Dominion Salt was established in this location in 1942 by our founder George Skellerup. During the Second World War years chemicals where in short supply, which included chemicals that used salt (Sodium Chloride). George recognised this and travelled to Lake Grassmere near Blenheim in NZ’s South Island to establish a salt industry.
The Lake Grassmere site was chosen for its large areas of suitable flat land, high sunshine hours and the dry nor-westerly winds which perfectly suited the solar evaporation process for salt making. Lake Grassmere continues to harvest and manufacture salt at this site today.
Seawater contains just over 2.5 per cent sodium chloride, together with significant amounts of other salts. Some 60,000 – 70,000 tonnes of salt are harvested from Lake Grassmere each year. Seawater is pumped into the 688 hectare main lake continuously through the summer. As nature does its work and evaporation increases the sea waters strength, it is pumped into a series of concentrating ponds, where further evaporation takes place.
When the brine reaches saturation point it is transferred into crystallisation ponds during the summer months. The salt making season is of six months duration commencing in early October. Harvesting salt usually begins by early March and can last from four to six weeks. During this time the salt crust is lifted from the bottom of the ponds by harvesting machinery, transported to two washing plants where it is washed in brine before stacking in 20 meter high piles.
The stacks of salt can contain 100,000 tonnes of salt and are readily visible by day and night from the Blenheim-Christchurch main highway. Salt production is highly dependent on low rainfall and evaporation, so it is necessary to hold large stockpiles of salt to counter the fluctuations in annual production.
As well as harvesting salt, Lake Grassmere has a refinery and during this process the salt is rewashed, crushed, dried, and screened before being packed into bulk bags or small bags then palletised ready for distribution.
Salt destined for the domestic table salt market accounts for a very small fraction of the harvest. This product is iodised and processed at the Cerebos Skellerup packing plant also located at Lake Grassmere.
In the early 1970’s, it became apparent than even with an annual output of 60,000 tonnes Lake Grassmere could not meet industry’s growing need for salt. In 1971 at Mount Maunganui in the North Island New Zealand, a site was chosen for a plant to process bulk salt from either Lake Grassmere or overseas. Situated adjacent to one of New Zealand’s largest export ports – the Port of Tauranga and in close proximity to key consumers such as the pulp and paper industry the site proved ideal.
During 1973 to 1974 Dominion Salt commissioned a vacuum refinery at Mount Maunganui, with a view to supplying high purity, fine salt for food products. A smaller unit was built at Lake Grassmere in 1974 to 1975. Vacuum salt is of much higher purity than solar salt and is formed by the artificial evaporation of treated pure brine in a near vacuum.
The salt is first dissolved, then treated to purify it. The clarified brine then goes through an evaporation plant where crystals are formed in a super-saturated solution. The crystals are removed in a slurry, then dried. Pure Dried Vacuum Salt (PDV salt) is highly versatile and can be used in a wide range of products. As part of the vacuum process pure salt can be separated by screening into fine and coarse particles. Extremely fine salt is milled in a flour-like consistency for use in dairy products and baking.
A Pharmaceutical Sodium Chloride grade was developed in 1977 and is made from specifically prepared high purity brine using the vacuum process. This premium grade meets the Pharmacopeia Standards of British (BP), European (PhEur) United States (USP) and Japanese (JP) and sold nationally and internationally. Pharmaceutical Salt is now our largest export product shipped to over 30 countries around the world.