Wine Culture and Information - Volume 13
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  Corkscrew Issue 19, May 2004   
Vine and GrapeVine and Grape  Contents 
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Vine and Grape

The small fruit of the vine is the fundamental element from which begins the amazing adventure of wine making, small colored berries producing the juice which originates endless styles of wine

 There are no sure and reliable evidences about the exact way it was possible to discover wine, and in particular, to the discovery of the events that from a small berry of grape, rich of sweet juice, it was possible to make a beverage very different from the original matter. The many cultures of the countries where wine is historically produced, believe the discovery of the beverage of Bacchus was because of a kind gift presented to the human kind by benevolent gods both for their joy and for their surviving. No matter the real origins of this millenary beverage, mythological or result of simple and revolutionary natural events, or even by the result of the accidental uncaring reserved to grape juice that with time got transformed because of fermentation, wine has always had a relevant place in the culture of the people in which it was present. It is amazing to know that everything originates by a “modest” and certainly tenacious plant - the vine - whose fruits, disposed in colored bunches, are rich of a sweet and properly acid juice capable of offering, after a series of extraordinary chemical modifications, a beverage of absolute value and importance: wine.

 Vine - the plant which bears the grape - belongs to the botanical family of Vitaceae, and of all the tens of members of this family, the genre vitis is the one having the highest importance for the production of wine. The most important of them is vitis vinifera - from which is made more than 99% of the wine produced in the world - and whose origins are from Europe and Central Eastern Asia. It is believed that the number of vitis vinifera varieties known all over the world is of some thousands. Vitis vinifera - despite it is the most common genre - it is not the only genre used for the production of wine. The other most common species suitable for the production of wine - although producing truly different results from the ones obtained by vitis vinifera - are vitis labrusca, vitis riparia and vitis rotundifolia, all originating from the American continent. These species however have a strategical and fundamental importance for the production of wine because they are, as opposed to vitis vinifera, resistant to the attacks of the devastating phylloxera. For this reason plants of vitis vinifera are grafted on rootstocks of American species - in particular vitis riparia - in order to contrast the devastating effects of this parasite.

 

The Seasons of Vine

 The vine is a very robust and tenacious plant, with remarkable capacities of adaptation in many environmental and climatic conditions. Thanks to its adaptation capacities, the vine has widely spread in many countries of the world, in particular in those places with a tempered climate. Europe certainly is the continent where viticulture practiced in the aim of making wine is mainly present, followed by America, Africa, Oceania and then Asia. The adaptability of vine is pretty remarkable, in fact in certain places with cold climate - such as Champagne in France or Mosel and Rein in Germany - it is capable of surviving to strong frosts. Another “secret” which allows the vine to survive in “extreme” environmental and climatic conditions, in places that would be hostile to other plants, is represented by the tenacity and the high development of its roots. Vine's roots can reach a length of even six meters (about 20 feet) digging the soil and searching for precious water and nutrients necessary for its development and surviving.


View of a vineyard
View of a vineyard

 The abundant quantity of leaves of the vine also contributes to the development and the surviving of this plant. Thanks to them the vine can do its functions of photosynthesis and to transform water and carbon dioxide naturally present in the air, by means of the light energy of the sun, into sugar, necessary both to the feeding of the plant and to the production of alcohol in wine. Hilly places generally represent the ideal environment for the cultivation of vine, both for the better drainage of water and for the sloping of soils which ensure a better incidence angle for sun rays and therefore a constant supplying of heat. The preference of cultivating vine in hills was already common and known since the very beginning of wine making, a practice witnessed also by the famous Virgil's phrase Bacchus amat collis (Bacchus loves hills). Hills also offer another advantage: the night cool air flows present in the bottom of valleys are warmed during the daytime and then go up to the slopes of hills and warm vineyards.

 Just like for every living organism, the biological and productive phases of the vine are regulated by events and phenomena which are repeated every year and that culminate with the bearing of fruits - the grape - that will be subsequently harvested. The productivity of the vine, as well as the quality of its fruits, obey to a biological cycle which evolves year after year. In the first three years of life, considered as its young age, vine is practically unproductive and it will be after this period of time the plant will enter an increasing productive phase. After the fourth or fifth year of age, the vine will begin to bear fruits suitable for the production of wine, however it will be in the age from twelve and twentyfive years that the highest quantitative production will be recorded. After twentyfive years the vine will progressively begin to diminish its productivity and harvests will therefore be lesser and lesser. For this reason some producers decide to replace their vineyards more than twentyfive years old with younger vines. Whether it is true that after this period vine begins to bear a lesser quantity of grape, it is also true that quality is considerably increased. The use of old vines forces a reduced production of grape, and therefore more management costs, with the result of a higher quality in wines and this is often a precise productive choice of many wineries.

 The many vegetative and productive phases of the vine are repeated every year and in every season take place specific events that will culminates with the ripening of the grape and therefore to the beginning of wine production. After harvesting and with the arrive of autumn, vine will have absorbed and stored a sufficient quantity of carbohydrates in the trunk and in leaves necessary to face the resting phase in which the plant survive while waiting for springtime and therefore resuming its vegetative cycle. The resuming of the vegetative activity is preceded by the so called “weeping of the vine” which signals the lymph - essential for the development of new sprouts - started to circulate again. The sprouting of buds usually takes place between March and April, whereas in the austral hemisphere takes place in September. The sprouting is also cause of the development of the leaves which will allow the resuming of photosynthesis and therefore the production of sugar and nutrients for the plant. After about 45-90 days - that in the boreal hemisphere takes place in the half of May and the end of June and in the austral hemisphere in the beginning of November and the half of December - begins the phase of blossoming.


 

 During this phase - which in the vine is pretty rapid - flowers blossom and free pollen that, by falling on the stigmas, allows fecundation. Not always fecundation is perfect and these cases in the berries of the grape there will be no development of pips, that is the seeds of the plant. After the fecundation berries will start to develop as a consequence of the increasing of the flower's ovary size. Flowers which was not fecundated dries and falls from the plant. In this phase the bunch begins to get its typical look and it will get developed in a pretty quick time: it is the beginning of the development of berries. In August - in the austral hemisphere in January - begins the ripening of berries which change their color - a phase called veraison - and from a green color they change to a green-yellow color for white berried grapes or red-blue for red berried grapes. Veraison takes place when inside the berry there is an increasing of a determined concentration of sugar and tartaric acid whereas tannins begins to hydrolyze. The beginning of veraison depends both by the climate and by the variety and signals the beginning of the ripening of berries.

 During the ripening phase, the berries grows up in size because of the increasing quantity of sugar, water and other components (including polyphenols, mineral elements and aminoacids) whereas acidity will progressively begins to diminish, the skins gets less thick and the pulp softer. This phase is pretty critical for the production of wine because it must be decided the right moment at which grape is ripe and therefore proceeding with the harvest. For this reason it is periodically measured - frequently every day - the quantity of sugar and acid in the juice - and for red berried grapes the level of polyphenols ripeness is measured as well - in order to decide the exact moment in which starting the harvest. Deciding the right quantity of sugar and acid in the grape is fundamental according to the style of wine to be made and according to the variety of grape. High quantities of sugar - condition which is ensured by ripeness and allows a higher production of alcohol - mean a lower quantity of acid and therefore a flabby wine. On the other hand, high quantities of acid - a condition ensured by underripe or not perfectly ripe grapes - allow the production of more crisp wines while having a lesser quantity of sugar and therefore a lower production of alcohol. After harvesting, the vine enters the resting phase again and the cycle repeats.

 

Composition of a Grape Berry

 The grape is the fruit of the vine and it develops in bunches as a consequence of the fecundation of flowers. The grape berry is fixed to the stem and this part, because of the substances contained in it and that would negatively affect the taste of wine, is eliminated before pressing the grape by means of a process called destemming. The grape berry's appearance is usually round or stretched and it is covered by the skin whose thickness varies according to each variety and it can also represent 10% of its weight. The skin is rich in pectin, cellulose, aromatic substances and polyphenolic components - generally defined as tannins - responsible for the color in red wines, as well as for the structure and astringency. Both aromatic substances and polyphenols contained in the skin can be extracted by means of maceration in the must - the grape juice produced by pressing - and the quantity of extraction is proportional to the time of maceration. These polyphenols are soluble in alcohol - which is produced during the fermentation of must - and in a lesser extent, in water as well. For this reason the skins of red berried grapes are being macerated in the must with the explicit purpose of giving color to red wines and to extract aromas and tannins.

 Grape juice, both of white berried species and red berried species, has a greenish yellow color, therefore in case the maceration of the skin in the must is completely avoided, it is possible to obtain white wines with red grapes, such as in case of many classic method sparkling wines produced with Pinot Noir. Likewise, a short maceration of the skins - usually of few hours - can be used for the production of rose wines with red berried grapes. It should be however considered that the quantity of colorant substances contained in the skin of red berries grapes is different according to each variety and therefore every red grape will have proper colorant capacities and qualities. The skin of the grape is covered by a waxy like substance - which can be easily observed in red berried grapes for its whitish color - on which can also be present yeasts, naturally present in the air, that will start alcoholic fermentation as they will get in contact with the juice. The pulp of the grape berry is rich in water, sugar - present in variable quantities between 15% and 25% of the total matter - acid, pectin, mineral elements, vitamins and nitrogenous substances. The concentration of these elements varies according to the inside zone of the berry.


Cross section of a grape berry
Cross section of a grape berry

 By observing a cross section of a grape berry, they can be individuated three distinct zones in which the pulp has different consistencies and concentrations of substances whose quantity varies according to the ripeness level (Figure ). The area which is just under the skin - the external part - is rich in tannins and aromatic substances, contains about 30% of sugar and about 20% of acids. In the middle part it is found the highest concentration of sugar - about 40% - and about 30% of acids. In the inner part are found pips and here is also found the highest concentration of acids - about 50% - and about 30% of sugar. Pips are rich in polyphenols - of pretty astringent nature - that will be extracted during the pressing of berries and that will get mixed to the must. In pips are also found fatty substances that can be used for the production of oil.

 As a consequence of the pressing of the berries it is obtained the must which is made of many liquid and solid substances present in the many zones of the pulp and of the skin. Water is the fundamental element and represent about 70-80% of the must, sugar for 15-30%, acids for 0.5-1.5% and other substances such as minerals, vitamins, polyphenols, aromatic components, pectin, nitrogenous substances, enzymes and microorganisms (yeasts, bacteria and molds). The main sugars of the must are fructose and glucose. Every gram of sugar contained in the must produces - because of the fermentation - about 0.67 grams of alcohol and therefore by measuring the quantity of sugar in the must it is possible to assess the alcoholic percentage in the wine at the end of fermentation. For example, in case a liter of must contains 20 grams of sugar, the alcoholic percentage in the wine will be of about 13.4% (20 × 0.67 = 13.4). The most important acids present in the must are tartaric acid, malic acid and citric acid. Tartaric acid - typical in the grape - certainly is the most important one and it is present in the highest percentage in relation to the others. Polyphenols - usually called tannins and present in variable quantities and according to many factors including climate, environment, grape variety and wine making practices - are responsible for the taste of wine as well as for the color and astringency in red wines. Among the most important polyphenols components are mentioned anthocyanins, responsible for the color in red wines, and flavones, which play an important role in the color of white wines.

 




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  Corkscrew Issue 19, May 2004   
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