1Department of Chemistry, Gauhati University, Guwahati, Assam, 781014, India

2Department of Chemistry, Dhanamanjuri University (D.M. College of Science) Imphal -795001, India.

3Mizoram University, Tanhril, Aizawl, Mizoram, 796004, India

Corresponding author email: bjbche10@gmail.com

Article Publishing History

Received: 13/04/2026

Accepted After Revision: 27/06/2026

ABSTRACT:

Conversion of sugar to ethanol is an age-old traditional fermentation methods and contemporary biofuel manufacturing. It involves based on the process that is glycolysis, where glucose is broken down to pyruvate, through anaerobic fermentation transformed into ethanol and carbon dioxide. Microorganisms like Saccharomyces cerevisiae are essential for fermentation. Some specific enzymes to speed up these reactions effectively in low-oxygen environments. Brewing and distilling has lots of cultural importance among tribal communities. Ethanol production holds significant industrial and environmental value in addition to its cultural importance in brewing and distilling. Because ethanol serving as a sustainable substitute for fossil fuels. Increasing environmental concerns, global energy demands and fossil fuel reserve depletion/shortage have intensified interest in renewable energy sources. Bioethanol derived from sugar-rich feedstocks offers more sustainable cleaner fuel option. Understanding the enzymatic mechanisms, biochemical pathways and technological advancements involved in ethanol production is crucial for enhancing production efficiency and meeting future energy demands.

This study provides a comprehensive review of the biochemical conversion of sugars into spirit, with particular emphasis on the glycolytic and alcoholic fermentation pathways. It examines the role of microorganisms, especially Saccharomyces cerevisiae, and the key enzymes involved in the metabolic transformation of sugars into spirit. Factors affecting substrate concentration, ethanol production, pH, and fermentation technologies were also studied through a comprehensive analysis of recent scientific literature. Here, the findings are based on an extensive analysis of recent scientific literature and current developments in bioethanol production research. Here, the findings indicate that glucose is efficiently converted into pyruvate through glycolysis, which is subsequently transformed into C2H5OH and CO2 under anaerobic conditions. Due to its high fermentation efficiency, Saccharomyces cerevisiae remains the most effective microorganism. Existing literature has established that ethanol production involves the biochemical conversion of sugars via glycolysis and alcoholic fermentation, primarily mediated by microorganisms such as Saccharomyces cerevisiae. This study provides a concise overview of these metabolic processes while highlighting the enzymatic mechanisms, key factors affecting production efficiency, and recent advances in fermentation technologies that enhance ethanol synthesis for sustainable energy applications.

KEYWORDS:

Sugar fermentation, Glycolysis, Ethanol, Renewable energy, Saccharomyces cerevisiae

Download this article as: Copy the following to cite this article:

Bhattacharya B, Shah A. H, Deka D. C. From Sugar to Spirit: The Biochemical Route of Ethanol Production for Applied Use. Biosc.Biotech.Res.Comm. 2026;19(2).

Copy the following to cite this URL:

Bhattacharya B, Shah A. H, Deka D. C. From Sugar to Spirit: The Biochemical Route of Ethanol Production for Applied Use. Biosc.Biotech.Res.Comm. 2026;19(2). Available from: <ahref=”https://shorturl.at/hFr9C“>https://shorturl.at/hFr9C</a>

INTRODUCTION

Fermentation, a microbial process occurs irrespective of presence or absence of oxygen. In 1837, Cagniard-Latour and Kützing during their study on alcoholic fermentation discovered that yeast is a microscopic plant which is responsible for the conversion of sugar to ethyl alcohol and carbon dioxide (Wolfe, 2005). But this theory was opposed by contemporary scientists who believed that fermentation is a chemical process. They believed that fermentation is caused by some chemical reagents and they need to be introduced from outside (Wolfe, 2005; Hahn-Hagerdal et al., 2006).

Controversy and thrill continued until Pasteur (Wolfe, 2005). Louis Pasteur was a chemist who first proposed that fermentation is a natural anaerobic process and this happens due to microbial activity (O’Neal and Poklis, 1996; Garrigues et al., 1997; Macfarlane and Macfarlane, 2003). With the help of some scientific evidences like the conversion from beet sugar to alcohol, he proved his statement. Again, he proved that conversion of sugar to lactic acid is also a fermentation process (Garrigues et al., 1997; O’Neal and Poklis, 1996).

For about 20 years (1856-1876), Pasteur worked on various microbial fermentation processes. He showed that different reactions were carried out by different microorganisms and the size and shape of the microorganisms depended on the environmental conditions in which the microbial reaction were carried out. He recognized some microorganisms that could generate energy by breakdown of organic compounds and reported that the amount of energy produced was directly related to the growth of bacteria (O’Neal and Poklis, 1996; Garrigues et al., 1997; Macfarlane and Macfarlane, 2003; Horváth et al., 2026).

But he noticed that fermentation was a slow process compared to other biochemical processes as that can led to the production of energy (Clark, 1989; Melchiorsen et al.,2001; Van Vuuren et al., Carr et al., 2002, Kamaljeet et al., 2026). It is now well established that fermentation is a biological process which converts sucrose into glucose and fructose in the presence of an enzyme invertase (Lynen et al., 1953; Hahn-Hagerdal et al., 2006; Pucino et al., 2019). Further, on the presence of zymase, glucose gets converted into ethanol and carbon dioxide (Hahn-Hagerdal et al., 2006; Pucino et al., 2019). Fermentation is of two types, aerobic and anaerobic. Aerobic fermentation is carried out in the presence of oxygen, whereas anaerobic fermentation is carried out in the absence of oxygen (Hahn-Hagerdal et al., 2006; Pucino et al., 2019; Sereme et al., 2026).

 Mechanism of fermentation : Mechanism of fermentation of sucrose: During natural fermentation, monosaccharides like glucose are converted to ethanol by microbial activity. Disaccharides and higher carbohydrates are first converted to monosaccharides. Natural or spontaneous fermentation takes place in the presence of microflora in an acidic aqueous environment (Macfarlane and Macfarlane, 2011).

Figure 1: A flow-chart showing fermentation of Sucrose into Ethanol
(Mitchell et al., 1979; Ueno et al., 2006, Gray et al., 2006; Zhang et al., 2010).

Following reactions can summarize the process of fermentation of sucrose into ethanol. Sucrose is a disaccharide which is composed of glucose and fructose (Mitchell, 1979; Ueno et al., 2006). Invertase an enzyme converts sucrose into glucose and fructose. Fermentation of 1 mole of glucose produces 2 moles of ethanol, 2 moles of carbon dioxide and 2 moles of ATP (Mitchell, 1979; Ueno et al., 2006).

Pyruvate is converted to ethanol and carbon dioxide in two steps, regenerating oxidized NAD+. In the first step, pyruvate is converted to acetaldehyde and this reaction is catalysed by pyruvate decarboxylase.

In another step, catalyzed by the enzyme alcohol dehydrogenase (ADH1 from yeast) acetaldehyde is converted to ethanol.

Alcohol dehydrogenase are group of enzymes found in many organisms, and these enzymes facilitates the interconversion between alcohols and aldehydes or ketones with the reduction of nicotinamide adenine dinucleotide (NAD+) to NADH or vice versa.

Saccharomyces cerevisiae is a microorganism which is used extensively for the conversion of sugar to ethanol during batch fermentation (Rogers et al., 1984; Rouviere and Wolfe, 1988). Glucose is the substance which is directly converted into energy in the mitochondria (Rogers et al., 1984). Remaining parts like fats, proteins are not easily converted into energy by mitochondria (Rogers et al., 1984). Glucose can provide energy in quick span of time but not by fats (Rogers et al., 1984, Brückner and Titgemeyer, 2002). Lots of metabolism, breakdown process is required for conversion of fat to energy (Brückner and Titgemeyer, 2002). Fats contain more amount of energy than glucose but it requires more span of time than the conversion of glucose to energy (Rogers et al., 1984; Brückner et al., 2002). Glucose is stored in our body in the form of glycogen or long chains of glucose (Rogers et al., 1984; Brückner and Titgemeyer, 2002; Kamaljeet et al., 2026).

Fatty acids, glucose, amino acids are the sources of energy in our body (Macfarlane and Macfarlane, 2011). More chemical conversions are required for the other chemicals (Brückner and Titgemeyer, 2002; Macfarlane and Macfarlane, 2011).

Figure 2: Flow diagram showing different steps leading to the conversion of ethylene, sugar, starchy material, lignocellulosic material to ethanol (Rogers et al., 1984; Rouviere and Wolfe, 1988; Macfarlane and Macfarlene, 2011).

But among all these, glucose provides energy in quick span of time. Most cells use glucose for ATP synthesis (Macfarlane and Macfarlene, 2011). Insulin and glucagon are the two hormones which controls the movement of glucose in our body (Macfarlane and Macfarlene, 2011; Sereme et al., 2026). Sugars are the microbial fuel and ethanol is produced as one of the metabolic byproducts during the microbial process of biomass fermentation (Kamaljeet et al., 2026).

Depending upon the microbes involved in the system, fermentation may be aerobic or anaerobic (Brückner and Titgemeyer, 2002). Wood or straw, more specifically cellulose containing biomass can be used for fermentation after acid or enzyme pre-treatment (Brückner and Titgemeyer, 2002; Macfarlane and Macfarlane, 2011). Sugar beet or corn, more specifically crops with high sugar content are well suited for fermentation. During the fermentation process, yeast or fungi break the organic matter into ethanol (Rogers et al., 1984; Brückner and Titgemeyer, 2002; Macfarlane and Macfarlane, 2011).

 Ethanol production by yeast and bacteria: Ethanol is produced through the fermentative breakdown of glucose and other hexoses by various yeasts, bacteria and fungi (Lynen and Ochoa, 1953; Pucino et al., 2019). Yeast, although not strictly facultative anaerobic microbes, can undergo anaerobic growth for a limited number of generations (Lynen and Ochoa, 1953; Pucino et al., 2019). Among the ethanol producing yeasts, Saccharomyces cerevisiae is considered as the primary species (Lynen and Ochoa, 1953; Pucino et al., 2019, Horváth et al., 2026).  

In yeasts, glucose breakdown occurs through EMP pathway (Zeikus, 1980; Wiegel,1982; Corry et al., 1986). Pyruvate undergoes decarboxylation by pyruvate decarboxylase leading to the formation of acetaldehyde (Zeikus, 1980; Wiegel,1982; Corry et al., 1986). Subsequently, the aldehyde is reduced to ethanol by alcohol dehydrogenase (Zeikus, 1980; Wiegel,1982; Corry et al. 1986).

Apart from yeasts, bacteria species can also facilitate the ethanol fermentation of glucose and other carbohydrates (Corry et al., 1986, Pucino et al., 2019, Horváth et al., 2026). Some bacteria like Zymomonas Sp., utilize the ED pathway for the conversion of pyruvate to glucose while others employ the EMP pathway (Wiegel, 1982; Corry et al., 1986, Pucino et al., 2019). The final step in the conversion of pyruvate to ethanol involves the action of enzymes such as pyruvate decarboxylase and alcohol dehydrogenase (Corry et al., 1986, Pucino et al., 2019).

The fermentative pathway is executed by various species, including Zymomonas mobilis, Zymomonas anaerobica, Sarcina ventriculi, Erwinia amylovora. Notably, pyruvate decarboxylase is a rare enzyme in bacteria (Zeikus, 1980; Lin and Tanaka, 2006). In bacteria like many lactic acid bacteria (like Streptococcus lactis, Leuconostoc mesenteroides), enterobacteria like Escherichia coli, Klebsiella aerogenes and Klebsiella clostridia, the substantial production of ethanol from carbohydrates is achieved through acetyl-CoA (Zeikus, 1980; Lin and Tanaka, 2006). Acetyl COA, a recognised high-energy intermediate in central metabolism plays a crucial role. The conversion of pyruvate to acetyl-CoA can occur oxidatively in aerobic conditions or non-oxidatively in anaerobic conditions (Zeikus,1980; Lin and Tanaka, 2006). Oxidative decarboxylation is facilitated by the pyruvate dehydrogenase complex while non-oxidative decarboxylation leads to acetyl CoA (Zeikus, 1980; Lin and Tanaka, 2006).

The acetyl-CoA’s fate can follow two alternative pathways: conversion to acetate or reduction to ethanol (Rouviere and Wolfe, 1988, Saier, 2013; Horváth et al., 2026). On the other hand, reduction of acetyl CoA to ethanol is facilitated by acetaldehyde or alcohol dehydrogenase, involving the formation of acetaldehyde and consuming reducing equivalents (Rouviere and Wolfe, 1988). Consequently, bacteria can regulate the amount of ethanol and acetate produced to balance their requirements for reducing nucleotides and energy (Rouviere and Wolfe,1988; Horváth et al., 2026).

Figure 3: Catalytic cycle for fermentation of glucose to ethanol through some enzymatic reactions. Reactions show different stages of conversion from pyruvate to ethanol (Rouviere and Wolfe, 1988; Van Vuuren et al., 1993; Carr et al., 2002).

Carbohydrates, on the other hand particularly glucose are the favoured sources of energy for numerous microbes (Rouviere and Wolfe, 1988; Saier, 2013). Microbes employ two main pathways for carbohydrate breakdown; the Embden-Meyerhof-Parnas (EMP) glycolytic pathway and the Entner-Doudoroff (ED) pathway (Rouviere and Wolfe, 1988; Saier, 2013). Both Pathways culminate in the production of pyruvate (Zeikus, 1980; Rouviere and Wolfe, 1988; Saier, 2013). The EMP glycolytic pathway prevalent in animals, plants, bacteria and yeasts, is the primary route for glucose uptake and conversion to pyruvate (Rouviere and Wolfe, 1988; Saier, 2013). The overall reaction involves glucose, 2ADP, 2NAD+, 2-inorganic orthophosphates generating 2-pyruvate, 2-ATP, 2-NADH and 2-protons (Rouviere and Wolfe, 1988; Saier, 2013).

The Entner-Doudoroff (ED) pathway, which is absent in mammals, is widespread among gram-negative bacteria but occurs less frequently in anaerobic organisms (Brückner and Titgemeyer, 2002; Macfarlane and Macfarlane, 2011). This pathway produces only one ATP per two pyruvate molecules (Brückner and Titgemeyer, 2002; Macfarlane and Macfarlane, 2011). Many microbes exhibit the ability to produce ethanol from glucose, with ethanol being a major product due to its highly reduced nature (Brückner and Titgemeyer, 2002; Macfarlane and Macfarlane, 2011).

Lactate fermentation: Certain bacterial genera, commonly known as lactic acid bacteria (LAB) are known for producing lactic acid as a primary product through carbohydrate fermentations (Van Vuuren et al., 1993; Carr et al., 2002). These bacteria are facultative anaerobes with limited biosynthetic capabilities (Diekert, 1990; Van Vuuren et al., 1993; Carr et al., 2002).  The LAB genera include Lactobacillus, Leuconostoc, Pediococcus, Lactococcus, Streptococcus and Enterococcus (Diekert, 1990; Carr et al., 2002). The classification of lactic acid bacteria is based on the primary hexose fermentation pathways they employ, resulting in two main groups (Carr et al., 2002). Homofermentative lactic acid bacteria metabolize glucose through the EMP pathway leading to the production of pyruvate, which is subsequently reduced to lactic acid by lactate dehydrogenase (Gibson et al.,1993). On the other hand, heterofermentative lactic acid bacteria transform glucose into mixed acid products such as lactate, acetate, ethanol and carbon-di-oxide (Gibson et al.,1993). Pyruvate can undergo conversion to lactate through lactate dehydrogenase or to acetyl CoA and CO2 by pyruvate enzymes, depending on the specific sugar uptake rat, whether it is high or low (Gibson et al., 1993). The subsequent reduction on acetyl CoA involves acetaldehyde and alcohol (Gibson et al.,1993).

The activity of dehydrogenases results in the production of ethanol as the final product, accompanied by the formation of acetate (Corry et al., 1986; Rogers et al., 1984). Lactate is considered as a significant subtract for post mortem ethanol formation, given the presence of lactate dehydrogenase and lactate in human tissues (Corry et al., 1986; Rogers et al., 1984). The conversion of lactate to pyruvate is achieved through LDH action. Subsequently pyruvate can be utilized for ethanol formation (Corry et al. 1986; Rogers et al., 1984). Moreover, lactate serves as a preferred substrate for propionic acid bacteria, which are organisms capable of thriving in anaerobic to aero tolerant conditions (Zeikus, 1980; Rogers et al., 1984). The theoretical stoichiometry of propionic acid fermentation is,

3 Lactate → 2 Propionate + Acetate + CO2 + H2O

Acetate can undergo conversion through the activity of acetate kinase or acetyl-CoA synthetase, leading to the generation of acetyl-CoA and contributing to ethanol formation. Alternatively, acetate may be accumulated in the medium (Corry et al. 1986; Rogers et al., 1984).

Figure 4: Fermentation of glucose by lactic acid bacteria through heterofermentative pathway to ethanol and lactate (Rogers et al., 1984; Corry et al., 1986; Rouviere and Wolfe, 1988; Macfarlane and Macfarlane, 2011).

 

Purification of alcohols: Alcohol production process comprises of several steps, including hydrolysis, fermentation, separation, purification. The initial steps involve milling, when lignocellulosic feedstocks are used. After fermentation, solid residues are separated, and maintained a constructive environment for fermenting organisms, ethanol is continuously removed and fermentation is enhanced and then purified to reach a fuel grade level attaining 99% purity (Corry et al. 1986; Zeikus, 1980).

Distillation is a widely used technique for purifying fermented product into fuel grade ethanol but it has limitations in terms of energy efficiency and cost effectiveness (Gibson et al., 1993; Pucino et al. 2019). As a result, more cost-effective and energy-efficient separation methods are being developed such as pervaporation, membrane-based separation, and chemical techniques, etc. Alcohol fermentation is a multi-step process that requires careful management from initial fermentation to waste disposal ensuring efficient and balanced operations (Rouviere and Wolfe, 1988; Pucino et al., 2019).

Fermentation components: Fermentation is a biological process that involves conversion of compounds such as carbohydrate into other compounds by microorganisms like bacteria, yeast or fungi (Zeikus,1980; Rogers et al., 1984; Corry et al., 1986; Rouviere and Wolfe, 1988; Macfarlane and Macfarlane, 2011). These microorganisms primarily drive the metabolic activities of fermentation. Here is a list of some chemical reactions and components involved in fermentation.

Substrate: Sugars are the primary substrate of fermentation. Some examples of sugars involved in the process of fermentation are: glucose, fructose, galactose, lactose etc (Macfarlane and Macfarlane, 2011). But for ethanol formation reaction, glucose is used as it takes fewer easiest steps for conversion to alcohol. Starch is used for fermentation, but it is a complex sugar. Before fermentation, it needs to be converted into lower carbohydrates (Macfarlane and Macfarlane, 2011). Yeast or bacteria: These are the microorganisms and they are responsible for fermentation. They play the most crucial role in fermentation (Lynen and Ochoa, 1953; Hahn-Hagerdal et al., 2006; Pucino et al., 2019). These microorganisms consume sugars and produce other compounds through metabolic process. Some common examples of microorganisms are: Saccharomyces cerevisiae (also known as Baker’s yeast or Brewer Yeast) for alcoholic fermentation and lactic acid bacteria for lactic acid fermentation (Lynen and Ochoa, 1953; Pucino et al., 2019). Glycolysis: It is the central metabolic pathway in fermentation which implies series of enzymatic reactions that takes place in the cytoplasm of cells (Wiegel, 1982; Corry et al., 1986; Robertson, 2005). It involves breakdown of one molecule of glucose into two molecules of pyruvate generating small amount of ATP and reducing equivalent number of NADH (Robertson, 2005). Pyruvate metabolism: Depending upon the type of metabolism and the specific fermentation process, the pyruvate can differ. Pyruvate is the central molecule in carbohydrate or sugar metabolism (Ueno et al., 2006). In alcoholic fermentation, pyruvate is converted into ethanol and carbon dioxide by yeast. This reaction regenerates NAD+ from NADH which is necessary to keep glycolysis going (Wiegel, 1982; Corry et al.,1986; Robertson, 2005). In lactic acid fermentation, pyruvate is reduced to lactic acid, resulting in generation of NAD+ (Corry et al., 1986). Bacteria like Escherichia coli (a gram-negative bacteria) produce a mixture of acids like as acetic acid, formic acid, succinic acid with hydrogen and carbon dioxide (Corry et al. 1986; Ueno et al., 2006; Fan et al., 2012). Other compounds: Variety of other compounds are produced because of fermentation. It depends on the type of microorganism involved and special conditions. For example, in fermentation of wine or beer, esters, alcohols, acids contribute to flavour and aroma and taste of the final product. Energy production: fermentation does not yield much more energy in aerobic respiration, but it allows cells to generate some ATP in anaerobic conditions (Corry et al. 1986; Ueno et al., 2006; Fan et al., 2012, Bernard et al., 2021) pH: Fermentation is influenced by factors like temperature. Different microorganisms have different pH ranges based on their microbial activities (Naik et al., 2010). Temperature: Fermentation is influenced by factors like temperature. Different microorganisms can perform their functions at different temperature ranges (Naik et al., 2010). End Products: Fermentation product may vary depending on the type of microorganism and the substrate. In addition to ethanol, fermentation can produce some other products like acetic acid, butyric acid and various gases (Naik et al., 2010).

Beer Chemistry: The chemistry of beer is complex but fascinating subject that encompasses a wide range of chemical enzymatic reactions and produces ethanol and some other compounds. Beer is primarily composed of water, barley’s grain or rice grain, hops and yeast. Several chemical transformations occur during brewing process resulting in flavours, aromas etc. Here are some of the critical aspects of beer chemistry:

3.1: Various steps during preparation of beer

Malting and mashing (Gray et al., 2006; Zhang, 2010): Malting: Grains are soaked, allowed to germinate and then dried. During this process, enzymes are activated, leading to breakdown of starches in the barley into fermentable sugars (mainly maltose) and non-fermentable sugars.

Mashing: The process where milled malt is mixed with water is known as mashing. This step includes enzymes (e.g.: amylase) that convert the starches in to sugars primarily maltose and this results in the formation of wort.

Boiling and Hopping (Gray et al., 2006; Zhang, 2010; Chandel et al., 2013): During boiling, hops are also added to the wort. Hops contribute bitterness, flavour and aroma to beer. Hops contain compounds called alpha acids that undergo isomerization during boiling, becoming bitter compounds. Hops also contain essential oils that contribute to the aroma and flavour of the beer. The oils can be volatile and can be lost during boiling, so late hop additions or dry hopping may be used to preserve these characteristics.

Fermentation (Rogers et al.; 1984; Rouviere and Wolfe, 1988; Macfarlane and Macfarlane, 2011): Yeast, typically Saccharomyces cerevisiae is added to the wort. Yeast converts fermentable sugars (mainly maltose) into alcohol (ethanol) and carbon dioxide in a process called alcoholic fermentation. During fermentation, ester compounds are also produced which contribute fruity and spicy aromas of beer. In a separate tank, some beers are allowed to undergo a secondary fermentation. This leads to the development of complex flavours over time. Yeast can produce higher alcohols (e.g. isoamyl alcohol). These alcohols can change flavour profile and mouthfeel.

Colour and caramelization (Rogers et al.; 1984; Rouviere and Wolfe, 1988; Macfarlane and Macfarlane, 2011):

The colour of the beer is influenced by the type and the roast level of the malt used. Caramelization during the boiling process also contribute to colour.

Protein and haze formation (Rogers et al.; 1984; Rouviere and Wolfe, 1988; Macfarlane and Macfarlane, 2011):

Certain proteins in beer can interact with polyphenols from hops and form haze.

Diacetyl and sulphur compounds (Rogers et al.; 1984; Rouviere and Wolfe, 1988; Macfarlane and Macfarlane, 2011):

Some yeast strains produce diacetyl which can impart a buttery or butterscotch flavour. Proper maturation and conditioning help reduce diacetyl levels. Sulphur compounds can also be produced during fermentation, but these typically dissipate with ageing.

The chemistry of beer is a rich field and the brewers must carefully manage these chemical reactions to create the desire beer characteristics. Factors such as ingredients, yeast grains, fermentation temperature and brewing techniques play a complete role in shaping the chemistry of beer.

Ethanol production in large scale

Ethanol is produced on a large scale through a process called fermentation. The production of ethanol, whether for use in alcoholic beverages or industrial purposes (e.g., biofuels), typically follows following steps:

Raw material selection: The primary source of fermentable sugars for alcohol production can vary depending on the intended use. Common raw materials include: Grains: (e.g., barley, corn, wheat, and rye) for alcoholic beverages like beer and whiskey. Sugarcane or sugar beets to produce sugarcane or beet-based ethanol. Starchy materials like cassava, sweet potatoes, or corn for fuel ethanol Lignocellulosic biomass like wood, straw, or agricultural waste for second-generation biofuels. Milling and preparation: Raw materials are processed to expose the starches or sugars for conversion. This often involves grinding, crushing, or milling the materials into smaller particles. Mashing: In the case of grains or starchy materials, the milled raw materials are mixed with water and heated to create a mash. This step allows enzymes to break down the starches into fermentable sugars. Enzymes may be added if natural enzymes are insufficient. Fermentation: The mash or prepared substrate is then inoculated with yeast or other microorganisms. For ethanolic beverage production, Saccharomyces cerevisiae is commonly used. The yeast consumes the sugars and converts them into ethanol and carbon dioxide in a process known as alcoholic fermentation. Distillation (Optional): To produce higher ethanol content beverages or industrial ethanol, the fermented liquid may undergo distillation. Distillation is a process that separates ethanol from water and other compounds, increasing its concentration. Purification: Distilled ethanol may undergo further purification processes to remove impurities, such as unwanted compounds or flavours. This is especially common in the production of high-quality spirits. Blending (Beverages): In the production of ethanolic beverages, the distilled ethanol may be blended with water and, in some cases, other flavouring components, such as botanicals for gin or aging in barrels for whiskey. Quality control: Throughout the production process, quality control measures are applied to ensure the final product meets desired specifications for ethanol content, flavour, and safety. Packaging: The final ethanol product is typically bottled, canned, or packaged in appropriate containers for distribution and consumption.

The production of ethanol on a large scale can vary significantly depending on the intended use and local regulations. While the steps outlined above are general, specific details may differ in practice. For example, the production of bioethanol for fuel may involve different purification processes and quality control measures compared to alcoholic beverage production. Additionally, there are efforts to develop more sustainable and environmentally friendly methods for large-scale ethanol production, such as utilizing lignocellulosic biomass and advanced fermentation techniques.

Fermentation offers several advantages for bioethanol production. It is environmentally friendly.  It utilizes renewable biomass resources which requires relatively low energy inputs, and can be performed on an industrial scale. Modern biotechnological advances such as metabolic engineering, synthetic biology, and CRISPR-mediated strain improvement have further enhanced fermentation efficiency through enabling microorganisms to tolerate higher ethanol concentrations and utilize a broader range of sugars (including pentoses derived from lignocellulosic biomass).

Recent developments include consolidated bioprocessing (CBP), where biomass hydrolysis, enzyme production and fermentation occur in a single step, significantly reducing production costs. Additionally, artificial intelligence-assisted fermentation optimization (AI Assisted fermentation optimization) is improving process control, ethanol yield, and industrial productivity (Rogers et al.; 1984; Rouviere and Wolfe, 1988; Macfarlane and Macfarlane, 2011).

Thus, fermentation acts as the key biochemical bridge that converts biomass-derived sugars into bioethanol, making it one of the most important technologies for sustainable biofuel production and the transition toward a low-carbon bioeconomy.

Fermented drinks: A wide variety of alcoholic and non-alcoholic drinks are commercially produced through fermentation.

Alcoholic beverages:

Beer: Beer is made from barley and other cereal grains in the presence of Saccharomyces cerevisiae which converts glucose to ethanol and carbon dioxide. Wine: Wine is a type of alcoholic fruit fermented drink. Fruits like grapes are crunched in the presence of yeast leading to the formation of ethanol. Spirit: Spirits are produced through fermentation followed by distillation to improve ethanol content. e.g. vodka, whisky etc. Cider: Cider is a fermented alcoholic drink specially made from apple. Mead: Mead is prepared by fermenting honey. Sake: Sake is a Japanese fermented rice beer which is made from fermentation of polished rice in the presence of yeast.

Non-alcoholic fermented drinks:

Kombucha: It is a fermented tea beverage obtained by fermenting tea with SCOBY (symbiotic culture of bacteria and yeast). It is known for its probiotic content. Water kafir: It is a non-alcoholic, probiotic beverage made by fermenting sugar water with water kefir grains. Milk kefir:  It is a probiotic fermented milk kafir product, which is a rich dairy product. Kvass: Kvass is a fermented beverage, made from other cereal grains or rye bread and it is popular in European countries.  Ginger beer: It is a non-alcoholic fermented beverage made by fermenting sugar, ginger and water, which is rich in probiotics.

There are many other varieties of fermented non-alcoholic drinks like fermented fruit juice, fermented coffee, fermented tea etc.

CONCLUSION

Simple sugar to ethanol transformation is an elegent engineering of biochemistry where human innovation is based on the technique that is glycolysis and fermentation. Microorganisms like yeast, convert sucrose into ethanol and carbon dioxide under anaerobic conditions. Glucose is the widely recognized most used sugar that can produce ethanol through the process of fermentation, but it is not the only sugar. Ethanol fermentation is a metabolic process which is carried out various fermenting enzymes such as yeast and other bacteria, as they metabolize sugars to produce carbon dioxide and ethanol.  Sugars like sucrose, fructose, maltose can also be used for fermentation to produce ethanol by various types of microorganism. In fact, different microorganisms have different efficiencies with different sugars. Some sugars require specific types of microorganisms to initiate the reaction.

This route of beverage production is crucial for understanding and important for the development of sustainable energy systems. Ethanol used as a biofuel, cleaner alternative to fossil fuels while reducing greenhouse gas emissions. Genetically engineered yeast and optimized fermentation systems can enhance efficiency and yield, paving the way for large-scale production with minimal waste.Ultimately, the journey from sugars to alcohol is more than just a chemical process – it shows how humans have learned to use nature’s pathways for many purposes, from age-old traditions to creating new energy solutions for the future.

Conflicts of Interest: The authors declare no conflict of interest.

Data Availability: All data are available with the corresponding author on reasonable request

Declaration on AI Usage: This manuscript has been prepared without the use of AI tools.

REFERENCES

Basumatary, S. and Deka, A.K. (2025). Utilization of solid post-fermented waste for green synthesis of gold nanoparticles: applications in removal of organic dyes from wastewater. Chemical Papers, 79(7), 4385-4401.

Bernard, P., Stelmachowski, P., Broś, P., Makowski, W. and Kotarba, A. (2021). Demonstration of the influence of specific surface area on reaction rate in heterogeneous catalysis. Journal of Chemical Education, 98(3), 935-940.

Bhattacharya, B. and Deka, D.C. (2023). Biochemical indices and consumption pattern of traditional alcoholic beverages by tribal communities of North-East India: a review. Current Research in Nutrition and Food Science, 11(2), 470-487.

Brückner, R. and Titgemeyer, F. (2002). Carbon catabolite repression in bacteria: choice of the carbon source and autoregulatory limitation of sugar utilization. FEMS Microbiology Letters, 209(2), 141-148.

Carr, F.J., Chill, D. and Maida, N. (2002). The lactic acid bacteria: a literature survey. Critical reviews in microbiology, 28(4), 281-370.

Chandel, A.K., Da Silva, S.S. and Singh, O.V. (2013). Detoxification of lignocellulose hydrolysates: biochemical and metabolic engineering toward white biotechnology. BioEnergy Research, 6(1), 388-401.

Chum, H.L., Nigro, F., McCormick, R., Beckham, G., Seabra, J., Saddler, J., Tao, L., Warner, E. and Overend, R.P. (2015). Conversion technologies for biofuels and their use. Bioenergy & sustainability: bridging the gaps, 72, 374-467.

Clark, D.P. (1989). The fermentation pathways of Escherichia coli. FEMS microbiology reviews, 5(3), 223-234.

Corry, J.E., Leclerc, M., Mossel, D.A.A., Skovgaard, N., Terplan, G. and Van Netten, P. (1986). An investigation into the quality of media prepared and poured by an automatic system. International Journal of Food Microbiology, 3(2), 109-120.

Diekert, G. (1990). CO2 reduction to acetate in anaerobic bacteria. FEMS Microbiology Reviews, 7(3-4), 391-395.

Erdei, B., Barta, Z., Sipos, B., Réczey, K., Galbe, M. and Zacchi, G. (2010). Ethanol production from mixtures of wheat straw and wheat meal. Biotechnology for Biofuels, 3(1), 16.

Fan, D., Dai, D.J. and Wu, H.S. (2012). Ethylene formation by catalytic dehydration of ethanol with industrial considerations. Materials, 6(1), 101-115.

Fuhrer, T., Fischer, E. and Sauer, U. (2005). Experimental identification and quantification of glucose metabolism in seven bacterial species. Journal of Bacteriology, 187(5), 1581-1590.

Garrigues, C., Loubiere, P., Lindley, N.D. and Cocaign-Bousquet, M. (1997). Control of the shift from homolactic acid to mixed-acid fermentation in Lactococcus lactis: predominant role of the NADH/NAD+ ratio. Journal of Bacteriology, 179(17), 5282-5287.

Gibson, G.R., Macfarlane, S. and Macfarlane, G.T. (1993). Metabolic interactions involving sulphate-reducing and methanogenic bacteria in the human large intestine. FEMS Microbiology Ecology, 12(2), 117-125.

Gray, K.A., Zhao, L. and Emptage, M. (2006). Bioethanol. Current opinion in chemical biology, 10(2), 141-146.

Hahn-Hägerdal, B., Galbe, M., Gorwa-Grauslund, M.F., Lidén, G. and Zacchi, G. (2006). Bio-ethanol–the fuel of tomorrow from the residues of today. Trends in Biotechnology, 24(12), 549-556.

Horváth, T., Kun, S., Sipos, L. and Pham, D.T. (2026). Automated monitoring of alcoholic fermentation: trends and challenges. Journal of Food Science and Technology, 1-14.

Hosseini, S.E. and Wahid, M.A. (2013). Biogas utilization: Experimental investigation on biogas flameless combustion in lab-scale furnace. Energy Conversion and Management, 74, 426-432.

Kamaljeet, Vijukumar, A., Shahi, A., Kumar, A. and Bhatia, R. (2026). Auto-brewery syndrome and the human microbiome: Insights into endogenous ethanol production and human diseases: Kamaljeet et al. Food Science and Biotechnology, 1-22.

Kang, A. and Lee, T.S. (2015). Converting sugars to biofuels: ethanol and beyond. Bioengineering, 2(4), 184-203.

Kostic, M.A. and Dart, R.C. (2003). Rethinking the toxic methanol level. Journal of Toxicology: Clinical Toxicology, 41(6), 793-800.

Kulkarni, S.J., Shinde, N.L. and Goswami, A.K. (2015). A review on ethanol production from agricultural waste raw material. Int J Sci Res Sci Eng Technol, 1(4), 231-233.

Lin, Y. and Tanaka, S. (2006). Ethanol fermentation from biomass resources: current state and prospects. Applied microbiology and biotechnology, 69(6), 627-642.

Liu, W., Lund, H., Mathiesen, B.V. and Zhang, X. (2011). Potential of renewable energy systems in China. Applied Energy, 88(2), 518-525.

Lynen, F. and Ochoa, S. (1953). Enzymes of fatty acid metabolism. Biochimica et biophysica acta, 12(1-2), 299-314.

Macfarlane, D. P. (2011) Metabolic pathways promoting intrahepatic fatty acid accumulation in methionine and choline deficiency: implications for the pathogenesis of steatohepatitis. American Journal of Physiology-

Endocrinology and Metabolism, 300(2), 402-409.

Macfarlane, S. and Macfarlane, G.T. (2003). Regulation of short-chain fatty acid production. Proceedings of the Nutrition Society, 62(1), 67-72.

Martinez-Guerra, E. and Gude, V.G. (2014). Transesterification of used vegetable oil catalyzed by barium oxide under simultaneous microwave and ultrasound irradiations. Energy conversion and management, 88, 633-640.

Melchiorsen, C.R., Jensen, N.B.S., Christensen, B., Væver Jokumsen, K. and Villadsen, J. (2001). Dynamics of pyruvate metabolism in Lactococcus lactis. Biotechnology and bioengineering, 74(4), 271-279.

Mitchell, P. (1979). Compartmentation and communication in living systems. Ligand conduction: a general catalytic principle in chemical, osmotic and chemiosmotic reaction systems. European Journal of Biochemistry, 95(1), 1-20.

Naik, S.N., Goud, V.V., Rout, P.K. and Dalai, A.K. (2010). Production of first- and second-generation biofuels: a comprehensive review. Renewable and sustainable energy reviews, 14(2), 578-597.

O’Neal, C.L. and Poklis, A. (1996). Postmortem production of ethanol and factors that influence interpretation: a critical review. The American Journal of forensic medicine and pathology, 17(1), 8-20.

Pucino, V., Certo, M., Bulusu, V., Cucchi, D., Goldmann, K., Pontarini, E., Haas, R., Smith, J., Headland, S.E., Blighe, K. and Ruscica, M. (2019). Lactate buildup at the site of chronic inflammation promotes disease by inducing CD4+

T cell metabolic rewiring. Cell Metabolism, 30(6), 1055-1074.

Robertson, D.G. (2005). Metabonomics in toxicology: a review. Toxicological Sciences, 85(2), 809-822.

Rogers, P.L., Goodman, A.E. and Heyes, R.H. (1984). Zymomonas ethanol fermentations. Microbiological Sciences, 1(6), 133-136.

Rouviere, P.E. and Wolfe, R.S. (1988). Novel biochemistry of methanogenesis. Journal of Biological Chemistry, 263(17), 7913-7916.

Ruthven, D.M. (2011). Molecular sieve separations. Chemie Ingenieur Technik, 83(1‐2), 44-52.

Saier Jr, M.H. (2013). Microcompartments and protein machines in prokaryotes. Journal of molecular microbiology and biotechnology, 23(4-5), 243-269.

Sereme-Mothobole, B., Loeto, D. and Jongman, M. (2026). Setopoti, A Homebrewed Traditional Alcoholic Beverage and Its Microbiomes: Toward Safer and Sustainable Fermentation Practices. Food Biotechnology, 40(2), 228-257.

Sun, Y. and Cheng, J. (2002). Hydrolysis of lignocellulosic materials for ethanol production: a review. Bioresource Technology, 83(1), 1-11.

Tephly, T.R., (1991). The toxicity of methanol. Life Sciences, 48(11), 1031-1041.

Ueno, Y., Sasaki, D., Fukui, H., Haruta, S., Ishii, M. and Igarashi, Y. (2006). Changes in bacterial community during fermentative hydrogen and acid production from organic waste by thermophilic anaerobic microflora. Journal of Applied Microbiology, 101(2), 331-343.

Van Vuuren, H.J.J. and Dicks, L.M.T. (1993). Leuconostoc oenos: a review. American Journal of Enology and Viticulture, 44(1), 99-112.

Wiegel, J., (1982). Ethanol from cellulose. Experientia, 38(2), 151-156.

Wolfe, A.J., (2005). The acetate switch. Microbiology and molecular biology reviews, 69(1), 12-50.

Yusri, I.M., Mamat, R., Azmi, W.H., Najafi, G., Sidik, N.A.C. and Awad, O.I., (2016). Experimental investigation of combustion, emissions and thermal balance of secondary butyl alcohol-gasoline blends in a spark ignition engine. Energy Conversion and Management, 123, 1-14.

Zeikus, J.G. (1980). Chemical and fuel production by anaerobic bacteria. Annual Reviews in Microbiology, 34(1), 423-464.

Zhang, L., Zhang, J. and Loh, K.C. (2018). Activated carbon enhanced anaerobic digestion of food waste–Laboratory-scale and Pilot-scale operation. Waste management, 75, 270-279.

Zhang, Y.H.P. (2010). Production of biocommodities and bioelectricity by cell‐free synthetic enzymatic pathway biotransformations: Challenges and opportunities. Biotechnology and bioengineering, 105(4), 663-677.