Worth Its Salt

For many food products, salt is indispensable. Imagine the flat flavor of a dill pickle, a cured ham or a potato chip without salt. Try to effectively and economically make an emulsified meat product or a crispy cracker if salt goes missing. While excessive use and subsequent excessive intake have painted this ingredient as nutrition's foe - more about that later - most food technologists consider it a good formulating friend.

Common, or table, salt consists mainly of sodium chloride (NaCl). Food-grade salt has a fairly high purity (most commercial brands contain 99.8% to 99.95% NaCl) that varies depending on its sources and processing, but can contain other substances, especially calcium, magnesium and potassium salts. Manufacturers require a high-purity salt "in any application where the impurities will cause an adverse reaction or detract from the quality of the finished product," says Jim Barron, technical services specialist, Morton International, Inc., Chicago. "Characteristics of high-purity salt are: high sodium chloride, more than 9.93%; low calcium and magnesium, less than 60 ppm; and tight specifications for sediment, less than 1 ppm extraneous matter."

Commercial salt may also contain additives, especially conditioning or free-flow agents, such as sodium hexacyanoferrate (II) decahydrate (also known as sodium ferrocyanide, yellow prussiate of soda or YPS). Although many think most salt contains iodine for fortification purposes, "very little iodized salt is used in food processing in the United States," notes Barron. "Iodized salt in this country is used in the home. In other parts of the world, iodization of salt is mandated for all salt, including salt used for food processing."

Manufacturers make food-grade salt by mining underground deposits, either directly or by dissolving the salt and pumping out a saline solution, or by evaporating sea salt. They then dry the brine through solar or physical, generally vacuum-pan, methods. "Evaporated salt produced domestically is obtained by dissolving underground rock-salt deposits, or redissolving solar salt and thermally evaporating the brine," says George Lutz, quality assurance technical service manager, Cargill Salt, Minneapolis. "If brine treatment is performed, purity levels of 99.95% as sodium chloride and higher can be obtained."

Today, sea salt has taken on a certain cachet. Many upscale, "gourmet" versions have been naturally evaporated by wind and sun and so contain all of the salts found in seawater, with sodium chloride at approximately 78%. "This does not meet the Food Chemicals Codex standard of 97.5% minimum for solar sodium chloride," Lutz observes. They also contain a high percentage of magnesium salts that impart a bitter taste. "In fact, they are the primary component of 'bitterns,' the salts left behind during solar-salt production of sodium chloride," he continues. "They are also highly deliquescent, drawing moisture readily from the air." However, he notes, the minimum purity of U.S. food-grade sea salt (99.8%) meets Codex criteria for both solar and evaporated sodium chloride (97.5% and 99% respectively).  

Salt crystals typically take a cubic form and are colorless. The crystal size varies when the tiny cubes bind together through ionic bonding of the sodium. And processing can provide specific sizes. These factors result in ingredients that range from a fine, pulverized salt of about 4 microns in diameter, to coarse, rock pretzel salts with a diameter of more than 1,000 microns.

In addition to pulverizing or grinding salt to effect a smaller particle size, salt manufacturers can also physically compact the salt to provide a flake shape. Or, they can use the Grainer evaporation process to form pyramidal, hopper-shaped crystals, often referred to as Alberger salt, that readily break into flakes with an uneven surface that enhances cling and solubility.

Salt is one of the four major sensory tastes and also enhances flavor, muting acidity and enhancing sweetness. In addition to this role, it also acts as a functional ingredient in many foods, contributing to their texture and structure by reacting with proteins, and controlling fermentation and lending preservation by altering aw and osmotic pressure.

Among its many functions, salt strengthens the wheat gluten in dough, providing uniform grain and texture. It allows the gluten to hold more water and carbon dioxide, so the dough can easily expand without tearing. In meat, it also increases water-binding by protein, raising yield and firming the texture. Salt helps extract proteins, which promotes binding between pieces of meat in processed meats and enhances the formation of emulsion in emulsified sausages.

Its many functions led to the creation of many salt forms with varying attributes: adherence, bulk density, blendability, crystal count, caking resistance, flowability, friability, liquid absorption, mean particle size, solubility and specific surface.

"Most of these attributes are due to the particle size and shape of the crystal," says Lutz. "Perhaps the three most critical attributes that dictate performance are adherence, blendability and solubility. For example, does the salt adhere to the chip and provide a clean salt taste because it dissolves instantly on the tongue? Does the salt blend well due to crystal size and shape and stay blended throughout packaging, shipping, stocking and use to maintain consistent shelf appeal and flavor profile?"

Purity is also critical in certain applications, notes Barron: "glass pack pickles, where excessive amounts of calcium and/or magnesium will cause cloudy brines; margarine and spreads, because calcium and/or magnesium may create problems with the emulsion, causing weeping; mayonnaise and salad dressing, because low calcium and/or magnesium helps maintain flavor and color; meat and poultry, where excessive calcium and/or magnesium causes numerous adverse effects in marinated and injected meat and poultry products."

According to Barron, "Calcium and magnesium will reduce the effectiveness of sodium tripolyphosphate in meat curing by precipitating free phosphate. Calcium and/or magnesium are pro-oxidants and may adversely affect meat color." In addition, an extremely low level of extraneous matter provides an appearance advantage in products such as spreads, margarine, mayonnaise and salad dressing.

What about the relationship between salt and hypertension? The numbers vary, but conventional wisdom says that it's not a problem for everyone. Dr. Myron Weinberger, director of the Hypertension Research Center at the Indiana University School of Medicine in Indianapolis, and author of a study that gauged the effects of salt intake, estimates that about 26% of Americans with normal blood pressure and about 58% of those with hypertension are salt-sensitive.

In fact, several studies reported in Hypertension and American Journal of Hypertension point out that low-salt diets can increase death rate, and that severe salt restriction can raise blood pressure (causing kidneys and adrenal glands to pump out large amounts of hormones that elevate blood pressure) and blood cholesterol. Evidence also points to the intake (or lack) of other minerals, such as potassium, calcium and/or magnesium, which might contribute to sodium's hypertensive effects.

While the jury is still out, the Federal recommendation is no more than 2,400 mg of sodium a day. The estimated minimum requirement for sodium is 500 mg a day. The average U.S. intake falls in the range of 3,000 to 4,000 mg a day.

Food processors that want to create lower-salt products could be faced with a dilemma: Reduce the salt and adversely affect the finished product. However, the best scenario is for manufacturers to optimize the type and amount of salt for each application, while consumers do their part by watching their intake.

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