Lake Grassmere today with its crystallisation Ponds. Compliments of Dominion Salt - Natural Salt Division
DID YOU KNOW?
The ponds pink coloration has two causes.
First, the normally green micro algae (Dunaliella salina) that live in the brine form a red pigment in high salt concentrations. The same algae gives the Red Sea its name.
Second, tiny pinkish-red shrimps – more commonly known as ‘sea monkeys’ – also inhabit the brackish waters. These small creatures are found in solar salt works all over the world.
These do not remain in the final stages of the production leaving NZ salt a nice cream colour.
Salt for the young New Zealand Colony
Salt is the main mineral in sea water, making up three-quarters of the 3.5% of dissolved minerals in sea water. Salt also occurs naturally in mineral deposits, where it is known as rock salt. Because New Zealand has no rock salt deposits, salt was imported from the time of European arrival in the early 1800s until the country developed its own NZ salt industry in the 1950s.
Salt was never produced by Māori in New Zealand. Nevertheless, Māori had a conception of saltiness in their word mātaitai, meaning tasting of salt, or brackish. Their sodium needs were met through a diet of fish and shellfish.
The beginnings of NZ salt production
In 1844 the Nelson Examiner reported that salt had been successfully evaporated from sea water in the local estuary. In 1866 an import duty was imposed on salt in the hope that this would stimulate domestic production. It did not. The government was keen to establish local industries. In 1892, the Department of Mines put a notice in the New Zealand Gazette , offering a bonus for the production of 500 tons of salt, locally. The bonus was never claimed because all early endeavours failed. Early salt makers struggled with the country’s high rainfall. In their efforts to produce solar evaporated salt, they set up industries in places as diverse as Rangitoto Island, Gisborne, Māhia Peninsula, Breaker Bay in Wellington, and New Brighton in Christchurch.
In 1942 Christchurch businessman George Skellerup became interested in making rubber, for the War effort. His business needed salt so he started constructing a NZ salt works at Lake Grassmere. Skellerup's plans for 20 concentration ponds covering over 400 hectares were never completed because of wartime shortages of equipment and floods.
Two years later a thin salt crust had formed in the final concentration ponds. After years of setbacks, the first NZ salt of any quantity, some 45 tonnes, was collected manually.
LAKE GRASSMERE - main center for NZ salt production
Until the 1940s the lake bed at Grassmere, Marlborough, was a mud bath in winter and a dust bowl in summer. Natural deposits of salt were only occasional.
Low rainfall (about 585 millimetres per year), makes Lake Grassmere well suited to solar salt production. In addition, the large area of flat land that makes up the lake bed is away from large rivers and close to the sea so it can draw in salt water. High evaporation from sun and wind occurs during summer, and the site has ready access to both sea and rail transport.
Customizing NZ salt production process
Manufacturing salt at Lake Grassmere is a process of concentrating the salt content of sea water by evaporation, then harvesting the crystallised salt.
Sea water is pumped through a series of ponds, which concentrate the water, and towards the end, crystallise the minerals out of it. NZ salt works has been modelled after overseas saltworks. But most located closer to the equator, thus relying mainly on the heat of the sun to evaporate sea water. NZ salt makers at Grassmere soon found that it was wind, rather than the sun, that did most of the work. Scientists then designed a process of moving the brines (salty water) from pond to pond as their concentration of salt increased. This special system, tailored to Marlborough’s unique evaporating conditions, increased the harvest year by year.
Demand exceeds production
In 1962, the design was perfected and new crystallisation ponds were built. The vastly improved works produced 28,000 tonnes of salt in 1965.
By 1970 the NZ salt harvest had increased to almost 52,000 tonnes, but this could not match demand, which had grown with industrial development. In 2005 Lake Grassmere provided for about half of New Zealand’s salt requirements.
Specialised industrial requirements are met through bulk shipments of salt from the Caribbean & Australia to Mt Maunganui where a vacuum salt plant has been built.
http://www.teara.govt.nz/en/salt (Full story by Carl Walrond, published 12 Jun 2006)