The Problem with Standard Recirculation

In a standard recirculating BIAB setup, all returning wort flows back into the brew bag through the sparge arm. This works well when the grain bill is coarse and porous, but becomes problematic when:

• The grain is finely milled or contains high percentages of wheat, oats, or rye
• The bag becomes partially clogged during the mash
• You increase pump flow to improve temperature distribution

When the bag cannot drain as fast as wort is being returned, the wort level inside the bag rises. Eventually the bag lifts off the false bottom, the false bottom loses its liquid seal, and the heating element can be exposed — a dry-fire risk that can damage the element and scorch the wort.

Reducing pump flow solves the clogging risk but creates poor heat distribution and temperature stratification in the kettle. You end up choosing between two problems.

Split Recirculation — How It Works

The split recirculation path solves both problems simultaneously. After the pump outlet, a tee divides the returning wort into two paths, each regulated by its own ball valve:

• Upper path (into the bag): Returns wort through the upper side-wall port and into the brew bag via the sparge arm. This path is throttled to a slow, controlled flow rate — enough to maintain temperature without overwhelming the bag's drainage capacity.
• Lower path (under the false bottom): Returns wort through a port below the false bottom, directed across the thermowell and onto the heating element. This path carries the majority of the flow and ensures the element stays covered and the heat is distributed throughout the kettle.

The lower path is the key innovation. Because wort is constantly returning below the false bottom regardless of the bag's drainage capacity, the element stays submerged, heat distribution is uniform, and you are free to throttle the upper (bag) return to whatever flow rate the grain bed will comfortably accept — without any trade-off.

System Design and Hardware

The setup centres on a tee installed after the pump outlet, with a ball valve on each leg. One leg connects to the upper side-wall port (sparge arm return into the bag); the other connects to a port below the false bottom. The valves can be mounted directly on the tee or at the kettle — mounting the lower-return valve at the kettle is preferable, as it allows the hose to be disconnected easily for circuit draining after mashing.

The front lower port of the kettle uses a short tee fitting with a long thermowell installed horizontally. The thermowell sits in the recirculating wort path below the false bottom, giving accurate temperature readings while the returning wort flows directly across the heating element. The BIAB Recirculating Kettle Set includes this short tee and thermowell.

Pump Connection at the Kettle Outlet

The pump inlet connects to the kettle bottom outlet via a short 90° elbow and a 10 cm stainless extension tube, or alternatively via two hose barbs with a short silicone hose between them. The type of connection is up to you - these parts are not included in the recirculating BIAB kettle set. 

Operating the Split Recirculation System

In normal operation, the lower port flow valve is always fully open during recirculation. It is only closed during the boil and when filling the fermenter. The upper port (bag return) valve is the one you adjust throughout the brew to control flow into the bag.

1. Initial heating: Both ball valves fully open. Recirculate freely to bring the water to strike temperature.
2. Adding grain: Close the upper port valve. Keep the lower port open and continue recirculating under the false bottom — this keeps the element covered and heat circulating while you stir in the grain.
3. Grain rest: Leave both valves as above for 3–5 minutes to let the grain swell and settle.
4. Mash recirculation: Slowly open the upper port valve, targeting a flow rate into the bag of approximately 1–2 L/min for 40L and 60L systems, or 3–4 L/min for 85L systems. The lower port continues at full flow. Monitor the wort level inside the bag — if it rises, the bag is not draining fast enough; stir and reduce the upper port flow rate.
5. End of mash: Close the upper port valve. Pull the bag. Continue recirculating through the lower port until just before the wort reaches boiling temperature.
6. During the boil: Close all valves and drain the pump circuit (see section below).
7. Post-boil: Reinstall the brew bag as a whole-kettle filter, or reconfigure for a traditional whirlpool. Either way, run hot wort through the full circuit briefly to sanitise before filling the fermenter. When ready to transfer, close the lower input port and use the upper port hose to drain the kettle.

Post-Boil: Brew Bag as a Whole-Kettle Filter

After flameout, reinstall the brew bag into the kettle and use the same split recirculation path to filter hops and hot trub. This method works better than a hop spider, sputnik filter, or tube-in-tube filter — the large surface area of the bag handles high hop loads without clogging, and the false bottom stays in place throughout so there is no reconfiguration needed between mashing and filtering.

Recirculate through both paths as during the mash. The bag gradually captures all hop material and hot trub, and the kettle drains completely and cleanly through the bottom port into the fermenter. When the wort temperature drops below 35–40°C, monitor the bag closely — cold break can clog the mesh at lower temperatures.

Draining the Pump Circuit

After mashing, a small volume of unboiled wort remains inside the pump and connecting hoses — typically 0.3–0.5L depending on hose length. If not drained, this unboiled wort enters the finished beer when the pump runs again post-boil. This exterior circuit should be drained during the boil:

1. Switch the pump off.
2. Close the kettle bottom outlet valve and lower front port input valve.
3. Disconnect the hose at the sparge return inlet. Careful - hot wort will be in the tube up to the level of wort in the kettle!
4. Lower the hose end in a jug or drain to below the bottom of the kettle — gravity and residual pressure empties the circuit.
5. Reconnect the hose before restarting the pump for post-boil use.

Wort Oxygenation

The recirculating BIAB offers a simple method for oxygenating wort before pitching yeast without any additional equipment. After chilling to pitching temperature, raise the sparge tube in the kettle so its outlet sits just above the wort surface. Restart the pump at low flow. Wort picks up air as it exits the return arm, adding oxygen with each pass. Run for 5–10 minutes, adjusting arm height to control the drop distance.

Physical Setup

Under-Kettle Access

Recirculation requires access to the lower Tri-Clamp port for the pump connection. Two options:

• 14 cm leg extensions (sold separately): The simplest solution for a table or workbench setup. Note that tables 80–90 cm in height can make the kettle awkward to work with at this raised height — a lower working surface is preferable.
• Open brew stand (not supplied by Craft Hardware): An open-frame stand with a grid or slatted shelf gives full access below the kettle from any angle.

Controller Placement

Mount the controller away from steam and splash at a comfortable eye level to the side of the kettle. Never position it directly above a boiling kettle.

Electrical & Controls

Craft Hardware heating elements are sold unwired. All electrical connections must be made by a licensed electrician before use. Every heating element circuit must be protected by a GFI/RCD breaker.

A Controller Is Required

Without a brew controller, maintaining stable mash temperature requires continuous manual attention throughout a 60–90 minute mash. A controller wired to the heating element, using a temperature sensor in the return path as its input, holds the mash temperature automatically and allows multi-step mash schedules to be programmed. A single-circuit controller such as the EINBREW 1V1P is the recommended starting point.

Grain Weight Limit

Batch Sizes

Extract efficiency (Sudhausausbeute) for recirculating BIAB is comparable to non-recirculating BIAB — typically 52–58% for German brewers. The main advantage over static BIAB is temperature stability and programmability, not efficiency. The figures below assume a 60-minute boil at 13°P original gravity.

* Volume including hot break. At the end of the boil, the heating element sits approximately 6 cm below the wort surface. For very small batches, reduce element power using a compatible brew controller or voltage regulator.

** 60-minute boil, 13°P original gravity, volume including hot break. For higher gravity beers maximum batch size reduces accordingly. Using a steam condenser reduces maximum batch size further.

*** Includes a 6 cm safety margin between wort surface and kettle rim. At maximum volume, take care to prevent boilovers — anti-foam agent may be required.

Bill of Materials

The easiest way to get started is with the BIAB Recirculating Kettle Set (available in 40L, 60L, and 85L). Complete the set with a pump, silicone tubing, hose barbs, hose clamps, and optional kettle leg extensions. We provide enough tri-clamps and gaskets with the set to make the recommended hose connections.

The split-path hardware in the set works as follows (see picture below): a short tee is mounted directly to the front lower port of the kettle, with the long thermowell pointing into the kettle. A ball valve on the tee controls flow to the lower return path. A second tee connects to that valve — one leg of this tee connects to the pump outlet, the other leg has a second ball valve to control flow to the upper port.

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