Airlocks & Blow-off Tubes

What is the difference between an Airlock and a blow-off tube?

An airlock is a water-barrier that allows co2 to escape during fermentation, without allowing airborne particles, bacteria or insects to enter the fermentation vessel.

A U-bend Style Airlock

A U-bend Style Airlock

A blow-off tube replaces the airlock in a fermentation vessel. One end attaches to the top of the fermentation vessel and the other end is submersed in a container full of water.

A Blow-off Tube

A Blow-off Tube

Which one should I use?

For most brews, an airlock is fine. The advantage of an airlock is that it is relatively small compared to the blow-off tube, and is much easier to maintain. The problem with airlocks is that a very aggressive fermentation can clog the airlock with Krausen, causing a build up of pressure in the fermentation vessel. When that pressure gets too much, either the airlock or the lid of the fermentation vessel will pop off with great force, causing a big mess. A blow-off tube is much less likely to clog up than an airlock.

If you are brewing a beer using a top-fermenting yeast (most wheat-beers are brewed using this type of yeast), then you should always use a blow-off tube. This is because top-fermenting yeast produce a much higher, thicker krausen than regular ale yeasts and are much more likely to cause problems when using an airlock.

How to make a blow-off tube.

1. Attach a piece of sanitised tubing to the opening of your demijohn (or lid of your fermentation bucket) using a sanitised stopper with a hole in it.
2. Half-fill a small container such as a measuring jug or pint glass with water, and place the other end of the tube inside, below the level of the water. You do NOT need to use bleach or sanitising solution for this!…