A fermentation lock or airlock is a device used in

beer Beer is one of the oldest and the most widely consumed type of alcoholic drink in the world, and the third most popular drink overall after water and tea. It is produced by the brewing and fermentation of starches, mainly derived from cer ...

brewing Brewing is the production of beer by steeping a starch source (commonly cereal grains, the most popular of which is barley) in water and fermenting the resulting sweet liquid with yeast. It may be done in a brewery by a commercial brewer, ...

and wine making that allows

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

released during fermentation to escape the fermenter, while not allowing air to enter the fermenter, thus avoiding

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

. There are two main designs for the fermentation lock. These designs work when half filled with

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

. When the

pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...

of the gas inside the fermentation vessel exceeds the prevailing

atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibar ...

the gas will push its way through the water as individual bubbles into the outside air. A sanitizing solution, sulphur dioxide or alcohol is sometimes placed in the fermentation lock to prevent

contamination Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc. Types of contamination ...

of the

beverage A drink or beverage is a liquid intended for human consumption. In addition to their basic function of satisfying thirst, drinks play important roles in human culture. Common types of drinks include plain drinking water, milk, juice, smoothies ...

in case the water 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, a popular fermentation lock that mounts on top of the fermentation vessel is the three-piece fermentation lock. Other models contain three bulbous chambers allowing for a broader range of pressure equalization. These bulbous fermentation locks were generally made of hand blown glass and are nowadays often made of clear plastic. The use of perforated rubber

balloon A balloon is a flexible bag that can be inflated with a gas, such as helium, hydrogen, nitrous oxide, oxygen, and air. For special tasks, balloons can be filled with smoke, liquid water, granular media (e.g. sand, flour or rice), or li ...

s 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.

References

{{homebrewing Homebrewing

See also

References