Three Kettle HERMS Systems

How does a three-kettle recirculating system work?

In a three-kettle recirculating system, you have a heated kettle for boiling, a directly or indirectly heated kettle for mashing, and a third heated kettle for the sparge  water (HLT).

In a HERMS system, the wort is recirculated through a heat exchanger in the HLT kettle, which ensures gentle heat transfer without the risk of burning. There is no heating element in the mash kettle, and the low false bottom stand can be used. Very important: you still need to pay attention to the flow rate, so that the grain bed does not compact and your lauter bottom or pump is damaged. However, the HERMS system is more foolproof than the direct fire system.

Remember, you'll need a controller to maintain the temperature of the mash.

Advantages of a three kettle system

Of all the recirculating systems, the 3 kettle system has the highest efficiency and yield. With proper controller, you can also make a double batch by mashing the second batch while the first brew is boiling.

A well-planned system requires only 2 or 3 hose changes per session with minimal wort loss due to dripping. Try it this way first to see if you can live with it or where you want to use a fixed connection.

Tips for ensuring an adequate flow rate

  1. Mill your grains at around a 1mm mill gap setting. This is fairly standard when ordering milled grains from your local homebrew shop, but it doesn't hurt to ask.
  2. If brewing with large percentages of high protein grains or adjuncts such as wheat, oats, or rye, consider adding rice hulls to improve drainage.
  3. Always turn off the pump when mashing in. Make sure your heating element is also turned off, to prevent overheating.
  4. Stir well when adding the grains to the mash kettle.
  5. Use a 3-5 minute grain rest period before turning the pump and heating element back on.
  6. Close the pump output valve almost all the way and turn the pump back on. Slowly open the pump valve. Doing this too fast can compact the grain bed. Lastly, turn on the heating element
  7. Don't walk away! Stay close and keep an eye on your kettle, the wort can thicken and slow the flow rate during the mashing process. if you ever notice the volume of the mash kettle rising, you are pulling a vacuum under the false bottom. Stop the pump and stir the grain bed.

    Design Considerations

    I recommend keeping things simple and connecting the kettles and pumps directly with silicone tubing. When you move from mashing to sparging, you only need to make two hose connections. Then when you move to the boil phase, you only have to move the pump input hose from the mash kettle to the boil kettle. If you're careful, you can limit spillage to a teaspoon or two. And at any point, you can just drain the lines into a bucket to empty the lines.

    In a HERMS system, it is recommended to place the temperature sensor for the controller near the return point of the sparge loop, just before the sparge arm. This is the best way to prevent the temperature from overshooting or oscillating.

    You should also have a valve at the input of the HERMS spiral. When you change the hose, you must close the valve so that your mash kettle is not drained! 

    The adjustable height sparge arm can also be used for whirlpooling with the 400 micron brew bag as a whole kettle filter. This works wonderfully to filter out hops and hot trub, and allows you to fully mix the kettle contents and completely drain the kettle.

    Note the 90-degree elbow on the bottom of the boil kettle (left). This makes it easier to connect the hose for filling the kettle during lautering. The HLT pump is connected with an elbow and a 10 cm wpool (for the 115 liter kettle you need at least 12 cm length). 

    Don't forget that starting with the 85L size, I recommend switching to 1" fittings (elbows, tube extensions, tees, etc.) and 19mm ID tubing.



    Whirlpool with Filtration:

    If you use the kettle filter option, you can also connect your boil kettle to the MLT on the pump inlet side, similar to the Duo system:

    If you don't want to use the whole kettle filter method with Brew Bag, you'll have to rethink the design. You'll want to put a 45 degree racking arm in the front of the boil kettle (don't forget the valve). However, this means you lose the temperature measurement point for the kettle, but you can add a tee and thermowell externally in the whirlpool loop.

    You probably want a dedicated whirlpool arm in the boil kettle. You might also want to add another 3-way valve to the pump outlet to avoid changing hoses when filling the boil kettle.

    Lastly, you should probably use at least one flexible silicone hose to connect the bottom drain of the MLT to the front port of the boil kettle: