Mash Tun Considerations for Gluten-Free Brewing
The mash tun is not just a vessel — it is a filtration system. For GF brewing, its design determines whether the lauter runs freely or collapses into a stuck, unworkable grain bed.
Because GF grains lack husks, the grain bed has no self-supporting structure. The mash tun's filtration system — false bottom, manifold, or screen — carries the entire weight of the grain bed and controls how wort flows out. A tun that works perfectly for barley may perform poorly for GF grain bills without adjustment.
False Bottoms vs. Manifolds
False bottoms are perforated plates that sit above the tun drain and support the grain bed across a large surface area. They work well for GF grains when the slot or hole size is small enough to retain fine particles. Larger slot sizes (common on equipment designed for barley) pass GF grist fines through into the wort, creating turbidity and losing fermentable material.
Bazooka screens / manifolds are slotted tubes that rest on the tun floor. They work by drawing wort from below the grain bed through the manifold slot openings. For GF grains, manifolds can be effective but require careful vorlauf — the grain bed tends to compact around the manifold rather than forming a uniform filter matrix as it does with barley.
General guidance: A false bottom with slot openings of 0.5–0.7mm works well for GF grain. If retrofitting existing equipment, confirming the slot size before your first GF mash saves troubleshooting time.
Grain Bed Depth
Shallower grain beds compact less and lauter faster. A grain bed depth of 12–20 inches (30–50cm) is workable for GF grains. Deeper beds increase hydrostatic pressure on the false bottom, accelerate compaction, and significantly increase stuck sparge risk.
If your batch size forces a deep grain bed, compensate with:
- Higher rice hull addition (toward the 15% end of the range)
- Slower sparge flow rate
- Recirculation pump assistance during runoff
Vorlauf: Recirculate Before Collecting
Vorlauf is the recirculation step at the start of lautering where wort is drawn from the tun and returned to the top of the grain bed until it runs clear. For GF grains, vorlauf is not optional — it is the step that allows a grain bed filtration matrix to form before collection begins.
Run vorlauf until:
- Wort runs visually clear (no visible grain particles or heavy turbidity)
- A consistent flow rate is established
- The grain bed surface is stable and not channeling
Rushing past vorlauf with a GF grain bill means wort full of fine grain particles entering the kettle, which carries through to finished beer as haze, astringency, or poor fermentation performance.
Equipment Crossover from Barley Brewing
Repurposed barley brewing equipment functions for GF production with appropriate cleaning protocols. The main considerations:
Cleaning: Gluten cross-contamination is the critical risk. Any equipment that has contacted barley, wheat, or rye must be thoroughly cleaned before GF use. For certified GF production, dedicated GF equipment is required — shared equipment is not certifiable regardless of cleaning claims.
Slot sizes: As noted above, verify false bottom or manifold slot dimensions match GF grist particle size before production.
Volume headspace: GF mashes can foam more than barley mashes — particularly with sorghum-heavy grain bills. Ensure the tun has adequate headspace above the grain bed to accommodate this.
Heat Source and Step Mash Capability
Standard insulated single-infusion cooler setups hold temperature adequately for barley mashing but cannot drive the mash through the temperature ramps required for sorghum step programs. Commercial GF sorghum production requires a steam-heated or direct-fired mash vessel capable of ramping to 185–190°F (85–88°C) for in-vessel gelatinization.
For homebrewers and small craft producers working with sorghum:
- Electric or gas-fired HERMS/RIMS systems can provide sufficient temperature control for step mashing if designed for active heating rather than passive temperature hold.
- Direct-fire kettles used as a mash tun give the most flexibility for step programs but require careful mixing to avoid scorching.
- Cereal mashing in a separate vessel is the practical alternative when the main mash tun cannot reach gelatinization temperatures. See Decoction Approaches.
For millet-only or pre-gelatinized adjunct bills, a standard insulated cooler remains adequate — this limitation applies specifically to recipes that include raw or under-modified sorghum requiring high-temperature gelatinization.
Mash tun problems specific to GF brewing:
- Large-slot false bottoms designed for barley — pass GF fines into wort
- Excessively deep grain bed — compacts under hydrostatic pressure, stuck lauter
- Skipping vorlauf to save time — grain particles carry through to kettle
- Shared equipment without verified cleaning protocol — GF contamination risk
A correctly configured GF mash tun delivers:
- Stable grain bed that holds its structure through the full sparge
- Clear wort with acceptable turbidity by end of vorlauf
- Consistent lauter efficiency batch to batch
- Predictable runoff flow rate and volume
Source Notes
False bottom slot sizing guidance based on craft brewing equipment specifications. Grain bed depth recommendations reflect production brewing practice for GF and adjunct-heavy grain bills.