White Winemaking

The future will be to manage the extraction of precusors of aromas from the grape during the skin contact steps of white and red winemakings... 

Consider the problem facing a winemaker who has bottled a white wine, for example, which he believes will develop a good bouquet and be organoleptically acceptable six months later and will continue to improve for two additional years after that the fruitiness and bouquet will probably diminish rapidly so that within the third year, the wine will be overaged. The winemaker wants the wine to be drunk at or near its peak, in this case 18-30 months after bottling. Since that precision is impractical commercially, he determines from the sales department that... 

Dry white table wines differ from red table wines in characteristics other than color. They contain lower concentrations of the puckery and astringent tannins. They usually have a higher acid content which makes them somewhat lighter in body and fresher on the palate. Dry white wines also are usually simpler in their aroma in contrast to the complicated aroma and bouquet that can develop in a red table wine. While it is possible to make white table wines from red-skinned varieties, for the home winemaker this task is very difficult because it is almost impossible to remove all traces of the pigment-containing skins from the juice quickly enough to prevent some reddish or amber color from developing. 

White wines are normally fermented in containers that can be partially closed so that the surface of the fermenting wine is protected from the air by a blanket of carbon dioxide. For the home winemaker, 5-gallon carboys serve admirably. An hour or so after adding S02, one adds approximately 3% of an actively fermenting pure-culture starter yeast. 

In terms of color, red ports vary from deep purple to light gold (Fig. 5.10). Designations of full, medium full or ruby, medium tawny, tawny, and light tawny are used to define each type. White ports come in various shades (pale yellow, straw, and golden white), all intimately related to the winemaking technique used. 

The North Coast area of California is well known for the excellence of its white table wines. Climate factors, primarily the cooling effects of the bays and ocean, provide optimum conditions for production of grapes and wines of distinctive character and proper balance. A history of wine production in the area has provided time for development and improvement of viticultural and vinification techniques. Recent substantial increase in demand for varietal white table wines has encouraged further development of new and improved winemaking techniques and has resulted in increased plantings of white wine grapes. 

Q. alba (American oak) is used less frequently with white wines than red wines, and it is widely acknowledged that American oak has a distinctively different effect on wines chemical and sensory properties than does European oak. The strong and distinctive oakiness of Q. alba can overwhelm the varietal character of a white wine, if not used with care. Some winemakers combine use of both European and American oak in their oak-aging practices. 

Fining is a winemaking technique used to enhance sensory or clarity properties of the wines. Common fining agents used with North Coast white wines are bentonite (a clay), casein (milk protein), gelatin (animal protein),... 

A variety of practices are used in North Coast white winemaking to protect wines from the undesirable effects of oxidation. Proper use of S02 is an essential part of North Coast winemaking because it is an effective antioxidant and results in less polyphenoloxidase activity. S02 is added as soon as the grapes are crushed, at levels of 50-100 mg/L, and maintained at 25-30 mg/L free S02 after fermentation, until bottling. At bottling, most white wines have 30-35 mg/L free S02. 

North Coast winemaking techniques are being developed and modified by a progressive, aggressive, dynamic industry, interested in consistent improvement of white wine quality, and aimed at world-wide recognition and enjoyment of that quality. 

In California, winemakers do not want white wine to undergo the bacterial malo-lactic fermentation that changes malic acid to lactic acid. The loss of acidity, increased pH, and freshness is considered to be detrimental. On the other hand, malo-lactic fermentation of red wines before secondary fermentation is common. This is because red wines undergo malo-lactic fermentation more easily than do whites and they generally are aged longer before use. The producers do not want a malo-lactic fermentation in the bottle. 

Also, today in the Interior Valley, the must may be pumped directly to juice predrainers (Figure 2), which rapidly separate the juice, primarily from white grapes. The drained pomace is conveyed to continuous presses (Figure 6) for further pressing of the remainder of the juice. In this type of separation, many winemakers claim that more suspended solids (pulp and skin material) pass through draining screens, usually with 3/32-inch-diameter perforations with the various juice fraction. In some screen systems, it is possible to get up to 8-10 percent suspended solids by volume. 

White Table Wines. The free-run grape juice is the most important fraction used in white table wine production. To the juice will be added S02 at 75-150 mg/L, depending on the grape condition. Most winemakers prefer to add not over 100 mg/L. The primary purpose of the S02 is to prevent browning and retard growth of wild yeasts and other undesirable microorganisms. 

As noted earlier, white wine grape varieties generally are crushed at a lower °Brix range than red varieties. Winemakers prefer to ensure a higher total acid. 

By careful processing, the winemaker brings the wine to a finished state. The white and rose wines will have maintained their bouquet and aroma and flavors. The red table wines will have been softened by careful fining with such agents as gelatin and PVPP, will be fruity, and will have distinctive varietal aromas and flavors with minimal astringency. 

The same chemical principles presented by the speakers on red (p. 59) and white table wine (p. 29) production are applicable to table wine production in the Interior Valley. Differences in the size of the winery operations and grape maturity are attributable to regional climatic conditions. With modern viticultural practices, the grapes grown for winemaking in this interior region now produce quality wines and they also comprise the largest volume of table wines produced in California. 

The fluidity of the plasmatic membrane is considerably affected by temperature (Rodriguez et al. 2007) and ethanol concentration (Jones and Greenfield 1987). Therefore, during alcoholic fervaeniaiionSaccharomyces cerevisiae must adapt the fluidity of the membrane to the changing environmental conditions. It should be emphasized that the temperature of fermentation and aeration depend on the type of winemaking. Usually, white wines are made at low temperatures (14-18 °C) and without aeration to conserve aromas whereas red wines are fermented at relatively high temperatures (28-30 °C) and are aerated in order to enhance colour extraction. 

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