What Is TOSNA & SNA? The Beginner's Guide to Mead Nutrient Scheduling

If your mead smells like rotten eggs or stalled halfway through fermentation, the culprit is almost certainly a nutrient problem — specifically, too little Yeast Assimilable Nitrogen (YAN) delivered at the wrong time. TOSNA (Tailored Organic Staggered Nutrient Addition) and its cousin SNA (Staggered Nutrient Addition) are the two protocols that fix this, and understanding the difference between them is one of the most important skills a new meadmaker can develop. Both methods split nutrients into multiple timed doses rather than dumping everything in at once, but they diverge sharply on which nutrients they use and how quantities are calculated per gravity point.

• What TOSNA stands for: Tailored Organic Staggered Nutrient Addition — developed by Sergio Moutela, it uses only organic nitrogen (Fermaid-O) and GoFerm rehydration, avoiding inorganic sources like DAP. ^[1]
• What SNA stands for: Staggered Nutrient Addition — the broader category of split-dose feeding that often includes Fermaid-K and DAP alongside or instead of Fermaid-O. ^[7]
• Why honey needs both: Honey is naturally almost devoid of YAN; without supplementation, yeast become stressed, producing sulfur off-aromas, fusel alcohols, and stalled gravity readings. ^[5]
• The four-addition schedule: Both TOSNA and SNA typically call for additions at pitch, 24 hours, 48 hours, and the one-third sugar break (when about one-third of sugars have been consumed). ^[5]
• Yeast matters: Low-demand strains like Lalvin 71B and EC-1118 use a YAN requirement factor of 0.75, while high-demand strains like RC-212 use a factor of 1.25, directly changing how many grams of nutrient you add. ^[4]
• The H2S risk: Adding DAP above 65 °F (18 °C) or during vigorous mid-fermentation can cause yeast to produce hydrogen sulfide — the notorious rotten-egg fault. ^[8]

TL;DR: TOSNA is the dominant modern mead nutrient protocol — use it to calculate how much Fermaid-O your yeast needs per gravity point, then spread that dose across four staggered additions to build clean, healthy fermentations from day one.

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Why Honey Needs Nitrogen: The Science Behind YAN

What Is Yeast Assimilable Nitrogen?

YAN refers to the pool of nitrogen compounds — primarily free amino acids and ammonium ions — that yeast can actually metabolise during fermentation. Unlike grape must, which contributes 150–300 mg/L of YAN naturally, honey contributes virtually zero usable nitrogen to the must. ^[5] This creates a nutritional vacuum: yeast have all the sugar they could want but none of the building blocks needed for healthy cell replication, alcohol tolerance, and aroma compound management.

When YAN is too low, the yeast stress response kicks in. Stressed cells ramp up production of hydrogen sulfide (H₂S) — a gas that smells exactly like rotten eggs — and fusel alcohols, the harsh "rocket fuel" compounds that give badly-made mead a solventy, headache-inducing burn. ^[3] They may also completely stall, leaving residual sweetness and a gravity reading that stops moving despite seemingly active airlocks. ^[5]

YAN is measured in parts per million (ppm) or milligrams per litre (mg/L) — those two units are numerically equivalent. A well-nourished low-gravity mead might need as little as 75 ppm of YAN, while a high-gravity sack mead at 1.130 OG can require 300 ppm or more. ^[4]

How YAN Demand Scales with Gravity

The TOSNA protocol (versions 2.0 and 3.0) ties YAN requirements directly to the sugar concentration of the must. The core formula, sourced from the Scott Labs fermentation handbook, works like this ^[4]:

Total Fermaid-O (g) = (Brix × 10 × N-factor × batch size in gallons) ÷ 50

Where Brix × 10 converts to sugar in grams per litre, and the N-factor is a per-yeast-strain multiplier:

So a 5-gallon traditional mead at 25 Brix fermented with Lalvin 71B (low demand) would need: 25 × 10 × 0.75 × 5 ÷ 50 = 18.75 g of Fermaid-O total, split across four equal additions of roughly 4.7 g each. ^[4]

Switch to a high-demand yeast like RC-212 at the same gravity and that jumps to 31.25 g total. Getting this calculation right is the whole game — both overfeeding and underfeeding have real consequences. ^[2]

Why Inorganic Nitrogen (DAP) Is a Double-Edged Sword

DAP (Diammonium Phosphate) delivers inorganic ammonium nitrogen cheaply and quickly, which is why it became popular in early home meadmaking. The problem is that DAP provides only nitrogen, with no vitamins, minerals, or amino acids. Used as the sole nutrient source, it can turbocharge the early growth phase, but yeast that run out of micronutrients mid-ferment still stall — just later and with more fusel by-products. ^[3]

More critically, DAP added above 65 °F (18 °C) or during the vigorous middle phase of fermentation can trigger H₂S production in a way that organic nitrogen does not. ^[8] This is why TOSNA 2.0 dropped DAP entirely in favour of Fermaid-O, an inactivated yeast derivative that provides a full spectrum of amino acids, growth factors, and vitamins in a form yeast assimilate more efficiently. ^[3]

Traditional SNA protocols that blend Fermaid-K (which contains both organic and inorganic fractions) with DAP can still produce excellent meads — but they require tighter temperature discipline and timing precision to avoid the H₂S trap. ^[7]

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The TOSNA Schedule: What to Add and When

The Four-Addition Framework

Both TOSNA and SNA divide the total calculated nutrient dose into four equal additions timed to specific fermentation milestones ^[5]:

1. Addition 1 — Pitch or lag phase (0–24 hours): Added just after pitching, while yeast are reproducing rapidly and nitrogen uptake is at its peak.
2. Addition 2 — 24 hours after pitch: Fermentation should be visibly active; this keeps nitrogen available as the yeast population peaks.
3. Addition 3 — 48 hours after pitch: Fermentation is hitting its stride; this addition supports alcohol tolerance development.
4. Addition 4 — One-third sugar break: When approximately one-third of the total sugars have been consumed (gravity has dropped by one-third of the difference between OG and an assumed FG). After this point, yeast have cleared the riskiest phase of fermentation and no further nutrient additions are needed. ^[5]

"The difference between a mead made with good nutrient practice and one made without is dramatic — and it shows up in the glass immediately, not after a year of aging." — Great Fermentations, Mead Nutrients Explained ^[1]

This four-stage cadence is far more forgiving than a single upfront dump because it matches nutrient availability to yeast demand. Early additions power cell replication; middle additions shore up alcohol tolerance; the final addition at the sugar break ensures a clean runway to the finish line. ^[5]

GoFerm: The Addition Before the Additions

Before the first nutrient dose — before the yeast even touch the must — comes GoFerm, a rehydration nutrient added to the warm (104 °F / 40 °C) water used to hydrate dried yeast. GoFerm loads yeast cells with sterols and micronutrients before they experience the osmotic shock of a high-sugar must, dramatically improving viability and stress resistance. ^[8]

Critically, GoFerm is only for yeast rehydration. It should never be added directly to the must during fermentation — doing so wastes its benefits and can contribute off-flavours at high doses. ^[8] For most 5-gallon batches, 12.5 g of GoFerm dissolved in 250 mL of 104 °F water is the standard starting point per the Scott Labs fermentation handbook.

Tracking the One-Third Sugar Break

The most important timing checkpoint is the one-third sugar break — the gravity reading at which roughly one-third of the fermentable sugars have been consumed. To find it, calculate: OG gravity points minus one-third of total gravity drop. For a mead starting at 1.090 targeting 1.000, the gravity drop is 90 points; one-third is 30 points, so the sugar break lands at roughly 1.060 SG. ^[4]

Tracking this accurately is exactly why pairing your nutrient protocol with a reliable ABV and hydrometer tracking tool pays dividends — missing the sugar break by more than a day or two means your fourth addition is either wasted or potentially triggers fusel production. ^[4]

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Common TOSNA & SNA Mistakes (And How to Avoid Them)

Mistake 1 — Using One-Size-Fits-All Dosing

The most common error beginners make is reaching for a generic "one teaspoon per gallon" rule copied from a forum post without checking which yeast they're using or what their starting gravity is. ^[2] As the TOSNA formula shows, a 1.130 high-gravity mead with a high-demand yeast needs nearly three times more Fermaid-O than a quick hydromel at 1.040 with a low-demand strain. ^[4]

The fix: always calculate using the gravity-and-yeast formula above, or use a dedicated SNA calculator — MeadMakr's Advanced SNA Calculator is one of the most used tools in the community because it handles all the maths based on your specific inputs. If you're new to the underlying calculations, our guide to SG-to-Brix conversions for mead walks through why the standard wine conversion table gives inaccurate readings that will throw off your nutrient totals.

Mistake 2 — Adding DAP at the Wrong Temperature or Time

DAP is pH-sensitive and temperature-sensitive. When added above 65 °F (18 °C) or after the initial 48-hour window when fermentation is most vigorous, DAP can cause yeast to off-gas H₂S in noticeable quantities, turning a promising batch into something that smells like a sulfur spring. ^[8] If you smell rotten eggs during fermentation, this is almost always the cause.

The fix: if you're using any inorganic nitrogen, add it only during the first 24–48 hours when must temperatures are cooler, or switch entirely to TOSNA's Fermaid-O-only protocol, which eliminates the H₂S risk. ^[8] Dropping a copper mesh wine whip into sulfur-tainted mead for a few days can also help bind up dissolved H₂S, but it's better not to create the problem in the first place.

Mistake 3 — Nutrient Additions After the One-Third Sugar Break

Nutrients added after one-third of the sugars are gone have diminishing returns on fermentation health — but they can create real problems. Late DAP additions are a known fusel alcohol precursor. Even organic Fermaid-O added after the sugar break can leave un-metabolised nitrogen behind, providing food for spoilage organisms and potentially contributing a salty or umami off-note in finished mead. ^[5]

The fix: respect the sugar break as a hard stop. Track gravity with a hydrometer at every addition and stop nutrient additions the moment you hit the one-third mark regardless of how many days have passed. ^[5]

Mistake 4 — Skipping pH Monitoring

Fermentation naturally drives the must pH downward. A must that crashes below pH 3.5 creates an acidic environment where even well-fed yeast struggle to continue. ^[2] Honey musts often have insufficient buffering capacity to prevent this drop, especially in high-gravity batches. TOSNA's use of Fermaid-O has a mild alkaline buffering effect compared to DAP, which actually acidifies the must — one of the key advantages of going organic. ^[7]

"Underfeeding your mead will undoubtedly cause many of the issues experienced by most amateur mead makers, such as stuck fermentations, severe drop in pH, and an increase in sulfur and fusel alcohol production." — Mead Made Right, Nutrient Additions ^[2]

The fix: check pH at each addition milestone with a calibrated pH meter or indicator strips. If pH drops below 3.7, a small addition of potassium bicarbonate or calcium carbonate can raise it back into the safe range (3.7–4.0) without affecting flavour.

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Putting It All Together: A Beginner TOSNA Walkthrough

Step-by-Step for a Standard 5-Gallon Traditional Mead

Here's a concrete worked example for a beginner's 5-gallon traditional mead at approximately 1.100 OG (25 Brix) using Lalvin 71B (low N demand):

Step 1 — Calculate total Fermaid-O: 25 Brix × 10 (g/L sugar) × 0.75 (low N-factor) × 5 gal ÷ 50 = 18.75 g total ^[4]

Step 2 — GoFerm rehydration: Rehydrate 71B in 12.5 g GoFerm dissolved in 250 mL of 104 °F water. Pitch when the temperature gap between rehydration water and must is under 10 °F.

Step 3 — Four equal additions: Divide 18.75 g into four portions of approximately 4.7 g each:

Step 4 — Degas before each addition: Stir or whip the must briskly for 30–60 seconds before each addition to drive off CO₂. Nutrients added to a CO₂-saturated must can cause violent foam-over. ^[5]

Step 5 — Track gravity, not just time: If fermentation is slow and the sugar break hasn't occurred by day 5, wait for the gravity reading — don't add the fourth dose early. Conversely, if your mead is ripping through sugar and hits the break at day 3, add it then and stop. ^[5]

Scaling for Different Mead Styles

The formula scales predictably ^[6]:

• Melomel (fruit mead): Multiply total Fermaid-O by 0.8 — fruit contributes some natural YAN of its own.
• Sack mead (high-gravity, 1.130+): Multiply by 1.3 — higher alcohol stress demands more nutritional support.
• Hydromel (low-gravity, under 1.060): Multiply by 0.6 — fewer sugars mean far less nitrogen is needed.

As your batches grow in complexity — multiple honey varieties, high-gravity blends, back-sweetened melomels — you'll eventually want to blend finished batches, which is where tools like MeadMakr's BatchBlendr become invaluable for hitting your final target numbers precisely.

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Mastering TOSNA and SNA is the single highest-leverage skill a new meadmaker can develop, but calculating the right doses batch after batch — especially across different yeasts, honey loads, and styles — is exactly where dedicated tools save hours of spreadsheet work. MeadMakr brings the Advanced SNA Calculator, ABV tracker, BatchBlendr, and SG-to-Brix converter into one purpose-built mead app, so every nutrient addition you make is grounded in the right numbers for your specific batch. Run your next mead through a proper TOSNA schedule and taste the difference it makes.