Grapes development

Changes in monoterpene composition with grape development. Several studies have been conducted in which changes were recorded in the concentration of free monoterpenes in ripening grapes (11,38,64-66) However, most of these works were carried out before the presence of glycosidically bound or polyhydroxylated forms of monoterpenes in fruit were recognized. 

Fig. 10.8. Evolution of respiration during grape development (Harris et al 1971). , respiratory qnotient , respiratory intensity...

In spite of their chemical similarity, these two acids have very different metabolic pathways. Their evolution is not identical during grape development and maturation. The malic acid/tartaric acid proportion varies considerably according to the grape cultivar and the maturation conditions. 

At the beginning of grape development, the cell walls are primarily composed of cellulose. The veraison period is characterized by considerable pectin synthesis to such an extent that it becomes the majority polyoside in some varieties (Silacci... 

The biosynthetic pathways are active as early as the start of grape development. Consequently, the total phenolic compound concentration continues to increase during this period. The rapid increase in tannin concentration at the beginning of development, however, is followed by a slower accumulation during maturation. The biosynthesis may therefore be less active than the increase in berry volume. 

Consequently, the definition of maturity varies, depending on the objective. For example, the production of dry white wines requires grapes whose aromatic substances are at a maximal concentration and whose acidity is still sufficient. In certain situations, an early harvest can be interesting. Conversely, when the elaboration of a quality red wine is desired, grape development must be left to continue to obtain the most easily extractable phenolic compounds. 

Temperature is one of the most important parameters of grape maturation and one of the essential factors that triggers it. Temperature affects photo-synthetic activity, metabolism and migration intensity in the vine. Its action is not limited to the period of grape development. Its influence on bud bmst and flowering dates also has important indirect consequences on grape quality. It is easy to... 

Table 10.6. Recent phenological observations on red grape development and maturation (Merlot and Cabernet Sauvignon) in Bordeaux (France) (vintages classified in order of forwardness)...

As mentioned previonsly (see Section 10.4.6), a regnlar water snpply is needed for grape development and maturation. 

In conclusion, the primordial influence of soil has been recognized for a long time in the form of viticultural terroirs. The soil must create favorable conditions for grape development and maturation (mineral and water supply and microclimate). The temperature above the soil and its water content also have an impact on the earUness or lateness of the vines growing season (Barbeau etal., 1998 Tesic et al 2001). These two parameters give an initial indication of the quality of a terroir. But a quality terroir must also limit the consequences of weather variations from one year to another. Soil study is difficult since all of the factors likely to influence the biochemical processes of maturation should be taken into account. 

Certain regions have difficulty in producing quality wines. Chapter 10 discussed the climatic and soil conditions which excessively favor vine growth and grape development. These conditions lead to musts with high sugar concentrations, but the resulting wines lack finesse and aromatic complexity. 

Snyder, E., 1937. Grape development and improvement. In USDA yearbook of agriculture, pp. 631-664. 

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