> ## Documentation Index
> Fetch the complete documentation index at: https://brewgravity.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Fermentation

> Logging readings and reading the curve.

The Fermentation tab is a running record of what the beer did after you pitched:
gravity, temperature, pH, volume, and whatever you want to write down. It is the
part of Brewgravity you will open most often, usually on a phone, usually standing
next to a fermenter.

## Adding a reading

A reading needs whatever you actually measured — nothing is required, and there
is no such thing as an incomplete entry:

<ResponseField name="Brewgravity" type="SG, °P, or Brix">
  Enter it in whichever unit your instrument reads in. Brewgravity converts to
  specific gravity for storage but remembers the unit you typed, so a Plato
  reading still displays as Plato.
</ResponseField>

<ResponseField name="Temperature" type="°C or °F">
  Beer temperature, not ambient — the difference during active fermentation is
  frequently several degrees and always in the direction you did not want.
</ResponseField>

<ResponseField name="pH" type="0–14">
  Optional, and mostly interesting if you are chasing a specific finish or
  working with mixed cultures.
</ResponseField>

<ResponseField name="Volume" type="litres or gallons">
  Useful when you rack, take samples, or account for trub loss.
</ResponseField>

<ResponseField name="Notes" type="text">
  Krausen fell, dry hops in, moved to the garage, smells like bananas.
</ResponseField>

<Tip>
  Refractometer readings on fermenting beer are wrong unless corrected —
  alcohol skews the refractive index. Choose the **Brix (Refract.)** unit and
  Brewgravity applies the correction using the batch's original gravity, rather than
  handing you a number that says the beer stopped fermenting on day three.
</Tip>

## Reading the chart

Readings plot as a gravity curve over time. The two milestones — your OG when
you started fermentation, and your FG when you completed it — are marked on the
curve automatically, so the chart always has its endpoints.

What the shape tells you:

<AccordionGroup>
  <Accordion title="A steep drop then a flattening" icon="chart-line">
    Normal and healthy. Most of the attenuation happens in the first 48–72
    hours; the tail is the yeast cleaning up.
  </Accordion>

  <Accordion title="A flat line well above expected FG" icon="triangle-exclamation">
    A stuck fermentation. Usually temperature, underpitching, or a mash that
    left too much unfermentable sugar. Two readings 24 hours apart that agree
    are the actual test — one reading is never enough to call it.
  </Accordion>

  <Accordion title="A curve that keeps creeping down" icon="arrow-trend-down">
    Something is eating what the primary yeast could not. Fine if you meant it
    with a Brett or mixed culture, worth investigating if you did not.
  </Accordion>
</AccordionGroup>

## Finishing up

When gravity is stable, enter your final gravity and press **Complete**.
Brewgravity records the FG, stamps the completion time, and the session summary
gives you the numbers that matter for next time:

| Number                   | Why it matters                                      |
| ------------------------ | --------------------------------------------------- |
| **Measured ABV**         | From your real OG and FG, not the recipe's estimate |
| **Apparent attenuation** | How this yeast actually performed on your system    |
| **Days fermenting**      | How long it really took, versus what you planned    |

Those three numbers are the reason to log at all. The next time you brew this
recipe, they are what you plan against.