The development of a grape berry happens in four phases during a single season. Each of these phases plays an important role in the development of quality grapes and berry size. Phase 1 Phase 1 starts as soon as blooming ends and the berries start growing in size. The duration of this stage is ten days and ends when the first grape-stones (pips) develop. During phase one, there is very little increase in the size of the berries and all the unfertilized flowers aborts from the vine, leaving only fertilized berries on the clusters. Phase 2 The duration of phase two is three to six weeks, depending on the climate conditions and variety. Pips start to develop and cell division begins takes place. Because of cell division, the berry increase in size at a phenomenal rate and photosynthesis takes place inside the berries itself. Phase 3 The start of Phase 3 starts as soon as there is a decrease in rate the berries gain size and the duration of this phase is about two to four weeks, again depending on the climate and variety. The main characteristic of this phase is veraison (coloring) of the berries. Phase 4 After cell division ends, the cells of the berry start to increase in size (cell enlargement). During phase two, the increase in size were because of cell division but in phase four increase in berry size is because of cell enlargement. The grape vine needs enough water during this phase. If there is as a lack of water, the grape vine abstract moisture from the berries and this will result in a smaller berry size. During phase four, the accumulation of carbohydrate (mainly glucose, fructose and sucrose) takes place and forms part of the ripening of the fruit. What happens during the above mentioned phases? Sugar Development of grapes: Phase 1 and 2, there are very little sugar in the berries and almost no fructose is present in the berry, only glucose. The berries in phase 1 and 2 are acidulous gathering organs of the grape vine. The total dissolved particles in a grape are mostly sugars and is measured in Brix (degrees Balling) with an instrument called a refractometer. 1*B equals 1 gram of dissolved sugar in 100 ml grape juice. During phase 4, veraison, the berry changes into a sugar accumulating organ and sucrose and fructose levels inside the berry is almost the same. The whole metabolism inside the berry changes and that is why we notice a decrease in the rate of berry enlargement. The level of fructose increase as the berries ripen until there is a much higher level of fructose inside the berry than there is glucose or sucrose. At this stage the berries are ripe. Leaving the clusters on the vine will resolt in an to high level of fructose and this stage is know as overripe. Acid development inside a berry: Tartaric acid and malic acid are the two main forms of acid in a grape and is responsible for more than 90% of the total acids levels. Citric acid is the third most important form of acid in a grape but it is only 0.02 to 0.03 % of the total acids. There are more than 20 different kinds of acid in a grape, but they are present in very low quantities inside a grape. During phase one and two, tartaric acid and malic acid levels in the berry is very high and starts to decrease at the beginning of phase three of berry development. The reason why the acid levels inside a grape berry decrease is mainly because of the conversion of acids into sugars by the vine, the dilution of acids because of the change in volume of the berry and an increase in the respiratory usage of acids, by the vine. The level of acid inside a berry is measured in pH and plays an important role in the development of coloring pigments (especially in red wines) and for taste. A table grape with very low acids, normally has a lower shelf life than one with a bit higher level of acid. Overripe grapes will have a very short shelf life. The aroma development: We often hear wine lovers say a wine has a great aroma. Where does this aroma come from? There are two groups of aroma you find in wine: 1.Natural which is formed inside the grape and gives the wine a natural aroma 2.Fermentation aromas which is formed by the fermentation cells The total aroma content of a wine is about 0.8 to 1.0 gram / liter, depending on the cultivar and climate in which the vine is grown. The precursor of the natural aroma of a wine is produced inside the leaf of the vine and transported to the grape berries. Coloring A wine gets its color from coloring agents found in the hypoderm, just underneath the skin of the berry. The green color of berries that is not ripe yet, comes from chlorophyll inside the skin of these berries. Because there are no coloring pigments inside the skin of a white wine, it has no color and therefore there is no use keeping the skins and juice together while fermentation is in progress, but with red wines, just the opposite happens. Danie The Grape Guy" www.My-Grape-Vine.com
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