To get a delicious and relaxing drink, you need the main ingredient - Brewer's yeast. It is they who carry out the process of converting the sugars of the wort into alcohol and carbon dioxide. Let's talk about classification brewer's yeast In this article.
Yeast is a single-celled fungus that reproduces by budding daughter cells. Yeast is used in baking bread, in winemaking and brewing, with their help they produce strong alcoholic drinks and dairy products. Brewer's yeast are the main component of the beer recipe that converts the sugars of the wort into alcohols.
Brewer's yeast- This is a natural protein-vitamin remedy that is used to treat and prevent various diseases. Dry brewer's yeast contains 50% protein, 25-40% carbohydrates and up to 3% fat.
Protein brewer's yeast characterized by a balance of amino acids close to animal protein, except for the content of the amino acid methionine, which is 2-3 times less than in the protein of meat and other animal products. It is easily absorbed by the human body.
brewer's yeast saturated with vitamins of group B (B1, B2, PP, pantothenic acid, B6), vitamins of group D.
Brewers distinguish between top yeast (formerly classified as S. cerevisiae) and bottom yeast (formerly classified as S. carlsbergensis and S. uvarum).
top fermenting yeast, used for the production of ale, ferment at relatively high temperatures (18-25 ° C) and at the end of fermentation are collected on the surface of the fermented wort.
bottom fermenting yeast used for brewing lager beer using the bottom fermentation method. Their fermentation temperature is much lower (8-12 °C). At the end of the fermentation process, the yeast settles to the bottom of the fermentation tank. Grassroots yeasts biochemically differ from top yeasts in the utilization of melibiose and raffinose. Relatively recently, other phenotypic differences between the two have been described, in particular the pattern of mixed carbohydrate fermentation, carbohydrate transport, and cation sensitivity. Comparison of the genomes of some grassroots and top yeast strains showed that horse yeast strains fermentation there is a strong variability bottom fermenting yeast strains originate, as a rule, from a single strain, most likely obtained by hybridization of top-fermenting S. cerevisiae and bottom-fermenting S. monacensis. Some special types of beer are made from yeast culture mixtures, which may include yeasts of other genera, in particular Brettanomyces (for example, in Gueuze beer) or even lactic acid bacteria (in Gueuze beer, Berliner Weisse, in Belgian sour ales).
Races of brewer's yeast.
have long been known top fermenting yeast, because fermentation was carried out at normal temperature (as in winemaking, baking). Wanting to get drinks saturated with carbon dioxide, they began to carry out fermentation at low temperatures. Under the influence of changed external conditions and were obtained bottom fermenting yeast with other properties.
In brewing, yeast varieties are used that differ from each other in one or more characteristics. They are obtained from one cell. Such cultures are called races (strains).
top fermenting yeast in the process of intensive fermentation, they float to the surface of the fermented liquid, accumulate in the form of a layer of foam and remain in this form until the end of fermentation. Then they sink to the bottom, forming a very loose layer at the bottom of the fermenter. In terms of their structure, these yeasts belong to dusty yeasts, which do not stick together, in contrast to flaky bottom yeasts, which stick together quite quickly and, accordingly, quickly settle to the bottom.
bottom fermenting yeast do not pass into the surface layer of beer - foam, but quickly settle at the bottom.
The ability of yeast to flocculate is of some importance for beer wort fermentation technology, as it accelerates the clarification of beer and facilitates the removal of yeast from the fermenter after fermentation, with subsequent use as seed yeast. Low temperature during fermentation promotes flocculation.
The acidity of the environment greatly affects the properties of yeast. For example, in an acidic environment at a pH of less than 3 and in an alkaline environment at a pH of more than 8, flaky yeast becomes dusty. Flaky yeast compared to pulverized ones, they have larger cells, are less susceptible to autolysis, give a large increase in biomass, have less fermentation activity, form less diacetyl and higher alcohols in beer, which positively affects its quality.
bottom fermenting yeast differ from top-fermenting yeasts in that they completely ferment raffinose. bottom fermenting yeast have an optimal temperature for growth of 25-27C, a minimum of 2-3C, and at 60-65C they die off. The maximum development of grassroots yeast occurs at pH 4.8-5.3. Oxygen dissolved in the wort promotes yeast reproduction, while fermentation products (ethyl alcohol, carbon dioxide, higher alcohols, acetaldehyde, acids), as well as an increased sugar concentration, inhibit the development of grassroots yeast.
Quality brewer's yeast must meet the following requirements:
- quickly ferment the wort,
- form flakes well,
- to clarify the beer during fermentation,
- give beer a clean taste and pleasant aroma.
TO highly fermentative and easy flakers include Froberg bottom-fermenting brewer's yeast (Saccharomyces cerevisiae Froberg), yeast races V and 776.
In breweries, yeast of the 776 race, which was bred at the beginning of the 20th century, was widely used. This yeast is considered particularly suitable for the fermentation of wort brewed with the addition of unmalted materials or from malted barley with a low degree of germination.
Top-fermented brewer's yeast are widely used in Britain in the preparation of Porter. They are used to make Berlin Lager beers and other beverages. For the preparation of Velvet beer, strain 191 K is used, which intensively ferments monosaccharides and maltose, but does not ferment sucrose, raffinose and lactose.
So, yeast for making beer are selected taking into account many factors, but the most important thing is that you need to use only high-quality material from trusted suppliers, and only then you are guaranteed excellent beer!
Doge races. At the moment, the brewing industry uses such races as: 11,776,41, S and P (Lviv race), as well as strains 8a (M) and F-2.
Strain 8a (M) was bred by selection from brewer's yeast of race S (Lviv) and is intended for use in bottom fermentation. These yeasts have the following parameters: adult cells of a one-day culture grown on liquid hopped wort with a mass fraction of solids of 11% have a size of 6.5-7.1 microns; fermentation activity 2.04 g CO2 per 100 ml. wort for 7 days at 7°C; flocculation ability is good; the taste and aroma are pleasant.
Under laboratory conditions, the strain is stored on slant wort - agar at a temperature of 6-7°C. Reseeding is done once every 2-3 months, first on hopped wort, and then on wort - agar. The duration of using yeast is no more than 5-8 generations. Their use intensifies the fermentation process and improves the quality of beer.
The F-2 strain was obtained by hybridization of race 44 brewer's yeast and differs from existing brewer's yeast strains in the ability to ferment wort carbohydrates, consisting of four monosaccharide residues. This bottom fermenting yeast has a cell size of 10*4.5-6.5 µm and a fermentation activity of 2.40 g CO2 per 100 ml. wort for 7 days at a temperature of 7°C. When using this strain, a deeply attenuated beer with increased persistence is obtained.
There are also new races of yeast.
Brewing yeast "Saccharomyces cerevisiae" both top and bottom is widely used for fermentation of malt wort and beer.
Under production conditions, yeast strains "Saccharomyces cerevisiae" are cultivated at a temperature of 25-30 ° C and an optimal pH value of 4.6-5.5, according to their physico-biochemical characteristics, they ferment glucose, sucrose, maltose, raffinose, and weakly galactose, and during cultivation they assimilate the following carbon sources: glucose, galactose, sucrose, maltose, raffinose, melicitose, ethanol, lactic acid and weakly trehalose and a-methyl-d-glucoside. Nitrates does not assimilate. The method, conditions and composition of the medium for storage and propagation is standard, i.e. diluted beer wort, temperature 25-30oC and pH 4.5-5.5.
Storage on solid wort-agar, propagation on liquid diluted wort, transfers during storage 1-2 times a year, provided that the culture is stored in a refrigerator.
Various strains of yeast "Saccharomyces cerevisiae" are known, in which individual variability within the species is observed, which leads to the production of beer with different flavors.
For example, the yeast "Saccharomyces cerevisiae" of the Pilsenskaya race, the Froberg-type race 776, is known, capable of fermenting hopped beer wort to produce light beer varieties.
Yeast of race 776 is considered particularly suitable for fermenting wort prepared with the addition of unmalted materials or from malt obtained by germinating barley with a low degree of germination.
The yeast culture of race 776 has a final degree of must fermentation of 75-77%, the main fermentation time is 6-8 days.
Known is the use of grassroots yeast "Saccharomyces cerevisiae" race 308 to obtain light beer varieties of good taste. The process of main fermentation is 7-10 days. During fermentation, the yeast gathers in flakes and settles to the bottom of the fermentation tank, forming a dense sediment. The final degree of fermentation of the wort is 82-83%.
The strain "Saccharomyces cerevisiae" D-202 was deposited at the All-Russian Research Institute of Agricultural Microbiology of the Russian Academy of Agricultural Sciences under number 11, is stored in the collection of cultures of microorganisms.
The strain is characterized by the following cultural and morphological features. A one-day culture of yeast in liquid wort is a single round-oval and elongated cells with buds in size (5.0-7.0), (7.5-10.0) microns. A thick precipitate forms at the bottom of the tube. On wort-agar, it forms smooth, convex, cone-shaped colonies of a whitish-cream color, pasty consistency with a smooth edge. On an acetate medium, on the fourth day, it forms bags with spores.
There is no growth on a vitamin-free medium. Strain D-202 is an auxotroph for biotin.
The strain is preserved by reseeding on slightly sloping malt wort - agar with 7% solids (pH 5.0-5.5), poured in a high layer (10 ml each) into test tubes. Transfers to fresh media are carried out once every 2-3 months. Test tubes with crops are placed for two days in a thermostat at 25-30oC. After that, the test tubes are closed with parchment caps and put in a refrigerator at 5oC with reseeding 1-2 times a year.
The cells of the strain ferment malt hopped wort with a mass fraction of solids from 10 to 20% at pH 4.4 at 14-18°C. Yeast multiplication factor 1:5.
The final degree of fermentation of the wort is 88.5%. The main fermentation time is 3-8 days (depending on the density of the must).
Settling ability is good. The quality of the resulting beer meets the requirements of technical specifications.
The industry produces food and technical ethyl alcohol. Food is obtained by fermentation during the processing of grain, potatoes, sugar beets, molasses; technical - fermentation of wood hydrolysates (hydrolytic alcohol), sulfite liquors or by synthesis from gases containing ethylene.
Alcohol factories produce: raw ethyl alcohol with an alcohol content of at least 88%; the content of impurities is 0.4 - 0.5%; ethyl alcohol rectified of various degrees of purification.
Microorganisms used in production. In the production of alcohol by a biochemical method, the following microorganisms are used:
Yeast. Alcohol production uses baker's yeast Saccharomyces cerevisia ( top-fermenting) or hybrid races of brewer's yeast Saccharomyces carlsbergensis and races of baker's yeast.
Yeast ferment glucose, sucrose, maltose, galactose, raffinose, accumulate alcohol up to 13% vol. The optimum temperature is 30 - 33 ° C. They tolerate the increased acidity of the medium when acidified with sulfuric acid during the purification of yeast in production.
Evaluation of the production properties of pure yeast cultures. The following requirements are imposed on the races of alcohol yeast:
high fermentation activity;
the ability to quickly and completely ferment the sugars of the environment, i.e. the ability to produce low offal;
resistance to high concentrations of alcohol;
resistance to acidification of the environment and to metabolic products of foreign microorganisms.
Mature production yeast entering the fermenters must have the following characteristics:
The number of budding cells is 10–15%;
The number of dead cells is not more than 2 - 4% (an increase in the number of dead cells indicates the presence in the environment of factors that inhibit the vital activity of yeast);
The number of cells containing glycogen must be at least 70%, a decrease in the number of such cells indicates that the yeast is poorly nourished and weakened;
The number of yeast cells in 1 ml of the medium should be at least 120-140 million;
microscopy should not reveal mobile forms of bacteria, and immobile - no more than 4 - 6;
· Races of yeast used for fermentation of molasses solutions must ferment sucrose, glucose, raffinose by 1/3 or completely.
The main factors affecting the vital activity of yeast in alcohol production are temperature, pH of the medium, wort concentration, content of organic and inorganic acids.
Temperature. The optimal growth rate of alcoholic yeast is 30–32 °C, however, yeast grown at a temperature below the optimum has a higher fermentation activity, so the fermentation process starts at a temperature of 18–22 °C, and during fermentation it is maintained at a level of 29–30 °C . A higher temperature causes a decrease in fermentation activity and promotes the development of lactic acid bacteria and wild yeasts.
pH of the environment. Hydrogen ions change the electrical charge of the colloids of the plasma membrane of the cell and, depending on the concentration, can increase or decrease the permeability of the cell membrane for individual substances and ions. The rate of nutrient entry into the cell, the activity of enzymes, and the formation of vitamins depend on the pH value.
When the pH of the medium changes, the nature of fermentation changes: if the pH shifts to the alkaline zone, then the content of glycerol and side substances in the mash increases. The optimal pH for yeast development is 4.8 - 5.0, but in alcohol production they try to maintain it at a level of 3.8 - 4.0 in order to suppress the development of lactic acid bacteria. The required pH is created by adding sulfuric, hydrochloric or lactic acid.
Sugar content in wort. Very high concentrations of sugar increase the osmotic pressure in the yeast cells, while low concentrations are economically unprofitable, therefore, the wort is fermented with a dry matter content, which corresponds to a content of 13-15% sugar in it. Depending on the initial concentration of sugar and production losses, the alcohol content in a mature brew is 8 - 9.5 vol. %.
Lactic acid bacteria. Sometimes lactic acid bacteria of the species are used to acidify the must in the production of alcohol from potatoes and grains. Lactobacillus delbrueckii. The cultivation of lactic acid sticks is carried out at a temperature of 50°C. In the wort, acidified with lactic acid bacteria, the content of soluble nitrogenous substances increases, which favorably affects the reproduction of yeast.
Mold mushrooms. To obtain sugar preparations that are cheaper and more active than malt, specially selected active strains are used. Aspergilus batatae, Asp. Nigeria, Asp. orizae and others. Such fungi are good producers of amylolytic enzymes.
The production of ethyl alcohol by biochemical means is based on the vital activity of yeast fungi Saccharomyces cerevisiae, converting the sugars of the nutrient medium into alcohol, carbon dioxide and a small amount of by-products, some of the sugars are used for synthesis processes during the growth of yeast cells.
The alcohol accumulated in the medium is isolated by distillation; carbon dioxide is captured by special apparatus and converted into liquid and solid carbon dioxide. By-products of fermentation, as well as yeast, are separated and used in technology and bakery.
Raw material preparation . The most commonly used raw materials are:
Depending on the processed raw materials, the technological process has its own characteristics.
Starch-containing raw materials. Starch is a complex polysaccharide. Yeasts do not ferment it due to their lack of amylase. Therefore, starch-containing raw materials must first be subjected to saccharification. However, the starch contained in the cells of a grain or potato is not accessible to amylase. To destroy or weaken the cell walls, the raw material is subjected to high temperature and pressure, resulting in boiling, gelatinization and liquefaction of starch. The next step is saccharification. This is the process of converting gluten starch raw materials into sugars under the influence of saccharifying enzymes. Sources of saccharifying enzymes are malt or mold fungi.
Seed preparation. Yeast is propagated in the yeast department of the plant in compliance with all necessary conditions to obtain pure and physiologically active industrial yeast. Pure culture of yeast is accumulated gradually, in several stages. For yeast propagation, optimal nutrition and temperature conditions are created.
Upon receipt of the inoculum of yeast, a laboratory pure culture is first obtained using sterile malt wort as a nutrient medium with a solids content of 8–10%.
The production stages of breeding a pure culture are carried out on a nutrient medium containing the raw materials that are processed at this plant: grain, potato or molasses. At the end of the production stage, the yeast is transferred to the yeast apparatus or yeast generator. In 1 ml of the medium, the yeast generator should contain at least 150-200 million yeast cells of a pure culture, since with such a quantity, the yeast is more resistant to infection by foreign microorganisms.
Basic fermentation. Yeast from the yeast generator enters the fermentation section of the plant, where the main fermentation process takes place.
There are several methods of fermentation of raw materials: batch, semi-continuous and continuous.
Flow culture methods are more productive. With the continuous method of fermentation, more favorable conditions are created for the vital activity of yeast - constant renewal of the environment, removal of harmful metabolic products and the possibility of maintaining all favorable parameters at the same level. In addition, the advantage of a continuous process is the possibility of its mechanization and automation.
Fermentation takes place in a battery of fermenters, connected in series by communications, through which the brew flows from one apparatus to another. The main fermentation takes place in the first apparatuses, in the subsequent ones, after-fermentation takes place.
Distillation of alcohol and its rectification. The fermented mature mash enters the mash tank, from where it is pumped to the mash distillation apparatus. In these devices, ethyl alcohol and all volatile impurities are separated from the mash. The resulting product is called raw alcohol, and the remainder is called stillage. Raw alcohol is used for technical purposes or subjected to purification from impurities - rectification. Fusel oils, aldehydes and esters contained in raw alcohol are selected during rectification and rectified alcohol of various degrees of purification is obtained.
Extraneous microorganisms of alcohol production.
Microorganisms dangerous for alcohol production, which reduce the yield of alcohol due to the inhibition of the vital activity of yeast by the products of their metabolism, include:
spore-forming bacteria both aerobic and anaerobic, most often it is butyric. When the grain is boiled, the spores do not die, and in the future they can multiply in the saccharified mass and cause its souring. In addition, these bacteria reduce the nitrates contained in molasses to nitrites, which inhibit the vital activity of yeast cells;
yeast Saccharomyces exiguus, Saccharomyces intermedius, yeast-like fungi genera Torulopsis And Candida
heterofermentative lactic acid bacteria. The metabolic products of these microorganisms - acetic and formic acids, esters and aldehydes - have a depressing effect on the fermentation ability of yeast, as a result of which the alcohol yield is sharply reduced.
Beer production
Beer is a low-alcohol drink made mainly from barley malt and hops by fermenting the wort with brewer's yeast.
Characteristics of races of yeast used in brewing. Yeasts used in brewing are of the species Saccharomyces cerevisiae And Saccharomyces carlsbergensis.
Yeast Saccharomyces cerevisiae related to yeast top fermentation and are rarely used, mainly for dark and specialty beers.
Yeast Saccharomyces carlsbergensis carry out bottom fermentation beer wort - settling to the bottom of the fermentation tanks. This yeast ferments well at 5-10°C and is widely used to make standard and varietal beers.
To produce high-quality beer, yeast must have the following properties:
· high fermentation activity. Fermentation activity is determined by the degree of fermentation of the wort (an indicator characterizing the ratio of the mass of the fermented extract to the mass of dry matter in the initial wort).
· flocculation ability- slowly and completely settle to the bottom of the fermenters at the end of the main fermentation. Differences in flocculation properties underlie the division of yeast into flaky And pulverized. Flaky yeast at the end of the main fermentation stick together into lumps - floccules and during the bottom fermentation they settle, forming a dense sediment, and during the top fermentation they rise to the surface. Pulverized yeast remains suspended throughout the entire process.
· moderate ability to reproduce. Very active reproduction of yeast is undesirable, because. at the same time, the extractive substances of the wort are consumed and a large amount of by-products is formed (on average, during the fermentation process, the yeast biomass increases by 3–4 times);
· stability of morphological and physiological properties; The morphological state of yeast reflects their physiological status. The presence of a large number of morphologically altered cells , especially in combination with reduced fermentation properties, is a sign of degeneration of the culture. A large number of cells with granular protoplasm, large vacuoles, and the absence of budding cells characterize the old culture. A high content of dead cells (more than 10%) indicates possible violations of the technological process: slow main fermentation, the development of certain types of foreign microorganisms. Fatness of yeast is determined by the content of glycogen in the cells, and its presence gives an idea of the ability of yeast to ferment. In normally nourished yeast, 70-75% of the cells contain glycogen. A lower number of cells with glycogen in industrial yeast indicates the old age of the yeast cells or their insufficient nutrition.
The main stages of the technological process.
Cultivation of pure cultures of yeast in the brewing industry.
The task of breeding a pure culture is to increase the yeast biomass from the volume of the test tube to the volume introduced into the fermenter.
Breeding a pure culture of yeast is carried out on sterile hopped wort with a solids concentration of 11 - 13%, gradually adapting the yeast to the wort and low temperature. The breeding process consists of two stages: laboratory and workshop.
Preparation of beer wort. Malt and other grain products required by the recipe are crushed to ensure and accelerate the physical and biochemical processes during mashing. Crushed malt is poured into the mash apparatus, into which heated water is first poured. Congestion heated at the required rate with maintaining pauses at certain temperatures. The completeness of saccharification is determined by the iodine test. Then the mash is pumped for filtration into the filtration apparatus. filtered wort and wash water is pumped into the wort brewer and subjected to boiling with hops.
The transformation of barley substances during malting and malt substances during mashing and boiling of the wort occurs under the action of malt enzymes without the participation of microorganisms. Under the action of malt enzymes during mashing and boiling in the wort, the content of fermentable sugars increases, the wort proteins are split first into peptides, and then into amino acids. The biochemical composition of the wort has a significant impact on the vital activity of yeast and the quality of the finished product:
carbohydrate composition determined by the presence of fermentable and non-fermentable sugars in the wort. The content of fermentable sugars in the wort is 70-80% dry matter. These are maltose (60 - 70%), maltotriose (15 - 20%), glucose (10 - 15%). Monosaccharides ferment the fastest, maltose slower, and maltotriose the worst.
nitrogen composition. Nitrogenous substances are necessary for cells to synthesize components that ensure their growth and reproduction. The most valuable and important sources of nitrogen are amino acids, purine and pyrimidine bases. The formation of aromatic substances depends on the biosynthesis and breakdown of amino acids. The amino acids formed during the biosynthesis of yeast give the beer a velvety texture. Under unfavorable cultivation conditions, they can cause yeasty flavors and haze in the beer.
Fermentation of beer wort with yeast. The clarified and cooled wort is fed into the fermentation tank.
The transformation of wort substances during fermentation is a biochemical process caused by microorganisms - brewer's yeast.
Microbiological processes in fermenting beer wort. For fermentation, seed yeast is given at the rate of 0.5 liters per 100 liters of must. The process of reproduction of yeast cells occurs in five stages. In the process of fermentation, the amount of yeast increases by 3-4 times.
The reproduction of yeast begins earlier than the process of alcoholic fermentation caused by them. However, reproduction occurs quickly and ends mainly in 3-4 days, while fermentation occurs during almost the entire stage of the main fermentation (7-10 days) and continues during the after-fermentation period.
The increase in yeast weight during fermentation depends on the amount of yeast given, the amount of extract in the must, the content of dissolved oxygen and temperature. With a small amount of seed yeast, the fermentation process is slower, but the growth will be large. Conversely, a large amount of given yeast provides a higher fermentation rate and a lower biomass gain. For production, the second way is the most beneficial, since it reduces the loss of the extract for the formation of yeast. In addition, reducing the growth of yeast during fermentation can be achieved by removing dissolved oxygen from the wort, since the presence of it accelerates the reproduction of yeast. Under aerobic conditions, the extract is consumed, but alcohol is not formed, and oxidized products accumulate in the medium, complicating and lengthening the last period of beer maturation.
The rate of yeast reproduction depends on temperature: At low temperatures, yeast reproduction slows down, but they grow larger with a large supply of reserve substances and high fermentation activity. With an increase in temperature, the need for nutrients in yeast increases, the size of the cells decreases, they do not contain reserve substances and grow weaker.
Many substances inhibit the reproduction of yeast. So, when the content of ethyl alcohol in the medium is more than 1.5%, their reproduction slows down, and at a concentration of more than 3%, the fermentation of wort sugars by yeast slows down.
Mineral and organic acids are also inhibitors: 0.5% sulfuric acid in the medium kills yeast in 1-2 hours; acetic acid also acts when it is contained in the medium in an amount of 1%. However, the content of 1% lactic acid in the medium is tolerated relatively easily by yeast.
Yeast, consuming the nutrients of the wort, increase their biomass. By the end of the main fermentation, due to a 3-4-fold increase in the biomass, the cellular specific surface of the yeast increases, which leads to their sticking (flocculation). When cells stick together, flakes (flocculi) are formed, which is why the ability of yeast to clarify beer is called flocculation or flocculation. In bottom fermentation, the flocculation of the yeast can be controlled to get the right attenuation and leave enough dispersed yeast to finish the beer.
Thus, the end of fermentation is determined by the flocculation of the yeast. The main fermentation is carried out for 5-10 days.
At the end of the main fermentation, a dense sediment consisting of three layers forms at the bottom of the vat. The bottom layer of yeast is formed by old weakly fermenting yeast cells that settle faster than others. The middle layer of yeast consists of the most actively fermenting yeast and large protein flakes, the top layer is formed by small yeast cells with reduced flocculation ability, as well as protein residue and hop resins. To obtain seed yeast, only the middle layer is used.
After the main fermentation, the yeast is separated, washed with cold water and used for industrial purposes, considering them to be the first generation. Production yeast, provided that it has good fermentation properties and is free of microorganisms harmful to beer, can be used up to 10 generations.
Biochemical processes in fermenting beer wort. The wort is fermented to obtain a certain amount of alcohol, corresponding to the type of beer. Most of the sugars in the wort are fermented to form alcohol and carbon dioxide. This is an exothermic process, which is accompanied by the release of heat.
As a result of fermentation, alcoholic fermentation products accumulate in the wort (in % mass): carbon dioxide 0.3 - 0.5 and ethanol 3 - 6, depending on the type of beer. A large role in fermentation belongs to nitrogenous compounds.
The nitrogen composition of the wort during fermentation changes significantly, since about 40% of amine and 60-80% of ammonium nitrogen are used to build the proteins of the multiplying yeast. After the cessation of yeast reproduction, the amount of amine nitrogen in beer may slightly increase due to the release of about 15% of assimilated nitrogen from them, as well as the formation of new amino acids from wort proteins under the action of yeast proteolytic enzymes; the total amount of protein nitrogen in the beer decreases.
During the fermentation process, by-products are formed in beer. Thus, aldehydes accumulate in beer at the beginning of fermentation, then under the influence of anaerobic conditions they are restored and their number decreases. Higher alcohols and esters are formed, which determine the aroma and taste of the finished product, and organic acids, the concentration of volatile substances in beer is very small - about 0.5%, but they participate in the formation of the bouquet - the taste and aroma of the finished product.
By-products of fermentation are four-carbon compounds such as diacetyl, acetoin and 2,3-butylene glycol. Four-carbon compounds, especially diacetyl, have a specific odor (domestic beers contain diacetyl 0.4–1.0 mg/l). By increasing the amount of diacetyl in the beer, a honey flavor appears, which was previously attributed only to a bacterial infection (the "sarcinic disease" of beer).
As a result of biochemical processes occurring in the wort during fermentation, the titratable acidity increases. The concentration of hydrogen ions (pH) in the medium also changes. Changes in pH and titratable acidity lead to a decrease in the solubility of proteins and hop substances. At the same time, part of the proteins precipitates, forming flakes, and hop substances and lighter particles of proteins rise to the surface, forming a “tire”, or deck. A change in the content of nitrogenous substances, phosphates and organic acids in beer leads to a change in the buffering capacity of the medium.
Fermentation and maturation of beer. Young beer is pumped to the after-fermentation apparatus located in a specially cooled room with a temperature of 2 - 3 o C, where it matures at a given temperature and pressure. The duration of fermentation is from 6 to 100 days, depending on the type of beer. The fermentation process is carried out by dusty yeast.
The product obtained at the end of the process is ready for consumption and bottling.
Microorganisms that infect wort and beer. Microorganisms introduced into the wort and beer cause various "diseases", expressed in the appearance of a smell and taste that are not characteristic of beer, and a decrease in its quality.
Various microorganisms are found in wort and beer. Some of them come from the air, with malt dust or with grain (epiphytic microflora). Microbes can also be introduced with water, where they enter from the soil with feces. At the same time, pathogenic microorganisms that cause human disease can also enter the wort and beer.
Microorganisms that develop in wort and beer belong to different groups - bacteria, molds and yeasts. They can be harmless, "comorbid" or pests of production.
bacteria. In terms of the number of representatives, as well as the damage they cause and damage to products, the first place belongs to bacteria. Once in production, they gradually adapt to the conditions of the technological process, change and adapt in such a way that the fight against them presents certain difficulties. The harm caused by them is expressed not only in the deterioration of the quality (persistence) of beer, but also in the deterioration of its taste up to complete unsuitability.
Lactobacillus. Lactic acid bacteria are potential pests that cause haze and almost always sour beer. The group includes microorganisms that, during the fermentation of carbohydrates, mainly form lactic acid (homofermentative bacteria). Lactobacillus resistant to high acidity and antiseptic action of hops.
lactococcus. In hopped wort and beer, they form haze, sediment, lactic acid or diacetyl, and sometimes mucus. Cause "sarcine" beer disease distorting its taste and smell. Beer acquires an unpleasant taste and a characteristic honey smell, which is caused by diacetyl formed by pediococci.
Acetobacterium- acid-resistant and develop in a wide range of pH - from 4.5 to 3.2. Since acetic acid bacteria use alcohol and sugars as carbon sources, they find ideal conditions for development in the brewery. May form in beer slime even with a limited amount of air, such as in bottled beer. When they grow in beer, a polysaccharide gelatinous substance dextran is formed. Intensive formation of mucus in beer depends on the content of dextrins in it. At the same time, sugar does not have any effect on the process of mucus formation.
Flavobacterium use glucose and fructose wort. Appears in infected beer silky haze, slight smell of hydrogen sulfide and apples.
Escherichia coli. E. coli is an indicator of the sanitary condition of the enterprise.
Zymomonas. Bacteria are resistant to hop substances and low temperatures. They form ethanol, acetaldehyde and CO 2 . When developing in beer, bacteria give it an unpleasant foreign smell and taste and cause turbidity.
Yeast. In the brewing industry, there are yeasts that can spoil the taste and impair the quality of the beer. With the development of wild yeast in the wort and beer, an extraneous smell, strong turbidity, unpleasant bitterness and taste, and sediment may appear. Wild yeast settles less well than cultured brewer's yeast, making beer clarification and yeast coagulation more difficult. Extraneous smell and taste to beer are imparted by higher alcohols, esters of volatile acids and bitter substances, which are formed by wild yeast.
Saccharomyces pastorianus ferment carbohydrates, give beer a bitter taste, an unpleasant odor, cause cloudiness.
Saccharomysec ellipsoidus. WITH ferment carbohydrates, cause spoilage of taste and turbidity.
Pichia. Volatile acids and other substances are formed in beer, due to which the beer acquires a fruity-ethereal and medicinal aftertaste.
Candida. They develop on the surface of wort and beer in the form of a white or grayish film. Give beer an unpleasant taste and smell.
Candida mycoderma does not ferment sugar. They have a high rate of reproduction and in case of infection are able to accumulate in large quantities.
Torulopsis. May cause haze in beer and impair its taste. The main danger is that dead cells serve as nutrient material for other microorganisms.
In brewing, representatives of several types are found. mold fungi.
Aspergillus- found on damaged grain, on hops, in damp factory premises, in containers and containers, on beer residues.
Oidium- milk mold, found on green malt, in grains, on wet walls of containers in contact with mash or wort.
Rhizopus- black mold. Products affected by mold are covered with white spider-like mycelium. Rhizopus is the most dangerous pest of the malt shop and causes the same harm to malt as Penicillium.
Wine production
Wine is a product of alcoholic fermentation of grape or fruit juice.
The technological process of wine production is based on the biochemical transformations of substances in grape or fruit juice (must) under the influence of yeast, the metabolism of which is regulated by the enzyme complex of the cell.
Classification of grape wines. The classification of wines is made taking into account the grape variety, color, production technology, alcohol and sugar content, aging period.
by color wines can be white, rosé and red.: White Grape wines are obtained by fermenting must from light grape varieties. Red Wines are made from red grapes by fermenting the must along with the skins and pips. During the fermentation period, the coloring tannins from the seeds and skins pass into the must, so these wines have a red color, astringent, astringent taste. Pink wines are made from white and red grapes or obtained by blending (mixing) white and red wines.
Depending on the type of raw material grape wines are produced varietal, obtained from a single grape variety, and blending, made from several varieties of grapes.
Quality and maturity grape wines are divided into ordinary, ordinary aged, vintage and collection. Ordinary wines are released for sale without aging, not earlier than 3 months from the date of grape processing. Ordinary aged The wines are aged for over a year. vintage wines- high-quality, obtained from certain grape varieties. These wines retain their properties regardless of the length of exposure. Duration of exposure - at least 1.5 years. Collection wines- Vintage wines of very high quality, aged for at least 6 years. After aging in barrels, they are additionally aged for 3 years in bottles.
Depending on production technology, alcohol and sugar content grape wines are divided into table, fortified, flavored and saturated with carbon dioxide.
Table wines. They are obtained by fermenting grape juice without the addition of alcohol. The alcohol content in them is from 9 to 14%; According to their sugar content, they are classified into dry table wines with a residual sugar content of up to 1%, table semi-dry and semi-sweet wines, sherry. IN dry wines, the fermentation process goes to the end, all the sugar is fermented. They contain up to 0.3% sugar and have a pleasantly refreshing sour taste. Table semi-dry and semi-sweet wines obtained by incomplete fermentation of sugar wort. The fermentation process is suspended by cooling or pasting. After bottling, semi-dry and semi-sweet wines are pasteurized. Semi-dry wines contain 9 - 14% alcohol and 0.5 - 3% sugar; semi-sweet -9 - 13 vol.% alcohol, sugar from 3 to 8%. They have a pleasant sweet and sour taste. Table sherry obtained by aging wine in incomplete barrels under a yeast film (solera). The color of the wine is golden, it has a special taste and a bouquet with a mushroom tone. Sherry is produced with a strength of no more than 14%, not sweet.
Fortified wines usually made with the addition of alcohol . According to the content of alcohol and sugar, they are divided into dessert and strong. Dessert wines obtained as a result of incomplete fermentation of grape must. Fermentation is stopped by adding alcohol to the fermenting must. The alcohol content in dessert wines is moderate, 12 - 17 vol.%. The group of dessert wines includes Cahors, Malaga, Pinot Gris, Muscat, sweet white, red, rosé, etc., which are made from dried or raisined and therefore very sweet grapes. Wines containing more than 20% sugar are called liquor. The higher the sugar content of wines, the less alcohol is required to ensure their biological stability. Fortified wines are different from desserts with a higher alcohol content - from 17 to 20 vol.% and less sugar. The sugar content of strong wines is low - up to 14%. This category includes dry and semi-sweet madeiras, ports, dry, semi-dry and semi-sweet sherries.
A separate group are flavored wines to which vermouths belong. Vermouth- grape wine infused with various odorous materials of plant origin. They include wormwood, from where the name came from (German. Vermuth- wormwood), vanilla, cinnamon, cinchona peel, cardamom, centaury, thyme, yarrow, mint, birch buds, Linden blossom, bison, etc.
Special group - carbonated wines: sparkling or champagne and sparkling wines. In France, the name "champagne", according to the law, have the right to wear sparkling wines produced only in the province of Champagne from local grapes and only bottled. Originally, champagne "vino secco" was a sweet wine made from berries that dried up when ripe.
Wine champagne is produced by bottle and tank methods. In the first method, the bottles are aged for 3 years. In this case, the bottles are kept upside down, in connection with which the precipitate forms on the cork, it is removed together with the cork after freezing. Bottled champagne is marked "aged" on the label.
With the tank method, champagne wine takes place in large containers, after which it is bottled, where fermentation continues for another one or two years. Champagne is made in this way in Abrau-Dyurso, at Rostov, Moscow and other factories.
distillation of grape wine cognacs. The birthplace of cognac is the French department of Charente (the center is the city of Cognac), so only the one made in Charente should be called real cognac. This is a strong alcoholic drink made from cognac spirit, obtained from dry white grape wines by distillation. Cognac alcohol with a strength of 65 - 70% is aged in oak barrels or tanks loaded with oak staves. Depending on the aging, ordinary cognacs (aged 3-5 years) and vintage cognacs are produced. The years of aging of ordinary cognacs are indicated by asterisks.
Characteristics of yeast races used in winemaking. The main role in the fermentation of grape and fruit must belongs to yeast. Under the influence of yeast, always present on the surface of ripe berries and fruits (epiphytic microflora), juice fermentation can occur spontaneously (spontaneously).
Grape juice is an excellent nutrient medium. The introduction of wild yeasts and yeast-like organisms into the wort can change the taste and cause spoilage of the finished product. To suppress unwanted microflora and to obtain a finished product in wine production, cultural yeast is used as the main fermentation agent.
Wine yeast belongs to the family Saccharomycetaceae, types Saccharomyces vini And Saccharomyces oviformis. Cell structure wine yeast does not differ from the structure of cells of other Saccharomycetes. The shape and size of cells in S. oviformis And. S. vini are the same.
Yeast Saccharomyces vini ferment glucose, fructose, mannose, maltose, sucrose, galactose and a third of raffinose; do not ferment lactose, pentoses, dextrin and inulin.
Saccharomyces oviformis - also reproduces well in grape juice and yields about 18% alcohol. On the surface of dry grape wine, they form a film. They are used in winemaking for the production of sherry. Yeast can ferment glucose, fructose, mannose, sucrose, maltose and a third
2 General characteristics and races of yeast used in fermentation industries
Cultural yeast belongs to the Saccharomycetes family and is called Saccharomyces cerevisiae.
The optimum temperature for yeast propagation is in the range of 25-30°C, and the minimum temperature is about 2-3°C. At a temperature of 40 ° C, growth stops and the yeast dies, but the yeast tolerates low temperatures well, although their reproduction stops. Yeast does not die even at -180°C (liquid air). At a high concentration of sugar in the medium, the vital activity of the yeast stops, as this increases the osmotic pressure, at a certain value of which plasmolysis of the yeast cells occurs. Plasmolysis is called contraction of the cell, followed by exfoliation of the protoplasm from the cell membrane due to dehydration of the cell and the associated sharp drop in cell sap pressure. The value of the maximum concentration of sugar for different races of yeast is not the same.
There are top and bottom fermenting yeasts. Within each of these groups there are several separate races.
Top-fermenting yeast in the stage of intensive fermentation stand out on the surface of the fermented medium in the form of a rather thick layer of foam and remain in this state until the end of fermentation. They then settle, but rarely form a dense sediment at the bottom of the fermentation vessel. Top-fermenting yeast is structurally a pulverized yeast that does not stick together, unlike bottom-fermenting flaky yeast, whose shells are sticky, which leads to agglutination and rapid cell settling.
Bottom-fermenting yeast, developing in the fermented liquid, does not pass into the surface layer - foam, quickly settles at the end of fermentation, forming a dense layer at the bottom of the fermentation vessel.
A distinguishing feature is the ability of bottom-fermenting yeasts to completely ferment raffinose, while most top-fermenting yeasts do not break down raffinose at all, and only a few species can only ferment it by one third. This main difference is explained by the fact that α-galactosidase is contained in the enzyme complex of this type of yeast.
Of the cultural yeasts, bottom-fermenting yeasts include most wine and beer yeasts, and top-fermenting yeasts include alcohol, baker's, and some races of brewer's yeast. Initially, only top-fermenting yeast was known, since the fermentation of all juices occurred at ordinary temperatures. Wanting to get drinks saturated with CO 2, a person began to ferment at a low temperature. Under the influence of changed external conditions, bottom-fermenting yeast with its properties has become widespread.
In addition to general properties, the yeast used in a particular production has specific characteristics. Moreover, in the same production, varieties are used that differ in one or more features. They are taken out of one cell. Such cultures are called races (strains). Each production has several races of yeast.
Races of alcohol production yeast
In alcohol production, those top-fermenting yeast races are used that have the highest fermentation energy, form a maximum of alcohol and ferment mono- and disaccharides, as well as part of dextrins. Of the yeast used in the production of alcohol from bread and potato raw materials, races HP, M and XV should be mentioned.
When processing molasses into alcohol, races I, L, V, G-67, G-73 are used. These races belong to the family Saccharomyces taceae, genus Saccharomyces, species cerevisiae.
The HP race was isolated in 1902 from compressed baker's yeast. Yeast cells of this race are round, ovoid, 5-6.2 x 5-8 microns in size.
The development and reproduction of HP yeast race is very fast. They ferment glucose, fructose, sucrose, galactose, maltose, mannose, raffinose by one third and can form up to 13% alcohol in the fermented medium.
Race M (Mischung - mixture), proposed by Genneberg in 1905, consists of a mixture of four races of top-fermenting yeast; it is intended for the fermentation of media containing a mixture of various sugars (dextrins, raffinose), which are fermented differently by different yeasts. Such a mixed culture is very resistant to various abnormal conditions encountered in factory practice.
Race XV is technologically similar to race HP. It is used along with the HP race for the fermentation of mixed grain-molasses raw materials.
Of these races, the HP race, which is also used in hydrolysis and sulfite-alcohol production, is the most suitable for fermenting wort from starchy raw materials. However, for the fermentation of sulfite liquors, sulfite yeasts have been specially bred to ferment glucose, fructose, galactose and mannose.
Yeast used in distilleries processing molasses must have a specific ability to quickly ferment quite concentrated sugar solutions and to tolerate high salt content in the medium well. So-called osmophilic yeasts, which tolerate very high osmotic pressure, can ferment solutions containing high concentrations of sugar.
Race Y, bred from molasses yeast by K.Yu. Yakubovsky. Race I has an exceptional ability to ferment high concentrations of sugar and tolerates high levels of salts and alcohol in the fermented molasses wort. Yeast race I ferment glucose, fructose, sucrose, galactose, maltose; raffinose is fermented only partially and dextrins and lactose are not fermented at all. Race I refers to top-fermenting pulverized yeast.
The yeast of race L (Lokhvitskaya) is close in its properties to the yeast of race I, but they reproduce somewhat better and ferment sugar more completely.
Race B (Hungarian), like race L, is adapted to a molasses environment. These races ferment well sucrose, glucose, fructose, and partially raffinose.
Yeast races L and B, along with high fermentation properties, also have good lifting power (the ability to raise the dough), which allows them to be separated from the mash and produced in a pressed form as a bakery.
Successful use is being made of hybrid yeasts bred at the Institute of Genetics of the USSR Academy of Sciences by crossing two types of yeast. Among the hybrids, G-67, G-73 are of the greatest interest. Hybrid 67 was obtained by crossing brewer's yeast S-carlsbergensis with S. cerevisiae of race I. Further crossing of hybrid 67 with hybrid 26 (obtained from crossing races I and HP) gave hybrid 73. Hybrids 67 and 73, along with other enzymes, contain α-galactosidase and possess ability to complete fermentation of raffinose. Other hybrid yeasts are also recommended for use.
Races of baker's yeast
In the yeast industry, fast-growing yeast races with good buoyancy and good storage stability are valued. The taste of baker's yeast should be pure, white or yellowish in color. The lifting force is determined both by the characteristics of the yeast races and by the method of production. The resistance of yeast is a property of the race, but depends on the internal state of the cells and the purity of the yeast.
In the production of baker's yeast from molasses, races VII, 14, 28 and G-176 are used.
Race VII, bred from pressed commercial yeast from the Tomsk Yeast Plant, multiplies rapidly and is well pressed to a moisture content of 71-72%. Race VII yeasts have good buoyancy and the highest storage stability compared to other yeasts known in factory practice. In addition, this culture is resistant to harmful impurities contained in molasses.
Race 14 is intended for the production of dry yeast. This yeast is characterized by a dense texture at a moisture content of 75%, high thermal stability.
From the hybrids of baker's yeast, hybrid 176 was selected, which has all the positive features: large cells (5.6-14.0 microns), resistance to harmful impurities of molasses and a high multiplication factor, which is higher in this race than in the most rapidly breeding race 14. Other promising hybrid races of yeast are currently undergoing production tests.
Races of brewer's yeast
In brewing, bottom-fermenting yeast is used, adapted to relatively low temperatures. Brewer's yeast must be microbiologically pure, as well as have the ability to flocculate, quickly settle to the bottom of the fermenter and give a clear drink with a certain taste and aroma. Highly fermenting and easy flaking yeasts include Froberg bottom-fermenting brewer's yeast (Saccharomyces cerevisiae Froberg), yeast races V and 776.
In breweries, yeast of the 776 race, which was bred at the beginning of the 20th century, was widely used. This yeast is considered particularly suitable for the fermentation of wort prepared with the addition of unmalted materials or from malted barley with a low degree of germination. Yeast of race 776 is medium-fermenting, during the period of main fermentation on wort with a concentration of 11%, they form approximately 2.7% CO 2 . Cells are ovoid, 8-10 µm long and 5-6 µm wide. Yeast mass gain 1: 5.4. The lightening ability is satisfactory.
Of the other yeasts, breweries use races 11, 41, 44, S-Lvovskaya and others, which differ in fermentation energy, sedimentation ability and growth energy.
Race 11 yeast is highly fermentative with good clarification capability. Beer made with race 11 yeast has good taste. This race has become widespread in breweries.
Yeast of race 41 is medium fermenting, with good sedimentation ability. When the wort is fermented with race 41, a mild beer with a clean taste is obtained.
Race 44 yeast is medium fermenting. Sedimentation ability is good. They give the beer fullness of taste and give good results when used in the production of water with increased hardness.
Race S yeast is medium fermenting. Sedimentation ability is good. Give beer with a mild clean taste.
Race P yeast is medium-fermenting, well clarifies beer and determines a pleasant clean taste.
Race F yeast is characterized by a good clarification ability and imparts a pleasant aroma to the beer. The race is resistant to the action of foreign microorganisms.
Yeast of race A (isolated at the Riga brewery "Aldaris") ferments the wort in 7-8 days, clarifies beer well and is resistant to infection.
way different ways selection at the All-Russian Research Institute of the Beer and Non-Alcoholic Industry, a number of highly fermenting yeast strains were obtained (28, 48, 102), which have a significantly higher fermentation energy than the yeast of the original race 11.
Top-fermented brewer's yeast is widely used in England in the preparation of Porter. They are also used to make Berlin lager beers and other drinks. For the preparation of Velvet beer, strain 191 K is used, which intensively ferments monosaccharides and maltose, but does not ferment sucrose, raffinose and lactose.
Wine yeast races
In winemaking, yeasts are valued for their rapid multiplication, the ability to suppress other types of yeast and microorganisms and give the wine an appropriate bouquet. The yeast used in winemaking belongs to a peculiar species of Saccharomyces ellipsoideus. Their cells are oblong-oval in shape. Yeast vigorously ferments glucose, fructose, sucrose and maltose. In different localities and from different young wines, several distinct varieties or races of this species have been isolated. In winemaking, almost all yeast production cultures are of their own, local origin. These include races Magarach 7, Massandra 3, Pino 14, Kakhuri and many others. Along with these races, some foreign ones are also used, for example, the Steinberg race, isolated in Germany in 1892 and 1893, and the Champagne-Ai race.
Most wine yeast is a bottom-fermenting yeast.
For the preparation of white table wines, the races Pinot 14, Feodosia 1/19, Aligote, Riesling Anapsky are used.
Race Pinot 14 has egg-shaped cells, well ferments grape must with a sugar content of 20% with the formation of 11.57% alcohol by volume; the optimum temperature for development and fermentation is 18: -25°C. This race is cold and acid resistant; the optimal pH value is 2.9-3.9.
Race Theodosius 1/19 - large-celled, pulverized, very energetic, quickly ferments grape must and ferments it well; has a wide fermentation temperature range (from 9 to 35°C) and can be used as cold-resistant and heat-resistant.
There are several races of Aligote yeast, and they are all strong, with high fermentation energy. Riesling Anapsky yeast also belongs to vigorous fermenters.
For the preparation of strong wines, the Massandra 3 race is used with an ovoid cell shape, pulverized; the optimal pH value is 3.7-4.05; the optimum fermentation temperature is 18-20°C. Grape must with a sugar content of 20% is completely fermented; when fermenting concentrated grape must (30% sugar), it forms 11.8% alcohol by volume and leaves 8.7% sugar unfermented.
Race Magarach 125, named to commemorate the 125th anniversary of the first planting of grapes at the Magarach Institute, is used to produce strong and dessert wines. This race well ferments highly concentrated grape must with a sugar content of 27-30%, cold-resistant.
Race Kakhuri 2 is widely used for the preparation of champagne wine materials and wines. It ferments grape must with a sugar content of 20% with the formation of 11.4% alcohol, 0.28% sugar remains unfermented. This race is quite cold-resistant (at a temperature of 14-15 ° C, the must ferments on the 2nd day) and ferments well; the optimal pH value is 3.4-3.6.
Race Champagne 7, used for champagnization of bottled wine, is isolated from race Kakhuri 5 and is characterized by the formation of a sediment that is difficult to stir up; intensively ferments at a temperature of 4-9°C, although the wort ferments only on the 5th-6th day.
Of the wine yeasts, the Leningradskaya race is considered the most cold-resistant, and the Ashgabat 3 race is considered the most heat-resistant.
In the production of sherry, special races of yeast are used, which are a variety of the Saccharomyces oviformis species. Sherry yeast forms a film on the surface of wine in incomplete barrels, thanks to the development of which the wine acquires a special bouquet and taste.
Through careful selection of the most important production characteristics, several races of sherry yeasts (13, 15 and 20) with high film-forming ability have been identified. Later, from the production that used the Sherry 20 race, a more effective Sherry 20-C race was selected, which was widely used in many sherry factories.
In fruit and berry winemaking, selected races of yeast isolated from various fruit and berry juices are used. Fruit and berry juices are rich in yeast, which has all the qualities necessary for production and is biologically adapted to the conditions of development in the original fruit and berry juices. Therefore, yeast strains isolated from strawberry juices are used to ferment strawberry juices, and yeast strains isolated from cherry juices are used to ferment cherry juices, etc.
The following strains have become widespread in fruit and berry winemaking: apple 46, 58, cranberry 17, currant 16, lingonberry 3, 7, 10, raspberry 7/5, 25, 28, 28/10, cherry 3, 6, strawberry 7, 4 , 9.
These yeast strains ensure the normal course of fermentation, the completeness of fermentation, rapid clarification and good taste of the wine; they ferment glucose, fructose, sucrose, maltose, galactose and do not ferment lactose and mannitol.
Yeast races Moscow 30, Apple 7, Cherry 33, Chernomorodinovaya 7, Raspberry 10 and Plum 21 are successfully used in fruit and berry winemaking. Pure yeast culture Moscow 30 is recommended for fermentation of cranberry must; Apple 7 and Cherry 33 - for the fermentation of apple must; Blackcurrant 7 and Cherry 33 - for the fermentation of blackcurrant and cherry must.
4 Chemistry of alcoholic fermentation. Secondary and by-products of alcoholic fermentation
Alcoholic fermentation is a chain of enzymatic processes, the end result of which is the breakdown of hexose with the formation of alcohol and CO 2 and the delivery to the yeast cell of the energy that is necessary for the formation of new substances used for life processes, including growth and reproduction. By chemical nature, alcoholic fermentation is a catalytic process that occurs under the action of biological catalysts - enzymes.
The modern theory of alcoholic fermentation is the result of the work of many scientists from around the world.
For elucidation of the processes of fermentation, the works of outstanding Russian scientists were of great importance: Lebedev, Kostychev, Favorsky, Ivanov, Engelhardt.
According to modern concepts, alcoholic fermentation is a complex continuous process of sugar breakdown, catalyzed by various enzymes with the formation of 12 intermediate products.
1 The initial stage of glucose conversion is the reaction of its phosphorylation with the participation of the enzyme glucosinase. A phosphate residue from the ATP molecule, which is located in yeast cells, is attached to the glucose molecule, and glucose-6-phosphate is formed, and ATP is converted to ADP:
C 6 H 12 O 6 + ATP → CH 2 O (H 2 PO 3) (CHOH) 4 CHO + ADP
Glucose Glucose-6-phosphate
As a result of the addition of a phosphate residue from the ATP molecule to glucose, the reactivity of the latter increases.
2 Glucose-6-phosphate, by isomerization under the action of the enzyme glucose phosphate isomerase, is converted reversibly into the form of fructose:
CH 2 O (H 2 RO 3) (CHOH) 4 CHO → CH 2 O (H 2 RO 3) (CHOH) 3 COCH 2 OH
CH 2 O (H 2 RO 3) (CHOH) 3 COCH 2 OH + ATP →
Fructose 6-phosphate
→ CH 2 O (H 2 RO 3) (CHOH) 3 COCH 2 O (H 2 RO) + ADP
Fructose 1,6-diphosphate
Esters of glucose-6-phosphate and fructose-6-phosphate form an equilibrium mixture, called the Emden ester and consisting of 70-75% Robison ester (glucose) and 25% Neuberg ester (fructose).
The formation of fructose-1,6-diphosphate ends with the preparatory stage of alcoholic fermentation with the transfer of high-energy phosphate bonds and with the conversion of hexose into a labile oxyform, which is easily subjected to further enzymatic transformations.
4 The next most important step is desmolysis - breaking the carbon chain of fructose diphosphate with the formation of two
phosphotriosis molecules. The symmetrical arrangement of phosphoric acid residues at the ends of the fructose molecule makes it easier to break its carbon chain right in the middle. Fructose diphosphate decomposes into two trioses: phosphoglyceraldehyde and phosphodioxyacetone. The reaction is catalyzed by the enzyme aldolase and is reversible:
CH 2 O (H 2 RO 3) (CHOH) 3 COCH 2 O (H 2 RO) → CH 2 O (H 2 P0 3) COCH 2 OH +
Fructose 1,6-diphosphate Phosphodioxyacetone
CH 2 0 (H 2 ROz) SUPERB (4)
3-phosphoglyceraldehyde
The main role in further transformations during alcoholic fermentation belongs to 3-phosphoglyceraldehyde, but in the fermented liquid it is found only in small quantities. This is due to the mutual transition of the ketose to aldose isomer and back under the action of the enzyme triose phosphate isomerase (5.3.1.1)
CH 2 0 (H 2 P0 3) COCH 2 OH; £ CH 2 0 (H 2 P0 3) SWEET
Phosphodioxyacetone 3-Phosphoglyceraldehyde
As phosphoglyceraldehyde is further converted, new amounts of it are formed during the isomerization of phosphodioxyacetone.
5. The next step is the oxidation of two molecules of 3^phosphoglyceraldehyde. This reaction is catalyzed by triose phosphate dehydrogenase (1.2.1.12), whose coenzyme is NAD (nicotinamide adenine dinucleotide). The phosphoric acid of the medium is involved in the oxidation. The reaction proceeds according to the following equation: 2CH 2 0 (H 2 P0 3) SHORTLY + 2H 3 P0 4 + 2NAD Triose phosphate dehydrogenase ->
3-phosphoglyceraldehyde
->- 2CH 2 0 (H 2 P0 3) CHONCOO w (H 2 P0 3) + 2NAD H 2 (5)
1,3-diphosphoglyceric acid
The 3-phosphoglyceraldehyde molecule adds phosphate, and the hydrogen is transferred to the NAD coenzyme, which is reduced. The energy released as a result of the oxidation of 3-phosphoglyceraldehyde is accumulated in the macroergic bond of the resulting 1,3-diphosphoglycerol
6. Next, the phosphate residue of 1,3-diphosphoglyceric acid
you, containing a macroergic bond, with the participation of an enzyme
phosphoglycerate kinase (2.7.2.3) is transferred to an ADP molecule.
3-phosphoglyceric acid is formed, and ADP, acquiring
additional macroergic bond, turns into ATP:
2CH 2 0 (H 2 P0 3) CHOHCOOH co (H 2 P0 3) + 2ADP-> 2CH 2 0 (H 2 P0 3) CHOHCOOH +
1,3-diphosphoglyceric acid 3-phosphoglyceric acid
7. Then, under the action of the enzyme phosphoglyceromutase
(2.7.5.3) the phosphoric acid residue moves from the third
carbon to the second, and as a result 3-phosphoglyceric acid
lota is converted to 2-phosphoglyceric acid:
2CH 2 (H 2 P0 3) CHOHCOOH ^t 2CH 2 0HCH0 (H 2 P0 3) COOH. (7)
3-phosphoglyceric acid 2-phosphoglyceric acid
8. The next step is the dephosphorylation of 2-phospho-
foglyceric acid. At the same time, 2-phosphoglycerol acid
by the action of the enzyme enolase (4.2.1.11) by dehydro
tiation (loss of water) is converted into phosphoenolpyrovino-
gradic acid:
2CH 2 OHCHO (H 2 P0 3) COOH qt 2CH 3: CO co (H 2 P0 3) COOH + 2H 2 0. (8)
2-phosphoglyceric acid Sosphoenolpyruvic acid
During this transformation, the intramolecular energy is redistributed and most of it is accumulated in the macroergic phosphate bond.
9. Very unstable phosphoenolpyruvic acid
easily dephosphorylated, while the phosphoric acid residue
by the action of the enzyme pyruvate kinase (2.7.1.40)
together with a macroergic bond to the ADP molecule. As a result
a more stable keto form of pyruvic acid is formed
you, and ADP is converted to ATP:
2CH 2: CO syu (H 2 P0 3) COOH + 2ADP - * 2CH 3 COCOOH + 2ATP. (3)
Phosphoenol pyruvic pyruvic
acid acid
10. Pyruvic acid under the action of the enzyme pi-
ruvate decarboxylase (4.1.1.1) is decarboxylated to cleave
nii CO 2 and the formation of acetaldehyde:
2CH 3 COCOOH - * 2C0 2 + 2CH 3 CHO. (10)
pyruvic aldehyde
11. Acetic aldehyde with the participation of the enzyme alcohol dehy-
rogenase (1.1.1.1) interacts with NAD-H 2 formed
earlier, during the oxidation of phosphoglyceraldehyde to phospho-
glyceric acid [see equation (5)]. As a result, vinegar
aldehyde is reduced to ethyl alcohol, and the coenzyme
NAD-H 2 is regenerated again (oxidized to NAD):
2SN 3 CHO + 2NAD H 2 Z 2CH 3 CH 2 OH + 2OVER. (eleven)
So, the final stage of fermentation is the reduction reaction of acetaldehyde to ethyl alcohol.
From the considered cycle of alcoholic fermentation reactions, it can be seen that 2 alcohol molecules and 2 CO 2 molecules are formed from each glucose molecule.
In the process of alcoholic fermentation, four ATP molecules are formed [see. equations (6) and (9)], but two of them are spent on phosphorylation of hexoses [see. equations (1) and (3)]. Thus, only 2 g-mol of ATP is stored.
It was previously indicated that 41.9 kJ is spent on the formation of each gram-molecule of ATP from ADP, and 83.8 kJ, respectively, goes into the energy of two ATP molecules. Therefore, during the fermentation of 1 g-mol of glucose, the yeast receives an energy of about 84 kJ. This is the biological meaning of fermentation. With the complete breakdown of glucose into CO 2 and water, 2874 kJ is released, and when 1 g-mol of glucose is oxidized to CO 2 and H 2 0, 2508 kJ is accumulated during aerobic respiration, since the resulting ethanol still retains potential energy. Thus, from an energy point of view, fermentation is an uneconomical process.
The fermentation of individual sugars occurs in a certain sequence, determined by the rate of their diffusion into the yeast cell. Glucose and fructose are the fastest fermented by yeast. However, sucrose as such disappears into the must (is inverted) at the beginning of fermentation. It is hydrolyzed by p-fructofuranosidase (3.2.1.26) of the yeast cell membrane to form hexoses (glucose and fructose), which are easily used by the cell. When there is almost no fructose and glucose left in the wort, the yeast begins to consume maltose.
Section 3. Production of beer.
Chapter 6 Fermentation of beer wort .
Brewer's yeast.
The structure of the yeast cell. Yeasts are unicellular organisms belonging to the class of marsupial fungi. The shape of yeast cells is oval, round and elliptical.
The yeast cell has a cell wall 1, under which the cytoplasmic membrane is located. The membrane has selective permeability, influencing the exchange of substances between the cell and the environment.
For example, amino acid and glucose molecules permeate the membrane faster than metal ions, which are smaller. Inside the cell contains a round or oval nucleus 2, surrounded by a double membrane. Inside the nucleus is the nucleolus. The nucleus is necessary for metabolic processes that ensure growth and
yeast reproduction.
The basis of the cell is cytoplasm 3, which is a viscous, slightly yellowish liquid. It performs many functions, for example, the first stage of respiration and alcoholic fermentation proceed directly in the cytoplasm. The structural elements of the cell are also located here: vacuole 4, mitochondria 5, ribosomes 6. Mitochondria are very small drop-shaped particles in which processes associated with oxidative metabolism occur. The ribosome is a vesicle surrounded by a membrane. Ribosomes are the site where protein synthesis takes place. Vacuoli are cavities filled with cell sap and separated from the cytoplasm by a vacuolar membrane. They contain metachromatin, which determines the growth and reproduction of yeast cells. Redox processes take place in vacuoles.
The size of yeast cells depends on the race, the physiological state of the yeast and the composition of the nutrient medium. Pressed yeast contains about 30% solids and 70% water. Yeast dry matter contains 90-95% organic matter and 5-10% inorganic matter. Among organic substances there are proteins and nitrogen-containing substances - 54-56%, carbohydrates - 24-40%, fats - 2-4% (by weight of dry matter). the main part of carbohydrates is represented by glycogen (reserve substance), similar in chemical structure to starch amylopectin. Among the inorganic substances, about half are phosphoric acid and 1/3 potassium.
The yeast ash contains (in%): P 2 O 5 -47-53, K 2 O- 28-40; CaO-0.4 -11.3; Mg O-3.0-7.4; SiO 2 -0.28-0.73; SiO 3 - 0.09-0.74; Cl -0.1-0.65. In addition, there are small amounts of S, Zn, Mn, Cu, Fe.
Phosphorus compounds are important in the metabolism of yeast cells, as they are part of the intermediate substances of alcoholic fermentation, and potassium plays a primary role in the construction of protein and carbohydrate molecules. Yeast is rich in B vitamins, contains ergosterol (provitamin D), etc. Yeast contains various enzyme systems involved in the processes of hydrolysis and synthesis, as well as in the processes of fermentation and respiration.
Yeast growth stage. Yeast growth is called an increase in the number of their cells, i.e. - reproduction. Yeast cells reproduce by budding under normal conditions. The mother cell forms a bud, which grows into a daughter cell. With a lack of nutrients or under other unfavorable conditions, partitions form inside the cell, and the cell disintegrates along these partitions, forming spores. In an environment with good conditions nutritional spores germinate and form new yeast cells. Beer wort contains all the necessary substances for cell reproduction, therefore, during the fermentation of wort, yeast reproduces only by budding, without forming spores.
After the introduction of yeast into the wort, their quantitative and qualitative changes are observed. The amount of yeast Increases several times, but their concentration in the dispersed state first increases, reaching a maximum value, and then decreases. Reproduction of yeast during the fermentation of beer wort takes place in several stages. Several stages can be distinguished on the growth curve. (Vertical - number of yeast cells, horizontal - time.)
In the initial phase, called the latent or lag phase (growth retardation), the yeast adapts to the new environment and prepares to reproduce. This phase is conditionally divided into two parts: the phase of actual rest, when the cells adapt to the environment, and the phase of the gradual start of reproduction. The duration of the latent phase for brewer's yeast is 1-1.5 days. In it, the cells increase in volume and elongate, the proportion of budding cells increases.
In the next phase, called the logarithmic, the rate of yeast reproduction is maximum, all cells are active and are in a roaming medium in suspension.
After the logarithmic phase, the stationary phase begins, when cell reproduction slows down, while the rate of death and reproduction are balanced, as a result of which the number of living cells remains unchanged.
The last phase, called the attenuation phase, is characterized by a decrease in cell activity, which is due to a decrease in the mass of nutrients and an increase in the amount of metabolic products. Reproduction stops, the cells die and settle to the bottom of the fermenter.
In a living yeast cell, vital activity is supported by various biochemical processes, and when it dies, the coordination of these processes is disrupted and autolysis begins, i.e. cell breakdown by its own enzymes. In this case, the cell structure is disturbed, the activity of some enzymes increases and the activity of others weakens.
For example, hydrolytic enzymes are activated, while the enzymes of respiration and fermentation die. During autolysis of yeast, protein substances, hydrocarbons, fats, organic phosphorus compounds are decomposed, low-molecular decomposition products are formed, which diffuse through the cell walls into beer and change its taste. With a slight autolysis, a slight yeasty aftertaste appears, and with a strong autolysis, a bitter foreign taste appears. The nitrogenous substances released during autolysis can be colloidal turbidity of beer.
Races of brewer's yeast. In brewing, only cultural yeasts are used, which belong to the Saccharomycetaceae family and the Saccharomyces genus. There are bottom-fermenting yeast Saccharomyces carlsbergensis (Saccharomyces carlsbergensis) and top-fermenting yeast - Saccharomyces cerevisiae.
Initially, top-fermenting yeast was known, since fermentation took place only at normal temperatures (as in winemaking, baking). wanting to get drinks saturated with carbon dioxide, they began to carry out fermentation at low temperatures. Under the influence of changed external conditions, bottom-fermenting yeast with certain properties was obtained.
In brewing, yeast varieties are used that differ from each other in one or more features. They are obtained from one cell. such cultures are called races (strains).
Top-fermenting yeast in the process of intensive fermentation floats to the surface of the fermented liquid, accumulates in the form of a layer of foam and remains in this form until the end of fermentation. Then they settle, forming a very loose layer at the bottom of the fermenter. in their structure, these yeasts belong to dusty yeasts that do not stick together, unlike flaky grassroots yeasts, the shells of which are sticky, which leads to sticking (agglutination) and rapid cell sedimentation.
Bottom-fermenting yeast does not pass into the surface layer of beer-foam, but quickly settles at the bottom of the fermenter.
The ability of yeast to flocculate is important for the technology of fermentation of beer wort, as it helps to accelerate the clarification of beer and facilitates the removal of yeast from the fermenter after fermentation, followed by their use as seed yeast. The low fermentation temperature promotes flocculation.
The reaction of the environment greatly affects the properties of the yeast. For example, in an acidic environment at a pH of less than 3 and in an alkaline environment at a pH of more than 8, flaky yeast becomes dusty. Flaky yeast compared to pulverized ones have larger cells, are less susceptible to autolysis, give a large increase in biomass, have less fermentation activity, form less diacetyl and higher alcohols in beer, which has a positive effect on its quality.
Bottom-fermenting yeast differs from top-fermenting yeast in that it fully ferments raffinose. Bottom-fermenting yeasts have an optimal growth temperature of 25-27C, a minimum of 2-3C, and at 60-65C they die off. The maximum development of grassroots yeast occurs at pH 4.8-5.3. Oxygen dissolved in the wort promotes yeast growth, while fermentation products (ethyl alcohol, carbon dioxide, higher alcohols, acetaldehyde, acids), as well as an increased concentration of sugar, inhibit the development of yeast.
Brewer's yeast must meet the following requirements: Quickly ferment the wort, form flakes well and clarify the beer during fermentation, give the beer a clean taste and pleasant aroma.
Fermentation activity of yeast is determined by the degree of fermentation of the wort. The degree of fermentation (V ) is an indicator, expressed as a percentage, characterizing the ratio of the mass of the fermented extract (E-e) to the mass of solids in the initial wort (E): V = ((E -e) 100) / E, Where e is the content extractive substances in beer, % by weight of beer.
According to the degree of fermentation, yeast is divided into strong or high fermentation (90-100% fermentation), medium fermentation (80-90%), low or low fermentation (less than 80%).
Highly fermenting yeast races include: 11, F (obtained in the Czech Republic), strain 8a (M). Yeast of race 11 is undemanding to the quality of raw materials, settles well, the beer is characterized by a full taste. Yeast of race F clarifies beer well, gives it a pleasant aroma, and is resistant to infection. Yeast of strain 8a (M) has a high fermentation activity, an increased multiplication factor, and settles well. The use of this yeast makes it possible to reduce the duration of the main fermentation from 7 to 5 days and obtain beer with a good taste.
Medium-fermenting yeasts include races 776, 41, 44, S (Lviv), P (Czech Republic),
A (Riga). Yeast race 776 is unpretentious to raw materials, it can be used for making beer using unmalted materials. The finished beer has a satisfactory taste with a sharp hop bitterness. Yeast races 41, 44, S, have a good ability to settle, the taste of beer is clean soft, Yeast race 44 makes it possible to obtain good beer when using water with increased hardness. Yeast races F, A brighten beer well, resistant to infection.
Top-fermenting yeast is used for dark and specialty beers.
The requirements for the quality of yeast are not always satisfied by one race, therefore, a mixture of races is used in production or the wort is fermented separately on different races, and then young beer is mixed.
Breeding pure culture yeast.
Dilution is understood as an increase in the mass of yeast in an amount from the mass in one test tube to the mass of the uterine, necessary for introduction into the fermenter.
The whole breeding process consists of two stages: laboratory (breeding of yeast in the laboratory) and workshop (breeding of yeast in the pure culture department).
The laboratory stage consists of several successive passages. First, a pure culture from a test tube is subcultured into flasks on a sterile wort, then the yeast is reseeded with a sterile fermented wort to a new sterile wort, the volume of which increases several times from reseeding to reseeding. The laboratory stage ends with the fermentation of 6 liters of wort in a copper Carlsberg flask for 5-6 days at 7-8 ° C.
The workshop stage is the cultivation of yeast on sterile hopped wort in special devices.
The figure shows a Grainer setup for breeding a pure yeast culture in a workshop (piping not shown). The installation consists of a sterilizer 4, two fermentation cylinders 3, the number of which varies depending on the amount of yeast used, a tank for pre-fermentation 1 and dishes 2 for sowing yeast.
The sterilizer and pre-fermentation tank are equipped with coils for heating or cooling the wort, air filters and instrumentation.
The fermentation cylinders have vessels for seed yeast with a capacity of 10 liters.
The sterilizer is intended for boiling the wort (sterilization) and its subsequent cooling, the Fermentation Cylinder - for the first stage of reproduction, the pre-fermentation tank - for sterilization and cooling of the wort, as well as for carrying out the second stage of reproduction of a pure culture. Air temperature in 
department of pure culture 8-9 o C.
Breeding pure culture is as follows. Hot hopped wort is collected from the brew kettle into the sterilizer 4, boiled for 1 hour, then cooled to 8-12 ° C. With the help of compressed sterile air, the wort is fed into cylinder 3, where a pure culture is introduced through a special faucet of a copper Carlsberg flask, then fermented within 3 days. At the same time, the yeast multiplies and increases in mass. by the end of the third day, the pre-fermentation tank is filled with wort, which is also heated to a boil and then cooled. A part of the pure culture from the fermentation cylinder 3 is taken for storage into a vessel 2 for seed yeast, where it is stored until the next distribution, and the main part is pumped into tank 1, where preliminary fermentation is carried out at 9 ° C for 3 days.
In the next breeding cycles, the yeast for sowing into the sterile wort located in the fermentation cylinder 3 is taken from the vessel 2. The process of breeding a pure culture in the Greiner unit is repeated many times until foreign microflora is detected in the yeast.
The fermented mass from tank 1 is pumped into a special apparatus for pre-fermentation with a capacity of 1000 dal, but filled by 1/3 with wort at a temperature of 5-7 ° C. After 12 hours of fermentation, another 400 dl of fresh hopped wort are added to this apparatus and fermentation is continued for another 36 hours keeping the temperature at 5-7C. Then the fermented wort is pumped into the apparatus for the main fermentation with 700 dal of wort, and after 1 day it is filled with wort to its full capacity and fermentation is carried out in the usual way, controlling the temperature, the concentration of the wort and clarification. The yeast that has settled during fermentation is washed off, washed with cold water and used in production as the first generation.
Yeast-and-plant apparatuses are sterilized with steam for 45 minutes at a pressure of 0.15-0.17 MPa before starting work. Air entering the sterilizer must pass through air filters.
