Production of wine from grapes Date: Wine is a product of alcoholic fermentation of fruit juices that are rich in fermentable sugars. Most wines are made from grapes. The alcoholic content ranges from 11-12%. Winemaking is still very much an art rather than science. Although grapes are by far the most often used fruit, various other fruits such as peaches and prunes may also be used to make wines. The procedures for making grape wine at home are quite straight forward. Yeast consumes the sugar in the grapes and converts it to ethanol and carbon dioxide. Grape juice is simply inoculated with a package of yeast starter culture. Primary fermentation lasts for approximately one week; during that time, most of the sugar, initially present in the juice, is converted to ethanol by yeast cells with the evolution of carbon dioxide. The excess yeast cells are then removed from the juice along with other sediments, and a slower secondary fermentation is allowed to proceed to develop the final flavor. Sugar may be added to the original must to achieve the desired alcohol content or to modify the flavor. The type of wine can be classified according to the color of the wine. Another classification is based on the sugar content, as listed in Table. Sl. No. Type Specific gravity Sugar Content (wt.%) 1. Dry Wine 1.085 - 1.100 21 – 25 2. 3. Medium Sweet Wine Sweet Wine 1.120 - 1.140 1.140 - 1.160 29 – 33 33 – 37 The overall process of fermentation is to convert glucose sugar (C 6H12O6) to alcohol (CH3CH2OH) and carbon dioxide gas (CO2). The reactions within the yeast to make this happen are very complex, but the overall process is as follows: . Glycolytic enzymes Glucose Pyruvic acid Alcohol + CO2 The primary categories of wine are table wines, fortified wines, and sparkling wines. This classification depends on the techniques of production, called vinification. Winemaking is called enology (or oenology), from the Greek words for wine and study. The term vintage signifies a single season's wine production, usually referring to the specific location in which a particular wine is produced. Aim: To study about wine fermentation and to prepare wine from grape Materials required 1. Grapefruits 2. Sucrose 3. Yeast culture (Saccharomyces cerevisiae ) 4. Glassware - primary fermenting vessel 5. Stirring spoons, funnel, Corks, or caps. 6. Tygon tubing 7. Fermentation locks (anaerobic seal)/rubber stopper 8. pH meter, Hand refractometer/ Brix meter, Procedure: 1. Preparation of starter yeast Suspend 1 g of dry wine yeast in 10 ml of warm water at about 35 ºC and let the yeast grow in a loosely capped container at room temperature for 24 h. 2. Primary fermentation Select fully ripened grapes, de-stem and crush the fruits to release the skin and seeds. Ripe and undamaged grapes should be used. Red grapes are crushed to yield juice plus skin, which is known as must. (Most wineries add sulfur-di-oxide either as gas or as a solid salt to prevent the growth of other yeasts and bacteria which cause spoilage. Sulfur-di-oxide is also produced by Saccharomyces during fermentation.)  Check the initial pH and sugar concentration of the Must (using Brix meter (the concentration of sugar should be 20-25 % )  Inoculate with 20 ml of starter yeast culture.  Plug the juice container with sterile cotton first for the growth of yeast (aerobic fermentation)  After 2-3 days, remove the cotton plug and seal the mouth of the container with a rubber stopper. A piece of Tygon tubing is extended from the stopper to provide a vent for the evolved carbon dioxide. The other end of the tubing is dipped in water. The water prevents the entry of oxygen, which alters the metabolism of the yeast and spoils the wine.  Keep this for complete fermentation under room temperature for one week. 3. Secondary fermentation  At the end of one week, decant the juice from the bottle to clean individual temporary containers.  Pour the juice back into the cleaned bottle. Put back the cleaned assembly of the rubber stopper and Tygon tubing.  Allow fermenting for another 4-6 weeks. Composition of Must (Haas, 1976) Particulars Sugars(Glucose & fructose) Acids (mainly tartaric & malic acid) Tannins White wine Red wine Pectins Ash Aroma substances Nitrogenous substances Higher alcohols Aldehydes Percentage 15-25 0.9-1.5 0.02-0.04 0.1-0.25 0.1-0.15 0.3-0.5 Trace Trace Trace Trace Typical composition of wine (Haas, 1976) Particulars Extract (Total solids) Carbohydrates Acids Ash Aminoacids Tannins Aroma substances Alcohol Percentage 2-3 0.03-0.5 0.5-1 0.15-0.3 Trace Trace Trace 6-9 wt (8-13 vol) FLOWCHART OF WINEMAKING Selection of good ripened & undamaged grapes  Removal of stalks  Washing in water  Weighing (1 kg)  Crushing (Manually using gloves or using crushers)  Check the pH of the Must (should be b/w 3.5-3.6)  Check the brix value using refractometer (add sugar till it attains 20-25°)  Pour the Must to a container  Add yeast inoculum @ 1 %  Cover it with sterile cotton (aerobic fermentation for 2-3 days)  Remove cotton and plug it with a rubber stopper (for anaerobic fermentation)  Decanting  Clarification (by adding clarifying agentsviz., tannin, casein etc.)  Decanting  Ageing and maturation (8-10 months)  Filtration  Pasteurization  Bottling&Labelling Observations to be recorded Parameters Initial pH Colour TSS (%Brix) Appearance Odor Taste Flavor 7 days 14 days 21 days 28 days Weight of the fruits = Weight of sugar added to bring brix to ______ = Final Volume of wine obtained = Review Questions 1. Differentiate primary metabolites and secondary metabolites with suitable examples. 2. Differentiate red and white wine. 3. How to avoid spoilage of wine? If spoilage occurs what is the end product?