A graduation tower is a large wooden structure over which brine is channelled. As it flows, the salt solution spreads over a large surface. Some of the water evaporates, while most of the salt stays in the brine, so the salt concentration rises. Historically, graduation towers were used mainly in salt production. Today, many have been preserved as industrial monuments, as part of spa parks or as places to visit.
The graduation tower at a glance
Graduation towers were an important part of many saltworks. Their purpose was to concentrate the brine before it was boiled. The less water the brine contained, the less water had to be removed later by heating it in the boiling pans.
The term “graduation” describes exactly this process: the salt content of the brine is increased through evaporation. To do this, the brine is channelled over as large a surface as possible.
How a graduation tower is built
A graduation tower is made up of several components that together create the large surface that gets wet.
The supporting structure is a sturdy wooden frame. Inside it is a large wall of brushwood, often blackthorn. This so-called thorn wall is made up of many branching twigs, which gives it a large surface area.
At the top of the graduation tower are the systems for distributing the brine. Below the thorn wall, the brine trickling down is collected again.
Historic saltworks often included other components too, such as pumps, pipes, collecting basins and boiling houses. So the graduation tower was usually part of a larger salt production facility.
How a graduation tower works
How it works can be explained in a few steps.
- The brine is carried upwards. From there, it’s distributed across the top of the graduation tower.
- The brine trickles down over the thorn wall. The many twigs spread it over a large area.
- Some of the water evaporates. As the brine comes into contact with the surrounding air, water turns into vapour.
- The salt concentration rises. Most of the dissolved salt stays in the brine.
- The brine is collected at the bottom. Depending on the facility, the process could be repeated several times before the concentrated brine went on to the boiling house for salt production.
In simple terms:
Carry the brine up → spread it over the thorn wall → water evaporates → the brine becomes more concentrated → collect the brine at the bottom.
Blackthorn as a large evaporation surface
Blackthorn was often used for the thorn wall. Its heavily branched twigs create a large surface in a comparatively small space.
As the brine runs over the twigs, it keeps spreading out again, so it comes into contact with the air over a large area. This large wetted surface is what makes graduation work.
So the thorn wall isn’t just a typical visual feature of a graduation tower. It has a central technical function.
From salt production to historic structure
Graduation towers were built mainly for economic reasons. In traditional salt production, water had to be removed from the brine before the salt could be obtained.
Evaporating large amounts of water completely in heated boiling pans needed a lot of fuel. That’s why people tried to let some of the water evaporate naturally beforehand.
Graduation towers made this step possible. The brine was spread over a large surface and concentrated before it reached the boiling houses.
For a long time, graduation towers were an important part of salt production at many saltworks. When saltworks were later able to use brine that was already concentrated, the towers lost this role.
Even so, many graduation towers have survived and still shape numerous former salt and spa towns in Germany today.
Brine, graduation tower and saltworks
The terms brine, graduation tower and saltworks are closely linked, but they describe different things.
Brine is highly saline water.
A graduation tower is a structure over which brine is channelled so that some of the water is removed by evaporation and the salt concentration increases.
A saltworks is a facility or site for producing salt. A historic saltworks could include wells, pumps, graduation towers, pipes and boiling houses, for example.
So a graduation tower was often part of a larger salt production system.
Graduation towers today
Today, many graduation towers are no longer used for industrial salt production. Numerous historic towers have been preserved or restored.
Many are still in operation. They’re often found in spa parks, former saltworks or historic salt towns.
There are many graduation towers in Germany, with different designs, sizes and histories. If you’d like to get to know individual towers in more detail, you can explore the graduation towers of different regions next.
Conclusion
Graduation towers were built to spread brine over as large a surface as possible. As the brine trickles down the thorn wall, some of the water evaporates, which raises the salt concentration of the brine.
Historically, this process was an important step in salt production. Today, many graduation towers have been preserved as industrial monuments and as testimony to the history of saltworks.
This article is for general information purposes only.
