Annual Growth Cycle of the Grapevine
Stages of Berry Growth
Berry growth occurs in three general stages: 1) rapid initial growth, 2) followed by a shorter period of slow growth, and 3) finishing with another period of rapid growth.
Stage 1 – Rapid Growth Phase
The first stage of berry development starts soon after fertilization of the flower and is characterized by strong growth of the seed and berry. During this stage, the berries are firm, dark green in color, and rapidly accumulate acid. In this period, the diameter of the grape berry may double in size.
Stage 2 – Lag Phase
The next stage, called the lag phase, is a time of slow growth. Berries remain firm, but begin to lose chlorophyll. Berries reach their highest level of acid content and begin to accumulate sugar slowly.
Stage 3 – Véraison Phase
The final stage of berry growth coincides with the beginning of fruit maturation (ripening). At this stage growth accelerates again; berries begin to soften, titratable acidity (TA) decreases and pH and soluble solids (°Brix) increases. Berries ripen unevenly among and within clusters. Within clusters, berries at the top (next to the stem) are riper (more sugar, less acid) than those at the tip.
Chemical Composition of the Fruit
Berry development includes accumulation and metabolism of Berry development includes accumulation and metabolism of hundreds of compounds, many in tiny quantities, which may contribute to fruit quality attributes. The single largest component of berries is water, followed by the sugars (predominantly fructose and glucose), then the acids tartaric and malic. Other important classes of chemical compounds found in grape berries include phenolic compounds, nitrogenous compounds, aroma compounds, minerals, and pectins.
The majority of soluble solids in grape juice are sugars, mostly glucose and fructose. Sugars increase in concentration during ripening, and may reach 25 percent or more of berry fresh weight by the time of harvest. At véraison, glucose exceeds the fructose concentration but at the ripening stage, glucose and fructose are usually present in equal amounts (1:1 ratio). In overripe grapes, the concentration of fructose exceeds that of glucose.
Next to sugars, organic acids are the most abundant solids present in grape juice. Acids give crispness, brightness, and thirst-quenching qualities to wines and are essential components of the balance in a fine wine. They have a marked influence on wine stability, color, and pH. Excessive grape acidity can lead to tart, acidic wines.
Phenolic compounds are often referred to as polyphenolics, polyphenols or simply phenols. Phenolic compounds are important constituents of grapes because they play a key role in determining fruit color and also provide most of the characteristic taste and aging properties in wine.
Grapes contain various nitrogenous compounds such as amino acids, peptides, and proteins. Nitrogen containing compounds are important because they serve as the nutrient for yeast and lactic acid bacteria.
Aroma and Flavor Compounds
Grapes contain numerous aroma and flavor compounds, which increase in complexity during the later stages of ripening. Some varieties have specific aroma compounds that give a variety its distinct varietal character. Examples of these include:
Minerals too play a role and generally include potassium, sodium, iron, phosphates, sulfate, and chloride.
Pectin substances are cementing agents present in the cell wall composed of polymers of galacturonic acids.
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