Fermentation lock

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

Is usually a double- U- shaped tube made ​​of glass or plastic on a perforated cap or rubber stopper. In the manufacture of fermented beverages such as wine, Met, apple wine or beer, it closes the opening of Gärballons or mash vessel. It is so constructed that, when released fermentation fermentation gas, mainly carbon dioxide, while escaping from the container, air or oxygen, however, can not penetrate from the outside. This allows to prevent oxidation of the vinegar must or mash. This is achieved through a water trap in the lower of the two U -shaped bends of the tube.

In addition, prevents the bung that come with the air or by insects unwanted bacteria or other microorganisms in the wine and cause errors in fermentation, which would spoil the end product.

It is also used a clay sheet whose upper surface has a cup-shaped rim and in a central, mutually open tube is inserted. This is slipped over by another, closed at the top tube dipping with its lower edge into the water-filled bowl. In a similar device made ​​of metal, the inner tube is just above ground and abuts against a plate made of rubber, with the bottom of the outer tube is fed inwardly. The evolving carbonic acid must overcome the pressure exerted optionally loaded with weights outer tube here by its own power.

In the fermentation of a liter of must to cider for example, up to 50 liters of fermentation gas arise that must escape from the Gärballon - thus you can not use a hermetically sealing plug.

Another use of the fermentation tube in qualitative analytical chemistry for the detection of escaping gases. In order to detect carbon dioxide, a barium hydroxide solution is introduced into the fermentation tube, for example. After the addition of acid to the analyte escapes gas exiting through the fermentation tube. Makes there a haze, it indicates that the carbon dioxide, as a sparingly soluble barium has deposited. It can also limewater for the detection of carbon dioxide are used. In case of contact with carbon dioxide to cloud the initially clear lime water as calcium carbonate precipitates.