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Fermentation Definition, Types, Principle, Products, Stages, Limitations

Fermentation is among the oldest techniques for processing food. The term “fermentation” refers to a procedure where chemical changes take place in organic substrates through the action of enzymes created by microorganisms. For instance yeast enzymes transform starches and sugars into alcohol, and proteins are transformed into peptides or amino acids. The fermentation process takes place without oxygen which produces ATP (energy).

It converts NADH and pyruvate that is produced during the glycolysis process into NAD+ as well as various other molecules, based on the kind of fermentation. The microorganisms involved in fermentation are primarily L.A.B. such as Enterococcus, Streptococcus, Leuconostoc, Lactobacillus, and Pediococcus and also yeasts and molds like Debaryomyces Kluyveromyces, Saccharomyces, Geotrichium, Mucor, Penicillium, and Rhizopus species.

History of Fermentation

The word “ferment” comes from the Latin word”fervere,” which translates to “to boil.” The process of fermentation was discussed by alchemists in the 14th century’s late 14th century however, not in a modern sense. The process of fermentation was the subject of scientific study in the 1600s.


The process of fermentation is natural. It was used to create wines mead, cheese and beer well prior to the time when biochemical processes became known. Between 1850 and the 1860s, Louis Pasteur became the first scientist or zymurgist to investigate fermentation after he proved the cause of fermentation was living cells. Yet, Pasteur was unsuccessful in his efforts to isolate the enzyme that is responsible for yeast cell fermentation. It was in 1897 that German scientist Eduard Buechner crushed yeast, extracted liquid from them, and discovered that the liquid could be fermented in into a sugar solution. Buechner’s discovery is considered to be to be the first step in the field of biochemistry. He was awarded his 1907 Nobel Prize in chemistry.

Definitions of Fermentation

Following are some examples of the term “flourish. They vary from general, informal usages to more precise definitions.

  • Food preservation methods using bacteria and microorganisms (general usage).
  • A large-scale microbial activity that occurs in the air or without (common definition in the field of industry).
  • Any process that results in the production of drinks that are alcoholic or dairy products that are acidic (general usage).
  • The process of releasing energy from the body is only performed under the conditions of anaerobic (somewhat science-based).
  • Every metabolic process that generates energy from sugar or any other organic molecule is not dependent on either oxygen nor an electron transfer mechanism, and relies on an organic molecule as the ultimate electron acceptor (most research-based).

Principle of fermentation

The principle behind fermentation is to obtain energy from carbohydrates, in presence of oxygen. Glucose first gets partially oxidized to pyruvate via glycolysis. Then , pyruvate is converted into acid or alcohol as well as regeneration of NAD+ , which is able to participate in glycolysis to create more ATP. Fermentation is only able to produce 5 percent of the energy produced by aerobic respiration.

Generic pathways for the production of certain end products of fermentation made using glucose by various organisms.
Flowchart: Generic pathways for the production of certain end products of fermentation made using glucose by various organisms.

Fermentation is a biological process that allows the production of energy via the partial metabolism of glucose and various carbon resources. The process of oxidation of the substrate, that occurs via the Embden-Meyerhoff (EMP) and Entner-Doudoroff(ED) pathways is the result of the production of pyruvate ATP in addition to NAD (P) H. In the absence of electron acceptors The pyruvate undergoes a reduction, which is followed by the regeneration of NAD+(P). This step is crucial in order for the process of fermentation to proceed and results in the production of various products (ethanol as well as organic acids). ATP is the principal product of fermentation and is created through phosphorylation on the level of the substrate. NADH can then be re-oxidized changing back to NAD+ in the next stage of fermentation, which reduces pyruvate to the fermenting products, like lactate and ethanol. For instance, during the glucose fermentation process by Streptococcus lactis it converts pyruvate into lactic acid, which is used to create NAD+ coenzymes, so the two ATP molecules are made. In yeasts such as Saccharomyces When pyruvate is transformed into ethyl alcohol (ethanol), NAD+ is then transformed.

Types of fermentation

1. Lactic acid homofermentation

Glucose → Lactic acid

Homolactic fermentation takes place by bacteria that belong to the genera Lactococcus, Enterococcus, Streptococcus and Pediococcus. It is also carried out by certain species of the Genus Lactobacillus. Homofermentative LAB converts glucose into the acid lactic. Lactococcus spp. is utilized for the starter dairy cultures.

2. Lactic acid heterofermentation

Glucose → Lactic acid + Acetic acid + Ethyl alcohol + 2CO2 + H2O

Heterolactic fermentation is performed by the bacteria belonging to the genera Leuconostoc, Oenococcus, and Weissella and through heterofermentative lactobacilli. Heterofermentative LAB can ferment glucose by using lactic acid, ethanol/acetic acids and carbon dioxide (CO2 ) as by-products. 

3. Propionic acid fermentation

Glucose → Lactic acid + Propionic acid + Acetic acid + CO2 + H2O

Propionic acid fermentation can be conducted by various bacteria that belong to the Genus Propionibacterium along with it is known as Clostridium propionicum. Propionic acid fermentation is a process in which lactate and sugar can be utilized as the primary substrate. If sugar is present in the bacterium, they make use of the EMP process to create the pyruvate. The pyruvate is carboxylated and converted to oxaloacetate. It is it is then reduced to propionate through fumarate, malate, and succinate. Other products that result from propionic fermentation include acetic acid and CO2.

4. Diacetyl and 2,3-butylene glycol fermentation

Diacetyl and 2,3-butylene glycol fermentation
Diacetyl and 2,3-butylene glycol fermentation

Butanediol fermentation can be carried out by the genera Enterobacter, Erwinia, Hafnia, Klebsiella, and Serratia. The reactions that result in the creation of 2,3-butanediol require the use of a double decarboxylation process.

5. Alcoholic fermentation

Glucose → Ethyl alcohol

Alcoholic fermentation is one of the most known of all the fermentation processes. It is performed by yeasts, as well as other bacteria and fungi. The initial stage of the alcohol fermentation process involves pyruvate. It is created by yeast through its EMP pathway, whereas it is extracted through the ED pathway for Zymomonas (bacteria). The redox balance in alcohol fermentation is achieved through the process of regeneration of NAD+ through the reduction of acetaldehyde the ethanol.

6. Butyric acid fermentation

Glucose → Acetic acid + Butyric acid

Butyric acid fermentation is a characteristic of many obligate anaerobic bacterial species that are mainly part of the Clostridium genus. Pyruvate, in turn, is transformed into acetyl-CoA through the production of H2 and CO2. The acetyl CoA component is transformed to acetic acid, which is produced by ATP production. Certain bacteria, like Clostridium Acetobutylicum, produce less acids and produce more neutral substances which is why they perform the acetone-butanol fermentation.

Types of fermentation
Types of fermentation

Products of fermentation


In ethanol fermentation, a glucose molecule is transformed into two ethanol molecules, and 2 carbon dioxide molecules. It’s utilized to create bread dough rise. The carbon dioxide bubbles form and the dough expands into foam. The alcohol is the ingredient that intoxicates that is found in alcohol drinks like beer, wine as well as liquor.Fermentation of feedstocks like sugarcane, corn and sugar beets, results in an ethanol which is then used in the production of gasoline. In certain species of fish like carp and goldfish it is a source of energy in times of low oxygen (along with the fermentation of lactic acid).

Ethanol fermentation
Ethanol fermentation

Lactic acid

Homolactic fermentation (producing only the acid lactic) is the most basic kind of fermentation. Pyruvate is produced from glycolysis and is subjected to a simple redox reaction that results in the formation of the acid lactic. In the end, one molecule of glucose (or any sugar with six carbons) transforms into two molecules of the lactic acid:


It is found within the muscle tissues of mammals when they require energy more quickly than blood supply of oxygen. It is also found in certain varieties of bacteria (such as lactobacilli) and fungi. It is the kind in which bacteria convert lactose to the acid lactic in yogurt, which gives its characteristic sour taste. The lactic acid bacteria perform homolactic fermentation, in which the product produced is primarily lactic acid or heterolactic, in which certain lactates are further metabolized to carbon dioxide and ethanol (via through the phosphoketolase process) Acetate, acetate, and other metabolic products, e.g. :


When lactose is fermented (as in cheeses and yogurts) it will be transformed into galactose and glucose (both six-carbon sugars that share the identical chemical formula):

C12H22O11 + H2O → 2 C6H12O6

Hydrogen gas

Hydrogen gas is created by various types of fermentation to help create NAD+, which is the precursor to NADH. Electrons are converted to ferredoxin which is then converted into hydrogenase by which it produces H2. Hydrogen gas serves as a substrate for methanogens as well as sulfate reducers that keep the level of hydrogen at a low level and encourage the production of an energy-rich substance.

Alternative protein

Fermentation can be used to produce other protein sources. For instance, plant-based protein sources like tempeh are made by fermentation. But, it can be utilized to create animal products from non-living materials in vitro. Eggs cheese, honey, and milk are examples of products made from different proteins. These proteins can be created through this particular method of fermentation.


Other types of fermentation include mixed acid fermentation, butanediol fermentation, butyrate fermentation, caproate fermentation, acetone-butanol-ethanol fermentation, and glyoxylate fermentation.

Different Stages of the Fermentation Process

Based on what you’re fermenting, the process may be divided into several phases.

1. Primary fermentation

In this short phase microbes are quickly working on raw ingredients like fruits, vegetables or dairy products. The microbes in the water (such as brine used to ferment vegetables) hinder putrefying bacteria from settling in the food. The yeasts and other microbes change carbohydrate (sugars) into various other substances, such as alcohols and acids.

2. Secondary fermentation

In this stage of fermentation that can last many days or even weeks, alcohol levels increase while yeasts and microbes die and their source of food (the carbohydrates) gets scarcer. Brewers and winemakers use secondary fermentation to make their alcohol-based drinks. In the course of secondary fermentation, the pH levels of winemaker’s or brewer’s fermentation will differ from the time it was first started and can affect the chemical reactions occurring between microbes and their surroundings. When alcohol levels are between 12 and 15 percent and destroys yeast and prevents further fermentation, it is necessary to distill the yeast to get rid of water, condensing alcohol and creating more alcohol.

Important Factors before starting fermentation

You may want to make pickles with your vegetables or to begin the process of making your own beer, these guidelines can help you get started making.

  1. Establish your “starter” cultures: Microbes are present naturally in the air we breathe, but to get started with fermentation, you’ll usually need a “starter” set of cultures like the whey (from yogurt) or an Symbiotic Colony comprised of Bacteria and Yeast, or SCOBY (for Kombucha) or even liquid from an earlier ferment. These starter cultures are already filled in beneficial microorganisms. If you incorporate them into your beverage or food product They’ll grow rapidly and help kickstart the fermentation process.
  2. Keep your equipment clean: To stop bad bacteria from getting into your ferment it is vital to clean and disinfect your kitchen equipment and surfaces you use for your work.
  3. Avoid exposure: The exposure of your ferment to the air can stop the proper fermentation process from happening and increase the chance of food poisoning and spoilage. There are a variety of ways to prevent that.
  4. To stop fermenting food from coming in the air around it, place the food in an acid solution (brine). If you are fermenting large chunks of food, such as chops of vegetables, this technique works effectively. You can alter the pH of the process which determines the amount of oxygen will be present using vinegar in your mix.
  5. Storage: To prevent contamination by air, place your fermenting food in a container that is sealable. A lot of home fermenters utilize an ordinary mason jar that has lids to seal out air, however there are other options. Storage containers typically have the ability to release carbon dioxide gas that is released in the course of fermentation. If you’re determined to monitor the quality of your ferment to ensure that it doesn’t get spoiled and spoil, you can open the sealed containers manually and release carbon dioxide. (If you’re making wine, kombucha, or any other final product which benefit from carbonation, you may opt-out of carbon dioxide venting.)
  6. Fermentation management: By regulating the temperature of your environment and the temperature of the air, you can alter the result from your ferment. In general, microbes perform well in warm or room temperature however, the optimal temperature will depend on the kind of microbes that you’re using and the type of fermentation you’re doing. The temperature you choose to change can affect your process in a significant way. Moving your product into an environment that is cooler like an air-conditioned basement or refrigerator, can slow down the rate of fermentation , and sometimes stop it completely. The heating of a ferment in the opposite way could kill your vital microbes.

Modes of operation

Most industrial fermentation utilizes the fed-batch or batch method however continuous fermentation may be more economical if several problems, such as the problem of maintaining sterility be overcome.


In a batch fermentation it is when all the ingredients are combined , and the reaction takes place without other input. The process of batch fermentation was employed for millennia to create alcohol-based beverages and bread as well as alcoholic beverages. It is used in many cases, particularly when the process isn’t widely known. But, it is expensive since the fermenter must be cleaned using steam at high pressure in between batches. In essence, there are often tiny amounts of chemical to regulate the pH or to prevent foaming.

Batch fermentation takes place through several phases. There is a lag period during which cells adapt to their surroundings and then there is a period in which exponential growth takes place. After a large portion of the nutrients are consumed, the growth slows down, and eventually ceases to be exponential, while the production of secondary compounds (including the most important antibiotics in the market and enzymes) increases. This is continued through a phase of stationary after the majority all nutrients are consumed and then cells die.


Fed-batch fermentation is a variant of batch fermentation, wherein certain ingredients are added to the fermentation. This permits greater control over the phases that the fermentation process goes through. Particularly, the secondary metabolites production can be enhanced by adding a smaller amount of nutrients in the non-expansive growth phase. Fed-batch operations are typically separated from batch operations.


The cost of sterilizing the fermentor in between batches can be avoided with different open fermentation methods that can withstand contamination. One method is to employ an naturally developed mixed culture. This is particularly beneficial in the treatment of wastewater, as mixed populations can be adapted to a variety of waste. Thermophilic bacteria produce lactose at temperatures of 50 degCelsius which is enough to prevent the growth of microbial colonies; and ethanol is made at temperatures that is 70 degC. It is below it’s boiling point (78 degC) which makes it simple to extract. Halophilic bacteria produce bioplastics under hypersaline conditions. Solid-state fermentation is the process of adding a small quantity of water onto a substrate. It is employed in the food industry to make flavors organic acids, enzymes and other flavors.


Continuous fermentation is when the substrates are added and the final product are removed in a continuous manner. There are three types Chemostats, which keep the level of nutrients at a constant level and turbidostats that keep the cell’s mass constant, and plug flow reactors where the culture medium is continuously flowing through a tube as cells are recirculated between the outlets to inlet.

If the procedure is successful it is possible to have a continuous flow of effluent and feed and the expenses of creating batches are eliminated. It can also extend the exponential growth stage and eliminate byproducts that hinder the process by continually eliminating the byproducts. It’s not easy to keep the state constant and avoid contamination, so the process is generally intricate. The fermenter typically has to be running for more than 500 hours to be efficient as batch processing.

How Does Fermentation Work?

To master the art of fermentation it is necessary to know the scientific process behind it.

  • Microorganisms can survive by consuming carbohydrates (sugars such as glucose) to generate energy and for fuel.
  • Organic compounds such as adenosine Triphosphate (ATP) provide energy to all the cells in cells when it is needed.
  • Microbes generate ATP using respiration. Aerobic respirationthat needs oxygen is the most effective method to accomplish this. Aerobic respiration starts with glycolysis, in which glucose is converted to the acid pyruvic. If oxygen is present aerobic respiration takes place.
  • The process of fermentation is similar to that of anaerobic respiratory respiration, the type that occurs in the absence of oxygen available. But, it also triggers the creation of various organic molecules such as lactic acid. It produces ATP in contrast to respiration which relies on pyruvic acid.
  • Based on the environmental conditions, the microbes and cells have the capability to switch between two different energy sources.
  • Organisms usually obtain energy through fermentation, however, certain systems make use of sulfate to be one of the last electrons to be accepted by the electron transportation chain.

What Happens During the Fermentation Process?

Fermentation takes place when oxygen is not present (anaerobic conditions) and when there are beneficial microorganisms (yeasts and molds as well as bacteria) that get their energy via fermentation. If there is enough sugar available certain yeast cells such as Saccharomyces cerevisiae, will prefer fermentation to aerobic respiration, even when oxygen is plentiful.

  • Through the process of fermentation beneficial microbes break down sugars and starches to alcohols and acids and make food more nutritious and also preserving it, allowing people to keep it for longer durations of time without it deteriorating.
  • Fermentation products supply enzymes needed to digest food. This is vital because we have a limited amount of enzymes and they diminish with the aging process. Fermented foods contain enzymes that breakdown them.
  • Fermentation can also help in the process of pre-digestion. In the process of fermentation the microbes consume sugars and starches and break down food before it’s eaten it.

Applications of fermentation

  • Application in medicine: Production of antibiotics, Production of insulin, Production of growth hormones, Production of vaccines, Production of interferon
  • Application in the food industry: Production of fermented foods (as cheese, wine, beer, and bread to high-value products), Food grade bio preservatives, Functional foods/Neutraceuticals, Production of single-cell protein.
  • Other Applications:
    • It can also be used to manage waste, such as biofuels production (biodiesels and bioethanol) butanol biohydrogen etc.).
    • It can also be utilized to create bio-surfactants and polymers, for example, the production of cellulose by bacteria.
    • Bioremediation is the process of developing (involving microbes or isolate enzymes) for wastewater and soil treatment.

Fermentation Facts

  • The process of fermentation is anaerobic which means that it doesn’t require oxygen to take place. But even when oxygen is plentiful yeast cells will prefer fermentation in favor of aerobic respiration if an adequate supply of sugar is in place.
  • Fermentation is a process that occurs within the digestive system of humans as well as other animals.
  • A rare condition known as auto-brewery or gut-fructose syndrome, the fermentation process in the digestive tract of the person can lead to ethanol-induced intoxication.
  • Fermentation is a natural process that occurs in the human muscle cells. Muscles are able to release ATP more quickly than oxygen is available. In this scenario, ATP is produced by glycolysis, which doesn’t require oxygen.
  • While fermentation is a popular method, it’s not the only way used by living organisms to generate energy from anaerobes. Certain systems employ sulfate as one of the last electrons to be accepted by the electron transportation chain.

Limitations of fermentation

  • Low-scale production that needs expensive costs and high energy
  • Potential for contamination.
  • Natural variations in time
  • The product is impure and requires further treatment
  • the unexpected and unintentional end product
  • The harmful microbes multiply and multiply, and the beneficial microbes die.

Advantages of Fermentation

Fermented foods are high in probiotics beneficial microorganisms that keep a healthy gut, so that it can absorb nutrients from foods.

  • Probiotics boost the immune system since the gut produces antibiotics anti-tumor, antiviral, and antifungal compounds and pathogens aren’t able to do very well within the acidic conditions that fermentation of food products.
  • Fermentation can also neutralize harmful nutrients such as phytic acid which is present in nuts, grains legumes, and seeds. It may cause mineral deficiencies. Additionally, phytates make starches fats and proteins less digestible, and neutralizing them can be extremely beneficial.
  • Fermentation may increase the amount of vitamins and minerals present in foods and increase their availability to be absorbed. Fermentation can increase B as well as C vitamins and boosts the absorption of folic acid, riboflavin the thiamin, niacin and biotin. Probiotics, enzymes and lactic acids in fermented food aid in their absorption and utilization of minerals and vitamins into the body.


  • https://www.masterclass.com/articles/what-is-fermentation-learn-about-the-3-different-types-of-fermentation-and-6-tips-for-homemade-fermentation#what-is-fermentation
  • https://microbenotes.com/fermentation/
  • https://en.wikipedia.org/wiki/Fermentation
  • http://www.vivo.colostate.edu/hbooks/pathphys/digestion/largegut/ferment.htmlhttp://www.vivo.colostate.edu/hbooks/pathphys/digestion/largegut/ferment.html
  • https://bakerpedia.com/processes/fermentation/
  • https://www.intechopen.com/chapters/69334


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