Fermentation lock

The fermentation lock or airlock is a device used in beer brewing and wine making that allows carbon dioxide released by the beer to escape the fermenter, while not allowing air to enter the fermenter, thus avoiding possible bacterial contamination.

There are two popular designs for the fermentation lock, or airlock, both of which work equally well. The two designs both work by being half filled with water. When the pressure of the gas inside the fermentation vessel exceeds the prevailing atmospheric pressure the gas will then push its way through the water as individual bubbles into the outside air. Some brewers use a sanitizing solution or vodka in the fermentation lock to prevent contamination of the beer in case the solution is inadvertently drawn into the fermenter.

This device may take the form of a tube connected to the headspace of the fermenting vessel into a tub of sanitized liquid or a simpler device mounted directly on top of the fermentation vessel.

Currently, the most popular fermentation lock that mounts on top of the fermentation vessel is the three-piece fermentation lock. Older models contain three bulbous chambers allowing for a broader range of pressure equalization. These bulbous fermentation locks were generally made of hand blown glass.