Fermented vegetables include any type of vegetable that is preserved by lactic acid bacteria. Raw, fresh vegetables are submerged in a liquid in a sealed container until they break down, releasing lactic acid and taking on a sour flavor. The longer the vegetables ferment, the more sour they taste, but they still retain many of their nutrients regardless of how long they sit. Lactic acid bacteria is released as the vegetables break down, preventing spoiling agents from forming and ruining the vegetables. Many kinds of vegetables can undergo fermentation, but cabbage is an especially common choice.
While whole vegetables are sometimes used for fermentation, most individuals shred or cut them into small pieces first. Cutting the vegetables increases the surface area, meaning that more area comes into direct contact with the liquid, which speeds up fermentation. The vegetable pieces are usually crushed, releasing their juices, and submerged into a salty liquid in a mason jar or crock. After sealing the container, an individual keeps it at room temperature for the first few weeks, but must keep it cool after a month or more passes.
Salt water and whey are the most common types of liquid to use for fermenting vegetables. Any moisture the vegetable contains gets drawn out by the salt through osmosis, which helps preserve the vegetable and prevent mold from developing. Using salt water for fermentation creates crisp vegetables but can give the final product a very salty taste. Whey ferments infuse vegetables with beneficial bacteria not found in salt water, but those who use whey for fermented vegetables still add a small amount of salt to the liquid. Since it is a by-product of milk, individuals with an intolerance or allergy to dairy should not consume vegetables fermented using whey.
Containers used for fermented vegetables must have a tight seal, since extended exposure to air can cause the vegetables to spoil. Mason jars are the simplest container to use for fermented vegetables; they are easy to obtain and prevent most excess air flow. A crock is a special container with a V-shaped gutter that keeps a thorough seal on the container while letting out gas bubbles that form as the vegetables break down. Some crocks even have weights inside that keep the vegetables submerged in their liquid, which ensures preservation and speeds up the process of fermentation.
A wide range of fermented vegetables exists, but cabbage is an especially popular choice due to the high levels of lactic acid bacteria it contains. Sauerkraut is a popular type of fermented cabbage found in the cuisine of several European countries, including Germany and Poland. Kimchi is typically made with napa cabbage and various spices, and is native to Korean cuisine. Similarly, suan cai is a type of pickled cabbage common to Chinese cuisine and curtido, which often contains a mixture of lightly fermented cabbage, onion, and carrot, is common to Salvadoran menus.