Table of Contents

Fermentation and its Types

Alcoholic Fermentation Definition and Occurrence

Agent of Alcoholic Fermentation

Equation for Alcoholic Fermentation

Products of Alcoholic Fermentation

More Sub-Products of Alcoholic Fermentation

Why does fermentation reduce towards the end?

Fermentation

Fermentation is a process where microorganisms are used to produce a beneficial and desirable change in food. It is commonly used in the alcohol industry, where alcoholic fermentation or ethanol fermentation is a biological method that transforms sugar into carbon dioxide and alcohol.

Fermentation is an anaerobic process that does not require oxygen, and is usually conducted by yeasts. The products of this process are alcohol, carbon dioxide, water, and heat. This process of ethanol fermentation has been used for thousands of years.

Fermentation occurs in anaerobic conditions, where oxygen is absent and beneficial microbes are present. These microbes gain energy through fermentation, even when there is enough oxygen and sugar present. In such cases, some of the yeast cells (Saccharomyces cerevisiae) choose fermentation over aerobic respiration.

Fermentation is a process in which microbes break down sugars into alcohols and acids, making food more nutritious and increasing its shelf life. Additionally, the products of fermentation provide enzymes needed for digestion. Therefore, food that has been fermented contains enzymes necessary to break it down.

Types of Fermentation

Fermentation used is of three types:

1. Aerobic
2. Anaerobic
3. Facultative

Lactic Acid Fermentation

Bacteria and certain strains of yeast can convert sugars or starches into lactic acid without the need for heat. Additionally, lactic acid fermentation also occurs in human muscle cells. During strenuous exercise, the body expends ATP faster than oxygen can be supplied to the muscles, resulting in the buildup of lactic acid and, ultimately, sore muscles.

In anaerobic conditions, glycolysis produces ATP, which disintegrates glucose molecules into two pyruvate molecules.

Alcohol Fermentation/Ethanol Fermentation

Yeasts break molecules of pyruvate during glycolysis, resulting in the metabolism of glucose into sugars or starch, and ultimately producing molecules of carbon dioxide and alcohol. This process of alcoholic fermentation is responsible for the production of beer and wine.

Acetic Acid Fermentation

Sugars and starches from fruits and grains ferment into condiments and vinegar with a sour taste.

In this Article, We Discuss Alcohol Fermentation in Detail

Definition of Alcoholic Fermentation: Alcoholic fermentation is a metabolic process in which sugars such as glucose, fructose, and sucrose are converted into cellular energy and thereby produce ethanol and carbon dioxide.

Alcoholic fermentation is the anaerobic transformation of fructose and glucose (sugars) into ethanol and carbon dioxide, which is conducted by yeasts and the bacteria Zymomonas mobilis.

The process of alcoholic fermentation regenerates the NAD+ taken up at the time of glycolysis, and provides yeast with an energy gain of 2 ATP molecules through the metabolized hexose.

The process of alcoholic fermentation occurs when Saccharomyces cerevisiae (a species of yeast) primarily directs the pyruvate from grape juice for the production of ethanol in order to regenerate NAD+ consumed during glycolysis.

Steps of Alcoholic Fermentation

1. Gather the necessary ingredients
2. Mix the ingredients together
3. Wait for the yeast to activate
4. Monitor the fermentation process
5. Filter the fermented liquid
6. Bottle the alcohol

The process of alcoholic fermentation can broadly be divided into two main parts:

Glycolysis - Glucose is broken down into two Pyruvate molecules.

Fermentation - Pyruvate molecules are converted into 2 molecules of Carbon Dioxide and 2 molecules of Ethanol.

Where Does Alcoholic Fermentation Occur?

The process of alcoholic fermentation occurs within the cytoplasm of cells.

Agent of Alcoholic Fermentation

It is a widely accepted fact that the most commonly used agent for alcoholic fermentation is S. cerevisiae. This yeast is often utilized as a microbial starter in various fermentation industries.

The S. cerevisiae becomes the dominant species during alcoholic fermentation of fruits and juices due to the low pH, high ethanol and sugar concentrations, and anaerobic conditions providing a strong selective environment.

Alcoholic Fermentation Equation: $$C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$$

The reaction occurring in alcoholic fermentation can be summarized as follows:

The process of alcoholic fermentation converts one mole of glucose into two moles of ethanol and two moles of carbon dioxide, resulting in the production of two moles of ATP.

The process of alcoholic fermentation is a complex one, involving a range of biochemical, physicochemical, and chemical processes that ultimately turn grape juice into wine.

Products of Alcoholic Fermentation

Pyruvate is initially decarboxylated into ethanal by pyruvate decarboxylase, which requires magnesium and thiamine pyrophosphate as cofactors. Afterwards, alcohol dehydrogenase reduces ethanal to ethanol, thus regenerating NADH to NAD+.

In Saccharomyces cerevisiae, there are three isoenzymes of alcohol dehydrogenase, with Isoenzyme I being primarily responsible for the conversion of ethanal to ethanol. Zinc is utilized as a cofactor by Alcohol dehydrogenase.

The final products of alcoholic fermentation are ethanol and carbon dioxide. Both are transported to the exterior of the cell by the process of simple diffusion. Apart from ethanol, some other compounds are generated all through the process of alcoholic fermentation, such as esters, higher alcohols, succinic acid, glycerol, 2,3-butanediol, diacetyl, and acetoin.

The derivative of pyruvate receives electrons from NADH, resulting in the production of ethanol.

Conversion of pyruvate into ethanol occurs in two steps

The production of acetaldehyde involves the elimination of a carboxyl group from pyruvate, resulting in the release of carbon dioxide and the formation of a two-carbon molecule, acetaldehyde.

NADH transfers its electrons to acetaldehyde, thereby regenerating NAD+ and forming ethanol.

Yeasts produce ethanol through alcoholic fermentation, which can be found in alcoholic beverages.

More Sub-products of Alcoholic Fermentation:

• Ethanol
• Carbon dioxide
• Acetic acid
• Glycerol
• Succinic acid

As previously mentioned, fermentation produces not only ethanol and glycerol, but also a number of other substances, due to its complex process.

Some of the sub-products of alcoholic fermentation are:

Acetic Acid

Diacetyl, Acetoin, and 2,3-Butanediol

Ethanal/Acetaldehyde

Esters

Higher Alcohols

Succinic Acid

Why Does Fermentation Reduce Towards the End?

At times, the process of alcoholic fermentation slows down as it nears completion. Yeasts dramatically reduce their consumption of sugar, and fermentation can cease before all fermentable sugars are metabolised. In this situation, two scenarios may occur:

Adding a delicious meal to accompany the wine is the perfect way to complete it!

High Risk of Bacterial Spoilage

Some causes of sluggish fermentation are:

Extremes of Temperature

Complete anaerobiosis

Presence of Medium-Chain Fatty Acids

Extreme levels of sugar concentrations

Presence of Antifungal Substances

Antagonism between Microorganisms

Nutrient Deficiencies

If the process of fermentation stops, the yeast should be reinoculated, as this can be caused by a combination of several factors which restrict the correct development of alcoholic fermentation.

Therefore, alcoholic fermentation is a complicated process that involves changing sugars into ethanol and other byproducts.

Glycolysis

![Glycolysis]()

Glycolysis is the metabolic process that converts glucose (C6H12O6) into pyruvic acid (CH3COCOOH). This pathway does not require oxygen, and the energy released is used as ATP and reduced NADH. The glycolysis process is composed of 10 reactions, all of which involve the action of enzymes.

Glycolysis, primarily taking place in the cytosol, is usually of the EMP (Embden–Meyerhof–Parnas) pathway.

Glycolysis and Alcoholic Fermentation

Under anaerobic conditions, when oxygen supply is limited during prolonged and heavy exercises, muscles derive their energy from glycolysis, while yeasts gain their energy from a similar process referred to as alcoholic fermentation.

In glycolysis, there is a chemical breakdown of glucose into lactic acid, making energy available for cellular activity in the form of ATP. Apart from the final step, alcoholic fermentation is similar to the process of glycolysis. Pyruvic acid in alcoholic fermentation is broken down into carbon dioxide and ethanol. The lactic acid produced from glycolysis can cause fatigue, while the products of alcoholic fermentation have been used in brewing and baking for a long time.

Glycolysis and alcoholic fermentation are both anaerobic processes that begin with glucose. Glycolysis requires 11 enzymes to transform glucose to lactic acid. For the first 10 steps, alcoholic fermentation follows the same enzymatic route. The lactate dehydrogenase, the last enzyme of glycolysis, is replaced by two enzymes in the process of alcoholic fermentation: Alcoholic dehydrogenase and Pyruvate decarboxylase. These two enzymes convert pyruvic acid into carbon dioxide and ethanol in the process of alcoholic fermentation.

Hence, neither alcoholic fermentation nor glycolysis results in any net gain of energy (ATP) until the tenth enzymatic reaction.