Salt of the Earth

From the salt store to the plate...

it “only” takes 270 million years.

Figure 1: Graphic on Carl Ochsenius's bar theory (drawing by Jan Schönfelder 2021)

270 million years ago, the Earth's mainland formed only one continent, Pangea. It was surrounded by a huge ocean. According to the “bar theory” of geologist Carl Ochsenius (1830−1906), salt water flowed from the ocean across a narrow strait into a large depression on the edge of Pangea. A shallow inland sea emerged. The evaporation of seawater increased the salinity in the inland sea. Carbonate rocks, sulfate rocks and rock salts were deposited. Potassium-magnesia salts were also formed as the inland sea dried out. This process was repeated seven times in what is now northern Germany. In Bad Salzdetfurt, the bottom of this primeval inland sea is at a depth of 2,000 meters.

Salzdetfurth's salt hats

Table salt was produced in Salzdetfurth for many centuries. In the 12th century, salty springs (brine springs) were discovered in what is now the city area. Salt boiling huts were built, which were called “Soltkothen” by the Low German-speaking people in Salzdetfurth. Inside there were large heated pans in which the brine from the springs was brought to the boil. The salt boilers, known as “Sölter” in Low German, allowed the brine water to boil away in the pans and skimmed off dirty foam during the boiling process. They filled the remaining salt mass into cone-shaped baskets to dry. Later they turned the baskets inside out: shaped salt hats emerged.

Figure 2: Replica of a Soltkothe in the old museum on St. Georgsplatz with a salt pan, fuel, table salt and the characteristic salt baskets. The hooks with which the salt pan is held on wood are part of the Salzdetfurth city coat of arms. (Photography 2018)

A path to sustainable salt production

The brine springs in Bad Salzdetfurth had a salt content of around eight percent. In order to extract table salt from it, the salt boiling process was used exclusively for centuries. At times more than 30 boiling pans were in operation - the consumption of firewood was very high. For the Salzpfännerguild, sustainable forest management in the surrounding timber mountains was an indispensable prerequisite.

In the 18th century, a new process, the graduation towers, became widespread to increase the saturated salt content of the brine in Salzdetfurth to 28 percent. The brine was pumped over the graduation towers up to ten times. Impurities remained in the branches of the blackthorn tree that were installed in graduation towers and water from the brine evaporated. Between 1746 and 1749 three graduation towers with pumping systems were built. This made it possible to noticeably reduce wood consumption.

Figure 3: Illustration: The saltworks in operational condition: At today's museum entrance there was an extension with an industrial chimney. Immediately behind them are the much longer graduation towers, which were dismantled in the 1970s due to their poor state of preservation. (Photography circa 1940s or 1950s)

Potash salts in Bad Salzdetfurth

The salt rocks sylvinite and carnallitite were mined in Bad Salzdetfurth. Sylvinite consists mainly of the mineral sylvine and halite, carnallitite consists of carnallite and halite. Halite is also known as table salt and rock salt. Sylvinite can be recognized by its typical orange-red color. Carnallitite usually looks red, less often white or green. Both salt rocks are called potash or precious salts. Until the 19th century, they were also called “waste salts” because they were removed after mining as a worthless by-product.

In 1856, miners in Staßfurt near Magdeburg came across carnallitite. They recognized its great value as a potassium fertilizer and soon afterwards the mining of potassium salts began in Germany and eventually in other countries around the world. In 1896, potash mining also reached Salzdetfurth - in that year the first shaft to extract potash salt was sunk.

Figure 4: Underground in the Salzdetfurth plant: The different colors of the salt rocks can be clearly seen: from white to orange to a reddish-brown tone. The color depends on the components and the pressure on the salt rocks during their millions of years of formation. (Photography 1987)