• Salt is a basic element for the preservation of food, especially meat and fish. Since prehistoric times it has been the oldest additive used in food and one of the main pillars of all cultures. Sea salt is a natural element that gives flavour to food, but is harmful to the human body. 
  • From the Middle Ages onwards, the salt mines turned the Galician coastline into a highly productive area. Salt production played a very important role in supporting fishing, as it allowed fish to be preserved and exported.
  • The introduction of tin cans to market fish after 1840 put an end to salting as the main method of preserving this foodstuff.

The O Ulló saltworks complex has a large artificial rectangular pond that was built taking advantage of a natural open inlet at the bottom of the estuary. 

Compartments of a salt mine in Aveiro (Portugal). M. Munné. Year 1945

It is a 7.78-hectare salt production area divided into three spaces: a water storage area, an evaporation area and a third area for crystallisation. All of them were filled using the force of the tides by means of interconnected floodgates and water channels.

The largest vessel or lagoon, located to the east of the salt pans, measures 12.74 ha and was built to create a pond in which to accumulate the water needed to power the tidal mill.

The rectangular space dedicated to evaporation and crystallisation was divided into grids in the form of orthogonal pits or ponds separated by runs and benches.

Ideal reconstruction of the salt pans at O Ulló
Current state of the O Ulló salt pans
  1. Storage area: the seawater remained stagnant for about 30 days until it reached approximately 18ºB, which allowed the salt to pre-crystallise. The Baumé scale (B), named after the French pharmacist Antoine Baumé (1728-1840), measures the level of salt concentration in the water.
  1.  Once it had reached the right level of salt concentration, the water was transferred, by means of channels, to the evaporation zone and, from there, passed to the crystallisers. Part of the seawater evaporated in these tanks thanks to the action of the sun and the wind.
  1. In the crystallisation zone, the water increased its temperature for about 15 days until it reached 22ºB or 24ºB, which allowed the salt to crystallise definitively, thus allowing it to be harvested. 

The salt pans of O Ulló to the east are delimited by thick perimeter walls (between 2 and 5 m. wide and between 2 and 4 m. high) that defend them from the onslaught of the sea.

In the salt pans, the marnotos or salt workers carried out their work in a completely handcrafted manner. They used flat hooks, stretchers, carts, rolls and shovels to collect the salt in the salt pans that were erected on the smaller sides of the grids used for crystallisation. The salt was then kept outdoors on the threshing floors for two days to dry and whiten, at which point it was ready to be stored in the salt cellar.

Tools and workers at the Aveiro salt works. M. Munné. Year 1945
Monumental fireplace of the Granxa das Salinas

To the southwest of the salt works at O Ulló, in the middle of the nearby forest, the remains of what was once the Granja de las Salinas, the main residence of the administrators of the salt works, who also ran a livestock farm, can still be seen. This building, of great architectural quality, conserves its monumental lar (lareira in Galician), all carved in top quality granite masonry. Next to this building, another attached two-storey house served as a dwelling for the farm’s landlords.

It is also certain that somewhere near the salt pans there was a salt storehouse, as well as shelves in which to store the tools and utensils needed for daily work.

The salt harvest

The preparatory work for the salt harvest began in the spring and the actual harvest was completed in September. The work involved was as follows:

  1. Cleaning and conservation: this consisted of extracting the water that had accumulated during the winter, as well as rebuilding and consolidating the passageways, the floors of the salt pans and the walls of the salt pans. This process took place from March to May approximately.
  1. Curing of the soil: this took place during the month of June and consisted of preparing the salt pans for the salt harvest, hardening and drying the soil of the pits to compact and smooth it, thus creating an impermeable mat that would facilitate the crystallisation and collection of the salt.
  1. Production: this is when the seawater enters the crystallisers to start the evaporation process. It took place between the months of July and September. Once the water had disappeared, the salt was transported in baskets and stretchers to the threshing floors, where it was piled up in conical or longitudinal salt cellars. The salt was then transported to the storehouse for storage.
Outline of working in a salt works

Once in the crystallisers, salt crystals appear on the surface of the water, which we know today as fleur de sel. This crystalline crust was a problem in the salt formation process, as it hindered the evaporation of the water underneath. To avoid this, the marnoto stirred water and broke this layer with the help of a rodo or trollo.

Once the seawater had evaporated completely, the marnoto gathered the salt at the end of the pit, where it was left to drain for several hours. The salt was then taken up to a passageway, forming a pile that was left out in the open to dry completely. Finally, the final product was transported in baskets and stored in the alfolí.

The salt harvest was completed in September. After that, the salt mine was abandoned and flooded for the whole winter.

Marnotos and seasonal workers

Different workers worked in the salt pans. The main one was the master salt mine worker or marnoto, a specialised worker who was responsible for keeping the salt works in a good state of conservation throughout the year. During the months when the salt was harvested, the owners also employed salineiras, waiters and carters who were responsible for supporting the work of the marnotos, cleaning the salt pans and transporting the salt from the salt pans to the alfolí or salt warehouse.

Marnotos working in a salt mine in Aveiro, Portugal, in the 1960s.

Did you know that?

  • The seawater enters the main tank of the salt works through a sluice using the force of the tides.
  • The salt pans are rectangular pits or ponds in which the salt water evaporates, allowing the salt to crystallise. 
  • The salt pans, delimited by benches, were interconnected by gates that opened and closed the marnotos, so that the water passed from one salt pan to another by decantation.
  • Collecting and cleaning the salt, preventing the dust from mixing with it, was an essential task of the master salter and the marnotos who worked in the saltworks.
  • The word “salary” (from the Latin salarium) comes from the time when Rome paid its soldiers a sum of money to buy salt. Nowadays, the salaried worker (participle of the verb wage-eaner) is the person who receives a salary for his or her work.
Remains of the salt mines of Larache


  • Alfolí: salt warehouse built of wood or masonry, usually rectangular in shape, with a ground floor and a gabled roof.
  • Rodo: this is a flat handle made up of a long handle, one end of which has a cross-shaped plank that allows it to rake and pile up salt. In Portuguese it is called rasoila.
  • Bancas: the very solid walls between 2 and 2.5 m thick and 3-4 m high that delimit the salt pans. They have a total length of 334 (main bench) x 500 m (dividing the lagoon from the benches).
  • Banquetas: the low walls that delimit the rectangular salt pans or crystallisers that allow the salt to be extracted. There is no trace of them in the O Ulló salt pans.
  • Channels: Artificial bed of variable dimensions built to introduce the water into the threshing floors or crystallisers. They are still visible at O Ulló.
  • Carts or wheelbarrows: human-powered device for transporting salt, consisting of a trough-shaped container for the load and a wheel.
  • Spade: utensil made up of a wooden sheet, generally square or rounded in shape with a certain concavity, which is adapted to a handle and was used to load the salt into the carts.
  • Palanquin bearers: utensil made up of two thick sticks with planks crossed in the middle, which was used to transport salt between two people.
  • Hut: A rudimentary wooden construction covered with reeds and other grasses. It had an earthen floor and was used to store tools, as well as shelter for the marnotos in bad weather.
  • Salt cellars: cone-shaped piles of salt that are placed to dry on the lower sides of the benches.
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