Maintaining Mash Temperature

When I did my first all-grain batch, I had no end of issues with keeping the mash temperature where I wanted it. It seemed simply impossible to get it even close to stable for a whole hour; I’d overshoot, then see the temperature drop too far, and I was always correcting by adding boiling or cold water. I had a few batches there where the results were just completely unpredictable, and it caused me a lot of frustration until I figured a few things out.

For me, there are two basic classes of methods for holding mash temperatures: low-tech and high-tech. The low-tech methods are usually pretty inexpensive. The high-tech methods, on the other hand, generally require some outlay.

Low-Tech Mash Temperature Methods

Get the mash out of the wind. One of the most frustrating brew days I ever had was on a buddy’s patio, in January. We were out of the rain, but while his system was set up in the protected corner close to the house, I was on the far corner where the cold wind was whipping through. I lost a ton of heat in my mash that day, and the beer was nothing like I had planned when it was all done. Still air around the mash tun will pull less heat out than moving air, so build a windbreak if you have to, or just set up out of the wind.

Mash in an insulated container. Of course, another great way to avoid losing heat to the surrounding air is to do the mash in an insulated container. A heavy-duty cooler (look for the ones that claim to keep things cold for seven days, for example) is a great way to do this. There are some additional complications, like figuring out the amount of heat you will lose in transferring strike water to the cooler, but with a little experience, you can get this nicely dialed in.

mash temperature

Insulate your existing mashtun. If you like a direct-fired mash tun, add insulation to it. You’ll have to be careful not to set your insulation on fire, but it can be done. There is a kind of insulation you can get at the home-improvement store that looks like aluminized bubble wrap – you can install a couple layers of this with metal duct tape, keeping the bottom edge away from any flames that might come up around the bottom. Or you could simply wait until the burner is out, then wrap the kettle up with old towels, blankets, and so on (don’t use the nice ones – they may get scorched or covered with sticky wort). You can even just move the whole mash tun into a box made from rigid foam insulation. No matter what insulation you use, don’t forget to cover the top, as most of the heat will want to go out that way.

Increase the mass. When I went from five-gallon to ten-gallon batches, my heat-loss issues diminished dramatically. It took me a while to realize why, but the basic reason is that a larger mash has more volume in relation to its surface area, so more of the heat is locked inside and not able to transfer out through the walls of the tun. There are a lot of other pros and cons to making larger batches, but if the idea of having twice as much beer around appeals to you, this could be a good side-effect of the jump.

High-Tech Mash Temperature Methods

herms system to keep mash temperature maintained

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Fair warnings: These methods will require some additional costs. Just how much is really down to how much you want to scavenge and tinker, compared to how much you want to buy off the shelf. You could do anything from spend a couple of hundred dollars to implement these to buying a complete pre-made system for a few thousand dollars. Either of these systems, though, will allow you to not only hold temperatures indefinitely, but also to do complex stepped mash programs with excellent accuracy.

RIMS: The Recirculating Infusion Mash System works by pumping liquor out of the mash tun and past an electronically controlled heating element, then returning it to the tun. Clearly, this won’t work without a pump and a heating element, but there’s also the electrical wiring and the electronic control to consider. This isn’t a project for those uncomfortable with electrical DIY, but it’s not un-manageably complex. Consider asking a skilled friend to help, and returning the kindness with a few homebrews once it’s all done. If you find yourself lacking in mechanically savvy friends, SABCO has a top of the line RIMS system available.

HERMS: The High Efficiency Recirculating Mash System addresses a few shortcomings of RIMS. In some RIMS setups, pumping mash liquor directly across a water-heater element can cause scorching, so HERMS removes that possibility by instead moving the wort through a coil which is immersed in hot water. The heat, either gas or electric, is applied to this tank of water, heating the liquor indirectly. The buffer offered by the water bath is more resistant to temperature loss, but can also take longer to ramp up if you’re doing a stepped mash. Setting up a HERMS system can, depending on your design choices, add plumbing for propane or natural gas into the project plan, so be sure you have the skill to do it right before you set out – or bring a competent plumber into the build team.

What's the Best Way to Maintain Mash Temperature?

There is no single answer to that question, and the best way for you may not be the best way for me. I’ve seen all of these methods in use, and they all work for the brewers that use them. I’ve been insulating my direct-fired mash tun for years now by wrapping it in an old blanket, and that has worked very well for me, especially with larger batch sizes. On the other hand, I’ve been chasing down a recipe with a friend, and it’s looking more and more like I’m going to have to update my system to allow me to do a stepped mash, which means I am looking into one of the high-tech methods described above. It might take me a few more years to finally put it all together, but I’m enjoying the ride along the way.

About the Author

Josh Drew is a second-generation homebrewer and has been brewing since 1992. At that time, information was much harder to find and other homebrewers were harder to connect with. As such, he learned to brew from Charlie Papazian, FIDONet, and a really terrible homebrew shop. Things are much, much better now, and so is the beer he’s making.

written by Josh Drew

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6 comments on “Maintaining Mash Temperature”

  • You never addressed the high tech / low tech in your cover photo. Who's system is that and explain the process.

    Reply
    • Hey, That looks like it could be a RIMS system, and somewhere in the hose loop there is probably a heating element (Not pictured). I see a thermal probe in the hose line as it exits the ball valve. The box to the right will use the output from the probe and send instructions to a heating element further down the line (I.E. Lower/higher temperature of external heating element the sweet work passes through)

      Reply
  • A Harbor Freight welding blanket works well on my half keg mash tun and it is not flammable.

    Reply
  • I've had no problem maintaining temperature with my 10 gallon pot by wrapping it with a yoga mat and covering the top with towels. Use a small clamp to hold it in place. Saw this tip elsewhere and it works very well. Too well, in fact - my last batch didn't cool as anticipated, and I think that is the reason for only 49% attenuation.

    Reply
  • I'm with Sean... I do BIAB in a 15 gallon keggle. I get my water to strike temperature, put in the grains, and it usually drops to within 1 - 2 degrees of what I'm looking for. I give it a stir every 15 - 30 minutes and if I'm down more than 3 degrees, I'll turn the burner on low and stir until I'm back at desired temp. I'm in NC where temps are moderate enough that even in the winter, I don't generally have to add much heat.

    Reply
    • I built a small fermentation cube out of foam insulation board and duct tape Used an Inkbird 110v temp controller and an infra red heat lamp to control the temp in the box. (indirect light...make sure you don't direct the light at the fermentation vessel) You can put the temp probe in a mash vessel to control room temp based on mash temp. Works perfectly, no matter how many tuns you have in the cube. I bought (2) 4 x 8 ft x 1" thick panels for about $10.00 ea, to build a room against my inside garage wall 4' x 4' x 4'. I can fit up to 16 buckets inside. Of course it could be built to any other dimensions needed to house your fermentation operation.

      Reply
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