RIMS or HERMS: Understanding Mashing Equipment

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If you’re looking for ways to maintain better consistency across your recipes every time you brew, you’ll want to look at consistency in your mash rests. Basic rests being Acid (95°F – 113°F), Protein (113°F – 138°F), and Saccharification (beta-amylase 131°F – 150°F, alpha-amylase 150°F – 160°F) . There are multiple other rests, and refined rests within these ranges, but these three are most likely the common ones you’ll come across starting your RIMS (Recirculating Infusion Mash System) or HERMS (Heat Exchanger Recirculating Mash System) endeavors.
Due much to the nature of the DIY efforts, and typical small batch sizes of homebrewing, your mash rests can often fall several degrees by the end. This can impact your final body, residual sweetness, and finish. Enter RIMS or HERMS. While these are both more advanced homebrew techniques, requiring more sophisticated technology, they’re well worth the extra effort to help produce consistent recipes, improve wort clarity, and invest in more homebrew gear that proves you are the Fermentation Engineer you bought those bib overalls for.

So… which is better RIMS or HERMS?

Which Olsen Twin is better? Arnold or Stallone? Thick or Thin cut bacon? I don’t know, that’s going to depend on the setup you want, space available, brewer preference, and in the end most likely, which one you think looks cooler in your home brewery. But what I DO know is they help with other processes you’re probably struggling with on your existing set up.
Both of these setups apply heat to your mash by pumping wort out of the bottom of the mash tun, circulating it against a separate heat source, and then returning it back into the mash tun. This is really useful when doing step mashes to increase the temperature as required to complete the desired mash rests (i.e. a protein rest to improve head retention and clarity, which is then stepped up to a saccharification rest to convert starches to sugar.) Ever try to apply a burner to a plastic mash tun? I hope not, if so I want a video. Below is a simple chart to understand the basic idea.

An additional benefit is aiding in mashing out. Eliminating the need of diluting the mash, overcompensating by having a hotter water temperature applied to your mash, and then mixing it all up to hit 170°F. Instead just keep it circulating while applying heat to increase the temperature. You can then sparge with 170°F water, and start moving wort to the boil kettle without going through a lengthy vorlauf.
In both instances you are going to need a pump and heat source. Let's dive into the main differences.

Heat Sources

RIMS - An electric heating element, positioned in the pump's recirculation loop, is applied directly to the wort. When creating your own you should use an electric heating element intended for a home water heater, and have a basic understanding of home plumbing.
HERMS - The wort is pumped through a coil inside the HLT, and heat is transferred from the hot water through the coil. You could potentially press your immersion chiller into double duty here and just drop it in the HLT, or you could build something similar and more permanent.

Key Considerations

RIMS - If you’re going to do step mashes, you want to make sure you have a heating element that is powerful enough to raise the wort temperature quickly enough. You can alternatively apply heat directly to the mash kettle while circulating, to augment the RIMS element. Personally I prefer the extra heat source method, because too large of an element can quickly scorch your wort if the pump stops, or your flow rate is slow.
HERMS - Make sure the coil has a large enough tubing diameter and length to allow the wort to flow easily enough for your pump to manage it. To help heat transfer through the coil it’s best to stir the HLT while running the pump. You can do this manually, or consider adding an electric motor and stirrer to the HLT. This is an important consideration for good performance. A simple stirring with a spoon will help, since if the water is not moving while you’re trying to apply heat through the coil, it will take a long time for the heat to transfer to the wort, negating much of your efforts for creating a system to maintain proper temperature in the first place.

Top Things To Watch Out For

RIMS - Scorching is something that should be monitored. If your pump goes out, or is not powerful enough to move the mash fast enough, and the heating element is too hot, you’ll most likely scorch your wort. If you’re using a burner to help raise temperatures, again be sure the wort moves fast enough to prevent scorching.
HERMS - Monitor your HLT temperature. Recirculating the wort through the coil will lower the water temperature. You want to keep it around 180°F, depending on what type of mash rest you’re doing.

System Design Considerations

Flow Rate - Regardless of the system type, it is vitally important you can control the rate of flow properly to hit your target temperatures. You’ll want to make sure the flow rate is fast enough that you can hit your step mash targets, but not so fast that it creates a suction that compacts your grain bed.
Optimal flow rate is about one gallon (3.8 L) per minute, and if your design includes a lauter grant, then you will also have more control over your grain bed. A lauter grant is simply a vessel that collects your mash via gravity before pump suction is applied. You’ll just need to be certain that you control the flow rate from it, so that you don’t end up running a dry pump (because the wort is taking too long to gravity drain from the MLT.)
Tiered Brewing Stands - There are many setups you could opt for with either system. A big factor which will affect your choice is how much space you have for brewing. Each system will also have different requirements for what type, and how many, pumps you need to include.
The basic options are three, two, and one tiers. The fewer tiers you use, the more pumps you will typically require to move wort to and fro. You will need to consider how to control the direction of flow in your build. Also a Single tier system typically requires two pumps as it doesn’t leverage gravity to fill any one vessel. However you could build a system of valves or hose transfers, and accomplish the same effect with one pump. You would then just have to batch sparge all your brews.
Automated Control Systems - If you don’t want to be constantly hovering over your thermometers and flow valves during your mash rests, you’ll want to consider some type of automated control system. There are so many ways of creating these, and they are a huge consideration in the final design if you’re going to implement one. So while you should consider it in your overall design, we’ll need to wait to cover this on another day.

Choosing A Pump

In many parts of the design for your RIMS or HERMS system you can be thrifty or save costs by sourcing materials from scrap yards or your existing brewing equipment. The pump however is something you are going to want to make a real investment in.
You’ll need something that is easy to clean (to stay on top of sanitation,) can handle the high temperatures of the wort being passed through the flow chamber, and powerful enough to move the wort and prevent scorching.
The most common type of pump is a magnetic drive pump. The reason being is it has a closed flow chamber which makes it easier to control sanitation. The downside to these pumps however is that they are not self priming and you need to leverage gravity to prime the pump before turning them on, so place them low in your system design if you’re going to use one.
Below are some pictures from the inside of the flow chamber of a magnetic drive pump. You can see the impeller is removable once the chamber is open. But when it’s closed it sits tight in the enclosure and rotates to push the worth through.

Bringing Your Brewery To Life

My recommendation for you to make a decision on which system to go with, is determine where you’re going to have your system live for your brew day. Once you know the spot for it, or if you want to create something mobile, you’ll have a good idea of how much space it can take up.
With that in mind start sketching ideas of what you’d want it to look like, and swap in different equipment based on both designs. You’ll start to develop your own list of pros and cons based on what your setup is going to be capable of doing, and what’s going to make for a more efficient and fun brew day.
In most of the HERMs system I have seen, including commercial ones, wort does not go through the coil, hot water does. It supposed to work on the same principal as immersion chilling, you send hot or cold water through a coil, to warm or cool the wort. With the right mix of controllers and valves, you use a balance of hot and cold water to maintain a precise temperature in the mash tun. To improve efficiency, you can whirlpool the wort inside the mash tun, which helps improve the thermal conductivity between the coil and the wort. This also coincides with post-clean up methods. It would be a bitch to have to clean and sanitize the coil because you ran wort through it. Much easier to just wash down and sanitize the outside of the coil that had contact with your wort.
Nice writeup. One other option for circulating water around a herms coil is to use a second pump. I have a small Solar pump to move water from the bottom of the HLT to the top to keep the water temp from stratifying. A Chugger pump is used to circulate worth through the herms coil.
The first thjng I read was HERMS - ".. You want to keep it around 180..." NOT! Have you actually used a HERMS system?
With continuous circulation, you want your temperature only slightly above the mash temp. You control the HLT temperature to control the temperature of the wort going into the mash tun. In mine, an electric system, the offset is 2 degrees F. Of couse you must mix the water in the HLT to avoid stratification and increase heat transfer. So 180 degrees woul ruin the batch. And, may I say, most of us do way faster recirculation rates.
Just like RIMS, but with the advantage of no accidental wort scortching.
Yea I would agree with not putting the HLT at 180deg for a HERMS system for a mash rest..Thats WAY to hot..I love my HERMS system and my HLT and MT are usually within no more than 2-3 degrees difference in temps when recircing during Mash rest once they equalize out.
I usually Mash between 149 and 153..my HLT water gets set for 154 and stays there until I raise the water temp to 169 to sparge out.
Well, that makes one of you. Nearly every design on here is for the wort to go through the coil, coil is submerged in hot water.
You describe only one of the two commonly used RIMS configurations. Direct heat (which you mention as an additional option with externally heated RIMS) can be used without an external heat chamber. Depending on the heat available and the flow rate, it can be more responsive than externally heated RIMS because you don't have to wait for the entire wort volume to make it through the heat chamber.
Ive literally never heard of anyone doing this. You always run your mash wort through the coil.
You clean by pumping your sparge water through the coil. After 10-15 minutes of sparging with 170F water there is no way my coil is dirty inside.
Cleaning the outside of the coil sounds like an absolute nightmare, im going to guess you don't actually own a HERMS. First most coils are stationary and do not ever come out of the pot they are installed in because they are a ton of work to get installed properly without leaks. Second they are coiled so packed together that the thought of cleaning the outside of my 50" SS coil scares the life out of me, it would take at least an hour or more to do properly.
Yea the 180F thing confused me, where did that number come from? Who (answer Nobody) sets their HLT to 180F and then modulates their Mash temp by turning on and off the pump? The rest of the article is pretty good, but that is just downright wrong. Go read the How to use your system pages at TheElectricBrewery if you want to know how to properly use a HERMS system.
Not all HERMS systems utilize a coil in the HLT. Back when I built mine, most of the examples out there had a standalone heat exchanger which is the design I went with. A few advantages of having a standalone HEX is it allows you to maintain mash temps independent of HLT temps, and because you're heating a much smaller volume of water, it responds to temp changes much faster. Even though the thermal mass is significantly smaller compared to an HLT-based exchanger, it's enough that I have very stable temps. Also, with a smaller vessel there tends to be less temperature stratification within the HEX. The only downside is you have to have a controller that's capable of controlling multiple devices (e.g. BCS-460) or you have to buy two single controllers to be able to control HLT and HEX. For anyone interested, I use a 2.25 gallon stainless Bain Marie pot with a coil consisting of about 10 feet of 1/2" copper tubing. You can mine here, http://www.microbusbrewery.org/2013/03/heat-exchanger-redesign.html
I really like this article. I thought it was really well written (although somewhat misguided from what some of these other comments on HERMS systems are saying about HLT resting temp) and it didn't feel like the author was bias at all. That being said, I have a direct fire RIMS and like the way it works as long as recirculation rates are high enough. I do have a question for the E-HERMS guys though. Do you guys find that it takes awhile to raise temps in the HLT, say, for like mashing out? I'm interested in possibly switching to all electric and would possibly switch to a HERMS system if I do. i don't like the thought of my wort running over an electric element to maintain proper temp.
Because of the volume in the HLT, it does take longer than I would prefer (1 to 2 degrees/minute) to raise to mashout using only the HERMS. I usually double up, using both the direct heat RIMS burner and the HLT burner/HERMS to make large temperature changes. If you go electric, I suppose that your concern about running wort past an electric element would discourage you from doing this. In that case, a separate HERMS chamber of smaller volume (as mentioned above) would be more responsive than an HLT/HERMS rig.
Actually, that's exactly how I have always done it. My system is a direct-fire, single-tier rig with burners under the Boil Kettle and HLT, and bottom-drain Mash Tun (in fact, that's my setup pictured on the article page). I have my HERMS coil inside my HLT, and I keep the HLT temperature around 180 deg F. Using Beertools I calculate the temperature of the strike water, and heat the water in the boil kettle and then transfer the strike water to the Mash Tun. After dough-in I circulate the mash to vorlauf and set the grain bed, and then circulate through the HERMS coil only as needed to raise the mash temp for step mashes, or for mash out if doing a single infusion. Because my MLT and HLT are both well-insulated there is no need to continuously circulate the wort during the mash. Using this method I regularly achieve 80-82% mash efficiency. I have been using this setup for years now with great results. More than one way to skin a cat...or make some wort.
Great example of all the options out there. It's difficult to cover off on all the options in one post. Thanks for posting!
Funniest thing I've read in a long time. I can't imagine that you actually use a HERMs system to brew.
I actually keep my HLT temp to 165 and have a recirc bypass set of valves (one N/O, one N/C). When call for heat is initiated, the valves cycle opening the N/C valve and allowing wort to flow into the coil, when heat isn't required it bypasses the coil altogether and goes straight back to the MT.