Hydrometer
Term from the Brauwerkstatt brewing glossary, category “Measurements and calculations”.
Explanation
Floating instrument for measuring original and final gravity, usually calibrated to 20 °C (68 °F). A warmer sample reads slightly low.
Work it out yourself
Final beer calculator – Work out the alcohol content, attenuation, colour and bitterness of your beer – before brewing as a plan, and afterwards with your measured values.
Test your knowledge
What does a hydrometer measure?
- The density of the wort and thus its sugar content
- The pH
- The temperature
Show answer
Correct: The density of the wort and thus its sugar content. The more sugar is dissolved, the higher the hydrometer floats. Measured before and after fermentation, it gives the alcohol.
What is an airlock for?
- It is a tube for bottling
- It lets CO₂ out but no air in
- It measures the temperature
Show answer
Correct: It lets CO₂ out but no air in. Bubbling in the airlock shows that fermentation is under way. But only a hydrometer measures it reliably.
Frequently asked questions
My fermentation won’t start. What should I do?
Stay calm: it often takes 12–48 hours before you see anything. An airlock that doesn’t bubble means little if the lid isn’t fully airtight. Better check with the hydrometer: if the reading drops, the beer is fermenting. If nothing has happened after 2 days, check the temperature and pitch fresh yeast if needed.
Related terms
All terms in “Measurements and calculations” · Brewing glossary