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Technology of Wine Making Introduction Wine Is the Product Obtained by Normal Alcoholic Fermentation of Grape Juic

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Technology of Wine Making Introduction Wine Is the Product Obtained by Normal Alcoholic Fermentation of Grape Juic Paper No. 6 Paper Title: Technology of Fruits and Vegetables Module No. 28 Module Title: Technology of Wine Making Introduction Wine is the product obtained by normal alcoholic fermentation of grape juice, although fermented juices of many fruits (apples, berries, peaches, plums, apricots and even herbs) are now called wine (usually peach wine, etc.). In another sense, wine strictly signifies non-distilled alcoholic beverage obtained by fermentation of grape juice resulting from yeast with proper processing and addition. The processes by which raw grapes are converted in to wine include crushing, extraction, fermentation, fining, racking, fortification etc. Classification of wine There are endless varieties of wine which differ in so many attributes that they are difficult to classify. Fortunately it is possible to classify wine in a more general manner on a basis of their gross composition, disregarding the fine distinction made by the wine specialist. There are four characterization bases on which wine can be classified. These are 1. Dry or sweet 2. Fortified or unfortified 3. Sparkling or still 4. Red or white These types are defined as: a) Dry wines are those in which practically all of the sugar has been converted in to alcohol by fermentation. They contain very little or no sugar that can be detected by testing. They are of comparatively low alcoholic content of around 8-12%. This includes Hock, Burgundy, and Moselle etc. b) Sweet wines are those wines in which sugar content is high enough which can be detected by taste. They contain some unfermented sugar and have alcohol content in the range of 13-15% by weight all of which is the result of fermentation. Examples are Sauterne and Tokay. Wines with 7-9% alcohol are known as ‘light’, those with 9-16% are ‘medium’ and those with 16-21% are known as ‘strong’ wine. c) Unfortified wines are those in which all the alcohol content is entirely derived from fermentation. The above two classes (a & b) are unfortified wines. d) Fortified wines are those wines in which distilled spirits such as grape brandy is added to increase the alcohol content in addition to those derived from fermentation. They usually contain 18-22% alcohol. Examples are Sherry, Port, and Champagnes etc. e) Still wines also known as table or dinner wine are those whose fermentation has been completed before bottling so that they contain only such proportion of carbon dioxide produced in the fermentation as can remain dissolved in the liquid in equilibrium with the air under the condition of manipulation. Most of those mentioned above are still wines. f) Sparkling wines are those wines which are bottled before the fermentation process is ceased so that they contain carbon dioxide gas in solution at greater than atmospheric pressure. These wines are characterized by effervescence when served. The typical level of carbon dioxide is around 4-6 atmospheric pressure. They may be dry or sweet, light or strong. Champagne, sparkling burgundy are sparkling wines. g) Red wines are those wines in which the skin, stems etc. of the grapes are present during the fermentation to extract the pigment and thereby colouring the fermented juice. Example includes Port, Burgundy, and Chianti etc. h) White wines are fermented grape juice only i.e. without skin, stems etc. The colour of the white wines varies from a pale straw colour to deep gold colour. Riesling, Sauterne and Champagne may be cited as examples. The distinction between the red and white wines is particularly based on a difference in manufacturing process. It is important because the variation in colour of so called red wines varies from tint of inky purple to pale pink and tan, and on the other side, the inclusion of skin, stems etc. in the fermented liquor requires different handling from white wines. These two types of wines are further differentiated on the basis of flavor and use. For example, red wines are more flavourful, typically drier, and more astringent than white wines. In contrast, white wines are generally more acidic, floral in nature, and come in a wide range of sweetness styles. Since most white wines are intended to be consumed with meals, they typically are produced to possess an acidic character. Factors affecting wine quality A number of factors affect the wine quality, the most important being the type of grape used. There are certain, constant factors that affect the taste and quality of wine. These include location, climate, weather etc. Climate and weather are the most important factors that influence the growth of grapes for high-quality wines. Climate is determined by geographical location, whereas weather is the result of how nature decides to affect that climate on a daily basis. Apart from these factors, chemical composition of the grapes also affects the sensory properties of wine and the fermentation process. These are 1. Water: Moisture content of the grapes varies from 70 to 85% which directly influence the yield of juice. 2. Sugar: The major sugars of fruits which are normally used for making wine are glucose, fructose and sucrose. The two reducing sugars predominate in grapes and occur approximately in equal proportion and one of the important parameter in deciding the maturity of grapes. Harvesting at the proper stage gives the optimum wine quality. 3. Organic acids: Amount of organic acids is low in wine, but it is an important constituent for tartness. Tartaric and malic acid have a significant effect on wine pH. pH of wine is associated with wine colour, spoilage and stability. Sulfur dioxide is widely used in the wine industry as sanitizing agent and antioxidant and a slight decrease in pH in the range of 3.0-5.0 increases the antiseptic action of sulfur dioxide. 4. Nitrogenous substances: Nitrogen compounds such as amino acids, ammonia and ammonium salts are essential for the growth and development of the yeast during the fermentation process. If these nitrogen compounds are not utilized completely during fermentation, re-fermentation and bacterial spoilage may occur in the finished wines. 5. Phenolic substances: Phenolic substances significantly affect the colour, appearance, taste and body of wines. The colour of red wines is primarily derived from the fruit anthocyanin through heat extraction or fermenting on the skins. Tannins, another group of phenolic substances, influence the body of wine and produce an astringent taste. 6. Inorganic constituents: Inorganic components of grapes significantly influence the production and quality of wines and are important for human nutrition. Generally excessive levels of inorganic constituents produce undesirable effects by altering the colour, appearance or taste of the wine. 7. Enzymes: Certain enzymes present in grapes may be responsible for wine disorders such as clouding, browning, and darkening or an oxidized taste. Enzymes found in grapes include peroxidases, catalases, invertases, tannases, polyphenoloxidases and pectic enzymes. Vinification Winemaking or Vinification is the process of wine production starting from the selection of grapes to the bottling of the finished wine. Vitis vinifera, the main genus and species of grapes used for wine, produces the best grapes in temperate climates with mild winters and dry summers; vines are killed by very cold winters and are susceptible to mold, mildew, and dis- eases in humid summer regions. Grapes must be picked at their optimum maturity stage and should reach the winery in good condition. The must (fresh pressed juice of grapes) contains sugar, organic acids, tannin, flavoring substances, proteins, mineral, salts, pectin and mucilaginous substances which it derives from the grapes. It also contains a large variety of yeasts, bacteria, and fungi, some of which are favorable and some the reverse. The production of wine falls naturally in to two broad divisions, red and white wines respectively. Manufacture of red wine When the grapes are at the proper stage of ripeness, bunches are plucked and brought to the winery. 1. Stemming: Stemming if practiced is done by hand or by use of screens which will pass the grapes but not the stems. It can be operated by hand or by mechanical means. Stemming may also be done after crushing. A strainer of suitable size with proper openings and fitted with revolving blades serves this purpose excellently. 2. Crushing: Crushing is done to liberate the juice and inoculate it with yeast. It is done with the help of basket press or roll machine. The crushed grapes may fall directly into the fermenting vat or into a tank whence they may be pumped to the proper vat. 3. Fermentation: Crushed grapes are started to ferment as desired either naturally or by means of starter under control temperature. Temperature control is desired as yeast works best between 70οF-80οF. Not only sugar is converted in to alcohol and carbon dioxide, many small changes also occur during fermentation. These include drop in acidity, formation of volatile compounds (esters and alcohol), extraction of tannin and colouring matter from skin and seeds etc. 4. Completion of First Fermentation: At the best, only 4% of sugar can be converted per day. For complete fermentation, the time required may vary from two days to three weeks. 5. Pressing/ Filtration: After draining of the considerable portion of the new formed wine after fermentation, the remaining saturated mass is transferred to press. The mass is placed in a strong filter cloth and pressure is applied to squeeze out the new wine. The obtained filtrate is again allowed to ferment for ten days in a cool place at around 50οF. During this yeast cell and other colloidal particles settles down. 6. Aging and racking: The new wine obtained is low in alcohol and contains some unfermented sugar, excess tartaric acid and tannin.
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