Fermentation is a metabolic process in which microorganisms convert carbohydrates into alcohol, acids, or gases. In food preservation, fermentation creates an acidic environment that prevents the growth of spoilage and pathogenic microorganisms. Fermented foods include sauerkraut, kimchi, yogurt, Cheese Making, bread, beer, wine, and vinegar. The process also enhances the nutritional value of the food by producing vitamins and breaking down anti-nutrients.
Fermentation is one of the oldest food preservation methods, with evidence of fermented beverages dating to 7,000 BCE in China. Fermented vegetables were a staple of the Roman diet, and sauerkraut was introduced to Europe by Genghis Khan's armies. In the 19th century, Louis Pasteur demonstrated that fermentation is caused by living microorganisms. Modern fermentation science has isolated specific bacterial strains for consistent, predictable results.
Lactic acid fermentation is the most common type for vegetable preservation. Lactic acid bacteria (Lactobacillus, Leuconostoc, and Pediococcus species) are naturally present on fresh vegetables. When vegetables are submerged in a salt brine, the salt inhibits undesirable microorganisms while allowing lactic acid bacteria to thrive. The bacteria produce lactic acid, lowering the pH to 3.5 to 4.5, which preserves the vegetables.
Fermentation vessels include glass jars, ceramic crocks, food-grade plastic buckets, and stainless steel containers. The vessel is cleaned and sanitized before use. A weight holds the vegetables below the brine surface to prevent mold growth. Airlocks allow carbon dioxide to escape while preventing oxygen from entering. The fermentation temperature is maintained at 15 to 22 degrees Celsius (60 to 72 degrees Fahrenheit) for most vegetable ferments.