Mead Fundamentals: Nutrients, TOSNA Protocol, and Clarity

Mead is wine made from honey. It is one of humanity's oldest fermented beverages and is undergoing a significant artisanal revival. Good mead is complex, fragrant, and balanced — the character of the honey front and centre. Poor mead smells like a chemistry lab. The difference almost always comes down to nutrients.

Understanding Why Mead is Challenging

Honey is an unusual fermentation substrate. Unlike grape juice, which contains amino acids, vitamins, minerals, and other compounds that nourish yeast, honey is essentially pure sugar with antimicrobial properties. It is:

• Very high in sugar (OG 1.100–1.150 typical for traditional mead)
• Low in Yeast Assimilable Nitrogen (YAN) — honey contains almost no nitrogen
• Naturally antimicrobial due to low water activity and hydrogen peroxide production
• Low in vitamins and minerals essential for yeast metabolism

This means mead must be supplemented aggressively to produce healthy fermentation without the off-flavour compounds that nutrient-stressed yeast produce — primarily hydrogen sulphide (H₂S, rotten egg smell) and fusel alcohols.

Yeast Assimilable Nitrogen (YAN)

YAN is the measure of nitrogen available to yeast for growth and fermentation. It consists of:

• Free amino nitrogen (FAN): amino acids from grape protein (high in grape juice, near-zero in honey)
• Ammonia nitrogen: from ammonium salts in must

Honey contains essentially no YAN — typically less than 10 mg/L versus 150–300 mg/L in grape juice. All the nitrogen must be added.

YAN Target for Mead

The YAN requirement is approximately proportional to the initial sugar concentration:

YAN needed (mg/L) = °Brix × 2.5

For a mead at OG 1.120 (approximately 29 Brix): 29 × 2.5 = 72.5 mg/L per Brix × Brix = 72.5 mg/L actual target

Wait — that formula is actually:

YAN target (mg/L) = Brix of must × some coefficient

A widely used TOSNA 3.0 calculator target for traditional mead: 200–250 mg/L total YAN for a standard gravity mead (OG 1.090–1.120).

For high-gravity meads (OG 1.130+): 300–400 mg/L YAN.

Nutrient Sources

Best practice: Use Fermaid-O exclusively, or Fermaid-O for the bulk of additions with a small amount of Fermaid-K. Avoid pure DAP in mead — honey's delicate aromatics are easily masked by the harshness that stressed yeast produce.

TOSNA Protocol (Tailored Organic Staggered Nutrient Addition)

TOSNA was developed by Sergio Moutela for mead fermentation. The key insight: staggered additions keep YAN available throughout fermentation without overwhelming the yeast with a single dose. "Organic" refers to using Fermaid-O (organic nitrogen) rather than DAP.

TOSNA 3.0 Schedule

Calculate your total Fermaid-O target and split into 4 equal additions:

Example: 20L mead, OG 1.110, target 200 mg/L YAN
Fermaid-O contains 40 mg/L YAN per g/L
Total Fermaid-O needed: (200 mg/L ÷ 40) × 20L = 100g Fermaid-O total
Split into 4 × 25g additions

Critical rule: Never add nutrients after 1/3 sugar depletion (typically gravity drop of 1/3 of OG-FG range). Beyond this point, yeast have enough internal reserves, and late nutrient additions can produce ethyl carbamate (a potential carcinogen) and other off-compounds.

For OG 1.110, FG target 0.998:
Total gravity drop = 0.112
1/3 sugar depletion = 0.112 ÷ 3 = 0.037
1/3 depletion point: 1.110 − 0.037 = gravity 1.073

Stop adding nutrients once gravity reaches 1.073.

Degassing

Honey musts must be degassed regularly during TOSNA additions. CO₂ dissolved in the must makes it appear lighter than it is (hydrometer reads incorrectly) and can inhibit yeast growth. Each time you add nutrients:

1. Stir vigorously for 1–2 minutes to release CO₂
2. Allow foam to subside
3. Add nutrients
4. Stir again gently to distribute

Yeast Selection for Mead

Achieving Clarity

Mead is notoriously slow to clear without assistance. Several factors cause haze:

• Protein haze: denatured proteins from honey
• Yeast in suspension: slow-flocculating strains or yeast shock
• Pectin haze: if fruit was used
• Starch or oligosaccharides: from some honeys

Fining agents for mead

1. Bentonite (0.5–1g/L): removes protein. Standard treatment. Can strip honey aroma if overdone.

2. Kieselsol + Chitosan (Superkleer): fast-clearing combination. Kieselsol is negatively charged; chitosan is positively charged — they attract each other and drag particles to the bottom. Works in 3–7 days. Effective for most meads.

3. Isinglass: derived from fish swim bladders. Excellent for whites and light meads. Not vegan.

4. Sparkalloid: polysaccharide fining, widely used in mead. Works slowly (weeks to months).

5. Cold crashing: chilling the mead to 1–4°C causes proteins and yeast to precipitate. Works well and adds no fining agents.

Patience

The simplest approach is time. Mead left undisturbed at a stable temperature for 3–6 months will clear to brilliance without any fining. Each racking clarifies further. Filtration (0.5–1 micron) achieves commercial polish levels if needed.

Checklist for Good Mead

• OG measured before pitching
• Yeast rehydrated in Go-Ferm
• TOSNA schedule calculated and followed
• Degassed at every nutrient addition
• Nutrient additions stopped at 1/3 sugar depletion
• Temperature controlled to strain's optimal range
• MLF prevented (SO₂ added after primary fermentation)
• Gravity stable before bottling
• Clarity confirmed before bottling