Wort Separation
Wort separation is the controlled process of draining clear, fermentable wort from the spent grain bed. How you start — vorlauf — determines how the rest of the lauter runs.
The goal of lautering is to collect as much fermentable wort as possible from the grain bed, at the right concentration, without passing grain particles or extracting astringent compounds. GF grain beds require more careful management than barley beds to achieve this — but the principles are the same.
Wort Separation At a Glance
| Control Point | Target | Why It Matters |
|---|---|---|
| Vorlauf duration | Until wort is visibly clear | Prevents grain particles entering kettle |
| Initial runoff rate | Slow, steady valve opening | Reduces bed compaction and channeling risk |
| Sparge water temp | 165-170F / 74-77C | Improves extraction without excessive tannin pickup |
| Runoff endpoint | 1.008-1.010 SG | Avoids low-yield, high-astringency over-sparging |
Vorlauf: The Critical First Step
Vorlauf is the recirculation phase at the start of lautering. Wort is drawn from the bottom of the mash tun and gently returned to the top of the grain bed, allowing a filtration matrix to form before collection begins.
For GF grain beds, vorlauf is not a minor formality — it is the step that stabilizes the bed and prevents grain particles from running through to the kettle.
What vorlauf accomplishes:
- Settles the grain bed into a stable, self-filtering layer
- Flushes grain fines from the initial wort flow
- Establishes a consistent runoff flow rate before collection starts
- Allows the brewer to visually assess bed behavior before committing to runoff
When to stop vorlauf: When wort runs visually clear and the flow rate is stable. In GF brewing this typically takes 5–15 minutes. Do not end vorlauf on a timer — use wort clarity as the indicator.
GF-specific note: Sorghum wort foams during vorlauf. This is normal and not a sign of contamination. Monitor clarity, not surface foam.
First Wort Collection
Once vorlauf is complete and wort runs clear, open the runoff valve and begin collecting wort into the kettle. This first runoff — sometimes called "first wort" — is the most concentrated wort of the lauter, closest to the full mash gravity.
Runoff flow rate: Slow and controlled is the key rule in GF lautering. A fast runoff creates a pressure differential across the grain bed that accelerates compaction. Open the valve gradually and maintain a gentle, consistent flow.
Practical target: Aim for a flow rate that drains the tun over 20–40 minutes for a typical homebrew batch. Commercial production rates vary by tun geometry but the principle — slow enough to avoid compaction — is the same.
Visual monitoring: Watch the top of the grain bed as it drains. A well-behaved GF bed drops slowly and evenly. Channeling appears as an uneven surface where one section drops faster than the rest — wort is bypassing the bed through a low-resistance channel rather than flowing through the full bed matrix.
Sparge and Second Runoff
Once first wort collection is underway, sparge water is added to the top of the grain bed to rinse remaining sugars from the grain.
Sparge water temperature: 165–170°F (74–77°C). Hot enough to reduce wort viscosity and improve sugar extraction, but not so hot that tannin extraction accelerates. Do not exceed 170°F — above this temperature, polyphenol extraction from grain material increases significantly.
Batch sparge vs. fly sparge:
Batch sparge adds all the sparge water at once, stirs, allows the bed to resettle, then runs off. It is simpler and faster but slightly less efficient.
Fly sparge (continuous sparge) adds water continuously while wort drains, maintaining a constant water level above the grain bed. It is more efficient but requires slower, more careful flow management — particularly important with GF grain beds that compact under continuous pressure.
End of runoff: Stop collecting wort when the runoff gravity drops below approximately 1.008–1.010 (2–2.5 Plato). Below this point, additional runoff adds very little fermentable sugar but increases the risk of astringent extraction from grain fines.
Wort separation failures:
- Skipping or rushing vorlauf — grain particles carry through to the kettle and persist into finished beer
- Running off too fast — creates a pressure differential that compacts the GF grain bed
- Sparge water too hot (above 170°F / 77°C) — accelerates tannin extraction, adds astringency
- Collecting past 1.008 runoff gravity — extended sparging of spent GF grain extracts astringent compounds with minimal fermentable sugar gain
A well-executed GF wort separation produces:
- Clear first wort with no visible grain particle load
- Stable, even runoff from first wort through end of sparge
- Pre-boil volume and gravity both on target
- No astringent character in the finished beer traceable to lautering
Source Notes
Vorlauf and sparge practice based on craft GF brewing production documentation. Runoff end-point gravity guidance reflects standard brewing efficiency practice. Tannin extraction thresholds from brewing chemistry literature.