Fermentation lock

A fermentation lock, colloquially air lock, is a device used in the production of fermented beverages, especially beer brewing and wine making. It allows carbon dioxide released during fermentation to escape the fermenter while not allowing air to enter it, thus avoiding oxidation.

There are two main designs for the fermentation lock. These designs work when filled halfway with water. When gas pressure inside the fermentation vessel exceeds the prevailing atmospheric pressure, said gas will push its way through the water as individual bubbles into the outside air. A sanitizing solution, sulfur dioxide{{cite web |archive-url=https://web.archive.org/web/20170704101031/http://www.zusatzstoffe-online.de/zusatzstoffe/63.e220_schwefeldioxid.html |access-date=2017-07-04 |archive-date=2017-07-04

Currently, top-mounted three-piece locks are the most popular form of fermentation lock. Other models contain bulbous chambers, allowing for a broader range of pressure equalization. These bulbous locks were generally made of hand-blown glass and are nowadays often made of clear plastic.

The use of perforated rubber balloons offers an easy and inexpensive alternative to conventional airlocks: as used primarily in homebrewing, the balloon is stretched over the orifice of the fermentation vessel and, if necessary, tightened with rubber bands. The balloon is then perforated with a needle. These punctures, while not completely airtight, sufficiently protect the vessel's contents from contamination and allow the gases produced by fermentation to evacuate from the vessel as the pressure rises and the balloon inflates.

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