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Split Recirculation for BIAB Systems

I love using a recirculating BIAB system as my home brewery. It's easy to use and clean, yet offers the temperature stability and programmability of pricier and more complex 2 or 3 kettle systems.

However, it still requires close attention while mashing to prevent dry firing your element. This can happen when the flow rate through the 400 Micron brew bag is lower than your recirculation flow rate. The bag fills with wort faster than it can drain, and if you are not there to stir or lift the bag up, eventually you will draw a vacuum under the false bottom and possibly dry fire your heating element. You may find you need to lower the pump flow rate to prevent this, which then causes poor heat distribution in the kettle, leading to temperature stratification. Bummer!

Split Recirculation

Introducing an ingenious and simple solution to conquer this frustration: behold, the split recirculation path:

Frequently I find that the best ideas are not my own! Bobby over at has hit upon a great way to achieve BIAB temperature stability without needing to stir frequently. The idea is simple: you split the recirculation return after the pump by using a tee. Two hoses are connected: one hose returns to the kettle underneath the false bottom, and a second hose goes into brew bag. The two paths are regulated with separate valves, so you can dial in the right flow rates. Bobby has a good article about his idea over on his website

System Design

The setup is straightforward. A tee is installed after the pump outlet, along with two ball valves. Connect one hose from the tee to the return port into the brew bag and a second hose from the tee to a port below the false bottom. The valves can be mounted directly to the tee or on the kettle. I recommend connecting the lower return port valve directly at the kettle - so you can disconnect the hose if needed, i.e to drain the line after mashing.

You might be tempted to install a 3-way ball valve in place of the tee and separate ball valves. This is not recommended, as you cannot control each flow rate separately. The 3-way valve is a good way to redirect the flow but unfortunately not to control the flow rate in each direction. 

Here's an example using the Craft Hardware bottom drain kettles: 

A tee is installed after the pump outlet, and a ball valve placed on each side of the tee. One path returns under the false bottom, the second returns into the brew bag. 

See the short tee and long thermowell on the front lower port of the kettle? They create the inlet under the false bottom. The thermowell stays in the kettle while also being in the recirculating wort path. The returning wort also flows directly onto the heating element. You can of course also use a dip tube in that location if you want to run a whirlpool after boiling. 

The green arrow shows the return path under the false bottom. The flow is directed over the long thermowell and directly towards the heating element. The yellow arrow is the upper flow path back into the brew bag.

You might notice that the top port of the kettle is used for recirculating back into the brew bag. This is made possible with our new brew bag eyelet installation service. You can also use a lid bulkhead with interior tube adapter instead. 

For a whirlpool setup, your options include:

  • Use the lower port with a dip tube for both mash return and whirlpool return. Find a separate location for your thermowell or place it inline with a tee. 
  • Install our two-piece whirlpool arm in the top port after mashing
  • Use the 400 micron brew bag as a whole kettle filter instead of traditional whirlpool

Regarding the last option, I find this method works better than a hop spider or any other external filter I have ever used including the mesh sputnik filter or more expensive tri-clamp tube-in-tube filters. You can keep the false bottom in place during the boil and put the brew bag back in after flameout to use the same split recirulation path to mix up your hops and slowly filter them out through the brew bag. No complicated system design or brew day reconfiguration needed! 

Craft hardware bottom drain kettle users: for a traditional whirlpool, you can use the single front port with a dip tube as a kettle inlet during mashing, then reconfigure that as the kettle outlet for whilpooling. You will need to reconfigure your hoses for this and add a two-piece whilrpool arm in the top port. You will also need another place for the temperature sensor, for example in a tee in the recirculation loop or in a tee in the bottom port of the kettle. You may wish to have another tri-clamp port welded in under the false bottom to simplify the build. Alternatively just use the brew bag kettle filter method!


In practice, usage is also straightforward. When recirculating, the lower port valve is always fully open. It is only closed during the boil and to fill your fermenter. The top port valve is opened and closed as needed throughout the brew to regulate flow rate and to turn off bag recirculation for a grain rest or when pulling the bag out. 

1. During initial heating, you can have both ball valves fully open.

2. When adding the grains, close the top port but keep the lower port open and continue recirculation.

3. Allow a short grain rest, then slowly open the top port ball valve targeting a relatively slow flow rate into the bag. According to Bobby you should shoot for about 1-2L flow rate through the top port when mashing. I think this is a good, safe target for 40-60L systems that allows enough recirculation to prevent temperature stratification. For 85-115L systems I would up that to at around 3-4L/min. In practice, you might find you can go with a higher return flow rate into the brew bag, depending on your grain bill and crush size. But I don't see this as necessary, and you will only create a higher risk of dry firing your element. 

Always make sure to keep an eye on the wort level in the brew bag, especially when dialing in your new setup. If the wort level rises, the bag is not able to drain fast enough, so stir it well and reduce the top port recirculation rate! 

4. When mashing is complete, close the top valve and pull the bag out. You can continue recirculating through the bottom port until the boiling point is reached.

5. During the boil, close both valves and drain your lines. 

6. Post boil, you can use the same setup with the brew bag kettle fillter technique, or reconfigure for a traditional kettle whirlpool. Either way make sure you run some hot wort through everything to disinfect. When it's time to fill your fermenter, close the bottom port. Disconnect the top port tube and use that to drain the kettle. 


I really like this idea and recommend it for all recirculating BIAB users. I have updated the recirculating BIAB sets sold in the shop to include the necessary hardware. The good news is, you can also easily retrofit any existing system. 

I think you will find this new setup very useful and a big improvement on the already great recirculating BIAB system. Let me know if you have any questions or any other tips to contribute! 

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