When I was little, I had a hefty chunk of rock salt that sat on a shelf in my bedroom. Every once in a while, I'd pick it up and touch the tip of my tongue to its smooth surface. I was always surprised to taste its saltiness. But somehow I never made the connection between my piece of amber-colored rock salt and the perfect little white crystals in the salt shaker on the dining room table.
Today when I look at a salt shaker I see and smell the ocean. I think of mines deep underground. I also marvel at how important salt has been in human history.
Salt is considered an essential nutrient. It's the only rock that we enjoy eating. Salt is a flavor intensifier in food. Humans like the taste of salt.
Several thousand years ago, people discovered that food, particularly meat and fish, could be preserved by packing it in salt. Ancient Egyptians found that food preserved with salt traveled well and could be traded with people who lived far away. (Egyptians also used salt to make mummies. Bodies were placed in salt for 70 days before being wrapped in strips of linen cloth and entombed.)
Salt became essential. And it gradually became clear that whoever controlled salt's production and distribution was going to be powerful. As the Romans expanded their empire, they developed or captured saltworks along the way. (Salt is also made by evaporating seawater in shallow ponds.) Sometimes Roman soldiers were paid in salt. Salt had a high value and could be consumed or traded for other goods. In fact, the word "salt" is at the root of the word "salary." Have you ever heard the expression that someone is "worth his salt"? It dates from Roman times.
Celtic people mined salt in the mountains of Central Europe for hundreds of years before they were defeated by the Romans in the first century AD. Celtic salt miners discovered they could reach the salt deposits more quickly if they dug shafts at steep angles. Some of these ancient miners would then clamber up and down mine shafts as steep as 45 degrees. They would have a sack of rock salt on their backs and a lighted torch gripped in their teeth for light.
Several centuries later, this area became famous again for its salt mines. The names of two towns in what is now Austria are related to salt: Salzburg means "salt town." Hallein means "saltwork." (Halite is another word for rock salt. It's from hala, the ancient Greek word for salt.)
The merchants of Venice proved that you don't need to mine salt to get rich from the salt trade. They made contracts with saltmakers and then resold the salt at a profit. After Columbus, but long before the Pilgrims settled, Europeans discovered huge schools of codfish off the coast of Newfoundland. Fresh fish would spoil on the long voyage home. But by preserving their catch with salt, fishermen created a new, cheap food source for their countrymen in the Middle Ages. Salted provisions also opened up exploration and settlement: If your food could last a long time, you could stay longer or travel farther.
In the early 1800s, the Erie Canal was dug to move salt from Syracuse, N.Y., east to the Hudson and west to the Great Lakes. It opened America to expansion.
Wars were fought and governments were overthrown partly because of salt. A tax on salt - the gabelle - helped incite the French Revolution of 1789. A British salt tax was one of the taxes protested by the American colonists that led to the Revolutionary War. Salt taxes helped topple the Chinese Imperial government in the early 20th century. Mohandas Gandhi protested British salt taxes in India in 1930. Gandhi became a central figure in India's struggle for independence, which succeeded in 1947.
Salt had a lot to do with where settlers settled. An early map of North America shows a seemingly random pattern of roads. Where were they going? According to Mark Kurlansky, who wrote "Salt: A World History" (Walker & Co., 2002), some of the seemingly haphazard roads were former animal trails that led to salt licks. Salt licks are places where salt springs exist or rock salt is exposed. Buffalo, N.Y., was one such area. Herds of buffalo created a broad road to a salt lick.
Salt is acquired in three basic ways. In solar evaporation, seawater is pumped into large shallow ponds or pans. As it sits, the sun's heat evaporates the water. Salt crystals settle to the bottom of the ponds, which are then raked. The process takes a while, and requires sun and wind to be effective. Evaporation ponds are still found in places like the Bahamas and Mexico, but in the 19th century, there were many evaporation pans on Cape Cod, in Massachusetts. Saltmakers there pulled big covers over their salt pans on rainy days.
Vacuum evaporation is the way most table salt is produced. Saltmakers pump brine out of the ground. Brine is water with a lot of salt dissolved in it. It's much saltier than seawater. Brine may occur naturally or it can be created by pumping water into a salt deposit.
The brine is first purified, then boiled in a vacuum evaporator. A vacuum evaporator is very energy efficient, since a liquid boils at a much lower temperature in a vacuum. This method produces uniformly sized salt crystals and the purest sodium chloride, which is the chemical name for salt. In the industry, most table salt is PDV, or "pure dried vacuum" salt.
Salt can also be mined. Geologists find where salt deposits - dried-up ancient seas - lie underground. Shafts are sunk and tunnels are dug through layers of rock salt. The layers may be a few feet or hundreds of feet thick. Rock salt is excavated the way you mine any hard rock deposit, like coal. (See story on facing page.)
The Wieliczka Salt Mine in southern Poland, near Krakow, has been in use since the late 1200s. Over the centuries, miners carved sculptures out of the rock salt. The mine contains entire underground churches, altars, and dozens of life-size or larger statues. It's a popular tourist spot.
The United States is the world's top salt producer. In 2002, it made or mined 48 million tons of it. Most salt is used in industry. Its next biggest use is as a road deicer, followed by use in water softeners, in agriculture, and finally as table salt. According to the Salt Institute, a US-based industry group, salt has more than 14,000 uses and the average American uses (directly or indirectly) 402 pounds of salt every year.
The next time you pick up a salt shaker, tap a few crystals in your hand. Look closely at them. Let your mind wander from mummies to medieval salt miners to the Erie Canal. Those tiny crystals helped to create empires and overthrow governments. They made fortunes for merchants, helped feed the masses, and set explorers on their way to discover new lands. Who knew?
Dave Plumeau and I stepped into the elevator that would take us 2,400 feet underground. We were going to a vast salt mine that spreads under Cayuga Lake in Lansing, N.Y. The mine is part of a huge salt deposit left when an ancient sea dried up millions of years ago. Stepping into the elevator was like stepping into a large tin can - it was cylindrical and kind of beat-up looking. It had a high ceiling so that small trucks could be tipped on end and taken down.
Before entering the elevator Mr. Plumeau, a senior engineer for Cargill Deicing Technology here, gave me a miner's helmet (with headlamp), a safety vest, steel-toed boots, and a belt that held my "self-rescuer" unit (in case of carbon monoxide).
This Cargill mine produces about 2.5 million tons of salt each year. Rock salt has been used on winter roads since the 1930s. Salt lowers the freezing point of water, turning frozen water (ice and snow) back into liquid. This is the deepest salt mine in America, a fact I didn't want to think about as we plunged down at 600 feet per minute in a tin-can elevator.
The first thing you notice as you enter the mine is the smell - diesel fuel mixed with salt - and the way the air feels (like being at the beach). Fresh air is pumped down the elevator shaft and circulated by huge fans. It exits from the other elevator shaft. That's the lift for hauling out the salt: 15 tons of it every two minutes.
Next you realize how dark it is, and you're thankful for your little headlamp. The footing is slick because the floor is rock salt, which feels greasy.
We got into a pickup truck and drove through the nine miles of tunnels. Rock salt is mined using the pillar-and-room method. The tunnel is about 30 feet wide and 8 to 10 feet high. Every 30 feet or so stands a huge pillar of salt maybe 15 feet wide that has been left to help hold up the roof. Four-foot-long bolts and plates drilled into the ceiling also stabilize it.
All the machinery is huge. It has to be cut apart to fit down the elevator shaft and welded together again. I watched a miner work a big yellow machine that had what looked like a 20-foot-long chain saw turned on its side attached to the front. He used it on the base of a rock wall to create the floor of a new mine section. Another miner drilled holes in the wall and packed them with explosives. Long fuses ran down the tunnel.
We drove to the end of a tunnel and waited. I felt a huge rush of air, then the muffled "kaboom, kaboom, kaboom!" as the charges exploded.
The pile of rock salt left after blasting is called "muck." After the ceiling and sides of the new section are scraped of loose salt, front-end loaders take over. They scoop up huge bucketfuls of muck and dump them into a bin. The salt falls onto a conveyor that snakes through the long tunnel to an underground room where it's crushed, sifted, and made ready for the trip out of the mine.
On the surface, the salt is bagged to sell in stores or dumped into huge piles. Trucks arrive, load up, and haul it all over the Northeast.