SOP — VDK Check (Diacetyl)¶

FUERST WIACEK Version 1.0 | Cellar — all fermentation tanks

Purpose¶

The VDK (vicinal diketone) check is used to detect the presence of diacetyl in fermenting beer before advancing to the next stage of the fermentation recipe. Diacetyl produces a butter, cream, or caramel-like flavour and must be reduced to an acceptable level before the beer is crashed.

The VDK check is performed when final gravity has been reached and confirmed. It can be carried out at the same time as the daily gravity sample to avoid a separate cellar visit.

Results are logged in the fermentation spreadsheet.

Equipment¶

Alcohol spray
Water hose
Small pitcher
2 lab bottles — one labelled 'Test', one labelled 'Control'
2 tasting glasses
Hot water from the HLT (hot liquor tank) — above 75°C
Cold water for cooling

Process¶

1. Pull Sample from Tank¶

Follow the standard tank sampling procedure as described in the Fermentation Monitoring SOP. Pull enough sample to fill both lab bottles.

Note

The VDK sample can be pulled at the same time as the daily gravity sample. Taking both at once avoids a second cellar visit.

2. Prepare Test and Control Samples¶

Fill the bottle labelled 'Test' with sample from the tank.
Fill the bottle labelled 'Control' with sample from the tank.
Fill the pitcher with hot water from the HLT. The water must be above 75°C.
Place only the Test bottle in the hot water pitcher. The Control bottle must remain at room temperature and must not be heated.
Allow the Test bottle to steep for approximately 30 minutes.
After 30 minutes, remove the Test bottle and place it in cold water to bring it back to room temperature before evaluation.

3. Sensory Evaluation — Four Eyes Principle¶

Both the Test and Control samples must be evaluated independently by two people before a result is agreed. Each person smells both samples without sharing their impression first. Results are then compared and a decision made together.

Warning

Do not share your impression before the other person has evaluated independently.

Pour approximately 100 ml of the Test sample into a tasting glass. Pour approximately 100 ml of the Control sample into a separate tasting glass. Mark each glass clearly with its label or the corresponding bottle cap.
Swirl each glass gently and smell.
In the Test sample, search for aromas associated with diacetyl: butter, cream, caramel, butterscotch, fatty or oily notes, vanilla cream.
Compare against the Control sample. The Control represents the beer without the forced VDK conversion — it should smell cleaner.
Each evaluator records their impression independently before discussing.
Discuss the result and agree on a pass or fail.

4. Recording the Result¶

Result	Criteria	Action
Pass	No diacetyl aroma detectable in Test sample, or clearly not above Control	Log 'VDK Pass' on fermentation sheet. Proceed to crash if FG confirmed and no other off flavours noted.
Fail	Diacetyl aroma clearly present in Test sample	Log 'VDK Fail' on fermentation sheet. Do not advance. Discuss next steps with team.

Note

A VDK Pass alone is not sufficient to advance. Final gravity must also be confirmed and no other off flavours noticed before the beer proceeds to the next step in the Botec fermentation recipe.

Troubleshooting¶

Issue	Likely Cause	Action
Diacetyl detected on VDK fail — beer not reducing	Yeast not active enough to reabsorb diacetyl	Do not crash. Check fermentation temperature. Discuss with team — may need to rouse yeast or raise temperature briefly.
Evaluators disagree on result	Borderline level of diacetyl	Treat as a fail. Repeat the VDK check the following day. Do not advance until both evaluators agree on a pass.
Test sample much warmer than Control at evaluation	Insufficient cooling after hot water steep	Cool the Test sample further in cold water before evaluating. Temperature affects aroma perception.
Off flavour noticed beyond diacetyl	Other fermentation issue	Note on fermentation sheet and flag to team immediately. Do not advance.