The fermentation of carbohydrates by yeasts to produce ethyl alcohol is used by the alcoholic beverage industry. Wine is the aged product of alcoholic fermentation of fruits. The wine-making process begins with crushing and stemming the grapes to produce a product called must (Figure 1 ). Sulfur dioxide is used to kill wild yeast and other organisms, and the must is then combined with species of Saccharomyces to ferment under carefully controlled conditions. The skins and seeds of grapes contribute to the color and flavor of the wine. Fermentation takes several days and results in a wine having an alcoholic content of about 15 percent. In dry wines, most of the available carbohydrate has been used, while in sweet wines, some carbohydrate remains.
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| Figure 1 | The process used in the commercial production of wine. | |
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An aging process follows in which the wine is placed in barrels to develop its full flavor, aroma, and bouquet. The wine extracts chemicals from the wood. Then it is filtered, pasteurized, and bottled for market, unless secondary fermentations are intended. For example, sparkling wines are inoculated with sugar and permitted to continue to ferment. The carbon dioxide produced accounts for the bubbles in a sparkling wine such as champagne.
For the production of beer, a type of grain, usually barley grain, is used. It is mashed, soaked, and filtered to produce a liquid called wort. The wort is inoculated with Saccharomyces and permitted to ferment. The final alcoholic content of the beer is approximately 7 to 8 percent. The beer is pasteurized or filtered before it is placed in cans or bottles for sale.
One of the most elegant expressions of industrial microbiology in the modern era is the science of biotechnology. In biotechnology, microorganisms are used to produce medically or industrially important products such as drugs, medicines, and pharmaceutical agents. Bacteria, yeasts, and algae are commonly used for this purpose. Gene manipulations are made, and the genetic constitutions of organisms are changed in the process of genetic engineering. Organisms are cultivated in huge volumes in tanks called fermenters. The desired substances are produced within these tanks.
Genetic engineering applications began when scientists discovered that they could open DNA molecules at desired points, insert foreign gene fragments, reclose the DNA segments, and introduce them to recipient cells. The cells would respond by encoding the proteins specified by the foreign genes. One of the first products so produced was insulin, first licensed for use in the 1980s. Human growth hormone, human interferon, and other substances such as clotting factors were subsequently developed by genetic engineering methods. These products are highlighted in earlier chapters.
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