Microorganisms - Food Fermentation

Food fermentation is a common technology in food processing. Fermentation is based on the principle of microorganisms turning organic stuff into alcohol, organic acids and carbon dioxide under anaerobic conditions.



One of the oldest kinds of food processing is fermenting. Well-know fermented products include beer, bread, sausages and vegetables. While fermentation processes have been used for thousands of years, Louis Pasteur was the one who discovered the mechanisms by yeasts and other microorganisms in the 19th century. All groups of microorganisms, namely bacteria, yeasts and moulds, are involved in fermentation.

Lactic acid bacteria (Lactobacillaceae) turn milk into yoghurt by producing lactic acid. Milk proteins precipitate and the fluid become thick. Lactobacillaceae are responsible for the structure and the typical taste of yoghurt. Another lactic acid bacterium, Lactobacillus plantarum, lives on cabbage and other vegetables. It is fundamentally in producing sauerkraut (“sour cabbage”). Sliced cabbage is given into a pot (e. g. a crock, a pot from clay) covered with a lid to produce anaerobic conditions. The lid is set under pressure, for example using a heavy stone. Now the bacteria start to work. Given enough time (a few weeks) you will get fine sauerkraut.


Figure 1: Schematic drawing of Sauerkraut production [source: D. Graubaum, Berlin]










The Romans used small fish in a pot, added with salt water or wine to produce paste, so called “garum” or “liquamen” in a similar way. They salted their meal with the paste. It is very salty and smells fishy. Why didn’t they simply use salt? Because they had to pay taxes for salt but not for fish.

Some species of moulds (Aspergillus, Penicillium) are used in fermenting cheese, vines and soy beans. Baker´s or brewer´s yeast is the main component in the baking and brewing process (see chapter yeasts). Enzymes of bacteria decompose macromolecular food components into smaller compounds. This helps us to digest food more easily and the food survive longer storage times. It is a simple way to keep food safe.

Do you know which food is fermented? Discuss the list below:

Black tea, kombucha, olives, bread, cheese, alcohol, non-alcoholic beverage, soy beans, kimchi, mixed pickles, sauerkraut, crème fraîche, fish paste, garum, pepperoni, salami, chorizo, …


Figure 2: Fermented pepperoni [source: D. Graubaum, Berlin]











This article was prepared by Prof. Diana Graubaum, Department of Food Microbiology, Beuth University of Applied Sciences Berlin, Berlin, Germany.

For further questions please refer to: graubaum@beuth-hochschule.de