Nutrients

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

The solution is supplementing the must with yeast assimilable nitrogen (YAN) and other micronutrients before and during active fermentation. Done correctly, nutrient addition eliminates H2S, reduces lag phase, improves fermentation rate, and produces a cleaner finished mead.

YAN stands for Yeast Assimilable Nitrogen — the fraction of total nitrogen in the must that yeast can actually consume. It is measured in parts per million (ppm) and represents the sum of free amino nitrogen (FAN) and ammonium nitrogen.

The YAN requirement is calculated from sugar concentration and yeast nitrogen demand. The formula used by this calculator follows the Scott Labs 2020 methodology: multiply the sugar concentration in g/L by the demand multiplier for the selected yeast (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 1.110 OG traditional mead with a medium-demand yeast requires approximately 200–250 ppm YAN. Higher-gravity batches require more. Honey varieties with naturally elevated nitrogen (forest, eucalyptus) require less.

GoFerm PE (also called GoFerm Protect Evolution) is a yeast rehydration nutrient. It is not a YAN source — it contains no nitrogen the yeast can use for fermentation. Its role is to protect the yeast cell membrane during the rehydration step before pitching, improving cell viability and establishing a healthier fermentation from the start.

GoFerm PE supplies sterols, unsaturated fatty acids, and micronutrients that strengthen yeast membranes against osmotic stress. This is particularly important in high-gravity musts (OG > 1.110) where the sugar concentration creates significant osmotic pressure on newly rehydrated yeast cells.

The YAN density of GoFerm PE for calculator purposes is 30 ppm/g/L. It is always Step 0 in the SNA schedule — added to the rehydration water before the yeast, never directly to the must. Typical dose is 1.25× the weight of dry yeast.

Fermaid O is an organic nitrogen source derived from inactivated yeast cell walls. It provides free amino nitrogen (FAN) rather than ammonium ions, making it the most yeast-bioavailable form of nitrogen. It also contributes vitamins, minerals, and cell wall components.

The YAN density of Fermaid O is 40 ppm/g/L — the lowest of the three main nutrient products. This means you need more grams of Fermaid O per litre to achieve the same YAN as Fermaid K or DAP. However, its organic origin means fewer risks of yeast stress or off-flavour development compared to inorganic sources.

Fermaid O is the backbone of the TOSCA 2.0 protocol for all four staggered additions. It is appropriate at any stage of fermentation including after the 1/3 sugar break when DAP should no longer be used.

Fermaid K is a blended nutrient containing diammonium phosphate (DAP), inactivated yeast, yeast hulls, magnesium sulphate, and other minerals. It provides both organic and inorganic nitrogen plus micronutrients in a single product.

The YAN density of Fermaid K is 100 ppm/g/L — substantially higher than Fermaid O, meaning smaller quantities are required per addition. It is efficient but the inorganic DAP component means it carries the same 9% ABV cutoff restriction as DAP alone: do not use Fermaid K after the must has exceeded approximately 9% ABV.

Fermaid K is commonly used in TOSNA and TiOSNA protocols as a complement to Fermaid O. Many meadmakers use Fermaid O as the primary addition and Fermaid K for early additions when the yeast's nitrogen demand is highest.

DAP (diammonium phosphate) is the most concentrated YAN source at 210 ppm/g/L — roughly 5× the density of Fermaid O. Small quantities go a long way, which makes it easy to overdose. Excess DAP can produce harsh, rough character and harsh volatiles in the finished mead.

The critical constraint with DAP is the 9% ABV cutoff. At alcohol levels above approximately 9%, yeast cells begin to lose their ability to assimilate inorganic ammonium ions. Adding DAP above this threshold provides no benefit and can produce off-flavours. The calculator enforces this cutoff automatically — DAP additions are only scheduled for early fermentation steps.

DAP is best used as a supplement to organic nitrogen sources rather than as the primary YAN source. In the TOSCA 2.0 protocol it may appear in early additions at low doses alongside Fermaid O, but Fermaid O carries the full YAN load later in fermentation.

Three staggered nutrient addition protocols are commonly used in mead, all based on the principle that nitrogen should be added in multiple small doses during active fermentation rather than all at once.

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

The 1/3 sugar break is the point in fermentation where approximately one-third of the original sugar has been consumed by yeast. It is calculated from the original gravity: if OG is 1.110 (110 gravity points above water), the 1/3 break occurs at approximately 1.073 (110 × 2/3 = 73 points remaining).

The 1/3 break is significant for two reasons. First, it marks the point of maximum yeast population and metabolic activity — nutrient additions before this point are most effective because the yeast is in its most active growth phase. After this point, the population stabilises and additional nitrogen has diminishing returns. Second, inorganic nitrogen sources (DAP, Fermaid K) should not be added after the 1/3 break to avoid off-flavour formation.

In gravity-based protocols (TOSNA, TiOSNA), the final nutrient addition is timed to coincide with the 1/3 break, measured with a hydrometer or refractometer. The calculator displays the target 1/3 break gravity in the outputs panel for reference.