“Never underestimate the power of a microbe!” Louis Pasteur at his best. This statement by the father of microbiology shows how useful bacteria can be to humans. These powerful creatures in the body keep us healthy and heal our bodies. In the world around us, they prove essential as well. In biotechnology they are used for applications in healthcare, agriculture, industrial processes and the environment. One application for example is the directed use of organisms in the food industry.

Man can use microorganisms to produce food and other useful substances. They grow very quickly and need only simple nutrients. This makes them suitable for, for example, fermentation processes. Bacteria help in the production of dairy products such as cheese, yogurt and butter. Yeast is an essential component in the brewing of beer and wine and in baking bread.


It was Louis Pasteur in the 19th century who proved that fermentation is caused by the growth of microorganisms. Fermentation means converting organic materials into a product, with the aid of bacteria, fungi or yeasts. The technique has been traditionally used to preserve food longer.

When microorganisms start to grow due to heat and moisture they create enzymes. These enzymes are proteins that allow or accelerate certain chemical reactions. They will change the acidity, taste, smell, appearance, digestibility and the shelf life of the product. This is fermentation. Fermentation can happen by the addition of microorganisms, but may also happen spontaneously.

Fermentation by yeasts

Alcoholic fermentation

Alcoholic fermentation is a fermentation process that produces alcohol by yeasts and certain bacteria. The yeast Saccharomyces cerevisiae converts sugar (glucose) into alcohol and carbon dioxide (carbonic acid) in the preparation of bread, beer and wine. Yeast is actually a single-celled, microscopic fungus that uses sugar as a nutrient.


Sugar is converted into alcohol and carbon dioxide during the fermentation process involved in making bread. The yeast cells produce gas bubbles that are trapped by the wheat gluten. They get stuck in the dough and the bread will start to rise. This is the fermentation process. The fermentation takes place in a short period of time so almost no alcohol is formed. This minute amount of alcohol evaporates during the baking process.


When brewing beer, carbon dioxide and ethanol (alcohol) are produced by the fermentation of sugar. Carbon dioxide adds the characteristic fizz to the beer. The Saccharomyces cerevisiae influences the fermentation process in normal beers. Certain special beers such as Belgium’s Geuze use other yeasts and bacteria. An interesting little tidbit for beer lovers: lagers are produced by bottom fermentation at a temperature of about 10°C. In contrast to these bottom-fermented beers, beers of high fermentation are produced at a temperature higher than 18°C, which is called top fermentation. And finally there is also a refermentation. This takes place in the bottle and is typical of abbey beers.


Vinification or winemaking requires fermentation as well. Ripe grapes contain lots of sugars in the form of glucose and fructose. Under the influence of yeast, the sugars are converted into alcohol and carbon dioxide, i.e. it is the wine yeast cells that convert the natural grape sugar. This process not only generates heat but also specific aroma and flavour components that stay hidden in fresh grape juice. In this case fermentation converts fresh grape juice into wine. There are two types of wine yeast cells that are suitable for the fermentation of wine: the known Saccharomyces cerevisiae and the Saccharomyces bayanus. Wines with an alcohol percentage up to 16 percent can be obtained through natural fermentation.

Series set around the process of making beer, in a US microbrewery.

Fermentation by fungi

In the fermentation process of soybeans fungi are the driving force. Fermented soybeans provide a rich assortment of foods such as miso and soy sauce. They owe their strong and distinctive flavour to the prolonged fermentation of the beans. Other popular products include soy tempeh, tofu and natto. For these products, the beans have gone through a quick fermentation process. It is the Rhizopus mould, which is responsible for fermentation. Under the influence of this fungus a natural lactic acid fermentation takes place in the water in which the beans are steeped. You can also artificially initiate the fermentation by adding lactic acid or acetic acid after the soaking process.

Fermentation by bacteria


In the production of yogurt, cheese and sausages lactic acid bacteria are essential. This usually involves bacteria such as Lactobacillus, Lactococcus and Streptococcus.

They are used in the production of dairy products such as cheese, cultivated (real) butter, sour cream, buttermilk, yogurt and kefir. These lactic acid bacteria feed on the sugars in fresh milk. The main sugar in milk is called lactose. Lactose is converted to lactic acid by these bacteria, hence the name lactic acid bacteria. During the fermentation process, the texture and the flavour of the milk changes: the milk becomes thicker and more acidic.

Pickled products

Lactic acid bacteria are also used in combination with acetic acid bacteria for the pickling of olives, preserved cucumber (pickles) and sauerkraut.

Tea and coffee

Believe it or not, bacterial fermentations also come in handy in the production of tea and coffee.

Fresh tealeaves are rolled and dried at a temperature of 25°C and a high humidity of 95%. This process frees the characteristic scent and flavour. This is the fermentation process of tea, which takes about 4 to 5 hours.

Fermented tea is black tea. The colour and the flavour are determined by the degree of fermentation. The longer the tea is fermented, the darker and stronger the flavour of the tea will be. Green and white teas are not fermented. In dry form they are green rather than black and they have a softer flavour.

In the production of coffee a fermentation process takes place as well. Fermentation is often used in order to create a useful product, but in the case of coffee it is about breaking down “waste”.

The coffee bean is contained in the coffee berry. When the berry is picked, the pulp is removed. A portion of this pulp, however, will stick to the bean. The natural yeasts and bacteria on the berry form enzymes, which are capable of degrading this layer of mucus. After this fermentation process the bean only needs to be washed and behold: a pure coffee bean.

Fermentation by bacteria and fungi

Fermentation by bacteria and fungi are another way to go. This happens with salami and Camembert.


Salami is fermented meat that is aged at warm temperatures. In this process lactic acid bacteria arise which ensure that competing organisms cannot survive. They break down proteins and fats in small aromatic moieties. While the sausage dries the salinity increases and a harmless white layer may arise. This fungus on the outside of the sausage enhances the taste and ensures that the sausage spoils less quickly.

Brie and Camembert

Brie and Camembert are actually cheeses with a surface mould. During the maturation process they develop a fluffy layer of fungi, which produce enzymes that make the cheese soft inside.

Fermentation throughout the centuries 

Fermentation processes have helped people preserve food throughout the centuries. We are so accustomed to fermented foods that we sometimes forget that they are the result of microorganisms. Fermentation and the use of bacteria, fungi and yeasts is part of our daily life and food.

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