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When eating, I am often guilty of a slightly heavy-handed useof salt. This activity ionically attracts unsolicited advice fromfriends, family and strangers – the core of which is that salt is‘bad’ for me. When quizzed for details, my educator usuallymakes vague reference to blood pressure and heart disease. Myblood pressure and markers for heart health are much betterthan average for my age, and my life-long disdain for popularopinions on health matters remains.

I have always argued back to the salty nay-sayers that mybody contains around half a kilogram of salts and that the fewmilligrams I am about to ingest hardly merits consideration. Ialso note that without salt in our diet we don’t survive very long.Indeed, migration patterns of ancient humans usually followedcoastal regions where salt was readily available and onlyextended inland when either salt deposits were discovered ortrading allowed reliable supply from coastal regions. That is, saltis a necessary input into our diet without which we cannot live.

Before the advent of technology, humans got their saltthrough ingestion of seafood or the use of dried ‘rock’ saltfound in naturally available deposits. By dry weight, sea salt isusually (it varies in coastal regions, near rivers for example)55.03% chloride, 30.59% sodium, 7.68% sulfate, 3.68%magnesium, 1.18% calcium, 1.11% potassium and trace levelsof bicarbonate, bromide, borate, strontium and others. Due tothe sequential precipitation in evaporating salt water bodiesthat form rock salt deposits, sodium chloride levels in rock saltsare typically 90–98%, the remainder being the usual sea saltminerals but in lower relative quantities.

But of course, humans being humans, we started playingwith these compositions as soon as we had the nous to do so.Driven by supply issues, and later on by food aesthetics as wellas productivity and profit motives, we have over a few thousandyears managed to reduce food salt to (almost) pure sodiumchloride plus a bunch of unnatural additives; more on this later.

In ancient times, humans either mined rock salt or extractedsalt from sea water by filling a ceramic pot with sea water(which is only around 2.5% total salts) and boiling it until itwas dry. This netted a greyish, somewhat hygroscopic salt withthe full gamut of trace minerals. The rest of the history of saltproduction can be summarised by three major innovations.

Firstly, humans started using concentration ponds toprecipitate and dry salt water, either brine from mines or seawater, whereupon careful removal of the layers of dried saltprecipitates resulted in various grades, including the preferredsodium chloride-rich evaporate (halite) for table salt use.

Later on, concentration ponds were used in series so thatunwanted and less soluble salts were first crystallised in onepond and then the pure sodium chloride brine was pumped intoits own pond to allow precipitation of a more pure saltproduced by a higher yielding process. Modern salt works havevery complex interdependent pond systems, so this is an over-simplification of what they are really up to. Chemical additives

are often added at each stage to help precipitate or floatunwanted impurities.

For over a hundred years, salt production facilities havebeing using a process in which the concentrated sodiumchloride brine from the pond system is thermally evaporatedunder near-vacuum conditions in a series of tanks. The resultingslurry is dried by centrifuge and a fluid bed drier, and containsvery pure sodium chloride cubic crystals of near-uniform andcontrollable dimensions – the perfect table salt. Salt productionfacilities, by extracting and purifying all the salts separately,can sell various salt types and grades for different consumerand industrial applications.

Common table salt is so ubiquitous that is viewed by healthauthorities as a useful carrier for a number of food additives,including iodide, fluoride and folic acid. These are variablyadded to salt to help combat common health issues associatedwith the deficiency of these chemicals in the average diet. Theaddition of iodide also requires the addition of a stabiliser, suchas sodium thiosulfate, sodium bicarbonate, basic phosphates ordextrin (yes, there may be sugar in your salt) to preventoxidation of the iodide to iodine.

Sodium chloride crystals are cubic and their flat surfaces aresusceptible to fusing together, especially in the presence ofwater. Anticaking agents are added at around 0.5% by weight toprevent this issue and can include desiccants such as sodiumalumina silicates, calcium silicates, calcium carbonates, calciumphosphates and magnesium carbonates. These desiccants areadded as very fine powders (relative to the sodium chloridecrystals) so they also act to physically inhibit the interactionsof sodium chloride crystals. Sometimes salt precipitation ismanipulated by using ferrocyanide salts to produce non-cubicsalt crystals that are less prone to caking.

Of late I have noticed the emergence of ‘sea salt’ as ahealthy alternative to ‘table salt’. Some salt is even labelled as

Chemistry in Australia36 | Dec 2014–Jan 2015

A very large grain of salt

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Salt stock pile at Dampier, Western Australia.

‘organic’! This is another example where common terminologycan confuse the chemically trained. All the salt that weconsume originates from the sea and yet some is confusinglyand proudly labelled as ‘sea salt’. What we normally don’t knowas consumers is how a particular ‘sea salt’ has been processed.It could be from some natural deposit or from a brine pondsystem, and in both cases it might contain more sodiumchloride than we imagine. The odd thing is that sea salts areusually much less processed than table salt and yet cost muchmore, a reflection of the efficiencies of industrial scaleproduction and also of a little price gouging of health-consciousconsumers by niche operators and retailers.

Does our level of salt consumption actually matter? Notaccording to Scientific American (8 July 2011 and 26 September2012). In these two articles, the author does a very good job ofdeconstructing the arguments and evidence that have beenused to drive the ubiquitous public health messages related tothe risks of high salt consumption. If true, this has frighteningramifications for the faith people might place in our so-calledhealth authorities. In 2013, the US Centers for Disease Controland Prevention retracted their previous advice to Americansthat they keep sodium consumption to less than2300 milligrams a day because a new study found no evidenceto support this previous advice.

Other commentators have taken a different approach andsuggested that natural sea salt, with its wonderful balance of

salts and minerals, can be consumed with abandon but that‘industrial’ table salt is in fact the real culprit that drives healthissues. The evidence supporting this argument is very tenuousbut nevertheless appealing to many. The most likely reality isthat an over-reliance on pure sodium chloride might result in adeficiency of certain minerals if these are not otherwise presentin a diet. In addition, a diet that is rich in industrial table saltis also possibly correlated to processed and fast foods, whichhave other negative health consequences.

For me it is simply a case of consuming carefully chosen and(to me) much tastier ‘sea salt’ – the grey version with salt inthe same proportions to salt in the sea and not the more purerock salt. This way I dodge all the xenobiotic additives inindustrial salt (which may or may not do harm) and get all thetrace elements (which I may or may not need). I tend to usesalt up to a quantitative level that is limited by my body’sreactions (yuk, too salty!). With routine trips to my doctor, Ialso intermittently monitor the key heart-health indicators,which one does anyway. However, the more processed or pre-prepared food I eat, the more industrial table salt that Iunwittingly ingest. If this matters enough to me, or if I everdevelop suspicious health issues, I will know what do.

Chemistry in Australia 37|Dec 2014–Jan 2015

Ian A. Maxwell (maxwell.comms@gmail.com) is a serial (andsometimes parallel) entrepreneur, venture capitalist and AdjunctProfessor in Electrical and Computer Engineering at RMITUniversity, who started out his career as a physical polymerchemist.

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