LEGACY RESEARCH INVENTORY — NOT CURRENT FERMUNITS DOCUMENTATION

This file is preserved as historical planning and research context. It may
contain superseded formulas, unsupported claims, approximate values, proposed
names that were never implemented, or items still awaiting authoritative source
verification. See ../README.md and the maintained reference documents in the
parent directory for current FermUnits behavior.

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          MASTER FERMENTATION CALCULATOR SPECIFICATION - PART 4: SAKE
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A technical backend manual covering the Nihonshudo dryness index, traditional
Japanese volumetric units, rice polishing metrics, and titration acidity math
mapped directly to standard SI metric base and derived units.
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1. DRYNESS INDICES & THE NIHONSHUDO SCALE
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*   Nihonshudo (Sake Meter Value - SMV)
    - Description: A custom specific gravity scale indicating the dryness or
      sweetness of the sake. It measures the density of finished sake compared
      to pure water at 15°C (59°F). Because alcohol is lighter than water,
      positive values (+4) signify lower density (drier sake), while negative
      values (-2) signify higher residual sugars (sweeter sake).
    - Core Users: Universal across all premium sake breweries (Kura), export
      traders, and consumer labeling.
    - Metric / SI Baseline Value: Inverse density-derived index. At a reference
      water density of 1.000 (1,000 kg/m³), the SMV value is exactly 0.

*   HIGH-PRECISION CONVERSION FORMULAS:
    - Specific Gravity (SG) to Nihonshudo (SMV):
        SMV = (1443 / SG) - 1443
    - Nihonshudo (SMV) to Specific Gravity (SG):
        SG = 1443 / (SMV + 1443)
    - Example Application: An SG of 0.9972 maps to an SMV of +4.0 (Bone Dry).
      An SG of 1.0020 maps to an SMV of -2.8 (Sweet).

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2. TECHNICAL ACIDITY BALANCING (SANDO & AMANDO)
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*   Sando (Sake Acidity Metric)
    - Description: Measures the concentration of organic acids (succinic, lactic,
      and malic) in sake. Distinct from wine titratable acidity, Sando is reported
      as a raw titration factor rather than a mass-per-liter value.
    - Calculation: The volume (in milliliters) of a 0.1M Sodium Hydroxide (NaOH)
      chemical solution required to neutralize exactly 10 mL of filtered sake.
    - Metric / SI Baseline Value: Volumetric titration index ($10^{-5}\text{ m}^3$ solution titration ratio).
      An average premium sake features a Sando value between 1.2 and 1.7.

*   Amando (Sweetness-Acidity Ratio Index)
    - Description: A calculated balance value used by brewers to evaluate the
      perceived balance between sugar concentration and structural tartness.
    - High-Precision Balance Formula:
        Amando = (Nihonshudo / 10) - Sando
    - Metric / SI Baseline Value: Dimensionless sensory tracking balance index.

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3. RICE ARCHITECTURE & PRODUCTION METRICS
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*   Seimaibuai (Rice Polishing Ratio)
    - Description: Measures the mass percentage of the raw sake rice grain that
      remains after the outer layers of fat and protein are milled away.
    - Core Users: Absolute classification standard. Determines legal grades
      like Honjozo ($\le$ 70%), Ginjo ($\le$ 60%), and Daiginjo ($\le$ 50%).
    - Metric / SI Baseline Value: Mass fraction percentage unit. Calculated as:
      (Milled Grain Mass in kg / Raw Grain Mass in kg) * 100 (SI Base: kg).

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4. TRADITIONAL JAPANESE CAPACITY & BOTTLING VOLUMES
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Sake brewing facilities evaluate batch capacities, raw water requirements, and
production tax compliance using legacy volumetric units dating back to the Edo period.

*   Koku (石)
    - Volumetric Size: Exactly 180.39 Liters / 47.65 US Gallons.
    - Description: The bedrock commercial volume unit used to measure total cellar
      capacity, government facility licenses, and yearly production output.
    - Metric / SI Baseline Value: Volume unit. Exactly 180.39 Liters ($0.18039\text{ m}^3$).

*   To (斗)
    - Volumetric Size: Exactly 18.039 Liters / 4.76 US Gallons.
    - Description: Equivalent to exactly one-tenth of a Koku.
    - Metric / SI Baseline Value: Volume unit. Exactly 18.039 Liters ($0.018039\text{ m}^3$).

*   Sho (升)
    - Volumetric Size: Exactly 1.8039 Liters / 0.476 US Gallons.
    - Description: Equivalent to exactly one-hundredth of a Koku.
    - Metric / SI Baseline Value: Volume unit. Exactly 1.8039 Liters ($0.0018039\text{ m}^3$).

*   Gou (合)
    - Volumetric Size: Exactly 180.39 Milliliters / 6.10 US Fluid Ounces.
    - Description: Equivalent to exactly one-thousandth of a Koku. It is the single
      serving size standard for traditional wooden sake cups (Masu).
    - Metric / SI Baseline Value: Volume unit. Exactly 180.39 mL ($0.00018039\text{ m}^3$).

*   Isshobin (一升瓶)
    - Volumetric Size: Exactly 1.8 Liters.
    - Description: The universal glass bottle size used for packing premium sake.
      Loosely derived from the historical Sho unit but rounded to a clean metric standard.
    - Metric / SI Baseline Value: Accepted Non-SI Metric Volume unit. Exactly 1.8 L ($0.0018\text{ m}^3$).

*   CONVERSION MATRIX FOR SAKE VOLUMES:
    - 1 Koku = 10 To = 100 Sho = 1,000 Gou
    - 1 To   = 0.1 Koku = 10 Sho  = 100 Gou
    - 1 Sho  = 0.01 Koku = 0.1 To  = 10 Gou
    - 1 Gou  = 0.001 Koku = 0.01 To = 0.1 Sho
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