The gravity of a beer corresponds to the amount of dissolved sugars in the wort (the liquid obtained after steeping the grains).
It is measured with a hydrometer or a refractometer and indicates the concentration of fermentable sugars before and after fermentation.

Two main values are distinguished:

• OG – Original Gravity
  This is the gravity of the wort before fermentation.
  It reflects the amount of available sugars for the yeast.
  → A high OG often means a stronger beer, because there is more sugar to convert into alcohol.

• FG – Final Gravity
  This is the gravity after fermentation, once the yeast has consumed most of the sugars.
  → A low FG indicates a drier and more alcoholic beer.
  → A higher FG produces a rounder, sweeter or more malty beer.

Link between OG, FG, sugar and alcohol

During fermentation, the yeast converts the sugars into ethanol (alcohol) and carbon dioxide (CO₂).
The difference between OG and FG therefore allows the alcohol content (ABV) to be estimated:

ABV ≈ (OG − FG) × 131 (approximate formula)

👉 In summary:

• The greater the OG − FG difference → the more alcoholic and dry the beer.

• The smaller the difference → the more mild and sweet the beer.