The Heat and Crash Method of HERMS Brewing

HERMS coils offer a great way to maintain your mash temperature by using the heat from your HLT to passively heat your mash tun. With a HERMS system there’s no risk of scorching your wort as it’s impossible to heat the coil itself to any temperature in excess of 212 Fahrenheit (boiling).

On most electric brewing systems HERMS coils are standard equipment simply because passively heating the mash tun doesn’t require an additional element or amperage beyond what’s already required to heat the HLT. The downside of the HERMS type system is that temperature transitions can be slow as you’re limited on the amount of temperature differential between the water in the HLT and the wort you are heating.

I want to share a tip that I call The Heat and Crash Method for speeding up the HERMS brewing process. The first step in brewing with HERMS is understanding how your HLT temperature relates to your mash temperature. I call this the ‘lag’ because your mash tun will always lag a few degrees behind your HLT temperature. Your wort flows out of the bottom of your mash tun and is pumped through the HERMS coil (preferably into the bottom port and out of the top port to expel all air from the coil) and then returns to the top of the mash tun. While traveling through the coil the surface contact that your wort makes with the inside of the tubing passively transfers heat from the water in the HLT to the wort. This is not a 100% efficient process, so while the wort comes out heated by the coil it’s not going to be the same temp as the water in the HLT. Once the wort is heated in the coil there is actually heat that is lost in the pathway back to the mash tun and the mash tun itself will constantly lose heat as well. The lag is the temperature difference between the HLT and your mash once all temps have stabilized. There are many factors that will affect this temperature difference including ambient temperature, length of hoses, flow rates, etc. I always tell our customers to start by assuming 4 degrees as this is a value that we have found to be pretty average in most conditions with our equipment. This means that an HLT at 154 degrees will eventually heat to and maintain a mash temp of 150 degrees. The measured temperature flowing into the top of the mash tun is typically about 2 degrees under the HLT temp and then I assume that the other 2 degrees is heat lost through the top and sides of the mash tun during the time it takes to cycle the entire volume of the mash tun through the coil. The challenge with HERMS is that if you filled your mash tun with cold water and simply heated and maintained your HLT to 154 degrees it would take several hours for the mash temp to reach 150. In this example the small amount of temperature differential between the two volumes makes the heating times very long and generally unacceptable. The only practical way to speed up the heating of the liquid in the mash tun is by significantly increasing that temperature differential. This is where the Heat and Crash method comes into play. If you take the HLT to a higher temperature such as 200 degrees, the liquid returning to the mash tun will be much hotter and will heat the volume of the mash tun much faster. The problem is that if this process is continued the mash tun would theoretically eventually heat to 196 degrees. The Heat and Crash method calls for crashing the HLT temp back down to your maintenance temperature (~4 degrees above your target mash temp) as soon as your mash hits the target temp by an infusion of cold water into the HLT.

I’ll use my process for mashing in as a step by step example of how this is actually done. I like to start by measuring the correct amount of strike water into the mash tun. For this example we’ll say that the strike water needs to be 166 degrees to hit a target mash temp of 150 once the grain is infused. To save time i’ll only fill the HLT with enough water to cover the HERMS coil. This smaller volume of water will heat quickly in the HLT and leave me room to add water when I crash. I’ll then set my HLT to boiling temperature so it will heat as fast as possible. While recirculating the strike water from the mash tun through the HERMS coil, I’ll monitor the temperature of the strike water in the mash tun until the entire volume hits the desired 166 degrees. At this point the HLT is likely going to be at or near boiling as the lag will be huge during large temperature transitions. Once the strike water hits the desired 166 degrees i’ll immediately stop the pump so that no additional heat is transferred to the mash tun. Then it’s time to add the grain and stir the mash to stabilize the mash temp at ~150 degrees. Once my mash-in is complete I’ll adjust the HLT controller to 154 degrees (4 degrees above the mash temp). Then I simply add cold water into the HLT and stir to Crash the HLT back down to 154 degrees. At this point I can restart the pump that circulates the wort through the HERMS coil to maintain my mash tun temperature of 150 degrees. I typically mash for 60 minutes and then I’ll adjust the HLT up to 170 degrees in preparation for sparging. I’ll let the wort continue flowing through the HERMS coil while the HLT is heating to 170 as it brings the mash temp up a little which aids efficiency (I personally no longer perform an actual mash out). This same method of Heat and Crash can effectively be used to quickly step mash with a HERMS coil by simply setting your HLT to a much higher temperature to decrease the time it takes between mash rests and then cold water crashing it down to the correct maintenance temperature for the duration of each rest. I will note that you should never set the HLT over 172 while step mashing as you don’t want the returning wort that’s hitting the grains at the top of your mash to exceed 170 causing extraction of tannins. You also need to constantly stir the mash while transitioning between rests as the hotter wort will layer on top of the colder wort in the mash tun causing very inconsistent mash temps.

If your system has the capability of heating the HLT and boil kettle simultaneously you can save additional time and steps by actually heating your strike water in the boil kettle while your HLT is heating at the same time. Then you can simply pump the strike water into the mash tun to mix with your grains. Another tip is that you can increase the efficiency of your HERMS coil by constantly recirculating the HLT itself during the entire process to keep water flowing around the outside of the coil. This probably all sounds somewhat complicated, but once you’ve done all of this a few times it all becomes very simple.

Feel free to ask me questions or provide any strategy that you use while HERMS brewing in the comments below.