Brew Log

Stores specific-gravity data for home-brewed beer runs in Mongo and turns it into useful figures — alcohol by volume, days in the fermenter, gravity trends.

Flask app, Mongo backend, no build step for the front end.

Running it locally

python -m venv .venv
. .venv/bin/activate
pip install -r requirements-dev.txt

export MONGO_HOST=192.168.178.229
export MONGO_USER=root
export MONGO_PASS=...
export SECRET_KEY=anything-for-local-use

cd src/flask
python -m beer_data            # dev server on :5000
# or, production-style:
python -m waitress --listen=0.0.0.0:5000 --call beer_data:create_app

Then open http://localhost:5000/ and sign in.

Tests

. .venv/bin/activate
python -m pytest tests/ -q

The tests use mongomock, so they need no database and no network.

Layout

src/flask/
  beer_data.py       entry point; exposes `app` and `create_app`
  app_factory.py     application factory, request-scoped Mongo repository
  brewing.py         pure domain logic — gravity parsing, ABV, run aggregation
  views/             blueprints: auth, brews, (later) analysis
  mongo/repository.py Mongo access for the beer_data and beer_runs collections
  templates/         Jinja templates
  static/            CSS, JS, fonts, logo (all served locally — no CDN)
tests/               pytest suite

brewing.py holds every piece of arithmetic and has no Flask or Mongo dependency, so the maths is unit-testable on its own.

Data model

beer_data — one document per gravity reading

Field	Type	Notes
_id	string	24 random characters
beer_run_id	string	The run this reading belongs to, e.g. "20"
beer_type	string	Beer/cider name. Free text, per reading — it drifts across a run
sg	string	Specific gravity in points: 1039 means 1.039
date	string	YYYY-MM-DD
final_reading	string	"True" / "False" — marks the last reading of a run
comment	string	Free text

The unique key is (date, beer_run_id): re-submitting a reading for the same run and day updates it in place rather than creating a duplicate.

A run is active while it has no reading with final_reading == "True".

beer_runs — one document per run (metadata)

Added alongside the readings to hold what cannot be derived from them: the canonical beer name, the tap number, the recorded original gravity, and brew notes. This collection is only ever inserted into, never written over by the backfill.

Alcohol by volume

Standard homebrew formula:

ABV% = (OG - FG) × 131.25

With gravity stored in points, the drop is already in points, so ABV% = points_drop × 0.13125.

The previous version of this app used (max - min) / 7.36 + 0.5, which is not a recognised brewing formula and overstated every result. The old figure is still computed by brewing.legacy_abv_percent() so the history page can show the difference between the two.

For a run still in the fermenter the figure is an estimate: it uses the run's first reading as the original gravity. A run with a single reading and no recorded OG has no reliable estimate, and the UI shows a dash rather than a misleading number.

Deployment

The image is built and pushed by .gitea/workflows/build_push.yml on push to master. See RUNBOOK.md for the cluster side.