White wine is an alcoholic beverage made from alcoholic fermented grape must, obtained from different red and white grape varieties of Vitis vinifera genus. The most relevant white varieties worldwide are: Chardonnay indigenous from Burgundy region; Sauvignon Blanc indigenous from Loire and Bordeaux; Riesling is the queen variety in Germany; Viura in La Rioja and Penedés appellations; Grüner Veltliner in Austria; Gewürztraminer used in the highly scented wines of Alsace; and finally Albariño in Rías Baixas, Galicia.
Which are the morphological features of white grapes?
White grapes, unlike red ones, have yellow-greenish skin colour. Therefore white varieties do not have any veraison, that is, they do not change its tone from green into red-bluish. White grape pomace is rich in tannins and in flavones, accountable for the aromatic fractions that we will find later on in the wine. The inside seed hold tannins and oily substances. At last, flesh is rich in water, sugar and organic acids such as Tartaric, Malic and Succinic. Due to the sugar in the flesh, as well as the saccharomyces yeasts action, must becomes white wine.
White wine traditional elaboration process…
White wine production starts with the late summer harvest, from August to end September, depending on the wine growing area. Northern regions with colder and more moderate climate delay the ripening of the grapes. Once the sugar content and the desired acidity are reached, manual harvest is performed and berries in boxes are conveyed directly to winery.
The harvest received is unloaded in the pneumatic press either manually, every box, or through a conveyor belt. Usually during this stage, the whole production is introduced, without de-stemming, into the press, as the stems help berries not to get compacted so the must is well drained. Otherwise, harvest can be de-stemmed but this is completely unadvisable. The next step is the pressing, in several cycles, where pressure is increased over time. The must released during the pressing is conducted through a piston centrifuge pump into stainless steel tanks. The first fractions of the must are very rich in sugar content and aroma, while when pressing is higher, it gets more tannic and full of green substances.
Then next step is the cold static racking or débourbage, in stainless steel vats. Cold is applied and usually some fining agents are added, such as bentonite, casein or isinglass which help keeping apart solid deposits from musts through by sedimentation or filtration. Racking usually takes 24hours at less than 10ºC. After that time, must is transferred into fermentation deposits pumping carefully only the clear part of the vat, free from any residue.
Now the saccharomyces cerevisiae yeasts are seeded and the alcoholic fermentation, that will transform must in white wine, starts. During this process carbonic gas is emitted (CO2) as a by-product. Fermentation temperature is around 17ºC. In the course of this process, yeasts turn sugar into alcohol. Sometimes a racking to a new vat is carried out in the middle of the cycle, to aerate must-wine and stimulate fermentative kinetics, as the carbon dioxide generated by the yeasts creates an anaerobic environment not suitable for fermentation.
Once alcoholic fermentation is finished, white wine is conveyed into a new tank, refusing the low part with the thick lees, not used for the winemaking process. Malolactic fermentation can be accomplished now, but this is rarely performed, only with those wines of extreme acidity, typical of very cold regions and grape varieties with high malic acid content, as Champagne base white wines for instance. Without it, white wine goes through a resting and stabilisation period for the next 3 to 6 months. Now the option is for the winery to choose between a young white wine and an aged white wine, either in oak barrels or big wood vats.
Before bottling it, white wine goes through tartaric stabilization by refrigeration. Wine is cooled to 5 - 2ºC, which crystallizes tartaric acid in potassium bitartrate salts. This procedure is highly recommended to avoid salts dispersion in flocs when the wine is cooled after its sale. Then, wine is filtered through a porous surface with a frame filter or by diatom soils, in order to withhold any suspended matter such as bacteria or yeasts, and thus obtaining a biologically secure white wine.
Finally, white wine is bottled and ready for distribution in the market.