| The store of salt in the oceans is virtually inexhaustible. It has been estimated the oceans contain about 1,370 million cubic kilometres of water. When it is realised that one cubic kilometre of sea water will yield more than twenty million tonnes of salt, one can hardly believe the tremendous quantity of salt contained in the seas. In countries where the climate is generally warm the suns energy is used to evaporate sea water, brine from inland salt lakes, or underground brine to produce "solar evaporated salt". Australia's total production of salt occurs by this method.
Sea water is the basis for producing most solar evaporated salt. It generally contains about 3.4% of total salts, of which 2.7% is sodium chloride. The other main constituents are magnesium sulphate, calcium sulphate and potassium chloride.
Approximate Composition Of Sea Water
| sodium chloride 2.68% |
magnesium chloride 0.32% |
| magnesium sulphate 0.22% |
potassium chloride 0.07% |
| calcium sulphate 0.12% |
other salts 0.01% |
| water 96.58% |
Covering large expances of ground, salt fields rely on the natural evaporative process of the sun and wind to create salt. Ponds are connected in series through gateways to control the flow of brine, maintaining appropriate depths and densities.
The salt water is pumped into a field consisting of a series of shallow concentrating ponds. As the action of the sun and the wind evaporates the water, the solution that remains becomes more concentrated. As the density of the brine increases due to natural evaporation, the brine is slowly moved forward through the concentrating ponds either by gravity flow or pumping. During the high evaporation periods of the year, seawater is continually being added to make up for evaporation loss.
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Every compound has a maximum level of solubility in water at any given temperature. When that maximum point is reached the solution is said to be 'saturated' with that compound. So it is with seawater and salt; the natural evaporation continues until the brine reaches the saturation point at an approximate specific gravity of 1.216 (beginning from seawater at approx. SG1.203. Saturated brine ready for the crystallisation of salt is known as "maiden brine".
Crystallisation and Harvest of Salt
Further evaporation now sees sodium chloride forming, to settle and build a thick, hard layer of interlaced crystals of salt on the floor of the crystalliser. Residual brine (known as bitterns) is discarded and replaced with fresh maiden brine.
The layer of salt is normally harvested once a year. During harvest, the crystalisers are drained one at a time to accept all the machinery. Self-propelled harvested separate and lift the layer of salt from the crystalliser floor. Trucks or conveyer belts take the salt to be processed and stockpiled.
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A number of factors affect the amount of salt produced; warm sunny weather is needed to provide sufficient solar energy and large amounts of land are required for even modest salt production needs. Rains will, of course, dilute the brines and dissolve salt, making low rainfall necessary for at least part of the year.
During the concentration stage the brine begins to take on a distinctly pink or red hue that can clearly be seen in panoramic views across a salt field or in photos. This natural phenomenon is the result of harmless salt-loving bacteria that thrive when virtually all other life does not. The extremely halophilic bacteria develop the red colour due to the carotenoids ßcarotene and bacterioruberin, and use those as a defence against strong sunlight. The halobacteria are present in such large numbers the brine appears pink to red in colour Halobacteria do not survive the drying phase in the factory.
Drying, Crushing, Sieving and Packaging.
As the salt produced by Cheetham Salt is of very high quality at harvest, further processing consists simply of washing, drying, crushing and sieving prior to packaging. The processes are basic and do not alter the natural qualities of the product.
Clean saturated brine is used to wash the salt to improve it's visual quality because it is seen as an important factor in salt for human consumption. Excess brine is removed by centrifuge that literally spins the brine off leaving salt crystals damp but otherwise clean. All of the remaining moisture is driven off by heating to just above 110oC to produce dry, free flowing salt crystals.
Crushing and screening to specific size ranges are the final steps in producing the various salt grades. Sizes vary depending on the use, ranging from very coarse salt used for pickling and presentation of oysters in restaurant meals, right down to micro-fine salt used in making butter. In between there is a wide variety of particle sizes that cater for all needs, from food ingredients to pharmaceuticals, textiles to industrial, stockfeed to swimming pools.
Some products do feature additives to aid in the flowability and anticaking but these are marked on the packaging. Salt may also be used as a carrier for iodine, this being added to 'Iodised Salt' after processing and in accordance with Australian Food Standards.
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