additional acronyms: the HLT and the MLT.

The hot liquor tank (HLT) is a kettle, or cooler full of heated water. The mash lauter tun (MLT) is where the grains are mashed, coveted to sweet wort, and lautered.

The MLT in this case is again usually a kettle or cooler, and has a false bottom to allow lautering.

A HERMS will rely on a heat exchanger, in most cases the hot liquor tank (HLT) in which a copper coil is placed, in other cases, another external vessel that is filled with a heating medium (water) in which a copper coil is immersed. The mash water is pumped through this coil, picking up heat from the surrounding water, and returned to the mash lauter tun (MLT).

A RIMS system relies on a form of direct heating where the mash water (wort) is pumped through a small tube in which an electric heating element has been installed. The mash water is pumped through this tube, past the heating element, and heated to the proper temperature prior to returning to the MLT.

Lets get more specific with the components and function of a typical HERMS. As previously stated this system is used to maintain and change the temperature of your mash, so the need for some level of automation is almost a necessity. Whether the HLT is heated with a gas burner, or with an electrical heating element, you have to control the temperature of the HLT water (heating medium) precisely in order to take full advantage of the systems ability. This control is accomplished easier when heating with electricity, where the switching (on/off) of a heating element is done via a simple temperature controller which is wired to the heating element. During operation the controller is reading the HLT water temperature via a temperature probe in the HLT water (heating medium).

To accomplish this with a gas fired HLT would require some additional equipment. This equipment would include items such as a gas solenoid valve to cut the gas to the burner when your target HLT temperature has been reached, as well as a pilot or spark ignition system to automatically re-light the burner when the temperature controller commands gas (heat) through the solenoid valve. Changing the temperature of the mash is as easy as changing the temperature setting on the temperature controller to adjust the temperature of the HLT water.

In this same system the wort is typically recirculated continuously, which is of great benefit to the all grain brewer for a couple reasons. First, you will have little or no temperature variation in your mash due to the constant draining and return of precisely heated mash water to the MLT. Second, you will have superior wort clarity since you are setting up your grain bed (filtration) during the mash while recirculating the wort. **When I say superior wort clarity, I would compare it to looking through a glass of any of the typical American Lagers that have been filtered, it is quite amazing. This recirculating of 150F-160F wort is no easy task for a simple pump, which is why most home brewers have come to rely on the March 809 pumps, which are high temperature, food grade, magnetic impeller pumps. They are a perfect fit for both HERMS and RIMS.

In brief, the RIMS is utilized to accomplish the same outcome as a HERMS, but by a slightly different means. In a RIMS you are passing the mash water directly over an electric heating element that is contained in a small tube with an inlet at one end and an outlet at the other. Controlling the temperature of a RIMS is nearly identical to the HERMS… as it is done with some type of temperature controller connected directly to the heating element. The major difference is that the temperature is measured at the OUTLET of the RIMS heating tube prior to the mash water returning to the MLT. Just as in a HERMS, the RIMS can easily change the temperature of the mash by simply adjusting the temperature on the temperature controller. A RIMS will also generally utilize a constant recirculation of the mash water via a March 809 pump, providing the same benefits to the brewer as it will in a HERMS.

The similarities in these systems are great, and the befits are many. So, why choose one over the other? Some choose the HERMS because it is more energy and equipment efficient. If you are already heating the sparge water in the HLT, why not also use this water as a heating medium? Makes perfect sense right?

Some will choose a RIMS due to the fact that they do not have to change the temperature of a large volume of water in the HLT in order to make temperature corrections, or in some cases (step mashing) large temperature changes. This makes perfect sense as well… though both systems, if used properly, can perform temperature changes, even large ones, quite effectively. The choice is yours!

  1. 10 Responses to “Introduction to RIMS and HERMS”

  2. Excellent topic and writeup. I just invested in a Sabco Brew-Magic system (RIMS) and am currently waiting for delivery in August. I had heard various pros and cons between herms and rims and was looking to gain a better understanding. Your article provided the insight I was looking for. Objective, non-biased. Thank you very much and good brewing!

    Ken Megal
    Milwaukee, WI – Brewtown USA

    By Ken on Jul 8, 2009

  3. Hey man! Nice post! One thing though: I don’t know about other RIMS systems, but mine doesn’t measure the temperature at the outlet of the heating element. It measures it at the inlet of the heating element, which makes more sense to me. You are not trying to control the temperature of the heated liquid, after all, you’re trying to control the temperature of the mash itself. The wort exiting the heating element tube could be 175 or higher and the mash be around 150 or something.

    My system is like so: The liquid is pumped out from the bottom of the mash tun. The temperature probe is inline there before entering the heating element. The wort is then pumped through a tube with that heating element and heated and deposited back into the mash tun from the top. There’s a mechanized rake stirring the mash constantly to distribute that heated wort back into the mash, and liquid is constantly sucked out the bottom, heated and deposited on top. The temp of the mash is set on the computer controller and the duration of the rest. The heating element turns on and off to maintain the mash temp.

    Anyway, nice post. That’s my system in a nutshell.

    By Matt Hollingsworth on Jan 12, 2010

  4. Just a question: Why doesn’t a HERMs system put the heat exchanger in the mash, and circulate HLT liquid through the mash instead of moving the wort? Then the temperature regulator could just turn the march pump on and off.

    Thanks for the article!

    By Jeff R. on Jan 16, 2010

  5. A response to Jeff,

    I think the reason you do not just run the HLT liquid through the wort is because of the inability of heat transfer to take place in a timley fashion.

    The heat would have to conduct through the wort by thermal transfer. I do not think that the transfer would be as efficient as moving the entire MLT contents thorugh the constant tempurature of the HLT.

    By Curt on Jan 19, 2010

  6. My question is the same as Jeff’s: Why not have the heat exchanger in the mash? I’ve seen it with steam, but would pumping ~180F water from the HLT work?

    By Rob Keyser on Jan 19, 2010

  7. Couple things. Placing the temp. probe at the INLET to the RIMS heater has in some cases caused serious temp. overshoot. While the wort coming in from the bottom of the kettle is for example 10F too low, all this does is command the heating element to turn ON. Full on? If so, the RIMS OUTLET temp., since it is NOT being monitored by the controller, could be 180F? 190F? How would your controller know? Do you want to heat the wort to that temp? No, you do not. Since your controller is ONLY seeing the INLET temp., it will not turn off the element until that potentially 190F wort filters down through your precious grain bed enough to trip the temp. probe at the RIMS inlet.

    I personally do not suggest placing a temp. probe at the INLET to the RIMS heater to control temp for this reason.

    If you want to place a HERMS coil in the mash. How will you distrubute the heat? Even in a HERMS you need to circulate the water around the coil to avoid temp stratification. So, will you run a mash mixer to mix the mash to avoid HOT spots near the coil? Avoid cold spots as you move away from the coil?

    A mash has A LOT of thermal capacity, it is a great insualtor, you need to distribute the BTUs that you are putting in there. In a typical HERMS it is easy, you recirculate the mash water. If you propose placing the coil in the MLT you will have to build a mash mixer OR recircualte the mash water AND recirculate the HLT water through the coil. In both cases you have seriously complicated the process, with no net gain.

    I would personally (and have) place my HERMS coil in my HLT and simply pump the mash water through it.

    By Rob on Jan 20, 2010

  8. I have to add this as well. For RIMS users, placing the temp. probe at the inlet of your RIMS tube can be a bad idea for another reason. Mashes get stuck… they do. If your RIMS inlet temperature is below your set point, commanding your PID to fire the heating element in the RIMS heater, and you get a stuck mash… the PID will never know that the internal temperature of the RIMS heater is exceeding 200F. You will boil your element(s) dry and melt them, mid brew session, in the RIMS heater.

    To address the concern of RIMS exit temp vs. mash temp. True you are trying to control the mash temp. But I do not know that you want to heat your mash water and ENZYMES to 175+ degrees in the RIMS heater. Denaturing of enzymes can become an issue, as well as what I stated previoulsy… By the time that 175F outlet wort reaches the bottom of your MLT again to trip your temp. probe and PID output, half of your mash has far exceeded your target mash temp.

    For all of the reasons posted above, either temp. overshoot in the MLT or the considerably higher likelihood of melting your heating element(s) in the RIMS heater if you encounter a stuck mash… I have to advocate placing the temp. probe at the RIMS outlet.

    If you do find a differential between the RIMS outlet and MLT temp, this is as simple as setting up a differential value in your PID, which is common on most RIMS and HERMS systems.

    By Rob on Jan 21, 2010

  9. I just recently built an E-HERMS setup. I am having a somewhat difficult time controlling my mash temp. I am currently taking my temp reading from the middle of my grain bed which goes to a PID which in turn controls the heating element in the HLT. Ofcourse I have a march 809 recirculating the wort through my HERMS coil. Instead of using the temp indication in the grain bed for control do you think I should simply use it for indication and install another thermocouple taking the reading on the outlet of the coil for control? Ofcourse I would then use the Auto tune function on the PID. Any advice you all have is greatly appreciated.

    By Matt Norrick on Apr 4, 2011

  10. Hi Matt,
    What you describe makes perfect sense to me. I can see how the temperature at the heating element would be different from the temperature in the grain bed.

    By Larry on Apr 10, 2011

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