Types of Fermentation

Fermentation is a process where organisms break down sugars or starches. This process is to produce energy. It occurs without oxygen and involves enzymes that support the chemical reaction. The end products are usually alcohol or acids.

The science of fermentation is called zymology.

Aerobic vs. Anaerobic Respiration

Fermentation is an anaerobic process (does not require oxygen). Aerobic respiration uses oxygen to make energy. They produce ATP but differ in their byproducts and efficiency.

How Fermentation Works

Fermentation begins with glycolysis, where one glucose molecule becomes pyruvate. This step creates two ATP molecules as energy.

Pyruvate is changed into alcohol, lactic acid, or other products. NAD+ is also regenerated from NADH to keep the process going.

Types of Fermentation

Fermentation is broadly classified into:

Lactic acid (Homofermentation - produces a single product; Heterofermentation - produces more than one product)
Alcoholic
Acetic acid
Butyric acid
Propionic acid, etc.

1. Lactic Acid Fermentation

In lactic acid fermentation, pyruvate converts into lactic acid.
This reaction takes place by an enzyme called lactate dehydrogenase.
NAD+ is also formed from NADH to continue the energy production.
Lactobacillus bacteria use this process to make yoghurt and curd.
Muscles also carry out this process when oxygen becomes limited during heavy activity.
The build-up of lactic acid in muscles can lead to soreness and fatigue.

2. Alcohol Fermentation

Alcohol fermentation produces ethanol and carbon dioxide.
Pyruvate breaks into acetaldehyde and CO₂.
Acetaldehyde is reduced to ethanol by enzymes.
NAD+ is also regenerated.
Yeasts and some bacteria carry out this process.
It is used to produce beer, wine, and biofuels.

3. Acetic Acid Fermentation

Acetic acid fermentation occurs in two steps.
Acetic acid fermentation is not purely anaerobic.
Yeast first ferments sugar into ethanol under anaerobic conditions.
Acetobacter oxidises ethanol to acetic acid in the presence of oxygen.
The overall process is partially anaerobic and partially aerobic.
This process is used to make vinegar.

4. Butyric Acid Fermentation

This fermentation happens in anaerobic bacteria like Clostridium.
It occurs in jute retting, rancid butter, and leather tanning.
In the human gut, fibre fermentation produces butyric acid.
Butyric acid provides energy to colon cells.
Glycolysis turns sugar into pyruvate as the first step.
Pyruvate then forms acetyl-CoA, giving off hydrogen and CO₂.
Acetyl-CoA is changed into butyric acid.
The process produces fewer ATP molecules compared to aerobic respiration. Exact yield is variable (about 3

ATP per glucose is not firmly established).

Advantages and Applications of Fermentation

Fermentation works in many environments and organisms. It is one of the oldest energy-producing processes.

Using different microbes and conditions, fermentation produces:

Wine
Beer
Biofuels
Yoghurt
Pickles
Bread
Sour foods with lactic acid
Some antibiotics and vitamins

Fermentation also improves food flavour and digestibility.

Health Benefits of Fermented Foods

Eating fermented foods helps digestion and keeps the stomach healthy.
They may also help lower the chance of getting some types of cancer.
Fermented foods help make the body’s defence system stronger.
They can also help reduce problems caused by not digesting milk well.

Other Uses of Fermentation

Fermentation produces methane gas in sewage treatment plants.
Methane is also produced in freshwater sediments.
Fermentation plays a key role in energy production and useful products.

It supports food production, health, and energy industries worldwide.

Summary

Fermentation is a natural way to get energy from sugar without oxygen. Sugar changes into useful substances such as alcohol and acids during this process. The first step splits sugar into smaller parts to release energy.

Yoghurt, beer, vinegar, and bread are all made by fermentation. Fermented foods help digestion and support the body’s immune system. Fermentation also creates fuels that provide energy.