Winemaking process
2020-02-18 14:08:30
Winemaking is the conversion of grapes into wine. It consists of two stages: the first stage is the physicochemical or physics stage, that is, when brewing red wine, solid components in grape berry are impregnated into the grape juice, and when brewing white wine, grape juice is obtained through pressing; The stage is the biological stage, namely the alcohol fermentation and the apple-lactic acid fermentation stage.
In the grape raw materials, 20% are solid components, including stems, peels and seeds, and 80% are liquid components, namely grape juice. Fruit stems mainly contain water, minerals, acids and tannins; seeds are rich in fat and astringent tannins; fruit juices contain sugar, acids, amino acids, etc., which are non-exclusive components of wine. The unique components of wine are found mainly in the fragments of the peel and pulp cells. In terms of quantity, there are also great differences between juices and peels. Fruit juices are rich in sugar and acids, they contain very little aromatic substances, and they contain almost no tannins. For the peel, it is considered to be the "noble" part of the grape berry because it is rich in the special components of the wine.
The goal of winemaking is to achieve a balance between these taste substances and aromatic substances that are essential for the wine's sensory balance and style, and then ensure the normal fermentation process.
Impregnation: brewing of red wine
In the brewing process of red wine, the components in the grape solids should be brought into the liquid part under controlled conditions, ie by promoting the exchange of substances between the solid and liquid phases, to make the best use of the aromatic potential and polyphenol potential of the grape raw materials. . This is the unique dipping phase of red wine production. Impregnation can be carried out during the alcoholic fermentation, before the alcoholic fermentation or after a few alcoholic fermentations.
In the traditional process, impregnation and alcoholic fermentation are carried out almost simultaneously. The raw material is crushed (the grape is broken down to facilitate the production of juice, which facilitates the exchange of solid-liquid phase materials). After removing the stem, it is pumped to the impregnated fermentor for fermentation. During the fermentation process, the solid part floats due to CO2 driving, forming a "cap" that is no longer in contact with the liquid part. In order to promote the material exchange between the solid and liquid phases, a portion of the grape juice is discharged from the bottom of the tank and pumped to the upper part of the fermenter to rinse the entire surface of the skin cap. This is the inverted can.
Aromatic substances are more easily leached than polyphenolic substances, so it is the leaching of polyphenols that determines when the impregnation is over. At this stage, the most difficult is to choose to leach anthocyanidins and high-quality tannins instead of leaching inferior tannins with bitterness and greenish taste. The increase of alcohol and temperature formed by fermentation is conducive to the extraction of solid materials, but should prevent the temperature is too high or too low: the temperature is too low (less than 20-25 °C), is not conducive to the extraction of active ingredients; temperature is too high ( Above 30-35°C), poor quality tannins will be leached and lead to the loss of aromatic substances. At the same time, there is the risk of alcohol fermentation being stopped.
Pouring cans is the best way to opt for high-quality tannins. However, strong mechanical treatment (crushing, stemming, pumping) of shredding the fruit pedicel and peel must be prevented because in this case the possibility of selective leaching is almost completely lost.
Among polyphenols, pigments are more easily leached than tannins. Therefore, depending on the length of the steeping time (from several hours to more than one week), we can obtain various types of wines: rosé wine, fresh red wine with rich aroma and fresh intensive wine, and mellow tannin-sensitive red Wine etc. The length of the immersion time also depends on such factors as the grape variety, the maturity of the raw materials, and the health conditions.
After the impregnation is complete, the solids are separated from the liquid by a can. The liquid portion (self-flowing wine) is sent to another fermenter for further fermentation and undergoes physical and chemical reactions during the clarification process. The solid portion also contains a portion of the wine, so press wine is obtained by pressing. Similarly, press wine should be sent separately to another fermenter for further fermentation. In some cases, after a short period of immersion, a portion of the grape juice is separated from the impregnation tank to make rosé wine. The rosé wine thus brewed is richer in aroma and color stability than the rosé wine brewed after crushing the raw materials.
Heating impregnation of raw materials is another impregnation technique. It is to crush the raw material, remove the stem, and heat it to about 70°C for about 20-30 minutes, and then squeeze it. The grape juice is cooled and then fermented. This is hot dip fermentation. Hot dip fermentation is mainly used to increase the temperature to enhance the extraction of solid parts. Similarly, pigments are more leaching than tannins. We can use the control of temperature to achieve the purpose of selecting the color and tannin potential of raw materials, so as to produce a series of different types of wine. Hot soaking also controls the activity of oxidases, which is extremely beneficial to the raw materials of grapes that are harmed by Botrytis cinerea because they are rich in laccases that break down pigments and tannins. A few minutes of hot dipping on the color can achieve the same effect as a few days of ordinary dipping. At the same time, as impregnation and fermentation are carried out separately, they can be better controlled.
The impregnation of the raw materials can also be carried out using a complete raw material in carbon dioxide gas. This is carbon dioxide impregnation fermentation. The impregnation tank is saturated with carbon dioxide and the grape raw material is completely filled into the impregnation tank. In this case, a portion of the grapes were crushed and grape juice was released; the alcoholic fermentation in the grape juice ensured the saturation of carbon dioxide in the closed tank. After 8-15 days of immersion (the lower the temperature, the longer the immersion time), the wine should be separated. Press the dregs. Since gravity and pressed wines also contain a lot of sugar, the self-flowing wine and pressed wine are mixed or continue to be fermented separately. In the process of carbon dioxide impregnation, undamaged vine berries undergo a series of anaerobic metabolism, including intracellular fermentation to form alcohol and other volatile substances, decomposition of malic acid, hydrolysis of protein, pectin, and diffusion of vacuolar substances. The dissolution of polyphenolic substances, etc., and the formation of a special pleasant scent. Since the peduncles are not damaged and are not soaked by the grape juice released by the damaged grapes, only the impregnation of the peels, and thus the carbon dioxide impregnation, provides a good balance between aromatic substances and phenolic substances. The carbon-impregnated wines have a soft, rich aroma and ripeness. It is currently the only known brewing method for obtaining aromatic wines from neutral grape varieties. Baozuoli fermentation method is a combination of carbon dioxide impregnation fermentation and traditional brewing method, it was called semi-carbon dioxide impregnation fermentation method.
Direct juice, white wine brewing
Like red wine, the quality of white wine also depends on the balance between the main taste substances and the aromatic substances. However, the balance of white wine is not the same as the balance of red wine. The balance of white wine depends on the reasonable ratio between the aroma of the variety and the fermented aroma on the one hand, and on the other hand, the balance between alcohol, acidity and sugar. Polyphenols cannot be intervened. For red wine, we require a structure, skeleton, mellowness, and mellow that combine with deep purple, while for white wine, we require refreshing, fruity, and elegant combination with a greenish-toned*, and it is generally necessary to avoid oxidation. With amber tones.
In order to obtain these organoleptic characteristics of white wines, the composition of the solid part of the grape material should be minimized, especially the dissolution of polyphenolic substances. Because the polyphenolic material is an oxidized substrate, oxidation can damage the color, mouth feel, aroma, and fruit aroma of white wines.
In addition, when raw materials are harvested and alcohol is fermented, the raw materials of the grapes will undergo a series of mechanical treatments. This will bring about two problems: On the one hand, it will destroy the cells of the grape berry and release a series of oxidative enzymes. Its oxidized substrate--polyphenols, unsaturated fatty acids that act as oxidation promoters and can produce green odors; on the other hand, can also form suspended solids that can affect the quality of wine during the alcoholic fermentation process. The formation of higher alcohols, while inhibiting the formation of esters of wine quality.
Therefore, the brewing process of white wine is very clear. The grape juice used for alcoholic fermentation should be the cellular juice of the grape berry as much as possible, and the process for extracting the juice must be as gentle as possible to minimize the negative effects of crushing, separation, pressing, and oxidation.
In fact, the brewing process of white wine includes: transporting raw materials into the winery in an intact manner to prevent any impregnation and oxidation during harvesting and transport of the grapes; crushing, separation, fractional pressing, sulfur dioxide treatment, and clarification; Alcohol fermentation is carried out with a clear juice at a temperature of 15-20°C to prevent the loss of aroma.
In addition, the entry of foreign iron should be strictly prevented to prevent the oxidation and turbidity of the wine (iron dilapidated). Therefore, all equipment is best to use stainless steel.
In the extraction of juice, it is best to use the direct pressing technique, which means that the raw materials of the grapes are directly loaded into the press directly and pressed in several times, so that the impregnation of the solid part by the grape juice can be avoided and the grapes can be better controlled. Grading of juice. With direct pressing technology, white wines can also be made from red grape varieties such as Pinot Noir.
The drawback of the above process is that the aroma of the grapes cannot be fully utilized, and the aroma of the varieties is very important for balancing the aroma of fermentation. Therefore, when using the above techniques, the selection of aromatic grape varieties comes first. In addition, in order to make full use of the aroma of the grape varieties, a cold soaking process may also be adopted. That is, the temperature of the cracked raw material is soaked at about 5° C. for 10-20 hours as quickly as possible so that the aroma substances in the peel will enter the grape juice and inhibit the phenols. The dissolution of the substance and the prevention of oxidase activity. After the impregnation is completed, the squeezing, squeezing, clarification, and fermentation at a low temperature are performed.
Fermentation
Fermentation is the biological process of wine production and it is also the main step of converting grapes and berries into wine. It involves yeasts converting sugar to alcohol and fermentation by-products, lactic acid bacteria, which break down malic acid into lactic acid, two biological phenomena, namely alcohol fermentation and malolactic fermentation. It is considered to be biologically stable only if the wine no longer contains fermentable sugars and malic acid.
For red wine, both fermentations must be thorough. Malolactic fermentation is essential: malic acid-lactic fermentation reduces acidity (converts diacids to monoacids), while reducing the raw green and bitter taste of raw wine, making it softer, rounder, and more plump.
For white wines, the situation is more complicated: For grape materials with high sugar content, alcohol fermentation should be stopped when the wine-sugar reaches its optimum equilibrium point, while avoiding malic acid-lactic acid fermentation; for dry white wine, there is a need Malic acid-lactic acid fermentation is performed after the alcoholic fermentation is finished, and malolactic fermentation cannot be performed for dry white wines that require a strong, refreshing flavor. In summary, for those wines that require alcoholic fermentation and malolactic fermentation, it is important that alcoholic fermentation and malic acid-lactic fermentation cannot be carried out crosswise because lactic acid bacteria can break down malic acid and break down sugar to form lactic acid, acetic acid and Mannitol, this is lactic acidosis.
Fortunately, grape juice is a medium that is more conducive to yeast growth. The growth of lactic acid bacteria is inhibited by its acidity and alcohol. Therefore, under normal circumstances, when the lactic acid bacteria begin to move, all fermentable sugars are consumed by the yeast. However, sometimes alcohol fermentation is difficult or even stopped.
The task of the wine technologist is to quickly and thoroughly ferment the alcohol and start the malolactic fermentation immediately after the end of the alcoholic fermentation (if needed). Therefore, it is necessary to promote yeast to temporarily inhibit the activity of lactic acid bacteria. But the inhibition of bacteria should not be too strong, otherwise it will delay the malolactic fermentation and even completely inhibit the malolactic fermentation.
The inhibitor of lactic acid bacteria is sulfur dioxide. It should be added as early as possible to the broken grape or grape juice. This is the sulfur dioxide treatment. The amount of sulfur dioxide used varies according to the raw material hygiene, acid content, pH, and brewing method. It is generally 30-100 mg/L (grape juice). Since sulfur dioxide also has anti-oxidation, anti-oxidation enzymes and promote flocculation and other effects, so in the brewing of white wine, its higher dosage to prevent oxidation, and promote the clarification of grape juice.
Currently, sulfur dioxide is almost the only bacterial inhibitor that can be used by wine technologists. However, when it is used, its effect on alcoholic fermentation must be considered. The alcoholic fermentation of grapes can take place naturally. This is because there are many yeasts on the surface of mature grape berries. These yeasts multiply quickly after the grapes break up. Due to the different ability of various yeasts to resist sulfur dioxide, sulfur dioxide has a selective effect on yeasts and can also inhibit all yeasts. Therefore, in most cases, high-quality wild yeast (usually wine yeast Saccharomyces ellipsoideus) can be selected by selecting the use concentration of sulfur dioxide, and all wild yeasts can also be killed, and special artificial selection yeast (such as aromatase yeast) can be selected. Non-pigmented yeast, etc.).
Once the grape material is treated with sulfur dioxide and the yeast is added, the wine technologist should promote yeast growth and its fermentation activity. In this process, wine technologists should control two factors. One factor is temperature. On the one hand, the temperature influences the reproduction rate of the yeast and it is extremely dynamic. On the other hand, it affects the alcoholic fermentation. Temperatures above 40°C will cause yeast death; temperatures above 30°C will increase the likelihood of fermentation being suspended. Therefore, the temperature range that meets the biological requirements of yeasts and the technical requirements of wines is 18-30°C. Another factor is oxygen. In a series of treatments before adding yeast, the dissolved oxygen in the grape juice is quickly consumed by the oxidase in the matrix. The oxygen left by yeast is rare. The yeast propagation conditions are therefore at least partly anaerobic conditions. Under anaerobic conditions, the main factors for the survival and reproduction of yeasts are sterols and unsaturated fatty acids in cells. But the biosynthesis of both must be oxygen. Therefore, oxygen must be supplied to the yeast. The best time for oxygen supply is before entering alcoholic fermentation. At this time, if we want the alcoholic fermentation to be complete quickly, we must carry out an open-top pouring.
After the alcoholic fermentation is over, it is lactic acid bacteria. Because of the high acidity, low pH, and high alcoholicity of wines, it is not conducive to the activity of lactic acid bacteria and the control of malic acid-lactic acid fermentation is more difficult. In order to promote the smooth progress of malic acid-lactic fermentation, several cans of raw materials are not subjected to sulfur dioxide treatment during alcohol fermentation, and slight chemical acid reduction is performed. After the alcohol fermentation is completed, these cans of wine and other cans are used. The wine mix, while preventing the temperature from being too low, should be controlled at 18-20°C. After the malic acid-lactic acid fermentation is completed, sulfur dioxide treatment should be immediately carried out to prevent lactic acid bacteria from decomposing Etang and tartaric acid.
Obviously, alcohol fermentation does not only convert sugar to ethanol, it also plays an important role in aroma. It is at this stage that grape juice has the smell of wine. It is generally believed that the content of aroma of wine is about 1% of the amount of alcohol it forms. The role of the craftsman is to promote the formation of these aromatic substances and to prevent their loss due to the release of carbon dioxide.
After the fermentation is over, the biochemical phase of the wine ends. The second stage of brewing is the physicochemical stage. The role of this stage is to convert raw wines into mature wines that consumers can enjoy.
The stability and maturity of wine
The wine just after the fermentation is full of carbon dioxide and is turbid. The color of the red wine is not much like the purple color. It has a fruity taste, but its taste is light, sour and bitter, and unstable. If you put a bottle of raw wine into the refrigerator, tartar and pigmentation will occur in a few days. This is a normal phenomenon that occurs slowly during the wine filling or maturing in the barrel. This maturation process can last several months or several years.
The analysis showed that these precipitates were mainly tartaric acid, potassium, pigments, tannins, proteins, trace amounts of iron and copper. In fact, wine is both a chemical solution and a colloidal solution. It contains a variety of chemical substances in the dissolved state, some of which are close to saturation, and it also contains a variety of macromolecular colloids, including carbohydrates, proteins such as pectin, polysaccharides, polyphenols such as tannin and anthocyanins, etc. Wait. The main reasons for wine stability and ripening are ion balance, oxidation, reduction, and colloidal reactions. In rare cases, there are enzyme reactions and bacterial activities.
During the ripening and stabilization process of wine, the fastest reaction is the precipitation of tartaric acid. At the pH of wine, tartaric acid binds with potassium ions to form potassium hydrogen tartrate. Potassium hydrogen tartrate is hardly soluble in alcohol and its solubility decreases at low temperatures. Therefore, after the alcoholic fermentation is completed, as the temperature decreases, crystals precipitate to form tartar. The layer of tartar that binds to the inner wall of the fermenter can sometimes reach several centimeters. Malolactic fermentation accelerates the precipitation of tartar, as this fermentation increases the pH of the wine.
The second important phenomenon involves polyphenols. The anthocyanidins are present in wine in the free state and in the bound state with tannins. The tannin itself is also formed by the polymerization of flavans with different degrees of polymerization. It also exists in the free and bound state, and its binding state is mainly combined with polysaccharides. During the storage of wine, the small molecule tannins are very active and they either polymerize intermolecularly or bind to anthocyanins. In this way, the free anthocyanin gradually disappears, so the color of the aged wine is not the same as the color of the new wine. With the enhancement of the color tone, the color of the red wine gradually changed from purple red to ruby ​​red, and finally changed into a tile-red color. The astringency associated with the degree of polymerization of flavans also gradually decreases, making the wines softer and retaining their skeleton. The tannin with the highest degree of polymerization becomes unstable and flocculates. These conversions of wine polyphenolic substances must pass through oxidation reactions catalyzed by the trace amounts of iron and copper normally present in wine. However, these oxidation reactions must be within the control range. Therefore, the maturity and stability of wine must be aerobic, but the amount of oxygen must be controlled. During maturation and stabilization, the addition of oxygen is achieved through the separation of the wine or through the barrel wall. Therefore, determining the separation time of a wine or the aging time in a wooden barrel is the key to the art of wine aging.
Through this reaction, the wine slowly and slowly reaches its ion, colloid and sensory equilibrium.
It is usually necessary to accelerate these precipitations and flocculation reactions during the wine aging process in an artificial way. The first method is low-temperature treatment, that is, the temperature of the wine is reduced to near its freezing point, and after a few days, it is filtered at a low temperature. Then the glue is applied, that is, substances that promote colloidal precipitation are added to the wine. They either have opposite charges to the colloids in the wine, or can be combined with the colloidal particles in the wine. As used in white wine for the removal of protein from the bentonite, it is used in red wine to remove too much tannin gelatin and protein. During the flocculation process, they will also take part of the suspension, which will make the wine more clarified.
The mechanism of clarification under glue is more complex than filtration. It causes flocculation between proteins, tannins, and polysaccharides, while also absorbing some non-stabilizing factors. Therefore, the glue not only can clarify the wine, but also can make the wine stable.
After low temperature processing and gluing, the wine can be bottled. Before bottling, it needs to be subjected to a series of filtration, the pore size of filtration should be smaller and smaller, and the last filtration should be sterile filtration. After bottling, the wine enters the in-bottle storage phase under reducing conditions, which is an essential stage for converting fruit aromas into aromas. However, the principle has not yet been fully understood.
In the grape raw materials, 20% are solid components, including stems, peels and seeds, and 80% are liquid components, namely grape juice. Fruit stems mainly contain water, minerals, acids and tannins; seeds are rich in fat and astringent tannins; fruit juices contain sugar, acids, amino acids, etc., which are non-exclusive components of wine. The unique components of wine are found mainly in the fragments of the peel and pulp cells. In terms of quantity, there are also great differences between juices and peels. Fruit juices are rich in sugar and acids, they contain very little aromatic substances, and they contain almost no tannins. For the peel, it is considered to be the "noble" part of the grape berry because it is rich in the special components of the wine.
The goal of winemaking is to achieve a balance between these taste substances and aromatic substances that are essential for the wine's sensory balance and style, and then ensure the normal fermentation process.
Impregnation: brewing of red wine
In the brewing process of red wine, the components in the grape solids should be brought into the liquid part under controlled conditions, ie by promoting the exchange of substances between the solid and liquid phases, to make the best use of the aromatic potential and polyphenol potential of the grape raw materials. . This is the unique dipping phase of red wine production. Impregnation can be carried out during the alcoholic fermentation, before the alcoholic fermentation or after a few alcoholic fermentations.
In the traditional process, impregnation and alcoholic fermentation are carried out almost simultaneously. The raw material is crushed (the grape is broken down to facilitate the production of juice, which facilitates the exchange of solid-liquid phase materials). After removing the stem, it is pumped to the impregnated fermentor for fermentation. During the fermentation process, the solid part floats due to CO2 driving, forming a "cap" that is no longer in contact with the liquid part. In order to promote the material exchange between the solid and liquid phases, a portion of the grape juice is discharged from the bottom of the tank and pumped to the upper part of the fermenter to rinse the entire surface of the skin cap. This is the inverted can.
Aromatic substances are more easily leached than polyphenolic substances, so it is the leaching of polyphenols that determines when the impregnation is over. At this stage, the most difficult is to choose to leach anthocyanidins and high-quality tannins instead of leaching inferior tannins with bitterness and greenish taste. The increase of alcohol and temperature formed by fermentation is conducive to the extraction of solid materials, but should prevent the temperature is too high or too low: the temperature is too low (less than 20-25 °C), is not conducive to the extraction of active ingredients; temperature is too high ( Above 30-35°C), poor quality tannins will be leached and lead to the loss of aromatic substances. At the same time, there is the risk of alcohol fermentation being stopped.
Pouring cans is the best way to opt for high-quality tannins. However, strong mechanical treatment (crushing, stemming, pumping) of shredding the fruit pedicel and peel must be prevented because in this case the possibility of selective leaching is almost completely lost.
Among polyphenols, pigments are more easily leached than tannins. Therefore, depending on the length of the steeping time (from several hours to more than one week), we can obtain various types of wines: rosé wine, fresh red wine with rich aroma and fresh intensive wine, and mellow tannin-sensitive red Wine etc. The length of the immersion time also depends on such factors as the grape variety, the maturity of the raw materials, and the health conditions.
After the impregnation is complete, the solids are separated from the liquid by a can. The liquid portion (self-flowing wine) is sent to another fermenter for further fermentation and undergoes physical and chemical reactions during the clarification process. The solid portion also contains a portion of the wine, so press wine is obtained by pressing. Similarly, press wine should be sent separately to another fermenter for further fermentation. In some cases, after a short period of immersion, a portion of the grape juice is separated from the impregnation tank to make rosé wine. The rosé wine thus brewed is richer in aroma and color stability than the rosé wine brewed after crushing the raw materials.
Heating impregnation of raw materials is another impregnation technique. It is to crush the raw material, remove the stem, and heat it to about 70°C for about 20-30 minutes, and then squeeze it. The grape juice is cooled and then fermented. This is hot dip fermentation. Hot dip fermentation is mainly used to increase the temperature to enhance the extraction of solid parts. Similarly, pigments are more leaching than tannins. We can use the control of temperature to achieve the purpose of selecting the color and tannin potential of raw materials, so as to produce a series of different types of wine. Hot soaking also controls the activity of oxidases, which is extremely beneficial to the raw materials of grapes that are harmed by Botrytis cinerea because they are rich in laccases that break down pigments and tannins. A few minutes of hot dipping on the color can achieve the same effect as a few days of ordinary dipping. At the same time, as impregnation and fermentation are carried out separately, they can be better controlled.
The impregnation of the raw materials can also be carried out using a complete raw material in carbon dioxide gas. This is carbon dioxide impregnation fermentation. The impregnation tank is saturated with carbon dioxide and the grape raw material is completely filled into the impregnation tank. In this case, a portion of the grapes were crushed and grape juice was released; the alcoholic fermentation in the grape juice ensured the saturation of carbon dioxide in the closed tank. After 8-15 days of immersion (the lower the temperature, the longer the immersion time), the wine should be separated. Press the dregs. Since gravity and pressed wines also contain a lot of sugar, the self-flowing wine and pressed wine are mixed or continue to be fermented separately. In the process of carbon dioxide impregnation, undamaged vine berries undergo a series of anaerobic metabolism, including intracellular fermentation to form alcohol and other volatile substances, decomposition of malic acid, hydrolysis of protein, pectin, and diffusion of vacuolar substances. The dissolution of polyphenolic substances, etc., and the formation of a special pleasant scent. Since the peduncles are not damaged and are not soaked by the grape juice released by the damaged grapes, only the impregnation of the peels, and thus the carbon dioxide impregnation, provides a good balance between aromatic substances and phenolic substances. The carbon-impregnated wines have a soft, rich aroma and ripeness. It is currently the only known brewing method for obtaining aromatic wines from neutral grape varieties. Baozuoli fermentation method is a combination of carbon dioxide impregnation fermentation and traditional brewing method, it was called semi-carbon dioxide impregnation fermentation method.
Direct juice, white wine brewing
Like red wine, the quality of white wine also depends on the balance between the main taste substances and the aromatic substances. However, the balance of white wine is not the same as the balance of red wine. The balance of white wine depends on the reasonable ratio between the aroma of the variety and the fermented aroma on the one hand, and on the other hand, the balance between alcohol, acidity and sugar. Polyphenols cannot be intervened. For red wine, we require a structure, skeleton, mellowness, and mellow that combine with deep purple, while for white wine, we require refreshing, fruity, and elegant combination with a greenish-toned*, and it is generally necessary to avoid oxidation. With amber tones.
In order to obtain these organoleptic characteristics of white wines, the composition of the solid part of the grape material should be minimized, especially the dissolution of polyphenolic substances. Because the polyphenolic material is an oxidized substrate, oxidation can damage the color, mouth feel, aroma, and fruit aroma of white wines.
In addition, when raw materials are harvested and alcohol is fermented, the raw materials of the grapes will undergo a series of mechanical treatments. This will bring about two problems: On the one hand, it will destroy the cells of the grape berry and release a series of oxidative enzymes. Its oxidized substrate--polyphenols, unsaturated fatty acids that act as oxidation promoters and can produce green odors; on the other hand, can also form suspended solids that can affect the quality of wine during the alcoholic fermentation process. The formation of higher alcohols, while inhibiting the formation of esters of wine quality.
Therefore, the brewing process of white wine is very clear. The grape juice used for alcoholic fermentation should be the cellular juice of the grape berry as much as possible, and the process for extracting the juice must be as gentle as possible to minimize the negative effects of crushing, separation, pressing, and oxidation.
In fact, the brewing process of white wine includes: transporting raw materials into the winery in an intact manner to prevent any impregnation and oxidation during harvesting and transport of the grapes; crushing, separation, fractional pressing, sulfur dioxide treatment, and clarification; Alcohol fermentation is carried out with a clear juice at a temperature of 15-20°C to prevent the loss of aroma.
In addition, the entry of foreign iron should be strictly prevented to prevent the oxidation and turbidity of the wine (iron dilapidated). Therefore, all equipment is best to use stainless steel.
In the extraction of juice, it is best to use the direct pressing technique, which means that the raw materials of the grapes are directly loaded into the press directly and pressed in several times, so that the impregnation of the solid part by the grape juice can be avoided and the grapes can be better controlled. Grading of juice. With direct pressing technology, white wines can also be made from red grape varieties such as Pinot Noir.
The drawback of the above process is that the aroma of the grapes cannot be fully utilized, and the aroma of the varieties is very important for balancing the aroma of fermentation. Therefore, when using the above techniques, the selection of aromatic grape varieties comes first. In addition, in order to make full use of the aroma of the grape varieties, a cold soaking process may also be adopted. That is, the temperature of the cracked raw material is soaked at about 5° C. for 10-20 hours as quickly as possible so that the aroma substances in the peel will enter the grape juice and inhibit the phenols. The dissolution of the substance and the prevention of oxidase activity. After the impregnation is completed, the squeezing, squeezing, clarification, and fermentation at a low temperature are performed.
Fermentation
Fermentation is the biological process of wine production and it is also the main step of converting grapes and berries into wine. It involves yeasts converting sugar to alcohol and fermentation by-products, lactic acid bacteria, which break down malic acid into lactic acid, two biological phenomena, namely alcohol fermentation and malolactic fermentation. It is considered to be biologically stable only if the wine no longer contains fermentable sugars and malic acid.
For red wine, both fermentations must be thorough. Malolactic fermentation is essential: malic acid-lactic fermentation reduces acidity (converts diacids to monoacids), while reducing the raw green and bitter taste of raw wine, making it softer, rounder, and more plump.
For white wines, the situation is more complicated: For grape materials with high sugar content, alcohol fermentation should be stopped when the wine-sugar reaches its optimum equilibrium point, while avoiding malic acid-lactic acid fermentation; for dry white wine, there is a need Malic acid-lactic acid fermentation is performed after the alcoholic fermentation is finished, and malolactic fermentation cannot be performed for dry white wines that require a strong, refreshing flavor. In summary, for those wines that require alcoholic fermentation and malolactic fermentation, it is important that alcoholic fermentation and malic acid-lactic fermentation cannot be carried out crosswise because lactic acid bacteria can break down malic acid and break down sugar to form lactic acid, acetic acid and Mannitol, this is lactic acidosis.
Fortunately, grape juice is a medium that is more conducive to yeast growth. The growth of lactic acid bacteria is inhibited by its acidity and alcohol. Therefore, under normal circumstances, when the lactic acid bacteria begin to move, all fermentable sugars are consumed by the yeast. However, sometimes alcohol fermentation is difficult or even stopped.
The task of the wine technologist is to quickly and thoroughly ferment the alcohol and start the malolactic fermentation immediately after the end of the alcoholic fermentation (if needed). Therefore, it is necessary to promote yeast to temporarily inhibit the activity of lactic acid bacteria. But the inhibition of bacteria should not be too strong, otherwise it will delay the malolactic fermentation and even completely inhibit the malolactic fermentation.
The inhibitor of lactic acid bacteria is sulfur dioxide. It should be added as early as possible to the broken grape or grape juice. This is the sulfur dioxide treatment. The amount of sulfur dioxide used varies according to the raw material hygiene, acid content, pH, and brewing method. It is generally 30-100 mg/L (grape juice). Since sulfur dioxide also has anti-oxidation, anti-oxidation enzymes and promote flocculation and other effects, so in the brewing of white wine, its higher dosage to prevent oxidation, and promote the clarification of grape juice.
Currently, sulfur dioxide is almost the only bacterial inhibitor that can be used by wine technologists. However, when it is used, its effect on alcoholic fermentation must be considered. The alcoholic fermentation of grapes can take place naturally. This is because there are many yeasts on the surface of mature grape berries. These yeasts multiply quickly after the grapes break up. Due to the different ability of various yeasts to resist sulfur dioxide, sulfur dioxide has a selective effect on yeasts and can also inhibit all yeasts. Therefore, in most cases, high-quality wild yeast (usually wine yeast Saccharomyces ellipsoideus) can be selected by selecting the use concentration of sulfur dioxide, and all wild yeasts can also be killed, and special artificial selection yeast (such as aromatase yeast) can be selected. Non-pigmented yeast, etc.).
Once the grape material is treated with sulfur dioxide and the yeast is added, the wine technologist should promote yeast growth and its fermentation activity. In this process, wine technologists should control two factors. One factor is temperature. On the one hand, the temperature influences the reproduction rate of the yeast and it is extremely dynamic. On the other hand, it affects the alcoholic fermentation. Temperatures above 40°C will cause yeast death; temperatures above 30°C will increase the likelihood of fermentation being suspended. Therefore, the temperature range that meets the biological requirements of yeasts and the technical requirements of wines is 18-30°C. Another factor is oxygen. In a series of treatments before adding yeast, the dissolved oxygen in the grape juice is quickly consumed by the oxidase in the matrix. The oxygen left by yeast is rare. The yeast propagation conditions are therefore at least partly anaerobic conditions. Under anaerobic conditions, the main factors for the survival and reproduction of yeasts are sterols and unsaturated fatty acids in cells. But the biosynthesis of both must be oxygen. Therefore, oxygen must be supplied to the yeast. The best time for oxygen supply is before entering alcoholic fermentation. At this time, if we want the alcoholic fermentation to be complete quickly, we must carry out an open-top pouring.
After the alcoholic fermentation is over, it is lactic acid bacteria. Because of the high acidity, low pH, and high alcoholicity of wines, it is not conducive to the activity of lactic acid bacteria and the control of malic acid-lactic acid fermentation is more difficult. In order to promote the smooth progress of malic acid-lactic fermentation, several cans of raw materials are not subjected to sulfur dioxide treatment during alcohol fermentation, and slight chemical acid reduction is performed. After the alcohol fermentation is completed, these cans of wine and other cans are used. The wine mix, while preventing the temperature from being too low, should be controlled at 18-20°C. After the malic acid-lactic acid fermentation is completed, sulfur dioxide treatment should be immediately carried out to prevent lactic acid bacteria from decomposing Etang and tartaric acid.
Obviously, alcohol fermentation does not only convert sugar to ethanol, it also plays an important role in aroma. It is at this stage that grape juice has the smell of wine. It is generally believed that the content of aroma of wine is about 1% of the amount of alcohol it forms. The role of the craftsman is to promote the formation of these aromatic substances and to prevent their loss due to the release of carbon dioxide.
After the fermentation is over, the biochemical phase of the wine ends. The second stage of brewing is the physicochemical stage. The role of this stage is to convert raw wines into mature wines that consumers can enjoy.
The stability and maturity of wine
The wine just after the fermentation is full of carbon dioxide and is turbid. The color of the red wine is not much like the purple color. It has a fruity taste, but its taste is light, sour and bitter, and unstable. If you put a bottle of raw wine into the refrigerator, tartar and pigmentation will occur in a few days. This is a normal phenomenon that occurs slowly during the wine filling or maturing in the barrel. This maturation process can last several months or several years.
The analysis showed that these precipitates were mainly tartaric acid, potassium, pigments, tannins, proteins, trace amounts of iron and copper. In fact, wine is both a chemical solution and a colloidal solution. It contains a variety of chemical substances in the dissolved state, some of which are close to saturation, and it also contains a variety of macromolecular colloids, including carbohydrates, proteins such as pectin, polysaccharides, polyphenols such as tannin and anthocyanins, etc. Wait. The main reasons for wine stability and ripening are ion balance, oxidation, reduction, and colloidal reactions. In rare cases, there are enzyme reactions and bacterial activities.
During the ripening and stabilization process of wine, the fastest reaction is the precipitation of tartaric acid. At the pH of wine, tartaric acid binds with potassium ions to form potassium hydrogen tartrate. Potassium hydrogen tartrate is hardly soluble in alcohol and its solubility decreases at low temperatures. Therefore, after the alcoholic fermentation is completed, as the temperature decreases, crystals precipitate to form tartar. The layer of tartar that binds to the inner wall of the fermenter can sometimes reach several centimeters. Malolactic fermentation accelerates the precipitation of tartar, as this fermentation increases the pH of the wine.
The second important phenomenon involves polyphenols. The anthocyanidins are present in wine in the free state and in the bound state with tannins. The tannin itself is also formed by the polymerization of flavans with different degrees of polymerization. It also exists in the free and bound state, and its binding state is mainly combined with polysaccharides. During the storage of wine, the small molecule tannins are very active and they either polymerize intermolecularly or bind to anthocyanins. In this way, the free anthocyanin gradually disappears, so the color of the aged wine is not the same as the color of the new wine. With the enhancement of the color tone, the color of the red wine gradually changed from purple red to ruby ​​red, and finally changed into a tile-red color. The astringency associated with the degree of polymerization of flavans also gradually decreases, making the wines softer and retaining their skeleton. The tannin with the highest degree of polymerization becomes unstable and flocculates. These conversions of wine polyphenolic substances must pass through oxidation reactions catalyzed by the trace amounts of iron and copper normally present in wine. However, these oxidation reactions must be within the control range. Therefore, the maturity and stability of wine must be aerobic, but the amount of oxygen must be controlled. During maturation and stabilization, the addition of oxygen is achieved through the separation of the wine or through the barrel wall. Therefore, determining the separation time of a wine or the aging time in a wooden barrel is the key to the art of wine aging.
Through this reaction, the wine slowly and slowly reaches its ion, colloid and sensory equilibrium.
It is usually necessary to accelerate these precipitations and flocculation reactions during the wine aging process in an artificial way. The first method is low-temperature treatment, that is, the temperature of the wine is reduced to near its freezing point, and after a few days, it is filtered at a low temperature. Then the glue is applied, that is, substances that promote colloidal precipitation are added to the wine. They either have opposite charges to the colloids in the wine, or can be combined with the colloidal particles in the wine. As used in white wine for the removal of protein from the bentonite, it is used in red wine to remove too much tannin gelatin and protein. During the flocculation process, they will also take part of the suspension, which will make the wine more clarified.
The mechanism of clarification under glue is more complex than filtration. It causes flocculation between proteins, tannins, and polysaccharides, while also absorbing some non-stabilizing factors. Therefore, the glue not only can clarify the wine, but also can make the wine stable.
After low temperature processing and gluing, the wine can be bottled. Before bottling, it needs to be subjected to a series of filtration, the pore size of filtration should be smaller and smaller, and the last filtration should be sterile filtration. After bottling, the wine enters the in-bottle storage phase under reducing conditions, which is an essential stage for converting fruit aromas into aromas. However, the principle has not yet been fully understood.
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