“Fermentation is one of the oldest and simplest means of preserving foods. It requires no particular kind of climate, no cooking, and so no expenditure of fuel: just a container, which can be a mere hole in the ground, and perhaps some salt or seawater,” quoted from the ever-insightful Harold McGee, author of On Food and Cooking: The Science and Lore of the Kitchen.
The third article in this mini-series is going to be scientific and a little bit nerdy. Get ready to learn the nitty-gritty behind fermentation.
Fermentation begins in the vegetable or fruit. The naturally-occurring microbes in the food proliferate under the right conditions – namely, under the lack of air. At the same time, these beneficial microbes suppress the growth of harmful microbes that rot the fruit or vegetable. The good microbes metabolize the plant’s sugars and carbohydrates before the bad microbes get a chance. In a way, fermentation is a “controlled-rotting” process: the difference between sauerkraut and rotting cabbage is which microbes are allowed to grow.
When protected from air, these microbes get to work producing lactic acid, alcohol, carbon dioxide, and other compounds and nutrients.
Ferments can be made by crushing the vegetables or fruit until enough liquid is let out, ensuring that the vegetables are covered and protected from the air. Usually, though, the vegetables need a little bit of help: salt draws out the liquids, sugars, and other nutrients, and so ferments are often dry-salted or submerged in a salt-and-water brine before being stored in a covered container.
As the plants ferment, much of the material remains intact, hence crunchy kimchi and sauerkraut as opposed to being mushy or slimy (two problems which usually signify contact with air; check out a great troubleshooting link). As the vegetables ferment, not only do they retain their vitamins, but additional nutrients are formed in the process: namely Vitamin B, folate, and the production of enzymes. New flavors and aromas begin to develop, and continue to age and change for as long as you ferment your food.
The salt concentration of the brine and the temperature during fermentation are the two main components that determine which beneficial plant microbes flourish and, consequently, the flavors and aromas that result. Vegetables with a low-salt brine and fermentation under low temperatures will produce mild but complex flavors with Leuconostoc mesenteroides. Fermentation done in high temperatures will produce almost exclusively lactic acid bacteria, from the Lactobacillus plantarum microbe. Also, fermentations undergo a dual process: they produce the first microbe, Leuconostoc mesenteroides, which is then taken over by Lactobacillus plantarum during the second stage of fermentation.