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Fermentation: Definition, Process and types of fermentation

The microorganisms like Yeast and some other bacteria obtain energy by fermentation. Fermentation is a form of anaerobic respiration as it occurs in the absence of oxygen. With the help of fermentation food and beverages can be stored for several days without any contamination, and contamination is the very first stage of food spoilage. Fermentation is a chemical process in which glucose breaks into ethanol and carbon dioxide and it can be chemically represented as:

C6H12O6 (glucose) → 2 C2H5OH (ethanol) + 2CO (carbon dioxide)

The process of fermentation has been utilized by humans for several years. This process was used for the preparation of various food and beverages such as cheese, curd, beer, wine, etc.

Definition and Uses of Fermentation

In biology, Fermentation is the process in which single-celled, non-green microorganisms like Yeast and some other bacteria, convert carbohydrates or sugar into other products like alcohol and carbon dioxide. The process of fermentation takes place in the absence of Oxygen. The primary function of fermentation is to extend the shelf life of the food as it is the most useful food preservation method. A few examples of fermentation which has been utilized for centuries to produce different products have been mentioned below:

  1. Fermentation is commonly used for the production of food and beverages such as bread, beer, wine, cheese, fermented food, and yogurt as it increases the flavor, extends shelf life, and gives a unique texture to the food.
  2. It is also used in the production of biofuels like ethanol, which can be used as an alternative to fossil fuels.
  3. Some medicines and antibiotics are also produced through fermentation by different single-celled microorganisms.
  4. Many organic acids, enzymes, vitamins, and other chemical compounds used in various industries are also formed by fermentation.
  5. Fermentation is also used in the breakdown of organic waste and produces biogas. This biogas is a renewable energy source.
  6. During fermentation, lactic acid is formed which is used to produce cultured dairy products such as yogurt and buttermilk.
  7. Acetic acid fermentation is used to form vinegar from alcoholic beverages.

Mechanism of Fermentation

The well-defined mechanism of fermentation involves Glycolysis, which is the primary pathway for glucose metabolism. Fermentation is primarily carried out by microorganisms like yeast or bacteria. We have mentioned a detailed explanation of the process below:


The fermentation process begins with glycolysis. This process takes place inside the cytoplasm of the cell. In glycolysis, one molecule of Glucose (which is a 6-carbon sugar) is broken down into two molecules of pyruvate (which is a three-carbon compound) inside the cytoplasm. This process generates a very small amount of energy in the form of ATP (Adenosine Triphosphate) and NADH (Nicotinamide adenine dinucleotide).

Fermentation Pathway

Fermentation depends on the organisms and conditions. According to this, there are different types of fermentation pathways:

  1. Alcoholic fermentation takes place in yeast and some other bacteria. In this type of fermentation, pyruvate is converted into ethanol and carbon dioxide and helps in the production of beer, wine, and making bread.
  2. Lactic Acid fermentation takes place in animals including humans and some other bacteria. In this process, pyruvate is converted into lactic acid and helps in the production of yogurt and cheese.

Purpose: The main purpose of Fermentation is to regenerate NAD+. During glycolysis, this NAD+ is converted to NADH as it accepts electrons from glucose. As Fermentation does not produce as much energy as aerobic respiration, so fermentation is used as an alternative way for the generation of ATP (energy) during intense when there is a scarcity of Oxygen in the muscles.

Now let’s take an example: We will carry out a simple and easy experiment in which we will perform the fermentation of sugar by yeast.

Step 1: Take some sugar solution (or fruit juice) in a test tube and add a very small amount of yeast to it.

Step 2: Close the mouth of the test tube with a cork and allow it to stand for some time.

Step 3: Now, open the cork and smell the sugar solution (or fruit juice). A characteristic smell of ethanol (ethyl alcohol) is obtained from the test tube.

C6H12O6(glucose or sugar solution) → 2C2H5OH (ethanol) + 2CO2 (carbon dioxide gas) 

CO2 gas evolves during the fermentation of sugar. When this gas is passed through the lime water, the lime water turns milky; which shows the presence of carbon dioxide gas.

The experiment tells us that the product of the fermentation of sugar by the presence of yeast are Ethanol and Carbon dioxide.

Types of Fermentation

Fermentation takes place in the absence of oxygen in many microorganisms like yeasts or bacteria and gives alcohol, acid, and carbon dioxide as a byproduct. Fermentation is a very process that helps in the preservation of food. Fermentation is of two different types:

  1. Alcoholic Fermentation
  2. Lactic Acid Fermentation

Alcoholic Fermentation

Alcoholic fermentation takes place in single-celled microorganisms like yeast and some other bacteria. This alcoholic fermentation has been practiced for several years. During fermentation, yeasts convert sugar (glucose) into carbon dioxide and alcohol or ethanol. Alcoholic fermentation is used for preparing beverages such as beer and wine. It is also used in baking as carbon dioxide produced in alcoholic fermentation is used to raise the dough. At the time of alcoholic fermentation, the yeasts consume sugar (usually glucose and fructose) present in fruits, grains, or other raw materials. The enzymes present in yeasts help in the breakdown of these sugars into ethanol and carbon dioxide.

During Alcoholic fermentation, one molecule of glucose is converted into two molecules of ethanol (alcohol) and two molecules of carbon dioxide. It is carried out in the absence of oxygen. The chemical equation for Alcoholic Fermentation is given as:

C6H12O6 (glucose) → 2C2 H5OH (ethanol) + 2CO2  (carbon dioxide) 

Importance of Alcoholic Fermentation

  • Alcoholic fermentation is the process that converts sugars, such as glucose and fructose into carbon dioxide and ethanol (alcohol) with the help of yeast or some other bacteria.
  • The carbon dioxide formed during fermentation is used in baking and making carbonated drinks.
  • Alcoholic fermentation plays a very important role in the food and beverage industry.
  • In the production of biofuels, alcoholic fermentation acts as a key step.

Lactic Acid Fermentation

Lactic Acid Fermentation is a metabolic process that takes place in certain microorganisms and muscle cells. During this process, a product of glycolysis pyruvate is converted into lactic acid, regenerating NAD+ and allowing glycolysis to continue. Lactic acid fermentation commonly occurs in bacteria such as Lactobacilli which helps in food fermentation, this process also takes place in the muscles at the time of heavy exercise when oxygen is limited.

In lactic acid fermentation, one molecule of glucose is converted into two molecules of lactic acid. This process takes place in the absence of oxygen and is very important in energy production when oxygen is limited during intense exercise. The chemical equation for lactic acid fermentation is as follows:

Glucose (C6H12O6) → 2 molecules of Lactic acid (2 C3 H6O3 )

Importance of Lactic Acid Fermentation

  • Lactic acid fermentation is a natural method of food preservation, as the acidic environment created during fermentation stops the growth of harmful bacteria.
  • Fermented food contains probiotics, which are beneficial bacteria that help to maintain a healthy gut and improves digestion.
  • In many industries lactic acid fermentation is used to convert agro-industrial waste and organic waste into valuable products such as biodegradable plastics, biofuels, and other chemicals.
  • Lactic acid fermentation is used in the production of many food products like yogurt, cheese, kimchi, and picked.
  • The lactic acid fermentation not only preserves food but also adds unique flavor and texture to it.

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Fermentation: FAQs

Q1. Define fermentation in simple words?

Ans. Fermentation is a natural process in which sugar is broken into simple substance by the help of microbes.

Q2. What are the two different types of Fermentation?

Ans. The two different types of fermentation are: Alcoholic and Lactic acid fermentation.

Q3. How many molecules of lactic acid are formed in lactic acid fermentation?

Ans. In lactic acid fermentation 2 molecules of lactic acid are formed.

Q4. Why is fermentation important?

Ans. Fermentation helps to protect the food from contamination.

Q5. When is lactic acid produced in the muscles of humans?

Ans. Lactic acid is produced at the time of heavy exercise, as at that time there is a scarcity of oxygen in the muscles.

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