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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 safer to eat?
Salt as a Preservative

Salt preserves food in the following ways:

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. 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.
Salt kills microbes. High salt is toxic to most microbes because of the effect of osmolarity, or water pressure. 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 is greater than 10%. Molds can withstand even higher salt levels. To get 10% 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% salt? Have you ever accidentally swallowed water when swimming in the ocean? Seawater is 3.5% salt. Imagine drinking seawater that is 3 times saltier.
Which foods have enough salt (>10%) 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% salt
1 serving Doritos, Nacho Cheese flavor: 310 mg/50 g = 0.6% salt
1 serving Campbell’s chicken noodle soup (condensed): 890 mg/126 g = 0.7% salt
1 serving Hormel’s Spam: 767 mg/56 g = 1.4% salt

Note that none of these are even close to the 10% 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% salt requirement to inhibit bacterial growth?

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

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

Even traditionally salt-preserved foods do not meet the 10% 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, unless you want to risk getting sodium poisoning. Most foods listed above have salt levels less than ~2% (with the exception of soy sauce). But 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%, or roughly the saltiness of a dill pickle.