Curing vegetables in salt encourages fermentation, which in turn produces food-preserving acids. Plant foods are filled with benign bacteria, which grow under the right conditions and suppress the development of other bacteria that cause spoilage and disease. The good bacteria do this by being the first to metabolize the sugar in the vegetable, cutting off the food supply for the bacteria that cause spoilage. For example, cabbage contains salt-tolerant Coliform bacteria that produce acid that creates favorable conditions for Leuconostoc bacteria, which in turn produce acids favorable for Lactobacillus.
Antibacterial substances are produced along the way—notably lactic acid, carbon dioxide, and alcohol—that impede the growth of organisms that would otherwise rot the food. Not only do the fermenting bacteria leave most of the plant’s nutritional substances intact, including fiber and Vitamin C, but the process of fermentation also increases the amount of B vitamins, adding aroma and tang. Although most any fruit or vegetable can be fermented, among the most common are olives, cucumbers, cabbage, lemons, and radishes.
Sauerkraut and kimchi are examples of vegetables that may be cured with just salt, made through the process of fermentation by bacteria in the presence of water, where 2-3% of the entire mixture is salt. The bacteria are native to the cabbage, and break down the carbohydrates in the cabbage to create lactic acid. The environment must be carefully controlled to prevent contact with atmospheric oxygen, but allow gases produced in fermentation to escape. If the mixture is exposed to oxygen, it will promote growth of molds, yeasts, and other spoiling microbes.
The role of salt in sauerkraut production is crucial. First, it pulls fluid rich in sugar out of the cabbage, creating a place for the beneficial bacteria go grow and produce acid. Second, it prevents the growth of microbes and pathogens that would otherwise spoil food.