Ayr, Waggon Road, Blackthorn Salt, Graduation Tower

NS32SW 1046.0 NS33625 22983 Ayr, Waggon Road, Blackthorn Salt, Graduation Tower

NS32SW 1046.01 NS33573 22909 Ayr, Waggon Road, Blackthorn Salt, Pan House

1. Idea for the thorn saline Graduation Tower

The Graduation Tower was designed by Gregorie Marshall Managing Director of Peacock’s* of Ayr. Gregorie and Whirly Marshall became intrigued by creating food salt on the site of historical Ayrshire saltpans – originally a traditional industry until the 19th century in Scotland with its heyday in the 17th and 18th centuries prior to the introduction of Biscay salt and salt from other parts of the world.

Other salt small scale producers in Scotland tend to use brine from wells, as in Germany and Poland. However, none of them use the Graduation Tower method which is a Central European technique, originally using rock salt brine at about 8% salinity.

On the island of Tiree, Scotland, sunshine used in salt production and on the island of Skye, also in Scotland, polytunnels used as part of the evaporation process. So, Blackthorn is marketed as an ‘Eco’ salt as low energy levels are required to produce food salt using the Graduation Tower technique.

The Graduation Tower measures 8m by 25m and is of an ‘A’ frame construction. It is constructed from Douglas Fir and larch and blackthorn twigs and has 54 wooden taps at the top of the structure to moderate the trickle of the saline solution, depending on prevailing wind and sun. The tower works all the year round, even in a light drizzle of rain. Using 1600s knowhow from Germany and central east Poland, it is a relatively speedy process, producing a good quality salt. It is the only Graduation Tower in Europe that works as originally intended – for seawater salt extraction.

The last graduation tower producing salt for consumption was in Poland (brine springs) in the 1950s and now used as part of a spa complex, not for food preservation or human consumption. There are probably few people left who have built a graduation tower or have worked in one. So, the recreation of the Graduation Tower in Ayr involved a lot of research and development.

The blackthorn tower has a large surface area so the seawater is spread along the twigs increasing the surface area from which water can evaporate to remove the salt from the brine. The blackthorn twigs themselves will be replaced in 7-10 years and sourced from Dumfries, Ayrshire and Poland, although his supply line has not been fully developed as yet as still an infancy producing salt like this (first producing salt in 2020). The blackthorn is packed snugly to allow air to circulate. Strathclyde University worked with the Marshalls to improve the science and technology behind the blackthorn tower – specifically on the angle of the thorns to maximise the time droplets are kept on the twigs. The angle of the tower in relation to the prevailing wind was also calculated so that only the water evaporates efficiently and the salt stays. Modern equipment has been added, such as pumps and sensors which can control the now 20% (from 3%) brine ‘mother liquor’ flowing from the tanks to the pan house which is in a separate structure on site. The sensors can sense if the concentration of the brine is dropping, say when too much precipitation in the air. Salt can take 5 hours to 2 weeks to go through tower to reach salinity needed for the PAN HOUSE and is dependent on humidity. Blackthorn Salt has a beige tinge to it due to the tannins present in the blackthorn twigs.

Seawater is taken from Troon along the coast as the water there is regularly monitored for purity as langoustines are fished there. Also, there are no nearby burns running into the sea diluting the salinity as at Ayr.

2. Process

• TANKER brings in water (strained through a net to remove foreign bodies from the brine)

• The brine (salt water) is allowed to settle in a in tank and is filtered – 3% salinity at this point

• This 3% saline solution is sent to the Graduation Tower and circulated up to 5 times to reach 22-25% salinity – (26000 litres sea water reduced to 2,000 litres of sea water in tower so GRADUATION TOWER evaporates 24000 litres of water (in traditional salt pans 6-10 tons of coal needed to produce one ton of salt)

• 2000 litres at 22/25 % salinity is then pumped to the Pan House

• The saline solution is heated in a ‘bath’ (tank) in the Pan House for 5 days to create salt crystals very slowly and at a low temperature (of around 60 degrees C)

• The salt crystals grow slowly and capture more minerals, so 94% NaCl (sodium chloride) (Saxo is 99.9%; sea salt flakes – 99%), so 0.9% difference makes a great difference in the taste.

• The excess water is pumped out and the salt is scooped up and collected in bins

• It is then out into the oven to dry for 1 hour

• It then goes through a magnet and may be milled slightly

• It is then packaged and dispatched to customers.

• The Graduation Tower can process more water than just one bath and bath not running at full capacity

• Oil power and solar panels used for power

• Packaging bought from a local company in Irvine

*Blackthorn Salt is a product made by Peacock’s - salt dealers since the 19th century (started out as shipping agents in Glasgow) who supply de-icing salt for schools and Councils but do not make salt on site. There are, apparently, 14000 uses for salt.

Visited by HES, Heritage Research Service, (Miriam McDonald) 05 November 2021; information from Whirly and Gregorie Marshall, owners of Blackthorn Salt.