When making a straight honey mead, you’re asking the yeast to perform a gargantuan task — take the initial must (unfermented mead) from a high starting gravity down to a reasonable finishing gravity. In many cases, a drop in apparent attenuation of around 24 °Brix/SG 1.101 is desired. When accomplishing this, you also want the yeast to experience as little stress as possible. This will minimize the off characters produced by stressed yeast and allow the fermentation to progress in an orderly fashion. One key to achieving an ordered mead fermentation is ensuring that the yeast have adequate nutrition throughout the fermentation — and for this, both the amount and timing of nutrient additions play a role.
Yeast need nitrogen to survive and reproduce, but mead musts typically contain far too little free amino nitrogen (FAN) to support a fermentation that finishes in a reasonable amount of time and reaches a desirable final gravity. To support the fermentation of a must around 25 °Brix (SG 1.106), the yeast require about 300 ppm FAN. However, mead musts made from honey alone are usually under 20 ppm FAN. (Musts that include fruit may be substantially higher). To supply the yeast with enough nitrogen, and also other needed micronutrients, many mead makers rely on a blend of Fermaid-K and DAP (diammonium phosphate). The diammonium phosphate — a common wine yeast nutrient sold at any home winemaking shop — supplies the yeast with nitrogen. Fermaid-K — a complete yeast nutrient, which you’ll likely find in the same section of the wine shop as the DAP — supplies the must with not only nitrogen, but a range of other vitamins, minerals and biomolecules to support a healthy fermentation. Some meadmakers will also rehydrate their yeast with Go-Ferm, a yeast nutrient formulated to be added during dried yeast rehydration.
For most 5-gallon (19-L) mead recipes, the total amount of yeast nutrient added is in the range of 2.5 tsp. to 4 tsp. of mixed yeast nutrient. Dry meads, which start at lower original gravities, are on the low end of this range and the bigger sweet meads are at the high end. The blend of yeast nutrients usually ranges from a ratio of 1:1 to 2:1 DAP to Fermaid-K.
In the last few years, most mead makers have favored adding the nutrients in a staggered fashion. The total amount of nutrients to be added is split into 2 to 4 aliquots and added at separate times. The idea is to not overload the yeast initially with nutrients, but to supply them as needed. Early doses may be added when the must is prepared and/or when the first evidence of fermentation is indicated. And later doses are added up until the point that a third of the sugar in the must has been depleted (as indicated by hydrometer reading).
As an example of how a staggered nutrient addition might work, let’s say we’re making 5 gallons (19 L) of traditional sweet mead with a starting gravity of 28 °Brix (SG 1.120). We expect it to finish at about 2.5 °Brix (SG 1.010), a total drop of about 26 °Brix (SG 1.110). When we prepare the must, we rehydrate the yeast in water with added Go-Ferm (using the recommended dosage of 5 g per 100 mL of water) — this is our first nutrient addition. Then we wait until fermentation becomes evident, and a second nutrient addition is made — this time of 1 tsp. of DAP and 1 tsp of Fermaid-K. (Aerating the fermenting mead at this point may also help.) Then we wait until the hydrometer reading drops to around 20 °Brix (SG 1.084) and add our final nutrient addition — 1/2 tsp. DAP and 1/2 tsp Fermaid-K. (You would not want to aerate the mead at this stage.)
If you’re working with an old mead recipe that specifies adding all the nutrient at the beginning, reduce the total amount added to between two-third and three-quarters of the amount specified, as the yeast are assumed to make more efficient use of the nutrients when additions are staggered.
Staggering your yeast nutrient additions should supply the yeast with adequate nutrition when they need it most. In turn, this is likely to produce a fermentation that proceeds quickly, finishes at an appropriate final gravity and results in a wonderful mead.