The tannins in tanning are the tannins (hydroxy- polyphenols , especially gallic acid ). These are stored by the plants in order to keep predators away, as their digestion is negatively influenced by the absorption of tannins and an astringent feeling arises in the mouth . Tannins can be found in different concentrations in very different plants. Mainly be for tannery oak bark , chestnut , plant galls , galls , various Sumac , Hemlocktannenrinde or catechu used. The tannins are also found in plants such as wine , hops , in the Divi-Divi tree , black and green tea . In the mouth, tannins in food are perceived as dry, rough, and furry. For example, the taste of a red wine is fundamentally determined by which tannins it contains and in which concentration.
The tanning process takes about 20-30 months. Approximately 30 kg of bark or 20 kg of fruit or 90 kg of oak wood are used per cow hide. The tan is placed in a pit filled with water together with the skins, which creates a tannic acid bath after a few days. Lohe that had already been used and leached was then used in pressed form ( loa cheese ) as fuel or as fertilizer.
In the European Middle Ages, the pedunculate oak in particular was cultivated for tanning purposes in so-called slaw forests. The tannin bark of the trees was the so-called Lohlöffel peeled (the Middle High German word lo referred tear, peel, holes) and Bark Mill spent where it for eventual blaze was crushed. These mills were mostly located in the immediate vicinity of tanneries and give their names to streets and squares in German cities to this day. In downtown Cologne, for example, Rothgerberbach, Blaubach and Mühlenbach are reminiscent of Lohmühlen, which obtained their bark from the Rheinauhafen. Part of the market quarter was already called Lohmarkt in the 12th century. Other examples are the Lohmühleninsel on the Landwehr Canal in Berlin- Kreuzberg, where Lohe had been produced since 1750, and the Löbervorstadt district in Erfurt . Family names such as Lohmann , Lohmüller , Löhrer , Loher , Löhr or Luerer also go back to this craft.
- Fritz Stather : Gerbereichemie und Gernahmechnologie , 4th edition, Akademie Verlag, Berlin 1967.