Using Salt as a Food Preservative

Misconceptions about Preserving Foods with Salt

Homemade Preserved Lemons with Salt
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Preserving food with salt is an ancient human practice that dates back before written records. Beef jerky, pickles, and smoked salmon are all examples of common foods that are preserved using salt. But are salty foods really safe to eat? How does salt as a preservative compare with other methods of food safety?

Salt as a Preservative

Salt has been used as a preservative for ages, and works to preserve food in two ways:

  1. Salt dries food. Salt draws water out of food and dehydrates it. All living things require water and cannot grow in the absence of water, including the bacteria which can cause food poisoning. Salt is used to preserve beef jerky by keeping it dry, and it prevents butter from spoiling by drawing water out, leaving just the fat.
  2. Salt kills microbes. High salt is toxic to most (not all) microbes because of the effect of osmolarity, or water pressure. Water diffuses between cells in the environment so that the concentration of solutes (such as salt) are the same on both sides of the cell. In very high salt solutions, many microbes will rupture due to the difference in pressure between the outside and inside of the organism. High salt can also be toxic to internal processes of microbes, affecting DNA and enzymes. Solutions high in sugar also have the same effects on microbes, which is why it is used as a preservative of foods such as jams and jellies.

    Misconceptions about Salt Preservation

    Many people believe that saltier foods are more resistant to microbial growth. As a result, they are more willing to consume questionable foods if they have higher salt contents.

    Here are the facts. Most bacteria, with the exception of halophiles (salt-loving bacteria), cannot grow in conditions where salt concentration is greater than 10 percent.

    Molds can withstand even higher salt levels. To get 10 percent salt, you would need to dissolve 180 g salt in 1800 g water, which is approximately equivalent to 1 cup of salt dissolved in 7.5 cups of water.

    How salty is 10 percent salt? Have you ever accidentally swallowed water when swimming in the ocean? Seawater is 3.5 percent salt. Imagine drinking seawater that is three times saltier.

    What Foods Have Enough Salt (>10 Percent) to Stop Bacteria Growth?

    Here is a sample list of foods which many people would consider “salty.” The percentage of salt is calculated by dividing the total weight of the food by the weight of salt.

    • 1 serving McDonald’s French fries (medium): 266 mg/117 g = 0.2 percent salt
    • 1 serving Doritos, Nacho Cheese flavor: 310 mg/50 g = 0.6 percent salt
    • 1 serving Campbell’s chicken noodle soup (condensed): 890 mg/126 g = 0.7 percent salt
    • 1 serving Hormel’s Spam: 767 mg/56 g = 1.4 percent salt

    Note that none of these are even close to the 10 percent salt cutoff for preventing bacterial growth. Traditionally salt-preserved foods are either dried, such as beef jerky, or require refrigeration after opening, such as pickles or cured ham.

    What about Brines and Condiments?

    Brines and condiments are known to have high salt content, but do they meet the 10 percent salt requirement to inhibit bacterial growth?

    • 1 packet ketchup: 67 mg/6 g = 1.1 percent salt
    • 1 packet mustard: 57 mg/5 g = 1.1 percent salt
    • 1 packet soy sauce: 493 mg/8 g = 6.1 percent salt
    • Poultry brine: 180,000 mg/7560 g = 2.3 percent salt

    So, even soy sauce is not salty enough to prevent bacterial growth. Why can it be kept unrefrigerated? Since soy sauce does not have other essential ingredients necessary for microbial growth, such as proteins or carbohydrates, there is little risk to leaving it out on your countertop.

    What about Traditionally Salt-Preserved Foods?

    So far, the foods we've listed are known to be salty, but aren't usually foods in which we consider salt to be the reason the food can be safely eaten.

    How about the foods that are traditionally thought of as salt-preserved foods?

    • 1 dill pickle: 1181 mg/135 g = 0.9 percent salt
    • 1 piece beef jerky: 443 mg/20 g = 2.2 percent salt
    • 1 serving ham: 1.2 percent salt

    Even traditionally salt-preserved foods do not meet the 10 percent salt requirement to stop microbial growth. But additional features about these foods, such as dehydration (beef jerky) or addition of acid (pickles) or preservatives (ham), help prevent spoilage. In addition, many salt-preserved foods require refrigeration after opening in order to slow microbial growth.

    Do Higher Salt Levels Prevent Spoilage Better than Lower Salt Levels?

    For most edible foods, the answer is no, a higher salt concentration doesn't help keep your food fresh unless you want to risk getting sodium poisoning. Most foods listed above have salt levels less than 2 percent (with the exception of soy sauce).

    Higher Salt May Actually Help Bacteria Grow

    Did you know that bacteria grow best in conditions saltier than most foods we consume? Science labs where bacteria is routinely grown for experiments use a solution called “LB,” or Luria Broth, for optimal growth of bacteria. What is the salt concentration of LB? It is 1 percent, or roughly the saltiness of a dill pickle.

    Salt Intake is a Public Health Problem

    Even if salt were a good preservative, would it be a good idea? It's thought that the salt content of the Western diet is contributing to poor health, including kidney disease. From heart disease, to autoimmune disease, to osteoporosis, learn why you may want to throw away the salt shaker to live longer.

    The Salt of This Article

    There seems to be plenty of evidence that salty foods aren't microbe proof foods. That said, anyone asking these questions and learning about food safety is a very wise consumer. Food poisoning is common. In fact, roughly 75 percent of "stomach flu" in the United States is actually food poisoning.

    While salt isn't the solution, there are many things you can do to keep your food safe. First of all, practice good kitchen safety. Never use the same cutting board for raw meat and vegetables or fruits. Buy foods well before the expiration dates. Even if a food is not expired, if the smell is suspect, throw it out. Stay up to date on the news to hear of any food poisoning outbreaks. Avoid unpasteurized milk to reduce your risk of milk-borne infections.

    Refrigerate foods promptly after eating and use safe food storage practices. Heat foods thoroughly when re-heating. It's important to note that even reheating can sometimes lead to food poisoning. Some bacteria, such as Staph, produce toxins. While the bacteria are killed in reheating, the toxins are heat stable and persist. Finally, learn to recognize the signs and symptoms of food poisoning and talk to your doctor if you are not feeling well.

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