Nutrients & TOSCA 2.0

Honey is almost nutritionally void from a yeast's perspective: it is roughly 80% sugar and 20% water, with negligible minerals, vitamins, or amino acids. Grape juice, by contrast, naturally contains everything a yeast cell needs: nitrogen, minerals, lipids, and vitamins. Mead is essentially a solution of sugar in water, and yeast fermenting it without supplementation will stress, produce hydrogen sulphide (a rotten-egg off-flavour), stall, or produce excessive volatile acidity.

The fix is supplementing the must with nitrogen and other micronutrients before and during active fermentation. Done correctly, nutrient addition eliminates hydrogen sulphide, reduces lag phase (the quiet period after pitching before fermentation visibly starts), improves fermentation rate, and produces a cleaner finished mead.

Yeast assimilable nitrogen (YAN) is the fraction of total nitrogen in the must that yeast can actually use. It is measured in parts per million (ppm) and is the sum of two components: free amino nitrogen (FAN), from amino acids, and ammonium nitrogen, from ammonium ions.

The YAN requirement for a batch is calculated from its sugar concentration and the selected yeast's nitrogen demand. This calculator follows the Scott Labs 2020 methodology: multiply the sugar concentration (g/L) by the yeast's demand multiplier (Low = 0.75, Medium = 0.90, High = 1.25, Extra-High = 1.50), then subtract any honey-derived YAN offset (Forest honey: 15 ppm, Eucalyptus: 10 ppm).

A typical mead with an original gravity (OG) of 1.110 and a medium-demand yeast requires approximately 200–250 ppm YAN. Higher-gravity batches need more; honey varieties with naturally elevated nitrogen, such as forest or eucalyptus honey, need less.

A single large nitrogen addition at pitch oversupplies the must early in fermentation, when the yeast population is still small, then leaves the yeast undersupplied later during peak population growth, the phase of highest demand. It also creates a nitrogen spike that can stress the yeast or produce off-flavours.

Spreading the same total YAN dose across several smaller additions instead matches supply to demand. Early additions support the exponential growth phase, when new cells are dividing rapidly; later additions maintain nitrogen availability as the population peaks and the fermentation rate reaches its maximum. The total YAN delivered is the same regardless of timing — the difference is when the yeast actually needs it.

Staggered additions also reduce the risk of foam-over from CO₂ production triggered by sudden nitrogen availability, a real hazard with single-dose approaches at high gravity.

TOSCA 2.0 (Time-based Organic Staggered Compound Addition) is the current best-practice protocol for applying staggered dosing in mead, developed by Scott Laboratories and updated in their 2020 Fermentation Handbook. Each word in the name describes a principle: "Time-based" means additions are scheduled by hours after pitch rather than gravity milestones; "Organic" refers to the primary nitrogen source, Fermaid O; "Staggered" means the total dose is divided across multiple additions rather than one; "Compound" means multiple nutrient types are used together.

The protocol works across all common mead yeast strains and OG ranges. The calculator generates a TOSCA 2.0 schedule automatically from your yeast selection and honey quantities, and the schedule is saved with the batch for reference during fermentation.

TOSCA 2.0 defines four post-pitch additions at approximately equal intervals across the first 96 hours of fermentation. Each addition receives one quarter of the total nutrient dose. GoFerm PE (Step 0) is added before pitch, to the warm yeast rehydration water rather than the must itself, and is not counted in the four-addition numbering: it prepares the yeast cells for pitching rather than feeding the fermentation that follows — see Choosing your nutrients below for what GoFerm PE actually does.

The table below uses "±" to mark optional additions. Fermaid O is the backbone nutrient at every step. Diammonium phosphate (DAP), an inorganic (mineral-based) nitrogen source, and Fermaid K (a blended product that itself contains DAP) can be added alongside it early on, but only for a limited window: once alcohol by volume (ABV) rises above roughly 9%, yeast cells lose the ability to assimilate inorganic nitrogen efficiently, and using DAP past that point risks harsh, solvent-like off-flavours rather than helping fermentation. That is why DAP and Fermaid K are confined to the first two additions, and the schedule switches to organic nitrogen only (Fermaid O alone) for the final two.

The timing is approximate (±2 hours is fine either way). What matters is spreading the additions roughly evenly across the first four days rather than bunching them together: that even spread is what actually reduces the nitrogen-spike stress on the yeast that staggered protocols are designed to avoid. Degas the must before each addition (stir gently or use a drill-mounted degasser) to release trapped CO₂ first, since adding nutrients to a CO₂-saturated must risks a sudden foam-over.

TOSCA 2.0 uses four products, each with a different role and a different YAN density (how much yeast assimilable nitrogen a gram of product delivers per litre of must).

The 1/3 sugar break is the point in fermentation where approximately one-third of the original fermentable sugar has been consumed. It is calculated from the OG: for a must with an OG of 1.110 (110 gravity points above water), the 1/3 break occurs at approximately 1.073 (roughly two-thirds of the points, 73, still remaining).

The break marks two things. First, it is roughly where yeast population and metabolic activity peak, so nutrient additions before this point are the most effective; after it, the population stabilises and additional nitrogen has diminishing returns. Second, it is the point after which inorganic nitrogen (DAP and Fermaid K) should no longer be added, for the same reason described in Choosing your nutrients above: yeast loses the ability to assimilate inorganic ammonium efficiently around the alcohol level this milestone roughly corresponds to.

TOSCA 2.0's time-based schedule keeps every addition within the first 96 hours, which for most normal-gravity batches lands comfortably before the 1/3 break is reached — this is why TOSCA doesn't need a hydrometer at all. Gravity-based protocols work differently: see TOSCA vs TOSNA vs TiOSNA below. If your fermentation is unusually fast (a high-demand yeast, a warm room), monitor gravity and switch to Fermaid O only for any later addition if the 1/3 break arrives before Step 4.

TOSCA 2.0, TOSNA (Time-Organic Staggered Nutrient Addition), and TiOSNA (Time and Organic Staggered Nutrient Addition) are all staggered nutrient protocols built on the same principle: nitrogen added in several smaller doses beats one large dose. They differ only in how addition timing is determined.

TOSCA 2.0 is the recommended protocol for most home meadmakers: its time-based approach requires no gravity measurements and produces consistent results, which is why the calculator generates TOSCA 2.0 schedules by default.

Adding all nutrients at pitch. Front-loading the full nutrient dose creates a nitrogen spike that stresses yeast and may cause foaming or off-flavour formation. The entire point of the staggered approach is to match supply to demand.

Skipping GoFerm PE. Many meadmakers skip the rehydration step and pitch directly. GoFerm PE protects yeast cell membranes during the osmotic shock of rehydration: omitting it doesn't always cause a problem, but it increases early yeast mortality and extends lag phase unnecessarily.

Using DAP as the sole nutrient. DAP provides inorganic nitrogen but no micronutrients, vitamins, or fatty acids. Relying on it alone produces meads prone to hydrogen sulphide (H2S) off-flavours and stuck fermentations. Use organic sources (Fermaid O) as the backbone with DAP only as a supplement in early additions.

Not degassing before adding nutrients. Adding nutrients to a CO₂-saturated must causes rapid outgassing. Always stir or degas the must before each addition to prevent foam-over, especially in carboys and fermenters with narrow necks.

Ignoring pH. Nutrient additions are ineffective if must pH is below 3.2. Yeast cannot assimilate nitrogen efficiently at low pH regardless of how much is present. Always check and correct pH before pitching, particularly in fruit meads and batches using forest or eucalyptus honey.