A Grain of History
Today salt is so cheap and plentiful that it is easy to forget how highly it was once valued. A kilogram can be bought for less than the price of a cup of coffee, and a large share of the salt produced each year is never eaten at all but is spread on icy roads or used in industry. For most of human history, however, salt was a precious commodity, and the effort required to obtain it shaped trade routes, the location of towns and even the policies of governments.
The human body cannot function without salt. Sodium helps to regulate the balance of fluids and allows nerves to carry signals, and because it is lost constantly through sweat, it has to be replaced. Early hunters probably obtained enough from the meat they ate, since animal tissue naturally contains a certain amount of sodium. The need for extra salt seems to have grown when people began to farm. A diet based largely on cereals contains very little sodium, and domestic animals also needed salt to stay healthy. As a result, communities that settled down to grow crops had to find a reliable supply.
The oldest methods of production depended on geography. Along warm coastlines with long dry seasons, seawater could be let into shallow ponds and left to evaporate in the sun and wind. As the water disappeared, the concentration of salt rose until crystals formed and could be raked from the surface. In cooler, wetter regions this process was far too slow, so producers boiled seawater, or the water from salt springs, in large pans over fires. This consumed enormous quantities of fuel, and archaeologists have found that some inland salt-making sites were abandoned once the surrounding forests had been cleared for firewood. A third method was to dig out rock salt, the remains of ancient seas now buried deep underground. Mining was dangerous and expensive, but it produced salt of great purity, and some mines were worked continuously for several centuries.
Much of the value of salt lay in its ability to preserve food. Before refrigeration, meat and fish began to spoil within days, which meant that any surplus from a good harvest or a successful fishing season was quickly lost. Salt draws water out of food and creates conditions in which most harmful bacteria cannot survive. Packed in dry salt or soaked in brine, fish caught in summer could be eaten in the depths of winter or carried hundreds of kilometres inland. Salted food also made long sea voyages possible, since sailors could take months of provisions with them. In this sense, salt did not simply add flavour; it allowed people to store food and to move it.
Because it was both essential and unevenly distributed, salt became one of the earliest goods to be traded over long distances. Merchants carried it on the backs of animals along routes that were used for so long that some of them became permanent roads, and settlements grew up where these routes crossed rivers or met the coast. In certain regions, blocks of salt even served as a form of money and were exchanged for cloth, metal tools or grain. Many towns that later became wealthy owed their early prosperity not to farming but to salt springs or deposits nearby.
Rulers were quick to recognise that a product everyone needed could be a dependable source of income. Taxes on salt were introduced in many parts of the world, and in some states the government took complete control of production and sale. Such taxes had the advantage of being easy to collect, since salt was produced in a relatively small number of places. They were, however, deeply unpopular, because they fell most heavily on the poor, who spent a larger share of their income on basic food. On several occasions, anger over the price of salt contributed to public protests, and smuggling was common wherever the tax was high.
The position of salt changed dramatically in the nineteenth and twentieth centuries. New drilling techniques allowed producers to pump water into underground deposits and bring the salty solution to the surface, which greatly reduced the cost of extraction. Railways made it possible to move large quantities cheaply, and the spread of canning and, later, refrigeration meant that salt was no longer the main way to keep food. Prices fell so far that in many places salt taxes were no longer worth collecting. Today the concern is not that people have too little salt but that many have too much. Health authorities in a number of countries advise adults to reduce their intake, much of which now comes not from the salt added at the table but from processed foods such as bread and ready meals.
