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Understanding Fermentation: A Comprehensive Guide to Transforming Food

If you pluck a tea leaf and try to brew it, you will be very disappointed with the taste of the beverage. However, the same leaves are used to make very tasty tea. It’s all about fermentation, which changes not only the flavor but also the properties of the product.

Fermentation is one of the oldest types of processing, and it has been used for thousands of years all over the world.

Health Benefits of Fermented Foods

  • Fermented foods are better digested than their fresh counterparts and are also richer in vitamins, probiotics, and other potentially beneficial substances.
  • The most familiar examples of fermented foods include yogurt, fermented vegetables, wine, aged cheeses, miso, and kombucha.
  • While most of these foods are not yet fully understood, scientists are inclined to believe that consuming at least fermented dairy products reduces the risk of many chronic diseases and helps maintain a healthy weight.
  • People who are unaccustomed to fermented foods should consume them in moderation at first, as stomach aches may occur.
  • Fermented milk products are beneficial for children and pregnant women.
  • It is important to buy fermented products only from trustworthy sellers. If the production technology is grossly violated, harmful microbes can contaminate the food.

History of Fermentation

Fermentation, as a practice, has its roots in ancient civilizations. Historically, communities have used the principles of fermentation to produce a variety of beverages, including beer from malted barley, wine from grapes, chicha from corn, and octli, now called pulque, derived from agave. Despite its widespread use, the underlying biological mechanisms remained a mystery for centuries.

In the 17th century, Antoni van Leeuwenhoek’s work with microscopes discovered the existence of microorganisms, including yeast. Subsequent improvements in microscopic techniques further elucidated the diversity of microorganisms.

Among the first discoveries was that of Charles Cagnard de la Tour. He found that yeast played a potential role in the fermentation process.

However, the most significant advances in understanding the fermentation process were made by Louis Pasteur in the mid-19th century. Through careful experimentation, Pasteur convincingly demonstrated that live yeasts play an important role in the conversion of glucose to ethanol in fermented beverages. Moreover, Pasteur distinguished two major forms of fermentation: alcoholic fermentation, promoted by yeast, and lactic acid fermentation, driven by bacteria.

In the following years, the scope of fermentation was expanded by the identification of various organisms, including human muscle cells, capable of carrying out this process.

Fermentation vs. Putrefaction

There is a fine line between putrefaction and fermentation. In putrefaction, various bacteria enter the product, not all of which are beneficial. In fermentation, humans artificially create conditions for certain beneficial bacteria to thrive while keeping harmful ones out.

We have various methods to attract beneficial microbes and discourage harmful ones. Some organisms tolerate acid better than others. The same applies to oxygen, heat, and salt. By understanding the specific needs of beneficial microbes, we can manipulate these conditions to favor their growth and activity.

Bacteria and Fermentation

Bacteria are among the earliest life forms on our planet. Only a small fraction of them are known to science. Some bacteria, the pathogenic ones, secrete toxins that can kill organisms much larger than themselves. At the same time, billions of other bacteria, the beneficial ones, live on and inside us. In general, most of them are completely harmless to us.

Lactic Acid Bacteria (LAB) – Lactobacillales

These bacteria, appearing as rods and spheres, are abundantly found on the skin of fruits and vegetables, as well as on human skin. We utilize Lactobacillales for their ability to convert sugar into lactic acid, which imparts the characteristic sourness to pickles, kimchi, and other lactic acid-fermented foods. They thrive in low-alkaline environments. Additionally, they are halotolerant (able to withstand high salt concentrations) and anaerobic, meaning they actively multiply in oxygen-free conditions.

Acetic Acid Bacteria – Acetobacteraceae

Like lactic acid bacteria, acetic acid bacteria are naturally found on the surface of many foods. They acidify vinegar and kombucha by converting alcohol into acetic acid. We often use them in conjunction with yeast, which first converts sugars into alcohol. These bacteria thrive in the acidic environment they create and require oxygen to produce acetic acid, classifying them as aerobic bacteria.

Fact: It is not only the bacteria that are important but also the conditions in which they are used. Without access to oxygen, wine is produced; with access to oxygen, vinegar is produced.

Fungi and Fermentation

The kingdom of Fungi encompasses a wide variety of organisms, from single-celled yeasts to mold fungi or the giant puffball (Calvatia gigantea). Fungi secrete enzymes through their mycelium, breaking down food in their vicinity and then absorbing the nutrients from the environment.

Saccharomyces Cerevisiae – Brewer’s or Baker’s Yeast

Saccharomyces cerevisiae converts sugars into alcohol, giving humanity three of its culinary staples: bread, beer, and wine. Baker’s yeast is widely distributed in nature.

Yeasts can live and multiply in the presence of oxygen, but alcoholic fermentation occurs in an anaerobic environment.


Brettanomyces, a yeast with oblong, cylindrical-shaped cells, is used in brewing to produce beverages with a pronounced sourness. In nature, Brettanomyces is found on fruit peels.

Brettanomyces survives in an oxygenated environment but produces alcohol only under anaerobic conditions.

Aspergillus Rice – Aspergillus oryzae

Aspergillus oryzae is a spore-forming mold fungus also known as koji (or koji). Through centuries of selection, it has acquired the ability to grow incredibly quickly in warm and humid environments when given access to high-starch foods such as boiled rice or barley.

Koji produces enzymes that break down proteins, starches, and fats. It is used to make miso, soy sauces (shoyu), and garum.

Aspergillus Luchuensis

Aspergillus luchuensis, a relative of A. oryzae, processes starches and proteins, producing citric acid as a by-product. In Asia, this fungus is traditionally used to make bragga, the base of spirits such as Korean soju and Japanese avamori.

How is Fermentation Different from Salting and Pickling?

Salting and pickling food cannot be compared to fermentation. It’s like comparing roasting and braising. They are completely different processes that result in different products.

The idea behind fermentation is that we control what the bacteria do for us rather than killing them outright. Ideally, we kill all but one type of bacteria, whereas pickling and pickling usually don’t involve the development of any bacteria – that’s the fundamental difference.

Salting is about regulating the amount of salt, which happens through reverse osmosis (a process where water tends to flow outward to balance the concentrations). The salt doesn’t pass into the product itself, but moisture is released from the product (which increases the concentration of salt inside). At this level of salinity, no bacteria can survive.

When pickling, the product is preserved by adding more salt, vinegar, or other acid. The acid blocks bacteria’s activity and allows the product to stay longer.

Fermentation, on the other hand, requires the growth of bacteria that will later change the product. They will make it softer, modify the fibers, and impart a new taste and smell. Yogurt, miso, and yeast sourdough bread are fermented foods. And vegetables pickled in brine or vinegar are no longer.

Methods of Food Fermentation

There are two main methods of food fermentation.

  • Natural Fermentation

Natural fermentation relies on the microorganisms that are already present in raw foods to transform them. This traditional method has been used for centuries to create a variety of fermented foods. During natural fermentation, the existing bacteria, yeasts, and molds in the food multiply and initiate the fermentation process. Examples of foods prepared this way include sauerkraut and kimchi.

  • Adding Starter Cultures

Adding starter cultures involves introducing a small amount of a pre-prepared microbial culture to raw foods. This method provides greater control over the fermentation process, allowing for consistency and predictability in the final product. Starter cultures can include specific strains of bacteria, yeasts, or molds. For instance, sourdough bread is made using a sourdough starter, while yogurt is made by adding specific bacterial cultures to milk. This method is commonly used in commercial production to ensure that the product has the desired characteristics.

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