The Grape Berry
The Grape Berry
Beginning with fruit set (generally the grape berry is now between 1.5 and 3.0 mm, i.e., less than 1/8 of an inch in diameter) the grape berry growth is divided into three stages. Stages I and III correspond to periods of rapid growth, and the intervening slow growth phase is called Stage II. Generally the slow growth stage (Stage II) corresponds to the slowing of Stage I and the acceleration of Stage III, but it is clear that different grape cultivars have stages of different lengths even under ostensibly identical conditions. In the first stage of fruit set (also called “nouaison”) the actual development of the flower ovary into the grape berry begins. The seeds in the two seed cavities (the locules) and the flesh (the pericarp) begin to take form. The pericarp separates into the exocarp (the skin with its cuticle—a thin wax coating) and the mesocarp. The mesocarp, as it grows and divides, will eventually (by the end of Stage III) account for more than 90% of the grape’s weight. The exocarp, significantly thinner than the mesocarp, may be only five or six cells thick, and the cuticle only several layers of lipids (waxy, fatty acid esters, and compounds similar to those of cell walls and the chloroplast envelope, see pages 30 and 31). It is in this stage that the as yet undeveloped berries are green and hard (it has been suggested that this is because chlorophyll is present and photosynthesis in the berry—as well as in leaves—is occurring). The berries are low in sugar (sucrose) but high in carboxylic acids, predominately malic acid and tartaric acid along with, generally, a lesser amount of ascorbic acid (vitamin C), hydroxycinnamic acid, and some acidic tannins (Figures 13.1 and 13.2). The grape berry structure is generally divided into three types of tissue: skin, flesh, and seed (Figure 13.3). The first, skin, as already mentioned is also known as exocarp.
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