According to The Spruce Eats – There are three types of fermentation:
Lactic Acid Fermentation
Lactic acid fermentation is the type of fermentation at work when making fermented foods like kimchi and sauerkraut. How it works is that foods like cabbage are submerged in a salty brine. Salt kills bacteria that cause food spoilage, but doesn’t harm lactobacillus bacteria, which are present pretty much everywhere, including on cabbage and other foods. So after a while of soaking in this salty brine, the lactobacillus go to work converting the carbohydrates in the vegetables into lactic acid, which in turn aids in preservation while also imparting a tangy flavor. Tofu, miso, soy sauce, and even ketchup and pepperoni are also made using lactic acid fermentation.
Ethyl Alcohol Fermentation
Ethyl alcohol fermentation is what gives us beer, wine, sprits as well as bread. Note that sourdough bread uses a combination of ethyl alcohol and lactic acid fermentation. The yeast gives the bread its rise while the lactobacillus gives it its sour flavor. Beer and wine typically undergo two stages of fermentation, known as primary and secondary fermentation. The primary stage triggers a rapid production of alcohol, while the secondary stage is slower and helps to develop more complex flavors.
Acetic Acid Fermentation
Some people regard acetic acid fermentation as a third type of fermentation, although it is arguably a version of ethyl alcohol fermentation. It’s the process that turns wine to vinegar, so if you were wanting to make wine, it’s not good, but if your goal is vinegar, then it’s great. How it works is that certain bacteria, known as acetic acid bacteria, oxidize alcohol and sugar to to form acetic acid, which, when highly diluted, is simply ordinary vinegar. In addition to vinegar, this process is also a secondary fermentation stage in making kombucha, following the initial stage of ethyl alcohol fermentation.
Picking foods is different from fermenting. While the sour flavor of the food is the same, the process is quite different. Pickling involves submerging your foods into a vinegar brine. This will also preserve the food, but the healthful micro-organisms will not be present.