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White vinification

White vinification


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Winemaking

Wine production does not derive only from the alcoholic fermentation of musts or crushed grapes, but also from knowing how to extract the best part from the grape berry, i.e. the optimal quantity of substances that are decisive for the quality of the wine, limiting the diffusion of constituents that could alter the characteristics of the future wine. We will now go on to describe the processes for the vinification of white and red wines.

White vinification

Unlike red wines, which derive from an alcoholic fermentation in the presence of solid parts of the berry, white wines derive from the fermentation of only duva juice. The extraction and clarification of the must of white wines always precede alcoholic fermentation: the color of the wine does not therefore derive from the color of the grapes, but from the absence of maceration of the grapes mashed during the alcoholic phase. In any case, this does not mean that a certain maceration takes place, which takes place in the absence of alcohol, during the prefermentative phase, when the aforementioned extraction and clarification operations of the juice are carried out.

Collection criteria for white grapes

Since qualities such as the finesse, complexity and intensity of the varietal aroma are sought from a white wine, it is necessary to be able to maintain the aromatic profile that has matured in that year in that given territory until it is transferred to the cellar. It is therefore appropriate to maintain, first of all, a good health status of the grapes until harvest: in particular, particular attention must be paid, on the one hand, to the presence of gray mold (Botrytis cinerea), to which most of the white vines are very sensitive, given that a small quantity of botrytised grapes seriously compromises the quality of the wine obtained from it; on the other, in the presence of acid rot, which involves the formation of acetic acid in the affected berries / bunches, inevitably compromising the oenological characteristics of the grapes.
During the maturation phase of the grapes destined for the production of aromatic white wines, it is necessary to observe the aromas and their precursors as well as sugars and acidity: this is defined as "aromatic maturity". It is not easy to define the ideal aromatic composition of the grapes when ripe; in general, it can be said that luva goes from typically herbaceous and vegetable aromas, to fruity aromas, more or less stable at the end of maturation; it is up to the winegrower, based on the type of wine he wants to produce, to choose the ideal "aromatic" moment for the harvest.

The stages of white winemaking
As previously mentioned, the prefermentative operations, i.e. the processing of the grapes and the must, are crucial for the final quality of the product: during these phases, it is necessary to limit the losses of liquid, extract and clarify the juice, but at the same time, it must be favor the diffusion of some aromatic elements of the skins. A good extraction must also limit the phenomena of oxidation and the dissolution of the phenolic compounds of the skins, of the seeds and of the stalks. To achieve these goals it is advisable to follow the following guidelines:

  • exert low pressure on the harvest;
  • limit the mechanical actions that can offend the skins;
  • increase the pressure slowly and progressively;
  • use a juice extraction temperature of 20 ° C;
  • reduce the turning over of the marc to the minimum possible number;
  • protect the freshly extracted must from the air (and in particular from oxygen).

White winemaking scheme (source: images.slideplayer.it)

Destemming and pressing (extraction of the must)
After being transferred to the cellar, the grapes are de-stemmed and crushed; then the must is extracted, separating it from the solid phase (marc): extraction occurs by free draining or by light pressing of the marc. As mentioned above, for the qualitative improvement of the production we have gone to the use of "soft" machines, which allow to obtain a must with a low content of unwanted substances.

The cleaning of the must (defecation)
Defecation allows to reduce the content in coarse lees (peel fragments, earth etc.) before fermentation: thus the content in suspended solids is reduced, rich in polyphenolic substances and oxidizing enzymes. If necessary, a clarification can be carried out on the must, to remove further unwanted components: adjuvants such as potassium caseinate, gelatin, silicon oxide, egg albumin are used. The clarification of the must can be avoided if pectolytic enzymes are used, which increase the speed of clarification; in the absence of yeasts, it is possible to opt for physical clarification techniques, such as filtration, flotation, etc.

Protection must from oxidation
The protection of the must of white wines from oxidation is very important: it is necessary to avoid the loss of fruity aromas and browning of the color. Generally, at the must level, the most important oxidative activities are those carried out by oxidase enzymes (tyrosinase, which derives from grapes, and possibly laccase, which derives from moldy grapes -Botrytis cinerea-) for phenolic compounds. The cellarman can use different techniques to limit the oxidation of musts:

  • sulfitation, with antioxidant and antioxidant activity: it is the simplest and most effective method for controlling enzymatic oxidation activities; we recommend adding sulfur dioxide at once and homogenizing it quickly, avoiding the use of doses lower than 50 mg / l;
  • use of ascorbic acid, which has an antioxidant effect: this powerful reducing agent can be used instead of sulphitation, in order to avoid the extraction of phenolic compounds from the peel; has the drawback of not having antioxidant activity;
  • cooling of grapes and must: it is an extremely effective method in reducing the speed of oxidation reactions, just think that oxygen consumption is three times higher at 30 ° C compared to 12 ° C.

Conducting fermentation
Fermentation is the key process in the production of wine: in fact, the transformation of sugars into alcohol by yeasts takes place here; in particular, important secondary metabolites are also produced at this stage, necessary for the formation of the body of the wine.
Selected yeasts are mainly used (they are strains of Saccharomyces cerevisiae), which carry out a good fermentation even in conditions not particularly favorable to their metabolic activity and do not alter the organoleptic characteristics of the products. At this stage, it is useful to associate the use of fermentation activators with yeasts, such as thiamine, in order to have a ready fermentative activity that develops linearly regularly, without interruptions or abnormal fermentations. Generally, the temperatures to have a fermentation with good quality results are between 18 and 22 ° C; at these temperatures, moreover, the loss of aromatic compounds is limited. Once alcoholic fermentation is finished, generally, for white wines, malolactic fermentation is also not opted for: the wine is then stabilized, eliminating the yeasts by filtering and adding sulfur dioxide.

The refinement of white wine
The clarification of the wine is carried out through physical techniques, such as centrifugation and filtration; otherwise you can opt for aging on the fermentation lees, consisting of yeasts, mixed with tartaric acid salts, bacteria and cluster residues. The latter technique allows to have a reducing environment, which prevents wine oxidation; on the other hand, however, the reducing effect turns towards sulphured compounds, which give rise to considerable olfactory anomalies: it is therefore advisable to carry out periodic movements of the lees (1-2 times a week), so as to bring the lees back to the surface and favor a homogeneous distribution over the whole mass, ensuring a better release of the wall polysaccharides. The duration of this aging technique varies from 6 to 8 weeks.

Stabilizing and conservation treatments
The stabilizing treatments allow the wine to be kept for very long periods of time: physical treatments are certainly to be preferred. In general, low temperature treatments avoid tartaric precipitations; against protein precipitation, adjuvants such as bentonite are used; the microfiltration with membrane filters allows to have a chemical-physical and at the same time microbiological stability, using a suitable porosity of the membranes. Against oxidative phenomena, a stabilization of the product is obtained by reducing the contact with the air or keeping it in a protective atmosphere; optionally, sulfur dioxide can be used wisely. Finally, good wine storage is achieved at controlled temperature at 15 ° C, both before and after packaging.

packing
The packaging takes place in an aseptic environment: the bottling plants are capable of blowing inert gases inside the bottles, thus leaving the oxygen present; then the bottle is filled. Sulfur dioxide can also be added in this phase, always evaluating its content in the wine.

White wine (source: orvietosi.it)

Bibliography
- P. Ribéreau-Gayon-B. Donèche-D. Dubourdieu-A. Lonvaud, Treaty of Oenology 1, Edagricole 2007
- Plant Research and Production Center (CRPV), Viticulture and Biological Oenology, Edagricole, 2004


Video: Introduction To Winemaking (May 2022).