How much peat is needed for 1 cubic meter salt?
dr. K.A.H.W. Leenders
Almost 700 years ago, around June 24, 1301, the village of Oudenbosch (prov. North-Brabant, The Netherlands) was founded. A long contract tells about peatcutting for the production of turves as household fuel and the production of salt; about the building of sluices, canals, houses and saltsheds.
The events of 1301 are a nice introduction to the problem of the medieval salt production in the estuary of the Sceldt and Meuse rivers in and around Zeeland, The Netherlands. The central question is: how can we sufficiently reconstruct the salt production process, as it was followed in that estuary during the middleages, to be able to estimate the extend of the damage done to the landscape by this process in relation to the damage done by other processes.
The basis elements for this salt production are salt water (sea water), peat, clay, wind and the warmth of the sun. Salty peat is the main unknown element: how much salt did the peat contain, how was the salt bound to the peat, how fast did peat attract the salt and how and how long did it remain salty? From the salty peat turves were cut. After drying this turves were burned to ashes or "zel". From the ashes a brine was made by mixing with seawater and from the brine the salt was won by a cristallisation process. The efficiency of the whole saltproduction process is also not fully known.
In the 15th century the salt production on the basis of salty peat was replaced by refining of imported raw salt from southern Atlantic coasts. This was much cheaper. But this replacement may also have a connection with the widespread landscape damage done by the peat extraction. That is at least the "standard history". But nobody ever produced numbers or sufficiently accurate maps to support this claim. We need to know how much peat was cut away for the saltproduction or for the production of turves, and how much of the damaged peaty landscape was destroyed by the sea during strong gales and between the gales by the daily tides.
About the ashes left over from the salt production: Zelas at Steenbergen
There is a nice 16th c. painting Darink Delven at the Zierikzee townhall-museum, showing the first phases of the saltproduction process.