Airlock
Term from the Brauwerkstatt brewing glossary, category “Fermentation and yeast”.
Explanation
Small valve in the fermenter lid, filled with water. It lets the CO₂ from fermentation escape but keeps air and germs out. When it stops bubbling, fermentation is not necessarily finished; only the hydrometer tells you that.
Test your knowledge
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.