How to use a Bubbler Airlock
- Bev
- Aug 7
- 4 min read
Updated: 15 hours ago
An airlock is a piece of equipment used in homebrewing that allows CO2 (carbon dioxide) to escape from a fermentation without allowing oxygen or contaminants like bacteria and fruit flies from getting in. This is how to use a bubbler airlock.
What is a Bubbler Airlock?
A bubbler airlock is a long piece of clear plastic which has multiple ‘bubble’ chambers. You will also find other kinds of airlocks, such as handy airlocks which are virtually silent when in use. Here I’m focusing on the bubbler and I imagine this design is known by that name because you can watch the bubbles come through as your liquid ferments, and it makes a satisfying ‘bloop’ sound.
This design of airlock has a loose fitting cap on the top. They are often red though you do come across airlocks with caps of other colours. The cap keeps out fruit flies and dust and is designed to simply sit on the top of the bubbler airlock rather than be airtight.
How does an airlock work in homebrewing?
An airlock is designed to release the CO2 (carbon dioxide) which is produced during fermentation, whilst preventing bacteria, fruit flies and any other unwanted things from getting into the brewing vessel. When the airlock is half filled with water, that liquid creates a barrier which traps the gases and then allows them to escape. So your homemade beer, wine, cider or mead remains safe from contamination below the airlock.
You may or may not need a bung with a hole, either rubber or cork, when using an airlock. That will depend on the kind of vessel you’re using.
If you’re using a traditional glass demijohn, you will also need a rubber bung or a cork bung which fits snugly into the neck of the demijohn. That’s why you often see airlocks and bungs sold together. When you fit the neck of the airlock into the hole in the bung, that creates a seal. So whilst your airlock is working away above, your homemade beer, wine, cider or mead remains safe from contamination below the bung and airlock.
If you’re using a brewing bucket with a hole in the lid and a grommet fitted, you can fit the airlock directly into that grommet which, again, creates a seal. This is also the case when you’re using a PET plastic demijohn which has a lid with a hole in it fitted with a grommet, just like the bucket. So if you’re using a brewing bucket with a hole in the lid or a PET demijohn with a lid and hole in it, you won’t need a bung as well.
The added bonus of using an airlock is that it tells you fermentation may have finished. When there are no more gases being released through the airlock, the blooping stops.
What liquid do I put in the airlock?
You will sterilise the airlock before it is fitted, because the neck which fits into the top of the vessel may come into contact with the fermenting liquid. However everything above that won’t, so the liquid in the airlock can be simply water from the tap.
Put in enough water to approximately half full, then pop the cap on. I have read about people using vodka in airlocks. I believe that is to avoid the liquid evaporating in extremely hot climates. We don’t have that issue in the UK plus it’s an expensive way to do it and I have better uses for vodka. 🙂
How to use a Bubbler Airlock
1. Sterilise the airlock and cap (and bung, if you’re using a glass demijohn) with a suitable sterilising agent such as VWP or Milton.
2. Fill the airlock to around half full with water from the tap.
3. If you’re using a bung, insert the bung into the neck of the demijohn, then insert the airlock with water into that. If you’re not using a bung, simply insert the airlock into the hole in the cap or lid of the vessel. Either way, ensure the airlock is pushed in enough to create a seal.
4. When fermentation starts, gases will be released from the liquid in the demijohn or bucket below. They will start flowing up through the airlock and be released, and you will hear the reassuring ‘bloop’.
5. Usually recipes suggest you ferment initially in a bucket until any vigorous fermentation dies down. If you don’t do that and it happens in a demijohn, you may get some of the contents of the vessel in your airlock. If this happens, wait until it dies down as it always does, then remove the airlock, clean and re-sterilise it, put fresh water into it, then refit it and continue as before.
Homebrewing Airlocks - Final Thoughts
There are a variety of airlocks available, and they are an essential piece of equipment for homebrewing. The bubbler is one of these and probably the most popular airlock in the UK.
If you buy a homebrewing equipment kit it may well come with an airlock included. They are reusable multiple times, simply wash and sterilise and you're ready to go again. And if something happens and you need to replace an airlock, or you're struggling to get it clean after multiple uses, it's easy to source just one airlock and keep using the rest of your kit.
Do you put water in a handy airlock too please?