Fermentation lock

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A Nessler fermentation tube made of plastic as a fermentation seal on a fermentation tank in the hobby area

Fermentation lock , fermentation attachment or fermentation control attachment are collective names for various devices for closing the fermentation containers and restricting the gas exchange during anaerobic fermentation .

Purpose and types

Especially in the production of alcoholic beverages such as wine or beer , the fermentation seal should allow gases (mostly carbon dioxide ) to escape without air - and especially oxygen - being able to flow into the container. The fermentation lock thus has the function of a pressure relief valve .

Often the fermentation seal is placed in a pierced plug on the bung , i.e. the sealing hole of the fermentation vessel, and closes it tightly on one side, such as a water trap preventing the entry of oxygen and thus unwanted oxidation (provided there is no negative pressure in the vessel). Often, sulfur dioxide or alcohol is added to the water in the "trap" . The carbon dioxide escaping during fermentation is passed through the liquid and is visible through the formation of bubbles, sometimes also indicated acoustically, so that the fermentation process can be better controlled. There are different forms of fermentation closures such as the fermentation tube or the air bell or also very simple devices in which, for example, a hose attached to the closure hole is led into a container filled with water.

Fermentation tube

A fermentation tube or airlock is a form of fermentation lock. Other names for this are Nessler'sche Gärröhre , or just Gärröhre , Gärrohr , Gärpfeife , Gärglas , Gäraufsatz or bungs .

It is usually a double U-shaped tube made of glass or plastic on a perforated cork or rubber stopper . When producing fermented beverages such as wine , mead , cider or beer, it closes the opening of the fermentation balloon or mash vessel. It is designed in such a way that fermentation gas released during the fermentation process, mainly carbon dioxide ( about two moles of CO 2 per mole of glucose !), Can escape from the container, but air or oxygen cannot penetrate from the outside. This prevents the must or mash from oxidizing to vinegar . This is achieved by a water trap in the lower of the two U-shaped curves of the tube. If there is a risk of the sealing water being sucked back into the container, alcohol is occasionally added for disinfection.

In addition, the fermentation bung prevents unwanted bacteria or other microorganisms from getting into the must with the air or by insects and triggering incorrect fermentations that would spoil the end product.

A clay bung is also used, the upper surface of which has a cup-shaped edge and into which a central tube, open on both sides, is inserted. This is slipped over by another tube, closed at the top, which dips with its lower edge into the bowl filled with water. In a similar device made of metal , the inner tube is ground flat at the top and lies against a plate made of rubber with which the bottom of the outer tube is lined on the inside. The developing carbon dioxide has to overcome the pressure exerted by the outer tube, which may be loaded with weights.

The fermentation tube is also used in qualitative analytical chemistry for the detection of escaping gases. In order to detect carbon dioxide , a barium hydroxide solution , for example, is filled into the fermentation tube. When acid is added to the analysis substance, a gas escapes that escapes through the fermentation tube. If a cloudiness forms there, this indicates carbon dioxide, as barium carbonate that is difficult to dissolve has deposited. Lime water can also be used to detect carbon dioxide. When it comes into contact with carbon dioxide, the initially clear lime water becomes cloudy because calcium carbonate precipitates.

Air bell

The so-called air bell is a beaker with a tube in the middle that is connected to the container. A bell is placed over this tube, the lower edge of which must lie in the gap between the cup and the tube and lower than the open end of the tube. The gap is filled with water until the lower edge of the bell is safely covered, but no water can penetrate the pipe from above. As soon as fermentation gases begin to develop in the container, the bell is raised so far that the gases can finally pass under the edge to the outside. The bell then falls back into the water and closes the container airtight from the environment.

Air balloon

A simple device consists of a rubber balloon slipped over the opening of the container and perforated with a needle. The perforation allows gases to escape when the balloon inflates. Due to the internal tension of the rubber, the fine openings then close again.

When fermenting one liter of must into cider, for example, up to 50 liters of fermentation gas are produced, which have to escape from the fermentation balloon - therefore you cannot use a hermetically sealed stopper.


Web links

Wiktionary: Gärspund  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Effect of sulfur