Tips for recirculating an MLT or BIAB kettle

This article applies to any recirulated mash system, including HERMS, RIMS, direct fire, and recirculating-BIAB.

Having a good flow rate is critical to the performance of a recirculating mash system. A poor wort flow rate will lead to longer heating times and can also be an indication of an impending stuck mash. A stuck mash can create enormous vacuum force under the false bottom and even damage your equipment. If proper care is taken this is almost always avoidable.

Do not leave your recirulating system unattended when the pump is running. If you notice the water level in the mash tun is rising, this means the grain bed is not porous enough and a vacuum is forming under the false bottom. Immediate steps must be taken to prevent damage to the false bottom or pump! This is immediately solved by stirring the grain bed. That may only temporarily solve the issue, so if this happens once during a batch, stay extra vigilant, because it will likely happen again for this batch. This is more often the case when brewing with high percentages of high protein grains or adjuncts such as wheat or oats.

In this article I would like to provide some guidelines and tips on how you can make sure your grain bed is porous enough to ensure good flow through the false bottom.

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. If you are using a direct fired mash tun, make sure your heating element is also turned off to prevent overheating.
  4. Stir well when adding the grains to the mash kettle. You want to minimize clumping of the grain.
  5. Use a 3-5 minute grain rest period before turning the pump and heating element back on.
  6. Do not start the pump at a full flow rate. This can compact the grain bed. 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 if it was turned off in step 3.
  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.