first stage http://encyclopedia2.thefreedictionary.com/Wine-Making
Wine-making is divided into an initial stage and secondary stage.
The initial stage, including the processing of the grapes and the preparation of the wine materials, is alcohol fermentation. A pure yeast culture (2-3 percent) is introduced into the must for that purpose. Fermentation can also occur with the natural yeasts that are contained in the grape itself. As a result of fermenting the sugar in the grape must, ethyl alcohol and carbon dioxide are formed. The must is brewed until the sugar is completely fermented. During fermentation the must is kept at an optimal temperature (14°-18° C). When the must is fermented in a continuous-action unit the productivity of the equipment increases 30 percent, labor input is cut 50 percent, the diluted yeast preparation is introduced once at the start of the wine-making season, the maintenance of production parameters at the optimal level is easier, and higher wine quality is ensured. When fermentation of the wine has ended—that is, when the discharge of carbonate gas has stopped and the wine has cleared—the wine is poured off from the yeast sediment and pumped into a clean tank.
secondary stage http://encyclopedia2.thefreedictionary.com/Wine-Making
The secondary stage includes the processing and aging of the wine material to give it its characteristic taste, bouquet, aroma, and stability. Underground storage areas or above ground buildings with air conditioning are highly effective for aging and storing wine. The wines are stored in oak barrels and casks, as well as in enameled tanks. Aging is processing for the purposes of obtaining wines of a definite type and of achieving stability. Operations such as adding, racking, clarification, filtration, fining, blending, cooling, and pasteurization are done at this time.Wine is added to make up for wine lost because of evaporation and to protect it against souring.
Wine manufacturing in Napa Valley (www.melcarson.com/wp-content/uploads/2010/10/wine-making-napa-16.jpg)
Reference: “Wine-Making.” TheFreeDictionary.com. N.p., n.d. Web. 28 Apr. 2015.