Must, nutrients and stabilizing

These are the numbers a mead, a cider or a wine asks for and a beer mostly does not. They live in the journal as calculator blocks, so the inputs stay on the page beside the notes they belong to. None of them is ours: each follows the working a mead maker or a winemaker would do by hand, and cites where that working comes from.

Sugar to a gravity

Honey, sucrose and dextrose each raise gravity by a known amount per kilogram in a liter, and the calculation is that yield times the gap between the gravity you have and the gravity you want. We use the figures the common calculators use: 46.2 points per pound per gallon for sucrose and 42 for dextrose, from Palmer, and 35 for honey, from Schramm, which allows for honey’s water. The answer does not count the sugar’s own volume. A kilogram of honey adds about 0.7 liters, so a must built to a volume needs that room in the fermenter, and a mead you backsweeten ends up slightly larger than it was.

The same arithmetic serves three jobs: building a honey must, chaptalising a thin juice, and sweetening a finished drink you have already stabilized. The block does not know which you are doing and does not need to.

Nutrients

Honey has almost no nitrogen, and a mead fermented without any is the mead that takes a year to lose its sulfur. TOSNA, Sergio Moutela’s staggered nutrient schedule, feeds the yeast Fermaid O in four additions so the nitrogen arrives while the yeast can still use it. The total is set by the must’s gravity and by how hungry the strain is, low, medium or high, and the block splits it into four: at 24, 48 and 72 hours, and at the one-third sugar break or day seven, whichever comes first. Nothing goes in at pitch. We follow the published TOSNA 3.0 calculator and cite it as a calculator, because that is what it is.

Sulfite

Sulfite protects a cider or a wine only in its molecular form, and how much of the free SO₂ is molecular depends on pH: at pH 3.0 a little goes a long way, and at pH 3.8 it takes six times as much. The block takes your pH and the molecular target, 0.8 mg/L by convention, works back through the pKa of 1.81 to the free SO₂ that needs to be there, and converts to grams of potassium metabisulfite at 57.6 % SO₂ by mass. Tell it the free SO₂ you already have and it doses the difference. A cider much above pH 3.8 is one Lea would tell you to acidify first, and the note says so.

Sorbate

Potassium sorbate stops a stabilized drink refermenting when you sweeten it. It works with sulfite, not instead of it, and it needs less as the alcohol rises: Peynaud’s table runs from 150 mg/L of sorbic acid at 10 % down to 50 at 14 %, and we interpolate between his rows. Potassium sorbate is about three-quarters sorbic acid by mass, so the grams come out a little higher than the acid figure. Never use it on a wine that might still go through malolactic fermentation; the geranium note that produces cannot be undone.

Acid

Titratable acidity is reported as tartaric, so a gram of tartaric acid per liter raises it by one gram per liter, and malic or citric raise it a little more per gram because their equivalent weights are lower. The block takes where you are, where you want to be and which acid you have, and hands back the grams. Lowering acidity is a different job with different chemistry, and a target below the current figure answers zero rather than a negative dose.

The Pearson square

Blending two lots to a target is the winemaker’s oldest arithmetic: the share of each is set by how far the target sits between them. The block takes the two values, in ABV or gravity points, the target and the total volume, and gives the volume of each. A target outside the two values cannot be reached by blending them, and the block says so instead of answering.

The same arithmetic is behind Split for a target… on a blending session with exactly two beers in it, where the two ABVs are already on the cards and the answer goes back onto them.

The must these numbers come from

Reference pale ale — 20 L into the fermenter, a 60 minute boil.

Grist	Amount	Color
Crisp Maris Otter Pale Ale Malt	4.5 kg	2.8 °L
Thomas Fawcett Caramalt	0.35 kg	9.9 °L

Hops	Amount	Alpha	Addition
Magnum	15 g	13.5 %	60 min boil
Cascade	30 g	6.8 %	10 min boil
Citra	40 g	13 %	20 min stand at 80 °C

It comes out at
Original gravity	1.0507
Final gravity	1.0094
Alcohol	5.52 %
Bitterness	35.66 IBU
Color	5.14 SRM (10.12 EBC)
Into the fermenter	20 L

The numbers

Sugar to reach a gravity

5.85 kg, from extract-conservation.

kg = (target points − current points) × volume_L / yield in points·L/kg
⇒ Sugar to reach a gravity = 5.85 kg

Input	Value	Unit
Gravity now	1.02	SG
Gravity wanted	1.11	SG
Volume	19	L
Sugar	honey	—
Gravity points to add	90	—
Yield of the sugar	35	points per lb per US gal
Yield of the sugar	292.09	points·L/kg

What it assumes:

• Dosed as honey, at 35 points per pound per US gallon.
• The sugar’s own volume is not counted. A kilogram of honey adds about 0.7 L, so leave room for it in the fermenter.
• The same arithmetic serves a honey must, a chaptalized juice and a stabilized drink being backsweetened.

Sources:

• The Compleat Meadmaker — Ken Schramm, Brewers Publications, 2003

Fermaid-O for the ferment

23.43 g, from tosna-3.

g = (((Brix × 10) × N requirement factor) / 50) × batch size in gallons, split four ways
⇒ Fermaid-O for the ferment = 23.43 g

Input	Value	Unit
Volume	19	L
Original gravity	1.11	SG
Strength in Brix	25.93	°Bx
Demand	medium	—
Nitrogen factor	0.9	—
Nitrogen target	233.4	ppm
Batch size	5.02	US gal
Each of the four additions	5.86	g

What it assumes:

• Split into 4 equal additions: 24, 48 and 72 hours after pitching, and at the 1/3 sugar break of fermentation or day 7, whichever comes first.
• Honey carries about 30 ppm of nitrogen of its own, against the 150–200 ppm the published protocol says a healthy fermentation wants.
• The ÷ 50 is the published divisor, grams of Fermaid-O per US gallon per ppm of nitrogen. TOSNA does not state Fermaid-O’s YAN per gram, so neither does this.
• Organic nitrogen only. Fermaid-K and DAP are a different protocol, and this does not dose them.

Sources:

• Nutrient Additions: TOSNA, the Tailored Organic Staggered Nutrient Addition — Sergio Moutela (Mead Made Right)

Potassium metabisulfite

1.05 g, from molecular-so2-at-ph.

free SO₂ = molecular target × (1 + 10^(pH − 1.81)); g = ΔSO₂ × V / 1000 / 0.576
⇒ Potassium metabisulfite = 1.05 g

Input	Value	Unit
Volume	19	L
pH	3.4	—
Molecular SO₂ target	0.8	mg/L
Free SO₂ already there	0	mg/L
Free SO₂ needed	31.9	mg/L
Molecular share of the free SO₂	0.0251	fraction
SO₂ in potassium metabisulfite	57.6	%

What it assumes:

• Only the molecular SO₂ does the work, and the fraction of free SO₂ that is molecular falls tenfold for every unit of pH.
• The free SO₂ already present is the figure you measured. Nothing here estimates it from an earlier addition, because binding cannot be computed from the dose.

Sources:

• Principles and Practices of Winemaking — Roger B. Boulton, Vernon L. Singleton, Linda F. Bisson & Ralph E. Kunkee, 1996
• Craft Cider Making — Andrew Lea, 2008

Potassium sorbate

2.54 g, from peynaud-sorbic-by-alcohol.

g = sorbic acid mg/L (from the alcohol) × V / 1000 / 0.747
⇒ Potassium sorbate = 2.54 g

Input	Value	Unit
Volume	19	L
Alcohol	12	%
Sorbic acid needed	100	mg/L
Sorbic acid in potassium sorbate	74.7	%

What it assumes:

• Peynaud’s table runs 150 mg/L of sorbic acid up to 10 % alcohol, then 125, 100, 75 and 50 at 11, 12, 13 and 14 %. Between rows it is interpolated; outside them it is held flat.
• Only alongside sulfite. Sorbate stops yeast budding and does nothing to bacteria.
• Never on a drink that may still go through malolactic fermentation: the lactics turn sorbic acid into the geranium note, which cannot be undone.
• The legal ceiling on sorbic acid is 300 mg/L in the US (TTB) and 200 mg/L in the EU.

Sources:

• Knowing and Making Wine — Émile Peynaud, 1984

Acid to raise titratable acidity

28.5 g, from ta-equivalent-weight.

g = (target TA − current TA) × (equivalent weight / 75) × volume_L
⇒ Acid to raise titratable acidity = 28.5 g

Input	Value	Unit
Volume	19	L
Titratable acidity now	4.5	g/L
Titratable acidity wanted	6	g/L
Acid	tartaric	—
Equivalent weight of the acid	75	g per equivalent
Acidity to add	1.5	g/L
Dose per liter	1.5	g/L

What it assumes:

• Titratable acidity is reported as tartaric, so tartaric is dosed one for one and the other two are scaled by their equivalent weights.

Sources:

• Chemical Analysis of Grapes and Wine: Techniques and Concepts — Patrick Iland, Nick Bruer, Greg Edwards, Sue Weeks & Eric Wilkes, 2004

Pearson square, first component

11.4 L, from pearson-square.

V_first = total × (target − second) / (first − second)
⇒ Pearson square, first component = 11.4 L

Input	Value	Unit
First lot	14	—
Second lot	9	—
Target	12	—
Total volume	19	L
Share taken from the first lot	0.6	fraction
Second lot	7.6	L

What it assumes:

• A weighted average solved for its weights. The two values are unitless here: alcohol, gravity points, or anything else that blends linearly.
• Not for pH, which is a logarithm and does not average. Blending a pH is weighted by [H⁺].
• A target outside the two values cannot be reached by blending them, and neither can two components that are already the same.

Sources:

• Concepts in Wine Chemistry — Yair Margalit, 2004