To optimize fermentation and prevent issues like hydrogen sulfide (off-odors) or stuck fermentations, nitrogen additions should be tailored to the specific needs of the yeast strain and the sugar content ($Brix$) of the must.
For every 1° Brix increase above 21°, it is generally recommended to add an additional 7.5–10 mg/L of YAN to the target.
The 400 mg/L Ceiling: Exceeding 400 mg/L is risky. High residual nitrogen after fermentation can lead to microbial instability (spoilage organisms like Brettanomyces or Acetobacter eating the leftovers).
Timing of Additions: * At Inoculation: Add organic nitrogen (like Fermaid O) to build yeast biomass.
At 1/3 Sugar Depletion: This is the most critical window for inorganic nitrogen (DAP) additions, as the yeast has high transport capacity but is starting to feel the stress of rising ethanol levels.
The 1/3 Rule: Avoid adding inorganic nitrogen (like DAP) after 1/3 sugar depletion (roughly 8–9° Brix drop from the start). Beyond this point, yeast transport proteins for inorganic nitrogen are inhibited by alcohol, meaning the DAP will just sit there and feed spoilage bacteria like Brettanomyces.
The "Brix Drop" vs. "Absolute Brix": "1/3 depletion" is relative to your starting point.
Example: If you start at 24° Brix, your 1/3 depletion point is 16° Brix.
Rehydration Nutrients: Always use a rehydration nutrient (like Go-Ferm) during the yeast blooming process. This does not count toward your YAN addition calculation; think of it as "vitamins" rather than "food."
Avoid the "End of Fermentation" Feed: Never add nutrients when the wine is near dryness (under 5° Brix). It won't help the yeast and will likely lead to microbial instability in the cellar.