White wine is obtained from soft pressing of grapes white or red.
Following the immediate removal of the same, particularly if colored, or for some wines of greater value, a short maceration, in order to obtain a fruit wine with a more or less rich color (curious that white wines are defined as such when, in reality they are yellow), more or less structured, more or less long-lived.
For some white wines of significant workmanship, it is possible to make short macerations on the skins in order to enrich the wine with phenolic substances since the more pigments there are, the healthier the wine (because it contains greater quantities of antioxidants and risks less any alterations caused by oxygen).
Once the white vinification is completed, generally triggered by the addition of selected yeasts, the juice obtained by pressing the grapes is immediately collected in steel containers (to obtain a wine in which primary aromas prevail), or in wooden barrels (if a more articulate and capacious white wine is preferred). White wine.
But let's go step by step: once crushed and pressed, the grapes are brought to the fermentation tanks, where the must has some compounds which, to varying degrees, we will still find in white wine; while others we will find them completely transformed such as, for example, sugars that are totally destroyed during fermentation, to produce dry wines.
There are two grape sugars: glucose and fructose, with a sweeter taste. They make up the 15-25% of the berry components.
In the must we then have the organic acids of the grape, in quantities slightly higher than those which we will then find in the finished wine: in fact the tartaric acid will partially precipitate, thanks to the cold stabilization of the wine and the malic acid, in the case of white wines , will decrease in fermentation of 20-30%, by the yeasts.
Then we have the phenolic compounds, particularly abundant in musts from very ripe grapes and in vintages with great insolation: they are leucoantocians, catechins and tannins. Chlorophyll, the most common pigment in the plant world, is also found in some white wines and is particularly visible in white wines from slightly unripe grapes, therefore harvested in advance or in unfavorable years. Finally, pectins, mucilage, vitamins, aromatic substances, etc. are present in the must.
All this in addition to the quantitatively most important component of the must, namely water. From the characteristics of the must it will be possible to guess what the characteristics of the wine obtained from it will be.
Alcoholic fermentation consists in the transformation of the sugars present in the must into ethyl alcohol plus carbon dioxide. The future white wine will soon become such thanks to the activation of alcoholic fermentation: the process by which the sugars present in the must are transformed into ethyl alcohol and carbon dioxide. Sugars = Ethyl alcohol + Carbon dioxide.
The absolute protagonists of this complex transformation are the yeasts which are found in nature on the grape skin and which, upon pressing, end up in the must, thus triggering the fermentation of the sugars contained in it. By attacking the sugars present in the must (glucose and fructose), they transform them into ethyl alcohol and carbon dioxide, in addition to a series of secondary products (so called because they are produced in smaller quantities) such as glycerin (from 2 to 10 g / lt.) , acetic acid (from 0.2 to 0.4 g / lt. in healthy wines), succinic acid (from 0.6 to 1 g / lt.) and others in even lower quantities, in the order of mg / lt (acetic aldehyde, higher alcohols, etc ...).
In a freshly pressed must you can find different kinds and species of yeasts, some good fermenters, others less: fortunately, normally the former take over the others. However, in order to avoid further risks, so called "selected" yeasts exist on the market, that is, chosen after many selections, for their peculiar fermentative quality ..).
It is very important to control the temperature during the fermentation phase because it allows a regular course and a better organoleptic quality of the finished product. There are steel containers ideal to prevent the optimum temperature from being exceeded between 18-22 ° C in white wines.
The vinification in white, contrary to what one might think, is used not only for the production of white wines, but also for the production of rosé wines from very colorful grapes. The grapes delivered to the cellar can follow two different processes: in the first, the more traditional one, the grapes are eventually de-stemmed (or placed directly in the press) and pressed; in the second, a crushing destemmer is carried out, then a cryomaceration, to enhance the aromatic set of the must and, subsequently, the pressing.
At this point the two techniques are reunited continuing in the following way:
• Press must - It is the last portion of must obtained by pressing; the richest in polyphenols and extract which will give rise to a slightly long-lived wine with less ample and fruity aromas.
• marcs - They are sent to the distillery and then fermented in a saturated container, previously, with carbon dioxide or in hermetically sealed bags. After fermentation they can be distilled for the production of grappa.
• Flower must - The first portion of must drained from the press, before it reaches relatively high pressures (1 / 1.5 atm).
• Refrigeration - It is carried out in order to avoid that the must obtained starts fermentation before its clarification, necessary so that the white wine does not acquire bad smells.
• Clarification - Once sulphitation has been carried out, it is necessary to make the must clear. For this purpose, protein-based clarifiers such as gelatin and casein are used. These compounds, reacting with each other, form a floccule which, absorbing the suspended particles, deposit on the bottom, leaving the must practically clear.
• racking - After 24 or 48 hours from clarification, the must can be decanted, or filtered, in order to separate the bottoms created by the clear must. At this point any corrections will be made (acidity, sugar level, nitrogenous substances and vitamin content) and the inoculation of selected yeasts (almost indispensable in this type of winemaking where, the must has been clarified, and therefore also depleted of yeasts naturally contained).
Fermentation will be controlled at a temperature around 20 ° C .; once this has been completed, you can choose whether to transfer it to eliminate the bottom created (mainly consisting of dead yeast cells) or to prolong the permanence of the wine on it in order to characterize the product with a slight hint of yeast and give greater fullness taste. Malo-lactic fermentation is almost always prevented in white wines because of the negative effects it produces on wine.
The white wine is now ready to be bottled unless, by virtue of a great vintage and a preventive choice, we do not intend to refine it for a short period in wood in order to enrich its organoleptic characteristics thanks to a micro-oxygenation that the wood entails.
Compared to red wine, white wine is more difficult to connote historically. Its discovery, as often happens, was the result of pure randomness and the archaeological finds inherent in the discovery of grapes or fermented grape juice are many. The oldest even date back to the Neolithic period but there is no known knowledge if white wine or red wine was consumed, at least until the Greeks who normally consumed white wine, very alcoholic and sweet but there is no certain information regarding the grape variety, the area of origin and winemaking techniques. It seems that some white wines were made from black grapes, separating the skins from the must before fermentation.
Piero Canopoli and Giuliana Dalla Longa