FAN and Sugars
FAN and sugar composition explain why two worts with similar gravity can ferment very differently. These measurements are central to diagnosing stalled or stressed fermentations.
| Metric | What It Indicates | If Low | If High |
|---|---|---|---|
| FAN | Yeast-available nitrogen | Slower starts, stress risk, weaker attenuation | Usually not harmful, but may alter flavor profile |
| Fermentable sugars | ABV potential and dryness | Lower attenuation potential | Drier beer and higher ABV tendency |
| Dextrin fraction | Residual body potential | Thinner body | Fuller body, lower attenuation |
Why This Matters in GF Brewing
GF malts and adjunct blends can produce wider nutrient and sugar-profile variation than conventional barley grists. Measuring FAN and sugar balance helps separate yeast issues from wort-composition issues.
Practical Use in Troubleshooting
If fermentation is slow or under-attenuated, check FAN sufficiency and fermentable sugar share before changing yeast strain. If beer is consistently thin, review dextrin-building steps in mash design rather than only lowering yeast attenuation.
Frequent FAN/sugar interpretation errors:
- Assuming gravity alone describes fermentability
- Treating yeast strain as the only variable in poor attenuation
- Ignoring nutrient additions when comparing batches
What good FAN/sugar analytics delivers:
- Cleaner fermentation diagnostics
- More predictable attenuation outcomes
- Better control of ABV/body balance
Source Notes
FAN and sugar interpretation based on brewing fermentation science and production QC diagnostics.