What are grapes composed?

Grapes are the fruit of the vine and develop in clusters as a result of the fertilization of the flowers. The grape berry is attached to the stem, part that is removed before pressing the grapes through a process called destemming, otherwise it would leave a bitter taste in the wine.

The grapes usually have a spherical or elongated shape and are covered by a skin whose thickness varies according to each variety and can represent 10% of its weight. The skin is rich in pectins, cellulose, aromatic substances and polyphenolic components (tannins), responsible for a large part of the structure and astringency.

Both the aromatic substances and the polyphenols contained in the skins can be extracted by macerating in the must, and the amount of extraction is proportional to the maceration time. These polyphenols are soluble in alcohol and, to a lesser extent, also in water. For this reason, the skins of the red grapes are macerated in the must to give color to the red wines and extract aromas and tannins.

The skin of the grape is covered by a waxy substance (the bloom, more visible in red berry grapes due to its whitish color) in which yeasts can also be found, naturally present in the air, which in contact with with the must they will activate the alcoholic fermentation. The pulp of the grape berry is rich in water, sugars (between 15% and 25% of the total matter), acids, pectins, mineral salts, vitamins and nitrogenous substances.

The concentration of these elements varies depending on the area of ​​the berry.

Let's see some concepts, what is the xylem and the phloem?

Development of the grape | Foto: Ana Gómez

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The grape cluster is a complex flower made up of a stem, a peduncle, a rachis and the fruit. In order for the grapes to develop, they need to have the necessary nutrients. These are extracted from the xylem, which transports water, minerals and sugars from the root to various parts of the plant, and the phloem, which is responsible for transporting carbohydrates from the leaves to the main part of the vine, and to the fruit. The xylem and phloem form the vascular system of the plant.

At the beginning of plant development, the phloem has a relatively small function and the xylem does the main job. However, the phloem becomes the main source of fruit nutrition after veraison begins.

What are the stages of grape development?

There are three stages of grape development.

Rapid growth of grapes

Stage I: the fruit begins to form and grow as a result of cell division. The grapes expand and accumulate acids (tartaric and malic). Malic acid accumulates in the fleshy part of the fruit, while tartaric acid accumulates mainly in the skin of the fruit. Tannins also accumulate in this first stage of grape growth, and are present in the skin and the seeds. They are responsible for the bitterness and astringency of the wine.

Slowed growth: seed maturity

Stage II: there is a pause in the growth of the grapes, temporarily stopping cell division. At this stage the embryos that are contained in the seed begin to form and grow. The grapes have already reached half the final size. During this phase the seeds reach their final size.

Change of color of the grapes: Veraison

Stage III: veraison begins, which is the stage of the color change of the grapes. The grapes accumulate sugars and metabolize acids. Once veraison has occurred, the grapes contain a higher concentration of sugars and are more palatable to animals. So it is the stage in which they "steal" the fruit and disperse the seeds. At this stage the grapes double their volume. Malic acid is reduced (especially in warm regions). The sugar concentration of the grapes depends on various factors, such as the variety, the time we let them mature before the harvest, the climate, the water, etc...

During the formation of the grapes, the synthesis of other aromatic compounds occurs, which will affect the aromas and flavors of the wine. The grape is a perfect biochemical factory.