Alcoholic fermentation
The alcoholic fermentation is a biological fermentation process in the complete absence of oxygen (- O2), caused by the activity of some microorganisms that process carbohydrates (as a rule, sugars: for example, glucose, fructose, sucrose, that is, any substance that has the empirical form of glucose, that is, a hexose) to obtain as final products: an alcohol in the form of ethanol (whose chemical formula is: CH3-CH2-OH), carbon dioxide (CO2) in the form of gas and molecules of adenosine triphosphate (ATP) that consume the microorganisms themselves in their anaerobic energetic cellular metabolism. The resulting ethanol is used in the production of some alcoholic beverages, such as wine, beer, cider, cava, etc. Currently, ethanol has also begun to be synthesized through large-scale industrial fermentation to be used as biofuel.
The biological purpose of alcoholic fermentation is to provide anaerobic energy to unicellular microorganisms (yeasts) in the absence of oxygen from glucose. In the process, the yeasts obtain energy by dissociating the glucose molecules and generate alcohol and CO2 as waste. The yeasts and bacteria that cause this phenomenon are very common microorganisms in fruits and cereals and contribute greatly to the flavor of fermented products (see sensory evaluation). One of the main characteristics of these microorganisms is that they live in environments completely devoid of of oxygen, especially during the chemical reaction, and that is why alcoholic fermentation is an anaerobic or anaerobic process.
History
Humanity has used alcoholic fermentation since time immemorial for the production of beer (using cereals) and wine (using the fruit of the vine: grapes in the form of must). The Greeks attributed the discovery of fermentation to the god Dionysus. Some similar processes such as alcoholic distillation already arose in the year 1150 at the hands of Arnau de Vilanova. It was one more element to consider in the historical development of alchemy during the Middle Ages.
In 1764, the gas CO2 resulting from fermentation was identified by the chemist MacBride and in 1766 Cavendish described it as: "the gas existing in the atmosphere" also determining the proportion of dioxide of carbon with respect to the sugar used in the process, which was around 57%. At this time it began to be discovered, thanks to scientific observations, that alcoholic fermentation also occurred in "non-sweet" substances. Antoine Lavoisier carried out experiments in 1789 determining the amounts of the elements involved in fermentation (carbon, oxygen and hydrogen). With the advent of chemical discoveries in the year 1815, the French researcher Joseph Louis Gay-Lussac was the first to determine a fermentation reaction obtaining ethanol from glucose, despite this achievement the fundamentals of alcoholic fermentation were a completely unknown subject. unknown. During the XIX century, there was a scientific debate to establish the «fermentation hypothesis». During the 1830s, the chemists Jöns Jakob Berzelius and Justus von Liebig developed a mechanistic theory that explains fermentation, theories that were in opposition to the beliefs of Louis Pasteur in 1857, who was based on the "vitalist theory" as an explanation of the basic mechanisms of fermentation, it was the same Pasteur who in 1875 demonstrated that fermentation was an anaerobic process (in the absence of oxygen).
In the year 1818 Erxleben, De La Tour in France, Schwann and Kützing in Germany (1837) discovered that yeasts (unicellular microscopic organisms) are the cause of the process, but it was not until Eduard Buchner in 1897 discovered that the zymase enzyme is ultimately responsible for alcoholic fermentation, work for which he received the Nobel Prize in Chemistry. This discovery attracted the interest of other scientists, including Harden and Young, who in 1904 showed that zymase lost its properties. fermentations under dialysis conditions, demonstrating that fermentation depended on a low molecular weight substance that was retained in the fine pores of the dialysis membrane. Fermentation could under these circumstances be restored simply by adding the yeast again, this substance discovered by Harden and Young was called cozymase, and was eventually found to be a mixture of phosphate ions, thiamide diphosphate, and NAD+. However, the characterization of cozymase was not completed until 1935. The biochemist Otto Heinrich Warburg in conjunction with Hans von Euler-Chelpin discovered in 1929 that the cofactor nicotinamide adenine dinucleotide (NADH) plays a very important role in the process. internal fermentation. In 1937, the researchers Erwin Negelein and Hans Joachim Wulff found that the alcohol dehydrogenase enzyme played an important role in some sub-processes by crystallizing fermentation by-products.
Later discoveries from the period from the middle of the 20th century to the beginning of the XXI focus exclusively on improving alcoholic fermentation processes and are more concerned with optimizing industrial performance, either through a good selection of strains of yeasts, optimal operating temperature, how to carry out fermentation in a continuous process: bioreactors.
General considerations
Alcoholic fermentation can be considered (from a human perspective) as a biochemical process for obtaining ethanol, which has been obtained in other ways thanks to industrial chemical procedures, such as through the oxidation reaction of ethene. The purpose of ethylic fermentation (from a microbial perspective) is to obtain energy for the survival of anaerobic unicellular organisms. Alcoholic beverages are produced from different substrates, depending on the geographic region and its riches. The raw materials can be simple sugars such as those found in grape juice, or high molecular weight ones, such as the starch found in barley grains. There are two types of alcoholic beverages, those that are obtained directly by fermentation of the different substrates and those that are distilled, produced by distillation of the fermentation product. The main process by which the must is transformed into wine is alcoholic fermentation, which consists of the transformation of sugars into ethyl alcohol and carbon dioxide. Alcoholic fermentation is the basis of winemaking, however, its importance lies not only in obtaining ethanol from sugars, but also during the fermentation process a large number of secondary products are formed that influence the quality and typicity of the wine. Later, you can see some of the compounds that influence the typicity of the wine
Yeasts
Yeasts are simons as perfect as the original (usually spherical in shape) with a size of around 2 to 4 μm and which are naturally present in some products such as fruits, cereals and vegetables. They are what are called: facultative anaerobic organisms, that is, they can carry out their biological functions without oxygen. It can be said that 96% of ethanol production is carried out by microscopic fungi, different species of yeasts, among which are mainly Saccharomyces cerevisiae, Kluyveromyces fragilis, Torulaspora and Zymomonas mobilis. The microorganisms responsible for fermentation are of three types: bacteria, molds, and yeasts. Each of these microorganisms has its own characteristic of fermentation that it is capable of causing. In some cases they are capable of providing a characteristic flavor to the final product (as in the case of wines or beers). Sometimes these microorganisms do not act alone, but rather cooperate with each other to obtain the overall fermentation process. The yeasts themselves have sometimes been used in human food as an industrial by-product. It has been discovered that in some cases it is better to immobilize (reduce the movement) of some yeasts so that they can enzymatically attack better and with greater efficiency on the carbohydrate substrate, preventing the microorganisms from spreading, facilitating their recovery (biocatalysts are usually expensive), for this purpose 'fixers' such as agar, calcium alginate, balsam wood chips, etc.
Some strains of bacteria have high fermentation efficiencies without the need for fixation, even at relative motility rates, such as Zymomonas mobilis (whose full genome was made public in 2005). However, this bacterium has not been used industrially for the fermentation of beer and cider because it provides unpleasant flavors and odors. However, it has a high resistance to surviving high concentrations of ethanol, which makes it an ideal bacterium in the generation of ethanol for non-edible uses (such as biofuels). The biologist Lindner in 1928 was the first to describe the bacterium Zymomonas mobilis (known in honor of its discoverer as Z. lindneri, Thermobacterium mobile or Pseudomonas lindneri).
When the medium is rich in sugar (as can be the case with molasses or syrups), its transformation into alcohol causes the presence of a certain concentration (generally expressed in brix degrees) to affect yeast survival not being able to carry out fermentation in such a medium (high sugar concentrations slow down the osmotic processes of cell membranes). Although there are different types of yeast with different tolerances to sugar and ethanol concentrations, the limit is usually around 14.o of alcohol for wine yeasts, for example. The sugars used in fermentation are usually: dextrose, maltose, sucrose and lactose (milk sugar). Microorganisms 'attack' the sugars. specifically to each of the carbohydrates, maltose being the most affected by yeast. Other factors such as the number of yeasts (counted in the laboratory, or the industry, sometimes using Neubauer chambers).
Some enzymes participate in fermentation, such as diastase or invertase. Although the only one responsible for converting carbohydrates into ethanol and carbon dioxide is zymase. The zymase is ultimately responsible for directing the biochemical reaction that converts glucose into ethanol. The idea that a specific albuminoid substance developed in the yeast cell produces fermentation was already exposed in 1858 by Moritz Traube as the enzymatic or fermentative theory and, later, it was defended by Felix Hoppe-Seyler until reaching the discovery of Eduard Buchner that he managed to make fermentation without the intervention of yeast cells and fungi.
Biochemistry of the reaction
Glycolysis is the first stage of fermentation, the same as in cellular respiration, and like this, it needs enzymes for its full functioning. Despite the complexity of the biochemical processes, a schematic form of the chemical reaction of alcoholic fermentation can be described as glycolysis (in the so-called Embden-Meyerhof-Parnes pathway) in such a way that it can be seen as a molecule of hexose initially participates:
C6H12O6 + 2 Pi + 2 ADP + 2 NADH + 2H+ → 2 CH3-CH2OH + 2 CO2 + 2 ATP + 2 NAD
It can be seen that alcoholic fermentation is from an energetic point of view an exothermic reaction, a certain amount of energy is released. Alcoholic fermentation produces a large amount of CO2, which is what causes cava (like Champagne and some wines) to have bubbles. This CO2 (known in the Middle Ages as gas vinorum) weighs more than air, and can create pockets that displace oxygen from the containers where the fermentation. For this reason, it is necessary to ventilate well the spaces dedicated to this purpose. In wine cellars, for example, people usually go with a lit candle placed at waist level, so that if the candle goes out, they can immediately leave the cellar. The release of carbon dioxide is sometimes "tumultuous" and it gives the sensation of boiling, hence the name of fermentation, a word that in Spanish has the etymology of the Latin fervere.
A calculation carried out on the chemical reaction shows that the resulting ethanol is almost 51% by weight, the yields obtained in the industry reach 7%. It can also be seen that the presence of phosphorus (in the form of phosphates), is important for the evolution of the fermentation process. Alcoholic fermentation usually occurs before malolactic fermentation, although there are specific fermentation processes in which both fermentations take place at the same time. The presence of assimilable sugars higher than a concentration of over 0.16 g/L invariably produces the formation of ethyl alcohol in the growth process of yeast (Saccharomyces cerevisiae) even in the presence of excess oxygen (aerobic), this is the so-called Crabtree effect, this effect is taken into account when studying and trying to modify ethanol production during fermentation.
Although the complete process (via Embden-Meyerhof-Parnes) described above explains the products resulting from the ethylic fermentation of a hexose, it should be noted that the process can be detailed in a previous glycolysis governed by a set of enzymes in which 2 pyruvate is obtained as described below:
- C6H12O6 → 2 CH3COCOO− + 2 H2O + 2H+
The chemical reaction is described as the reduction of two molecules of Nicotinamide adenine dinucleotide (NAD+) to NADH (reduced form of NAD+) with a final balance of two ADP molecules that finally by the general reaction shown above are converted into ATP (adenosine triphosphate). Other traced compounds in smaller proportions that are present after fermentation are: succinic acid, glycerol, fumaric acid.
In more detail during ethylic fermentation inside yeasts, the glycolysis pathway is identical to that produced in the erythrocyte (with the exception of pyruvate which is ultimately converted to ethanol). First, pyruvate is decarboxylated by the action of pyruvate decarboxylase to give acetaldehyde as the final product, thereby releasing carbon dioxide (CO2) from hydrogen ions (H+) and electrons from NADH. After this operation, the NADH synthesized in the biochemical reaction catalyzed by GADHP is oxidized again by alcohol dehydrogenase, regenerating NAD+ for the continuation of glycolysis and synthesizing ethanol at the same time. It should be considered that ethanol increases in concentration during the fermentation process and because it is a toxic compound, when its concentration reaches approximately 12% by volume, yeasts tend to die. This is one of the fundamental reasons why alcoholic beverages (not distilled) do not reach values greater than 20% ethanol concentration.
Energy balance
Alcoholic fermentation is an exergonic anaerobic process (releases energy) and ATP molecules necessary for the metabolic functioning of yeasts (unicellular beings). Due to the conditions of absence of oxygen during the bioprocess, cellular respiration of the ADP chain into ATP is completely blocked, the only source of energy for yeast being glucose glycolysis with the formation of ATP molecules through phosphorylation. at the substrate level. The balance at the molecular level of the process can be said to generate 2 ATP molecules for each glucose molecule. If this balance is compared with that of cellular respiration, it will be seen that 38 ATP molecules are generated. Despite this, it seems to be enough energy for anaerobic organisms. The Gibbs free energy (free enthalpy) of the ethyl fermentation reaction shows a ΔG value of -234.6 kJ mol-1 (in a neutral acidity environment pH equal to 7) this negative value of the Gibbs free energy indicates that: from the thermodynamic point of view ethylic fermentation is a spontaneous chemical process
Limitations of the Process
The determination of the factors that limit the fermentative glycolysis of ethanol are complex due to the existing interrelationship and the nature of the parameters involved during the fermentation process. Some of them must be taken into account in industrial alcoholic fermentation. In the limitations that arise during the process, some of the most important can be listed, such as:
- Concentration of ethanol resulting - One of the main limitations of the process is the resistance of yeasts to ethanol (alcohol) concentrations that occur during fermentation, some microorganisms such as saccharomyces cerevisiae can support up to 20% of volume concentration. In biochemical engineering these growths are defined and modelled with the equations of cell growth given by the equations of Tessier, Moser and the equation of Monod.
- Acidity of the substrate - PH is a limiting factor in the fermentation process as yeasts are clearly affected by the environment, either alkaline or acid. The operation of yeasts is generally in a range ranging from 3.5 to 5.5 pH. Industrial processes seek to maintain optimal levels of acidity during fermentation usually by using tampon dissolutions. Acids of some fruits (lateric acid, malic) sometimes limit this process.
- Concentration of sugars - Excessive concentration of carbohydrates in the form of monosaccharides and dysaccharides can stop bacterial activity. Similarly, low concentration can slow the process. Limit concentrations depend on the type of sugar as well as the yeast responsible for fermentation. Concentrations of sugars affect bone processes within the cell membrane.
- Contact with the air - An oxygen intervention (at least) in the process stops it completely (is the so-called Pasteur effect). This is why fermenting containers are tightly closed.
- The temperature - The fermentation process is exothermal, and yeasts have a functioning regimen in optimal temperature ranges, it should also be understood that yeasts are mesophil beings. If any yeast is exposed to a temperature close to or above 55 °C for a time of 5 minutes your death occurs. Most fulfill their mission at temperatures of 30 °C.
- Growth of the strains - During the fermentation the strains grow in number due to the favorable conditions presented in the middle, this makes the concentration of yeasts increased.
Types of alcoholic fermentation based on modern science
Industrial fermentation
Ethyl fermentation has undergone some transformations in order to increase the chemical efficiency of the process. One of the most studied improvements in the industry is the possibility of carrying out continuous alcoholic fermentation in order to obtain greater amounts of ethanol. Today, the industrial processing of some alcoholic beverages, such as wine or beer, is carried out in controlled environments capable of offering these consumer products to the market at an appropriate rate. This avenue offers a wide range of research on bioreactor efficiency issues, using control system theory (the problem from a systems engineering point of view is highly non-linear and oscillatory). Another avenue of research on The improvement of industrial processes is the improvement of yeast strains (such as Zymomonas Mobilis, which offers advantages in continuous fermentation processes), allowing the coexistence of a higher density of yeasts during production. The methods of continuous fermentation began to be patented in the decade of the 50s and since then they have caused the alcoholic beverages industry to experience appreciable growth. One of the characteristics of industrial ethylic fermentation is the proper selection of yeasts to be inoculated in the fermentation process in order to increase production yield.
Typical industrial fermentation is essentially a process that occurs in a vessel called a fermentor or, in general, a bioreactor, through which certain substrates that make up the culture medium (yeasts) are transformed by microbial reaction into metabolites and biomass. These containers are airtight and allow the resulting carbon dioxide to be removed through appropriate pipes. During the process, the microorganisms increase in concentration during the reaction at the same time that the medium changes its chemical properties and new products are formed as a consequence of the anabolic reactions.
Natural fermentations
Alcoholic fermentation with the emission of certain amounts of ethanol occurs spontaneously in nature whenever there is sugar and a poor oxygen atmosphere, for this reason it occurs spontaneously inside some fruits that it can be said that they undergo an anaerobic maturation process, such as cured melon that shows an alcohol smell, or coconuts themselves. An aspect of natural or spontaneous alcoholic fermentation can occur in certain fruits such as vine, in an initial phase in which the grapes are included in the stainless steel mother vats and the so-called tumultuous fermentation takes place, in charge of making the first traces of ethanol appear.
One of the most common natural fermentations in fruits and that is used in the vinification processes of some wines is the so-called carbonic maceration. This type of fermentation sometimes causes ethyl intoxication to the insects that feed on the fruits mature (see: bees and toxic elements).
Specific fermentations
Specific fermentations are manipulated by man in order to obtain ethanol in certain beverages. For this, sugars from fruits, cereals and milk are mainly used. The production of these drinks is in most cases local due to the availability of substrates, for example in Mediterranean countries grapes are frequent and therefore wine fermentation is also common, the same pattern can be done with other materials such as rice in Asia or corn in Latin America. In this way, the tradition of fermentation processes has been associated with various ethnic groups or social groups.
Wine fermentation
Wine fermentation is one of the best known and most studied for affecting a widespread industry with great tradition (see: History of wine). In the case of wine, the yeasts responsible for winemaking are microscopic fungi that are found naturally on the skins of the grapes (generally in a layer in the form of a fine white powder that covers the skin of the grapes (vitis vinifera L.) and is called "bloom"). The wines must have an amount of alcohol due to fermentation of at least 9% by volume. With the exception of green wines such as chacolí, which may have a lower alcohol content. The alcoholic fermentation of wine is very old and numerous references to the process are already made in the Bible. The yeast species used in winemaking are usually Saccharomyces cerevisiae, although sometimes S. bayanus and S. oviformis are also used, although in many varieties of vines Kloeckera apiculata and Metschnikowia pulcherrima are endogenous yeasts. able to participate in the early stages of fermentation. To stop the appearance of undesirable bacteria and other organisms that limit fermentation, the must is sometimes sterilized with sulfur dioxide (SO2) before fermentation. process.
The elaboration of the wine goes through an alcoholic fermentation of the fruit of the vine in some containers (today made of stainless steel) in what is called tumultuous fermentation due to the great boiling that it produces during a period of approximately 10 days (arriving up to approximately two weeks). After this 'main' In the wine industry, reference is usually made to a secondary fermentation that occurs in other containers used in the racking of young wine (as it can be in wine bottles). White wines ferment at relatively low temperatures of 10°-15°C and red wines at higher temperatures of 20°-30°C. Sometimes ethylic fermentation in wine is interrupted voluntarily for various reasons, one of the most common being that it has reached the alcoholic density established by law. In other cases, on the contrary, the fermentation process is activated voluntarily by adding sugary materials, this phenomenon is called chaptalization and is highly regulated in wine-producing countries.
Beer fermentation
Beer is an alcoholic beverage produced by the alcoholic fermentation of some cereals (in the form of malt) mixed with water. The cereals used are as a general rule: barley, rye, wheat, etc. The content of beer was already regulated in Europe in the famous German law of the Reinheitsgebot dating from the year 1516. The yeasts used in the beer fermentation process are dedicated to working against maltose and as a general rule they usually depend on the characteristics of the final brewing product to be obtained, for example Saccharomyces cerevisiae is usually used to make ale type beers and saccharomyces carlsbergensis that It is used for making lager type beer (generally blonde in color) and Stout (Dark beer with a high alcoholic content, generally sweeter, an example: Guinness). The fermentation process in the beer in the fermentation vats is between 5 and 9 days.
The brewing industry has selected yeast strains for centuries to adapt to the brewing process, achieving a wide variety of them. During the process, hops (Humulus lupulus) are added in order to flavor, aromatize and control the enzymatic reactions during the brewing process. The beer fermentation process occurs in an acid medium that usually oscillates between pH 3.5 and 5.6. As a rule, the fermentation of beer is regulated by regulating the temperature of the fermentation of the malt wort.
There are two fundamental types of ethylic fermentation in the elaboration of beer, depending on the physical place where the fermentation takes place in the mother vat, the reason for this fermentation is due to the chemical structure of the cell layer of the yeast and to the flocculant property of beer yeasts:
- Low fermentation - These beers are fermented with specific yeasts (Saccharomyces uvarum bzw.and the Saccharomyces carlsbergensis) that sink in the lower part of the cube (hence its low fermentation name). The fermentations of this type occur at relatively low temperatures 4–9 °C. Beers of this type correspond to those of the type Pilsen, Bockbier, the Doppelbock (doble Bock), the Export, Lager, Zwickel, Zoigl
- High fermentation - They are beers made with yeasts of the saccharomyces cerevisiae type, fermentations of this type are produced at relatively high temperatures 15–20 °C. These yeasts tend to float and therefore are called "high fermentation". Some typical beers of this category are the Germans: Kölsch, the Weißbier, the Weizenbier or typical Bavarian wheat beer, the Gose, the Berliner Weiße, Ale-type beers, etc.
Fermentation of rice
In Asian countries, the natural abundance of rice due to climatic characteristics allows it to be used in the preparation of alcoholic fermentations in the form of a drink such as sake (known in Japan as nihonshu (日本酒, nihonshu? "Japanese alcohol")), as well as rice wine. The main microorganisms used in the production of these rice-based alcoholic beverages are Aspergillus oryzae, Lactobacillus sakei, Leuconostoc mesenteroides var. sake and Saccharomyces sake. Fermentation takes a period ranging from 30 to 40 days. Sake has three production phases: koji, motto and moromi, which is carried out in what is known as solid-state fermentation.
In sake, apart from a concentration of between 15 and 20% ethanol product of fermentation, the main components responsible for its characteristic flavor are: succinic acid (500 to 700 mg/L), malic acid (200 to 400 mg/L), citric acid (100 to 500 mg/L), acetic acid (50 to 200 mg/L), isoamyl alcohol (70 to 250 mg/L), n-propanol (120 mg/L), 2 -phenyl ethanol (75 mg/L), isobutanol (65 mg/L), ethyl acetate (50 to 120 mg/L), ethyl caproate (10 mg/L) and isoamyl acetate (10 mg/L). These metabolites can also be found in beers and most wines since they come from alcoholic fermentation. Ethylleucinate must also be added to these components, which is the one that contributes the most to the aroma of sake. However, the concentration of all these compounds in sake is significantly higher. We must not forget the presence of lactic acid (0.3 to 0.5 mg/L) which is almost entirely the result of the activity of the lactic acid fermenting bacteria present during the moto stage (initial stage in the fermentation vat). A variety of amino acids are also detected, albeit at lower concentrations. The presence of these tends to be the minimum possible, since they give the Saké an unpleasant taste.
A large number of genetic improvements have been carried out on Saccharomyces sake strains in order to increase the presence of some of these metabolites (such as phenyl ethanol, isoamyl alcohol or ethyl caproate), as well as reduce that of others (amino acids, ethylcarbamate, urea). There have also been cases of strains designed to improve productivity, either by reducing foam formation, increasing tolerance to ethanol or the non-proliferation of toxin-producing strains. Fermented rice products are not exclusive to Japan, they can be found in various cultures around the world such as: binburan (Philippines), pachwai (in India it is called 'rice beer'), arrack (the so-called عرق, ‛araq is very popular in the Middle East, frequently distilled), rakshi (drink made with rice and millet in Nepal), etc. some of these spirits being distilled.
Alcoholic fermentation of milk
Milk generally undergoes lactic fermentation (most dairy products) which produces some alcoholic beverages. The process is fueled by lactose (natural milk sugar) and by the enzyme lactase secreted by some specific yeasts (see lactic cultures). Lactic and ethylic fermentation is very sensitive to temperature and is often called heterolactic fermentation. Among the dairy drinks that have undergone ethylic fermentation is a drink called koumiss (very popular in Central Asian countries such as Kazakhstan) which is made by the addition of sucrose (cane sugar) to pasteurized milk and usually provides low-alcohol beverages, ranging from 1% to 3%, the microorganism responsible for this process is Lactobacillus bulgaricus. It is sometimes referred to as: "milk wine" and has a greyish appearance. In these milk drinks, lactic fermentation occurs at the same time as alcoholic, both cooperating in a complex interrelated process. Another of the drinks is kefir, very popular in the countries of the Caucasus and Central Asia, which contains a certain amount of ethanol, which can range between 0.040% and 0.300%, its low content is due to the relatively high pH levels that stop the alcoholic fermentation process.
Other alcoholic fermentations
Some fermented foods have certain amounts of ethanol due to small ethylic fermentation reactions that are carried out during the fermentation of the food, the different cultures of the world use this fermentation in one way or another as a cultural identification, perhaps because it is usually use some fruit or vegetable typical of the region. One of the examples is the nattō of Japanese cuisine. One of the most popular drinks in the towns of Northern Europe is the mead made with fermented water and honey whose tradition dates back to the time of the Vikings, in the same way Ethiopian tej is made.
Fermentations carried out with cane sugar in sweetened wines such as Filipino basi, Japanese shoto sake. Palm wines made from palm leaves, some such as ogogoro from Nigeria, tuba from the Philippines, kalu from India. The pulque of Mexico made with the alcoholic fermentation of the tequilana agave juice (in which the bacterium Zymomonas mobilis participates), some similar drinks are the colonche (or nochoctli) made from the fermentation of cactus. In Mexico, tesgüino made with the fermentation of corn, tibicos, and tuba are also known. A drink made from panela is a variant of guarapo, which is an alcoholic beverage produced by the alcoholic fermentation of panela water, very popular in Colombia. Kenyan urwaga, which is a fizzy drink made from bananas typical of Rwanda, is similar to Uganda's mwenge, made similarly from sorghum and bananas. The corn fermentations that make Chicha, sometimes called tepache, in Colombia. In the same way it happens with the fermentation of the apple in the cider (very popular in countries like Spain, France, Great Britain) and in the apfelwein (German), a very popular drink in Germany and the countries of northern and central Europe, as well as in some areas of the Cantabrian Sea.
Homemade alcoholic fermentation
One of the lucrative activities of some people is home ethylic fermentation, it is a low-efficiency chemical process and from which ethanol is obtained in relatively high quantities. The basic equipment for home fermentation can consist of in the following parts:
- Fermentador or Cuba mother - It is usually a large container of 30 L (it is preferable to have a graduated scale on its walls). This container (usually polyethylene) can be filled with water with sucrose or any fruit juice (can even put ripe fruit inside it). The container should be wide in its upper mouth so that carbon dioxide can be released and facilitate its subsequent cleaning. It is sometimes called to this container simply as a fermenter, and it is the space in which fermentation is done. It should be of such size that it allows to be removed from time to time.recipient, or fermenter, must have a sufficient mouth caliber so that a fermentation cap can be hopped with a hole over which you can enter a airlock. This plug must guarantee the process's waterproofing, allowing only access through airlock.
- Rubber cover for plug - It should be noted that the plug must be covered with a rubber case to ensure the fermenter's waterproofing during the process. This accessory is not really necessary and its function is to guarantee the watering that the plug must provide.
- Airlock' - The mission of this device is to allow the output of the carbon dioxide generated while at the same time avoiding the air in the fermenter and thus avoiding the contamination of the process (which would oxidize the ethyl alcohol in acetic acid). The blocking of this apparatus is done through the use of water introduced in communicated amplets, these ampoulets allow the exit of CO2 but not the air entrance (O2). This device can be found in glass or plastic.
It is usually marketed to be able to make the initial mixture of different products with dehydrated yeasts inside, the choice of the product will depend fundamentally on the type of sugar used. Dehydrated yeasts must undergo a hydration period of a few hours before being added to the substrate. It should be considered that fermentation should begin approximately 10 hours after composing the system and usually lasts between two and four days. Sometimes they also include various essences that are added in the final preparation of these homemade drinks in order to flavor or provide different flavors. A thermometer and hydrometer should be included in the development kit.
This process is normally associated with the home distillation process to increase the purity of the resulting alcohol, thus allowing the production of spirits and other beverages with a high alcoholic content.
Uses of fermentation
The main use of fermentation processes by humans has been directed, since ancient times, to the production of ethanol for the production of various alcoholic beverages. This situation changed in the XX century, since since the oil crisis of the '70s studies and research on of possible alternative fuels has been of great interest to governments around the world. Within biotechnology studies, an attempt has been made to use the ethanol resulting from the alcoholic fermentation of agricultural waste (biomass)) to obtain biofuels (bioethanol) used in vehicle engines. An attempt has been made to focus the studies on the continuous fermentation reactors with the hope of being able to obtain not only large amounts of ethanol, but also increasing their efficiency. Research on the most suitable substrates, as well as the use of high-performance yeasts is the subject of constant study. Ethanol was one of the fuel energy sources that generated the most global demand at the beginning of the XXI century (with the exception of petroleum), in 2004 the United States produced more than 12.5 × 109 liters of ethanol, which represents a 17% increase over 2003. Despite the generation of CO2 during the process raises alarm about its use, due to the consequences that it can bring for climate change.
The uses of ethanol in industry are extensive and range from the production of cosmetic products, cleaning products, etc. The possibility of using ethylic fermentation in the treatment of garbage dumps has been investigated, thus achieving biofuel, the studies have not yielded conclusive applications. However, the use of alcoholic fermentation has potential success in the treatment of waste from the food industry. An industrial process much researched at the beginning of the century XXI is solid state fermentation used in biomedication and biodegradation of waste products, the biological transformation of agro-industrial residues, in the production of bioactive compounds, enzymes, organic acids, biopesticides, biofuels and aromatic compounds, among others.
Effects of ethylic fermentation
The effects of ethylic fermentation are derived from the products resulting from the process that are released in one way or another into the environment: ethanol and carbon dioxide. The effects of fermentation will depend on how each of these by-products is treated. One of the most surprising effects is found in the existing alcohol contamination in some insects that feed on fruit and flower nectar, a clear example being bees (see bees and toxic elements). In the same way, it can intoxicate the birds that feed on some ripe berries already partially fermented. Small-scale alcoholic fermentation occurs in the same way in the roots of some plants that are irrigated very frequently, the lack of aeration of the soil causes the anaerobic conditions that the yeasts need to act, being able to poison the soil through an increase in the concentration of ethanol which translates into a decrease in their production capacity.
Another important aspect is the effect produced in the human body by the repeated consumption in humans of alcoholic beverages from ethylic fermentation (see effects of alcohol on the body) since ethanol is a powerful psychoactive drug with a of side effects in addition to the addiction generated by its habitual consumption. The places where the fermentation of some alcoholic beverages takes place (usually basements) are usually dangerous since carbon dioxide 'displaces' the alcohol. oxygen and can cause suffocation to people who are in these places.