Friday, January 21, 2011


When conducting the mash, it’s common to conduct different rests at various temperatures so that you can tailor the outcome of the wort  (fermentability, flavor, body, head retention, etc).   Brewers have many options do to this, with the most rudimentary likely being adding calculated quantities of hot water to the mash to raise it to the desired rest temp.  There are more complicated methods however.  

In designing our system, we weighed the advantages and disadvantages of each, and with a goal of semi-automation and repeatability, a Heat Exchange Recirculating Mash System seemed like the best option for us.

With any recirculating brewing system, wort drains from the bottom of the mash tun, into a pump, which then pushes the wort back on top of the mash.  In many systems, some form of heat is supplied to the wort while in transit from the pump to the top of the mash in order to ensure constant temperature rests.  How this heat is applied depends on the type of system that you’re using.

In a HERMS system, once the wort exits the mash tun and pump, it passes through a heat exchanger which typically resides inside the Hot Liquor Tank (typically copper pipe).  As the wort goes through the exchanger, energy is transferred from one to the other and by the time it enters back into the mash tun, the wort should be the same temperature as the water surrounding the exchanger in the hot liquor tank.  

In order to maintain the proper temperature, a sensor is placed inline right as the wort exits the hot liquor tank and enters the mash tun.  Using a control panel, if the exiting wort falls below the desired set point, the control box can turn on whatever heat source is used to increase the temperature of the water in the hot liquor tank, thereby increasing the temperature of the wort in the heat exchanger itself.  If the brewer wants to conduct a rest at 122 degrees and then increase the temperature to 148, all that has to be done is change the temperature setting on the control panel and the system will regulate itself.

Advantages of using a HERMS system: 
  • Precise temperature control
  •   Repeatability – with the precise temp control, you’re ensured that you’re conducting the same mash over and over (at least from a temperature standpoint)
  •  Complex Mash Schedules are simple to conduct
  •  With constant recirculation, you end up with much clearer wort in the boil kettle and greater overall mash efficiency
  • Efficient – Your heated sparge water in the hot liquor tank is used to maintain mash temps
  • Impossible to scorch your grain or wort
  • Ability to raise your mash temps without increasing the water to grain ratio
Disadvantages of using a HERMS system:  
  • Costly and complicated to build (comparatively)
  • Compared to infusion mashing, step temperature changes may take longer to reach/equalize
  • More parts to maintain and clean
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