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updated 3/19/2008 4:40:00 PM ET 2008-03-19T20:40:00

One of our readers, Bob Kilpatrick, sent me an e-mail asking about the differences between salts. He noted that “these days it seems that there are more varieties of salts popping up on the store shelves; but truthfully isn’t salt … salt?”

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What might be surprising to learn is that salt is sold in many different sizes and forms, depending on its intended use. Although sodium chloride is the main component of all salt, the texture and shape of the crystals also impacts on taste and how the salt reacts with food. The three main varieties of salt are table salt, kosher salt and sea salt.

Coming from the earth or the sea, fine table salt usually contains additives to keep the small crystals from clumping due to moisture, which is more common in salts with smaller crystals. One such additive, iodine, has been added to table salt for years to help prevent iodine deficiency disorders (IDD). In the U.S., this process has effectively eliminated IDD, but around the world IDD continues to be a problem. Salt contains little iodine naturally, so fortifying it with added iodine can be an effective dietary solution, and the technology for doing so is readily available and inexpensive.

Kosher salt crystals are larger and coarser, and contain no additives. Many chefs prefer to cook with kosher salt, thanks to its crunchier texture and seasoning capabilities. This salt is also used to kosher meat. Harvested like table salt, kosher salt is raked during evaporation, giving the grains a blocklike structure.

Sea salt, like the name implies, is produced through the evaporation of seawater, and is usually less dense than table salt, and therefore less salty. Sea salt can come in different colors and adds either a briny, sweet or bitter taste to food, depending on the type of natural impurities it contains.

Other varieties of salt include fleur de sel, a slow-melting, hand-harvested crystalline salt that provides an earthy, pleasing flavor; chunky rock salt, which is used for making ice cream and de-icing roads; and fine-grained, concentrated pickling salt, which is used for brining pickles and sauerkraut.

Most salt is produced by one of three methods. The first and oldest method is called solar evaporation, and has been used since salt crystals were first noticed trapped in pools of seawater. Solar salt production is the process of capturing salt water in shallow ponds, and then allowing the sun to evaporate most of the water. Mechanical harvesting machines then gather the concentrated brine, and remove impurities. The result is pure salt crystallization.

A second common method is called rock salt mining, one of the most dramatic methods of gathering salt. Mined salt appears in veins or domes, which are formed as pressure from the Earth forces salt up through cracks in bedrock. Salt is mined by a room-and-pillar method in a checkerboard pattern, leaving some salt pillars up for roof support. Once above ground, rock salts are separated by size and shipped to customers.

The third method is called vacuum evaporation, or the evaporation of salt brine by steam heat in large commercial evaporators. This method, which results in high-purity salt that is fine in texture, is accomplished through the drilling of wells in salt deposits. Water is pumped into the well, dissolving the salt, and pushing the resulting brine up to the surface. Brine is then transferred to a processing area and boiled until all water is evaporated.

The National Academy of Sciences recommends that Americans consume a minimum of 500 mg/day of sodium to maintain good health. Most Americans, however, consume much more than that — on average, about 3,500 mg/day. A minority of the population can lower blood pressure by restricting dietary salt, but there is no conclusive evidence that reducing dietary sodium improves the risks for heart attacks or strokes in the general population.

In fact, two recent studies provided conflicting results. In April 2007, the British Medical Journal looked at two prior clinical trials and found a 25% lower risk of cardiovascular events in a group that had reduced their sodium intake years earlier. Meanwhile, an October 2007 analysis of a large Dutch database, published in the European Journal of Epidemiology, documented no benefit of low-salt diets in reducing death rates, stroke or heart attack. So, it seems, the verdict is still out.

What we do know is that the body’s salt-to-water ratio is vital to sustaining a healthy metabolism. Human blood contains .9% salt, which helps us maintain the electrolyte balance we need in and out of cells. Inadequate salt can lead to dehydration, especially in athletes.

China surpassed the U.S. as the world’s top salt producer in 2006, producing 48 million metric tons. The U.S. came in second, with 46 million metric tons. Germany, India and Canada produced 18, 16, and 15 million metric tons, respectively. Worldwide production equaled a whopping 240 million metric tons.

Throughout history, salt — or sodium chloride — has played an important role as one of the world’s most effective food preservatives. Salt was used well before recorded history, played a vital part in the European exploration of the Americas, and has served a key role in many wars, economies and religions — as well as in diet and folklore.

Phil Lempert is food editor of the TODAY show. He welcomes questions and comments, which can be sent to phil@supermarketguru.com. For more about the latest trends on the supermarket shelves, visit Phil’s Web site at SuperMarketGuru.com.

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