Alcoholic fermentation is widely employed for the preparation of beverages in which alcohol is major constituent. The conversion of grape juice to wine is a biotechnological tradition dating back to the dawn of civilization. Throughout the ages numerous winemaking strategies were developed resulting in the range of wine products, from champagne to port, available today.
Wine is an alcoholic beverage produced by the fermentation of sugars in fruit juices, primarily grape juice. In general, wines are classified into two types based on alcohol content: table wines(7 percent to 14 percent, by volume) and dessert wines (14 percent to 24 percent, by volume).
Fermentation is a relatively efficient, low energy preservation process which increases the shelf life, and decreases the need for refrigeration or other forms of food preservation technology. It is, therefore, a highly appropriate technique for use in developing countries and remote areas where access to sophisticated equipment is limited.
Fermented fruit wines are popular throughout the world, and in some regions, it makes a significant contribution to the diet of millions of individuals.
White wine fermentations are typically carried out for roughly one to two weeks at temperatures around 10 to 18 °C. Upon consumption of available glucose and fructose, the main sugars in grape juice, the wine is considered “dry” and separated from the yeast and grape lees (sediment).
Red wines are produced slightly differently than white wines. Like white wines, the alcoholic fermentation commences either through the action of indigenous yeasts or via direct inoculation of a starter culture. During the fermentation the grape material tends to float to the top of the vat forming a “cap.” To better enable extrac-tion of red pigments and to influence wine flavor, winemakers typically punch down the cap or pump juice from the bottom over the cap.
Although residual sugars are of obvious importance to the sweetness of wine, fermentable sugars in grapes are absolutely essential for fermentation. The single most signifi cant by-product of fermentation is ethanol. In addition, sugars may be metabolized to higher alco-hols, fatty acid esters, and aldehydes.
Fermentation occurs in vats of stainless steel, lined concrete or wood. Fermenting at too low a temperature inhibits extracting the best material from the grapes; too high and aromatic and flavor complexity are lost.
The products of fermentation are as follows: Alcohol, glycerol, and carbon dioxide are obtained from yeast fermentation of various sugars; Butyl alcohol, acetone, lactic acid, monosodium glutamate, and acetic acid are products of bacteria action; and citric acid, gluconic acid, antibiotics,
After fermentation, all wines undergo a period of adjustment (maturation) and clarification prior to bottling. The process of maturation involves the precipitation of particulate and colloidal material from the wine as well as a complex range of physical, chemical, and biological changes that tend to maintain and/or improve the sensory characteristics of the wine.
Wine processing: Fermentation
