A pure sugar wash contains essentially zero natural nitrogen. Yeast need nitrogen — specifically yeast assimilable nitrogen (YAN) — to grow, multiply, and ferment cleanly. When nitrogen is absent, yeast become stressed and produce significantly more fusel alcohols as metabolic by-products. Adding nutrients correctly is not optional for clean spirit production: it is the most effective quality intervention available before distillation.
What Is YAN?
YAN stands for Yeast Assimilable Nitrogen. It is the fraction of total nitrogen in a wash that yeast can actually absorb and use. It is expressed in mg/L (milligrams per litre), sometimes written as ppm.
YAN comes from two sources: free amino nitrogen (FAN) from amino acids and small peptides, and ammoniacal nitrogen from inorganic sources like diammonium phosphate (DAP). Most wort and fruit musts contain natural YAN from the raw ingredients. Pure sugar washes — the standard base for neutral spirit, vodka, and white rum — contain zero natural YAN. Every milligram must be added as nutrients.
YAN Targets by Wash Type
The right YAN target depends on your starting gravity and the type of wash. Higher gravity means more sugar and more stress on yeast — requiring more nitrogen to maintain healthy metabolism.
| Wash Type | Starting OG | Target YAN (mg/L) | Notes |
|---|---|---|---|
| Light sugar wash | 1.040–1.060 | 150–200 | Minimal stress, base nutrition |
| Standard sugar wash | 1.060–1.080 | 200–250 | Most common home distilling scenario |
| High-gravity wash | 1.080–1.100 | 250–350 | Osmotic stress demands more N |
| Very high gravity | 1.100+ | 350–450 | Risk of stuck ferment without full nutrition |
| Fruit / cider wash | any | Add 100–150 | Natural YAN present — supplement only |
| All-grain mash | any | Add 50–100 | High natural FAN from grain proteins |
DAP vs Fermaid-K vs Fermaid-O
Three products cover the majority of distiller nutrient needs, each contributing YAN differently and with different effects on fermentation character.
| Product | YAN per gram | Type | Best for |
|---|---|---|---|
| DAP (diammonium phosphate) | ~210 mg/L per g/L | Inorganic (ammoniacal N) | Cheap nitrogen top-up; use with organic sources |
| Fermaid-K | ~100 mg/L per g/L | Mixed (organic + inorganic) | All-purpose; good default for most washes |
| Fermaid-O | ~40 mg/L per g/L | Organic (amino acids) | TOSNA protocol; lowest H₂S risk; best character |
For spirit production, Fermaid-O is the preferred primary nutrient. It provides organic nitrogen — amino acids, sterols, and fatty acids — that DAP cannot supply. Fermaid-O-fed fermentations produce less hydrogen sulfide (rotten egg smell), lower fusel alcohol levels, and cleaner finishing character than DAP-only fermentations. DAP is an acceptable secondary addition at low doses but should not be the sole nitrogen source.
Enter your volume, OG, and YAN target — get precise DAP, Fermaid-K and Fermaid-O doses with the full TOSNA staggered addition schedule.
The TOSNA Protocol
TOSNA stands for Tailored Organic Staggered Nutrient Additions. It was developed by Meadmaker Sergio Moutela and widely adopted by the craft fermentation community. The core principle is simple: divide your total nutrient dose across four equal additions timed to the first third of fermentation, rather than adding everything at pitch.
This approach mirrors how yeast actually need nutrition. The highest nitrogen demand occurs during the active growth phase — the first 24–72 hours. Adding nutrients over this window keeps nitrogen available when yeast are building biomass and establishes the healthiest possible fermentation environment before the main sugar-conversion phase begins.
Worked Example — 25L Sugar Wash at 1.070 OG
Target YAN: 225 mg/L (standard wash, mid-range). Using Fermaid-O as the sole nutrient source.
- Total YAN needed: 225 mg/L × 25 L = 5,625 mg
- Fermaid-O YAN contribution: ~40 mg/L per g/L = 40 mg per gram per litre
- Total Fermaid-O needed: 5,625 ÷ 40 = ~140 g
- Per addition (÷4): ~35 g per addition at 0h, 24h, 48h, 72h
This is a large dose — Fermaid-O is a lower-concentration organic source. In practice, many distillers use a combination of Fermaid-O and a small amount of DAP (e.g. 5 g/25L DAP + Fermaid-O for organic amino acids) to reduce total volume while maintaining organic nitrogen quality. Use the Nutrient Calculator to dial in exact doses for your batch.
Fermaid-O organic yeast nutrient. The recommended primary nutrient for the TOSNA protocol. Provides organic nitrogen (amino acids), sterols and fatty acids — significantly lower fusel output and H₂S than DAP-only washes.
Why Nutrients Reduce Fusel Alcohols
The direct link between YAN and fusel production is well established. When yeast lack nitrogen, they are forced to synthesise all amino acids from scratch via the anabolic pathway — a metabolic process that produces higher alcohols (fusels) as unavoidable by-products. Providing adequate YAN means yeast can absorb pre-formed amino acids instead, eliminating the need for de-novo synthesis and dramatically reducing fusel output.
Studies on wine fermentation show that moving from zero-YAN conditions to adequate supplementation can reduce fusel alcohol production by 30–60%. For a home distiller running a pure sugar wash, this translates directly to cleaner, smoother spirit with less burn, less solvent character, and reduced hangover contribution. See the fusel alcohol guide for a full breakdown of causes and effects.
Frequently Asked Questions
Whisky Tasting Journal. Track every run — OG, FG, nutrient additions, ABV, cuts and tasting notes. 100 structured entries, score /100. 6 × 9 in, 116 pages, cream paper.