The color of the wines does not depend on the color of the grapes, it might seem strange to say but it is just like that. We start from this statement, more or less strong, to understand what is the technology behind the production of the white wine.
The wine is called white (bianco in Italian) when it does not contain the polyphenols and the colouring substances naturally present on the grapes. This is obtained separating the marcs from the must immediately after the pressing phase, in order to avoid the maceration phase, which is instead very important in rosé and red wines.
In this way, white wine can be produced both from black grapes and white grapes, as the only matter that will be fermented is the grapes pulp. The whole process is called white vinification (vinificazione in bianco in Italian)
Phases of the white vinification
White vinification is a process composed of a series of mechanical and chemical transformations that starts from the bunch of grapes, as it is on the plant, and reaches the bottle of wine, completed with a label.
To simplify in minimum terms, you can imagine three macro-phases of the transformation during which the material, with the skilful intervention of the wine maker, loses its original appearance and acquires new forms and characteristics: from grape to must, from must to wine.
Maceration is the process that gives the wine its typical color: during this phase the must (that is the future wine) is in close contact with the marcs that, depending on the vine variety, releases a certain quantity of colouring substances.
The white wines are different from the others, rosé and red ones, exactly for the lack of this phase: in white vinification there is no maceration.
Once the grapes are brought into the vinery, the soft pressing is carried out in a short time, a more delicate mechanical operation of crushing and destemming used in red vinification. This, performed with a special hydraulic press that allows the immediate separation between the must and the solid parts (marcs and stalks), in fact allows to compress the grapes without breaking the grape seeds.
In white wine it is essential that the maceration does not take place, i.e. that the marcs does not come into contact with the must. But there is another type of maceration, called skin maceration, which replace in a sense the traditional one.
This practice, performed at the discretion of the winemaker, allows a certain extraction of substances contained in the skin that will enrich the tasting profile of the wine. It is usually used on a healthy and ripe grapes for the production of wines destined for ageing.
The destemmed grapes are placed up to a maximum of 8-10 hours in a saturated tank of carbon dioxide which prevents oxidation. The temperature of the container is kept between 5 and 15 °C - 41 and 59 °F - to avoid uncontrolled fermentation processes. Under these conditions, the transfer of precious olfactory and flavour substances from the skin to the must takes place without excessive transfer of polyphenolic substances with a colouring and astringent effect.
Treatments and corrections of the must
The must that comes out from the crushing is a turbid, dense and unstable product. Before procediing with the subsequent fermentation phase, it is possible to intervene with appropriate treatments and corrections.
The treatments are intended to stabilize or enhance some of its characteristtics, without removing or adding anything to the liquid. Among these, clarification and filtration, conducted alone or in combination, are ancient oenological practices that, recently added to the cooling, allow to obtain a greater degree of clarity, without depriving the must of all those substances that will give a certain characterization to the final product.
One of the most known but also controversial treatments is sulfitation, that is the practice that involves the introduction of sulfur dioxide. On the one hand it allows to reduce the instability of the wine, thus avoiding its possible transformations, such as sedimentation, darkening, colour changing (oxidase), mutation of the orgalolectic characteristics (oxidation) and uncontrolled fermentation; on the other hand, it is unpopular bacause, after certain doses, it is harmful.
Corrections, unlike the treatments, compensate for any deficiencies of acids or sugar, often due to adverse climatic trends. They can be addictive or subtractive.
The addiction of concentrated must or rectified concentrated must (in fact a solution of water and grape sugar) consents to increase the sugar content of the original must, without varying its sensorial profile. A blending with a less sweet must, on the other hand, reduces the sugar content.
The addition of tartaric acid into a must, which is particularly poor in acids, can guarantee a certain freshness to the final product, while the addition of calcium carbonate or potassium bicarbonate allows to smooth the sharp characteristics of grapes produced in cold lands or not particularly ripe.
Fermentation (without maceration)
Alcoholic fermentation is the key of winemaking. At this point of the process, after preparatory stages, the must and the marcs are placed inside a large inert container, usually is steel or fiberglass (not wood), where they are added with selected yeast. Thus begins the fermentation process with maceration during which, essentially, the yeast "operates" so that the sugar is transformed into alcohol, carbon dioxide and heat.
The fermentation is carried out with a temperature lower than the one of the red vinification, between 18 and 20°C - 64 and 68°F - by means of a special cooling system.
At the end of the fermentation the wine is racked, i.e. the all the liquid if poured into another container.
Malolactic fermentation, as realized by the name, is a process that involves two acids, malic acid and lactic acid, but it is not always used in the vinification process. In fact it is an option that the wine maker has in order to characterize more the wine in terms of softnesses, going to smooth too high acidities.
The malic acid is one of the key components that guarantee the acidity to the wine. It comes directly from the grapes and its quantity is related, in addition to the grapes variety, to the weather trend and to the fruit ripening process. Within a certain threshold, it has not unpleasant effects on the flavour profile but, in high concentrations, is produces a bitter and sour taste, similar to the one experienced by eating an immature apple.
The malolactic fermentation activates automatically after alcoholic fermentation (provided that the temperature is between 18 and 20°C - 64 and 68°F - the alcohol content is below 15% and the pH s higher than 4) but it can be further stimulated by introducing certain bacteria into the wine. The main product of the transformation is the lactic acid. This one is less pungent and sour than the malic, so the wine is softer and with more complex tasting profiles.
For this ability to smooth the acidity notes, this kind of transformation is very much used in wines destinated for ageing, both red and white ones. Is is less used, or even avoided, in young wines that must keep certain characteristics of freshness and fragrance.
After racking the wine is still immature and needs to rest for a certain time.
For most of the white wines on the market, the ageing takes place inside steel or fiberglass containers. In this way, fresh and fruity wines are obtained which should be consumed still young.
If you want to obtain a more complex wine, the wine is aged inside wooden barrels, where it acquires additional aromatic substances.
After racking or the eventual malolactic fermentation the wine, as in the case of the red fermentation, is still immature. For most white wines on the market, the ageing usually takes place in steel or fiberglass containers for a few months. This process allows to obtain young wines, fresh in scents and flavour.
The fining is the period in which the wine undergoes a real transformation: it improves its characteristics, stimulating the birth of new scents. In white wines it lasts a few months, but it depends on the type of the grapes and on the quality of the implemented vinification process.