Grapes are made into wine in various ways. The three basic methods vary according to the color and type of wine desired:
In the case of white wines the juice or free-run must extracted from the pulp is separated from the skins (whether light or dark) before fermentation begins. Avoiding contact with the skins means the wine takes little or no color from them.
Rosé wines are made by leaving the juice on the skins of dark grapes briefly before or during the first part of the fermentation to extract the desired amount of color.
In the case of red wines, the juice is left on the skins of dark grapes during the fermentation to extract color, tannins and other substances - a process known as maceration.
In general the modem vinification process consists of the following stages:
De-stemming and crushing
The first stage is the separation of the grapes from their stems. The fruit is then crushed or rotated in cylinders under pressure, a process which breaks the skins and releases the juice or must.
Grape must has two main components, water and sugar. Yeasts multiply in this solution, consuming the sugars which they convert into alcohol, and producing carbon dioxide - the phenomenon we know as fermentation.
This complex bio-chemical process is expressed in the formula,
C6 H12 Q6 -> 2C2 H5 OH + 2CO2
It is characterized by violent bubbling and the generation of considerable heat. (For this reason fermentation is commonly known as bollitura, or boiling in Italy).
Drawing the Wine Off the Lees
When the alcoholic fermentation has converted the must into wine, it is allowed to settle so that the solid matter known as the lees collects at the bottom of the tank. The wine is then pumped into other containers to separate it from the lees.
Most red wines, as well as some whites, undergo an important secondary fermentation induced by bacteria rather than yeasts. The process is much gentler than alcoholic fermentation and often is only made apparent by the small bubbles which rise to the surface of the wine with a soft buzzing sound. This malolactic fermentation transforms sharp-flavored malic acid into softer lactic acid, lowering total acidity and giving wines rounder and fuller flavors.
Stabilizing and Aging
All wine needs at least some period of ageing to stabilize and mature it before it can be bottled. White wines, rosés and reds made to be drunk young are generally stored briefly in large tanks made of glass-lined cement, fiberglass or (best of all) stainless steel for between four and six months.
For wines of greater concentration and complexity, whether red or white, the ideal containers for ageing are small wooden barrels. Oak is the best material (there are drawbacks with other types of wood). The ageing process stabilizes and harmonizes wines, and allows the extraction from the barrel of "noble oak tannins" that enhance flavor. Barrels allow miniscule amounts of oxygen to enter the wine, favoring the development of complex secondary aromas, a process known as controlled oxidation. Wood ageing may last from around six months to three years.
Young wines are usually stabilized by refrigeration and filtering before bottling and are subsequently stored for one to three months before release. Wood-aged wines are often fined using egg whites or protein compounds and sometimes lightly filtered before they are bottled to remove any suspended particles. Bottled wines are usually stored horizontally for six months to a year before release. In the bottle, in the absence of oxygen, a process known as reduction begins during which the color, flavor and aroma of the wine evolve. Lt is in this phase that wines develop their bouquet.