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How Wine Is Made
Wine is the fermented juice of grapes. Only one species of grape, Vitis vinifera, is used for nearly all the wine made in the world. From this species as many as 4,000 varieties of grape have been developed. These varieties differ from each other, though sometimes only slightly, in size, color, shape of the berry, juice composition, ripening time, and resistance to disease. Of the 4,000 or more varieties, only about a dozen are commonly used to make wine around the world. The chief varieties are: Riesling, Chardonnay, Cabernet Sauvignon, Pinot Noir, Gewurztraminer, Sauvignon Blanc, and Muscat.
Fresh and fully ripened wine grapes are preferred as raw material for wine making. The winemaker first decides which grapes to use and when to harvest them. Because of the effect upon grape composition, proper timing of the harvest is of great importance. Premature harvesting results in thin, low-alcohol wines; very late harvesting may yield high-alcohol, low-acid wines.
This decision is often made by measuring the amount of sugar in the grapes to determine ripeness. Also considered is the grape's acid content, flavor, and aroma. When the time is right, the grapes are usually harvested by hand and taken to the winery for processing. The mechanical harvesting systems, based on shaking the berries from the clusters or on breaking the stems, are widely used in California, Australia, France, and elsewhere. In some years, favorable conditions combine to produce a grape harvest (often referred to as a vintage) of especially high quality and those vintage years are considered superior.
In modern mechanized wine production, a machine called a crusher breaks the grape berries and removes them from their stems. Amazingly enough, this is a very gentle process and the stems that come out of the machine look as though each grape must have been removed by hand. The machine then crushes the grapes, skins, pulp, juice, seeds and all and the result is called must. Ancient methods of crushing with the feet or treading with shoes are rare.
Separating the Juice
The length of contact between the skin and the juice influences the color of red and blush wines and affects the taste of all wines. To make white wine, winemakers separate the skins and pulp from the juice immediately after crushing and before it enters the tank or barrel for fermentation. For red wine, the seeds and skins go into the fermentation tank with the juice.
The process of alcoholic fermentation requires careful control for the production of high quality wines. Fermentation is the chemical change in which yeast converts the natural grape sugars into alcohol. Some yeast grows naturally on the skins of grapes and many European wine makers allow this yeast to conduct the fermentation. The winemakers in most other countries, including the United States, add selected yeasts to the must to begin fermentation. Carbon dioxide gas is a by-product of the fermentation process and is released as bubbles. The yeast also produces various other by-products which may add to the flavor and aroma of the wine. Saccharomyces yeast is preferred because of its efficiency in converting sugar to alcohol and because it is less sensitive to the inhibiting effect of alcohol.
Contact with air must be restricted to prevent oxidation during fermentation.
Temperature control during alcoholic fermentation is necessary to (1) facilitate yeast growth, (2) extract flavors and colors from the skins, (3) permit buildup of desirable by-products, and (4) prevent excessive rise in temperature, killing the yeast cells. Fermentation releases heat, so most wineries refrigerate the must (unfermented juices) to keep its temperature constant. White wine is generally kept a good 20 degrees or so cooler than red wine. Fermentation temperature affects the rate of fermentation, the aroma, and the formation of yeast by-products. It also determines the rate at which the color and flavor of the grape skins transfer into the wine. Red wine ferments in 4-6 days while white wine takes 12-18 days.
Many red wines, and some white will then undergo a second fermentation by bacteria called malolactic fermentation which lowers the acid content.
A new wine appears cloudy after fermentation and winemakers clarify the wine by removing particles of grape skin, yeast and other unwanted substances either by filtration, allowing them to settle naturally, or separating them from the wine using a centrifuge. The wine maker may further clarify the wine by the addition of certain solutions that reduce the content of unstable or unpleasant components.
Once the wine is fermented and clarified, it is time for the aging process to begin and the wine is transferred into wooden barrels or stainless steel tanks where it will remain until bottling. Many wines improve in quality during barrel and bottle storage. The temperature and humidity conditions, the length of storage time and the size and age of the barrel all influence the aging process and thus the final character of the wine.
The wine is bottled after some aging, and will continue to age slowly in the bottle. Sterile new bottles are used in the United States. Elsewhere, bottles may be reused after they are thoroughly cleaned and sterilized. The bottle shape and color are dictated by custom and cost.
Most of the white wines are ready to drink almost immediately after bottling, but many reds need a few more years to soften their harsher flavors and allow more pleasurable flavors to evolve. Red wine is usually bulk aged for a year, and then bottle aged for extended years. However, generally, most red wines should not be aged beyond 10 years. Although you may then end up with an extraordinary wine, you may also end up with a costly bottle of vinegar.
Fortified wines, for instance port or sherry, are made by adding brandy to the fermenting must, and usually results in a sweet wine. Drier fortified wines add brandy near the end of the fermentation process. For sparkling wines, a second fermentation is used. In the traditional "Methode Champenoise" process (a special way of getting the sparkle in the wine) under-ripe grapes are made into still wines and bottled. Sugar and yeast is then added to the wine, causing fermentation and its by-product - carbon dioxide. The carbon dioxide is trapped in the wine in the form of tiny bubbles, creating sparkling wine.
When Is Wine Ready To Drink
These are long discussions without clear answers. Wines gain complexity and lose fruitiness as they age. But, the truth is that different people prefer wines at varying stages of maturity, and different bottles of the same wine may mature at different rates. Trying to find the "perfect" match between taste and development is like trying to hit two moving targets with one shot. In general, more expensive wines are usually designed to become better with age. Most inexpensive wines do not benefit from aging.
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