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contain superseded formulas, unsupported claims, approximate values, proposed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 3: DISTILLING
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A technical backend manual covering ethanol concentration, spirit proofing,
gauging math, tax calculations, historical aging barrels, and thermal volumetric
contraction mapped directly to standard SI metric base and derived units.
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1. ETHANOL CONCENTRATION & SPIRIT PROOFING
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*   Alcohol By Volume (ABV)
    - Description: The percentage of the total volume of a liquid that is pure
      ethanol at a standard temperature of 20°C (68°F) or 60°F (15.56°C).
    - Core Users: Absolute global standard for all commercial, craft, and hobby
      distillers. Used on legal product labels worldwide.
    - Metric / SI Baseline Value: Dimensionless volume fraction.
      Expressed as: (m³ of pure ethanol / m³ of total liquid) * 100.

*   US Proof
    - Description: A scale defined as exactly twice the percentage of Alcohol By
      Volume (ABV) at a standard reference temperature of 60°F.
    - Core Users: US Commercial Distillers, US Craft Distillers, and TTB Tax Auditors.
    - Metric / SI Baseline Value: Dimensionless integer scale.

*   UK Proof / British Proof (Sykes Scale)
    - Description: A historical spirit strength scale defined by a spirit sample's
      weight compared to distilled water using a Sykes hydrometer. "Proof spirit"
      (100 Proof) contains exactly 57.1% ABV or a specific gravity of 0.923.
    - Core Users: Historical legacy tracking. Used across the British Empire
      until the late 20th century; still referenced in vintage distillery logs.
    - Metric / SI Baseline Value: Dimensionless density-derived scale.

*   Gay-Lussac Scale (°GL)
    - Description: A percentage volume scale identical to modern ABV, measured
      at a standard reference temperature of 15°C instead of 20°C.
    - Core Users: Traditional European distilleries and older South American sites.
    - Metric / SI Baseline Value: Dimensionless volume fraction.

*   HIGH-PRECISION CONVERSION FORMULAS:
    - ABV to US Proof:
        US Proof = ABV * 2
    - US Proof to ABV:
        ABV = US Proof / 2
    - ABV to UK Proof (Sykes):
        UK Proof = ABV * 1.7535
    - UK Proof to ABV:
        ABV = UK Proof / 1.7535
    - US Proof to UK Proof:
        UK Proof = US Proof * 0.8767

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2. GOVERNMENT TAXATION & AUDITING UNITS
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*   Proof Gallon (PG)
    - Description: The volume equivalent of one US gallon of liquid containing
      exactly 50% alcohol by volume (100 proof) at 60°F. This is the absolute
      legal unit used to calculate federal excise tax in the United States.
    - Core Users: US Commercial/Craft Distillers, Accounting Teams, and the TTB.
    - Metric / SI Baseline Value: Volumetric ethanol-mass index. Equivalent to
      exactly 1.89271 Liters of pure ethanol ($0.001893\text{ m}^3$).

*   Liters of Pure Alcohol (LPA) / Litres of Absolute Alcohol (LAA)
    - Description: The actual volume of pure, 100% ABV ethanol contained within a
      given bulk volume of spirits at 20°C.
    - Core Users: Global Commercial Distillers, HMRC (UK), and international tax bodies.
    - Metric / SI Baseline Value: Accepted Non-SI Metric Volume unit. Exactly
      1 Liter of pure ethanol ($0.001\text{ m}^3$).

*   Wine Gallon (WG) / Bulk Gallon
    - Description: The raw, physical volume of a spirit liquid container regardless
      of its alcoholic strength or proof.
    - Core Users: US Distillers tracking inventory storage capacity.
    - Metric / SI Baseline Value: Volume unit. Exactly 3.78541 Liters ($0.003785\text{ m}^3$).

*   HIGH-PRECISION TAX CALCULATION FORMULAS:
    - Wine Gallons & Proof to Proof Gallons:
        PG = Wine Gallons * (US Proof / 100)
    - Bulk Liters & ABV to LPA:
        LPA = Bulk Liters * (ABV / 100)
    - Proof Gallons to LPA:
        LPA = PG * 3.78541 * 0.50 = PG * 1.89271
    - LPA to Proof Gallons:
        PG = LPA / 1.89271

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3. HIGH-PRECISION GAUGING MATH & WATER CONTRACTION
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When pure water and pure ethanol are mixed, a chemical phenomenon known as **volumetric
contraction** occurs due to hydrogen bonding. Mixing 50 mL of water and 50 mL of
ethanol yields roughly 96 mL of total spirit, not 100 mL.

*   The True Gauging Equation (Determining Blending Water):
    To dilute a high-proof spirit down to a target bottling proof, your calculator
    cannot use linear subtraction. It must use bulk mass weights or highly specific
    empirical tables (like the OIML or TTB Gauging Manual Tables).
    - Mass-Based Dilution Formula (SI Base: kg):
        Water to Add (kg) = [Bulk Weight of Spirit (kg) * (Current ABV by weight / Target ABV by weight)] - Bulk Weight of Spirit (kg)

*   Apparent Proof vs. True Proof
    - Description: Hydrometers change density readings based on fluid temperature.
      "Apparent Proof" is the raw reading off a glass hydrometer. "True Proof"
      is the corrected measurement calculated after adjusting for temperature.
    - Correction Formula (Linear Approximation near 60°F):
        True Proof = Apparent Proof - (0.05 * (Temperature in Fahrenheit - 60))
        *(Note: Commercial calculators must use the exact non-linear TTB Table 1 data arrays for legal compliance).*

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4. DISTILLERY AGING BARRELS & HISTORICAL VESSELS
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Unlike the wine industry, spirits producers select barrel sizing to optimize charcoal
filtration, wood-to-liquid contact ratios, and evaporative loss ("The Angels' Share").

*   Standard US Bourbon Barrel
    - Volumetric Size: 53 US Gallons / 200.6 Liters.
    - Description: The standard cooperage size for aging American Bourbon and Rye.
      Must be constructed from brand-new, charred white oak.
    - Metric / SI Baseline Value: Volume unit. Exactly 200.626 Liters ($0.20063\text{ m}^3$).

*   Hogshead (Whisky Standard)
    - Volumetric Size: 250 Liters / 66 US Gallons.
    - Description: Constructed by rebuilding broken-down US Bourbon barrels with
      additional staves. Universal standard for aging Scotch and Irish Whiskies.
    - Metric / SI Baseline Value: Volume unit. Exactly 250 Liters ($0.25\text{ m}^3$).

*   Quarter Cask
    - Volumetric Size: 45 to 50 Liters / ~12 US Gallons.
    - Description: Exactly one-quarter the volume of a standard historical UK barrel.
      Favored by Craft/Hobby distillers to accelerate wood-extraction aging.
    - Metric / SI Baseline Value: Volume unit. Standard target is 50 Liters ($0.05\text{ m}^3$).

*   Octave Cask
    - Volumetric Size: 50 Liters / 13.2 US Gallons.
    - Description: Exactly one-eighth the size of a standard UK historical barrel. Used
      for specialized, rapid wood-finishing trials in craft distilling.
    - Metric / SI Baseline Value: Volume unit. Exactly 50 Liters ($0.05\text{ m}^3$).

*   Gorda
    - Volumetric Size: 700 Liters / 185 US Gallons.
    - Description: Massive oak vats traditional to North American and Caribbean rum
      maturation, designed for slow blending and marrying of distinct batches.
    - Metric / SI Baseline Value: Volume unit. Exactly 700 Liters ($0.7\text{ m}^3$).

*   CONVERSION MATRIX FOR DISTILLERY BARRELS:
    - 1 Scotch Hogshead   = 1.25 US Bourbon Barrels
    - 1 Gorda             = 3.5 US Bourbon Barrels
    - 1 US Bourbon Barrel = 4.0 Quarter Casks
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