FermUnits

FermUnits is a Pint-based Python library for units, measurement scales, and conversions used in brewing, winemaking, cider making, mead making, distilling, and related fermentation industries.

Status: pre-alpha. The brewing implementation now includes vessel units, gravity calculations, color indices, analytical bitterness, diastatic power, and carbonation conversions. Some relationships remain provisional pending verification against original ASBC or EBC methods and tables.

Installation for development

uv sync --dev

Physical-unit example

from fermunits import Q_

cask = Q_(1, "firkin")
print(cask.to("liter"))

Gravity examples

from fermunits import (
    gravity_points_to_sg,
    plato_to_sg,
    sg_to_gravity_points,
    sg_to_plato,
)

points = sg_to_gravity_points(1.050)
specific_gravity = gravity_points_to_sg(points)

plato = sg_to_plato(1.048)
estimated_sg = plato_to_sg(plato)

The SG-to-Plato polynomial remains provisional pending verification against authoritative ASBC extract tables or methods. The inverse function numerically inverts the same polynomial to preserve internal consistency.

The current numerical inversion interval is an implementation limit rather than an ASBC-approved scientific range.

Wort refractometer correction

These functions represent a wort-specific refractometer correction. They are not general conversions between the Brix and Plato scales.

The correction factor must be supplied explicitly. FermUnits does not assume a default wort correction factor.

from fermunits import (
    plato_to_wort_refractometer_brix,
    wort_refractometer_brix_to_plato,
)

plato = wort_refractometer_brix_to_plato(
    apparent_brix=12.48,
    wort_correction_factor=1.04,
)

apparent_brix = plato_to_wort_refractometer_brix(
    plato=12.0,
    wort_correction_factor=1.04,
)

Beer color

Modern SRM and EBC color indices can be converted directly.

from fermunits import ebc_to_srm, srm_to_ebc

ebc = srm_to_ebc(10.0)
srm = ebc_to_srm(ebc)

Lovibond conversions are explicitly labeled as approximations because the older visual Lovibond scale is not equivalent to the modern spectrophotometric SRM and EBC scales.

from fermunits import (
    lovibond_to_srm_approx,
    srm_to_lovibond_approx,
)

srm = lovibond_to_srm_approx(10.0)
lovibond = srm_to_lovibond_approx(srm)

Analytical bitterness

FermUnits implements the coordinated ASBC/EBC-style analytical relationship between absorbance at 275 nm and bitterness units.

from fermunits import (
    absorbance_275nm_to_bitterness_units,
    bitterness_units_to_absorbance_275nm,
)

bitterness_units = absorbance_275nm_to_bitterness_units(0.5)
absorbance = bitterness_units_to_absorbance_275nm(bitterness_units)

Bitterness units are operational analytical results. They are not represented as an exact concentration of iso-alpha-acids or as a direct measurement of perceived bitterness.

FermUnits does not currently provide a separate arithmetic conversion between IBU and EBU because those names refer to coordinated analytical methods rather than clearly distinct numerical scales.

Diastatic power

from fermunits import (
    lintner_to_windisch_kolbach,
    windisch_kolbach_to_lintner,
)

windisch_kolbach = lintner_to_windisch_kolbach(60.0)
lintner = windisch_kolbach_to_lintner(windisch_kolbach)

The Lintner and Windisch-Kolbach relationship remains provisional pending verification against the original ASBC and EBC analytical methods.

Carbonation

from fermunits import (
    co2_grams_per_liter_to_volumes,
    co2_volumes_to_grams_per_liter,
)

grams_per_liter = co2_volumes_to_grams_per_liter(2.5)
volumes = co2_grams_per_liter_to_volumes(grams_per_liter)

The current factor is derived from an ASBC-hosted technical source. Its exact reference temperature, pressure, and relationship to the complete analytical method remain pending verification.

The same factor is used in both directions to preserve round-trip consistency.

Hydrometer temperature correction

FermUnits does not currently implement hydrometer temperature correction.

The provisional formula listed in the original project inventory was rejected because it omitted the hydrometer calibration temperature and produced physically implausible results.

A correction will not be added until an authoritative method or table can be implemented with:

• explicit sample temperature;
• explicit hydrometer calibration temperature;
• a defined temperature scale;
• supported temperature and specific-gravity ranges;
• a clearly identified sample matrix.

Solution chemistry and water treatment

FermUnits also provides shared solution-chemistry conversions intended for water-treatment and other fermentation engineering applications. These APIs keep chemical semantics explicit rather than hiding them inside ambiguous unit labels.

Chemical-equivalent concentration uses FermUnits' separate equivalent dimension. Converting from amount concentration requires an explicit equivalence factor:

from fermunits import Q_, amount_concentration_to_equivalent_concentration

calcium = Q_(1.0, "millimole / liter")
charge_equivalents = amount_concentration_to_equivalent_concentration(
    calcium,
    equivalence_factor=2.0,
)

For conventional water-analysis reporting, FermUnits implements the relationship 50 mg/L as CaCO3 = 1 mEq/L. The as CaCO3 reporting basis remains application metadata; it is not encoded as though calcium carbonate were necessarily the dissolved analyte.

from fermunits import (
    Q_,
    caco3_basis_mass_concentration_to_equivalent_concentration,
)

alkalinity_as_caco3 = Q_(100.0, "milligram / liter")
alkalinity = caco3_basis_mass_concentration_to_equivalent_concentration(
    alkalinity_as_caco3
)

Mass concentration and mass fraction are not treated as interchangeable. A conversion such as mg/L to mg/kg requires explicit solution density:

from fermunits import Q_, mass_concentration_to_mass_fraction

concentration = Q_(100.0, "milligram / liter")
density = Q_(1.05, "kilogram / liter")
mass_fraction = mass_concentration_to_mass_fraction(concentration, density)

Likewise, conversion between mass concentration and amount concentration requires an explicit molar mass supplied as a Pint quantity:

from fermunits import Q_, mass_concentration_to_amount_concentration

sodium_chloride = Q_(58.44, "milligram / liter")
molar_mass = Q_(58.44, "gram / mole")
amount_concentration = mass_concentration_to_amount_concentration(
    sodium_chloride,
    molar_mass,
)

FermUnits preserves Pint's generic ppm unit, but canonical chemistry data should use an explicit ratio such as mg/kg or microgram / kilogram when the intended basis is mass fraction. FermUnits does not define a generic ppb alias.

Design principles

• Pint remains the physical-unit engine.
• FermUnits adds fermentation-industry definitions and domain-specific APIs.
• Ambiguous names such as bare barrel are not defined.
• Existing Pint meanings are preserved when they are legitimate.
• Domain-qualified names distinguish conflicting industry meanings.
• Empirical scales and calculations are kept separate from physical units.
• Approximate and provisional formulas are labeled clearly.
• Input validation rejects nonfinite or physically invalid values.
• Every domain definition and calculation should have a documented source and tests.
• Restricted authoritative methods are recorded for later verification rather than treated as though their details were directly confirmed.
• Unsupported formulas are rejected rather than implemented merely because they appeared in the initial project inventory.

Current brewing scope

Implemented physical units include:

• modern British brewery cask units;
• modern US beer barrel;
• Imperial beer barrel;
• pin cask;
• firkin;
• kilderkin;
• domain-qualified wine and brewing hogsheads;
• domain-qualified brewing puncheon and butt.

Implemented brewing calculations include:

• specific gravity and gravity points;
• provisional specific gravity and degrees Plato conversion;
• explicit wort refractometer correction with a caller-supplied factor;
• SRM and EBC color-index conversion;
• approximate Lovibond and SRM conversion;
• analytical bitterness units from 275 nm absorbance;
• provisional Lintner and Windisch-Kolbach conversion;
• dissolved CO2 conversion between volumes and grams per liter.

Not yet implemented:

• hydrometer temperature correction;
• generic Brix, Plato, and Balling scale conversion;
• recipe-estimation formulas such as Tinseth or Rager bitterness;
• calculations that require unverified assumptions or inaccessible source details.

Additional wine, distilling, sake, cider, biofuel, and fermentation-process definitions will be added after their regional, historical, legal, or technical meanings are documented.

Source verification

Detailed source-status notes and unresolved questions are tracked in:

docs/asbc-verification.md

Items remain on that checklist until the original ASBC or EBC method, table, or publication can be reviewed directly.

License

FermUnits is distributed under the MIT License. See LICENSE.