The Bubbler Airlock (also known as a fermentation trap or fermentation lock) is an essential piece of home brewing equipment. It fits into a bored rubber or cork bung on the lid of your fermentation vessel and allows CO₂ produced during fermentation to escape while preventing oxygen and airborne contaminants from entering your brew.
To use, simply half-fill the airlock with water or sanitiser solution. As fermentation begins, you'll see bubbles passing through — a satisfying sign that your yeast is actively working.
Frequently Asked Questions
- What do I fill the airlock with?
- Fill to the fill line (roughly halfway) with either clean tap water or a weak sterilising solution. The liquid creates a one-way seal — CO2 from fermentation pushes through the liquid and escapes, but air cannot get back in. Using sterilising solution rather than plain water reduces the small risk of contamination if liquid is accidentally sucked back.
- My airlock has stopped bubbling — is fermentation finished?
- Not necessarily. Airlock activity slows significantly in the final days of fermentation and can stop while fermentation is still slowly completing. Never rely solely on airlock activity to judge when fermentation is done — always confirm with a hydrometer. Two identical readings 24 hours apart is the reliable test.
- The liquid in my airlock got sucked into the fermenter — is my beer ruined?
- Usually not. A small amount of sterilising solution or water being pulled into the beer during a sudden temperature drop is unlikely to cause a problem if the airlock was filled with sterilising solution. Taste the beer at the end of fermentation — if it seems off, investigate further, but in most cases it will be fine.
- How many airlocks do I need?
- One per fermentation vessel. If you run multiple batches simultaneously, you'll need one airlock for each. They're inexpensive, so it's worth having a few spares — they're easy to lose or break.
- My airlock is leaking around the bung — what should I do?
- The bung may not be seated properly or may have hardened and lost its seal. Press the bung firmly into the lid hole — it should fit snugly with no gaps. If the bung is cracked or hardened, replace it. A leaking seal allows oxygen into the fermenter which can cause oxidation and infection.