Red and white grapes’ chemical compositions are shown in Table 1. One of the main compounds of grapes is sugars in the form of glucose and fructose. The sugar concentration of 98 grape varieties analyzed by Liu et al. ^[1][19] presented 46–123 mg/mL of glucose and 48–131 mg/mL of fructose. Grape berries store glucose and fructose in identical quantities at a relatively constant rate during ripening ^[2][20].

About 90% of the organic acids in grapes are l-tartaric and l-malic acids ^[13][14][21,22]. Grapes also have minor quantities of citric, succinic, lactic, and acetic acids ^[15][23].

Nitrogen compounds in grapes comprise ammonium cations and organic nitrogen compounds such as amino acids, hexose amines, peptides, nucleic acids, and proteins ^[16][24]. The primary grape-free amino acids include proline (up to 2 g/L), arginine (up to 1.6 g/L), and, to a lesser extent, alanine, aspartic acid, and glutamic acid ^[17][25]. According to Hernandez-Orte et al. ^[18][26], the amino acids contribute to the wine's aroma, taste, and appearance.

Phenolic compounds present in grapes are mainly in the grape berries’ skins and seeds ^[19][27] and grape stems ^[20][28]. These compounds are essential because they are responsible for sensory characteristics like color and astringency. The phenolic compounds present in grapes include non-flavonoids and flavonoids. The non-flavonoid compounds comprise phenolic acids divided into hydroxybenzoic acids, hydroxycinnamic acids, and other phenol derivatives, such as stilbenes. Non-flavonoid phenolic compounds incorporate hydroxycinnamates acids, hydroxybenzoic acids, and stilbenes. Common hydroxycinnamic acids are p-coumaric acid, caffeic acid, sinapic acid, and ferulic acid since the most common hydroxybenzoic acids are gallic acid, gentisic acid, protocatechuic acid, and p-hydroxybenzoic acid, which are mainly found in their free form ^[21][22][29,30]. For flavonoid phenolic compounds, such as flavonols, flavanols, and anthocyanins ^[23][31], flavonols are the most abundant phenolic compounds in grape skins ^[24][32], while grape seeds are rich in flavan-3-ols ^[20][28]. The average quantity of the total phenolic compounds in different grape fractions varied from 2179 mg/g gallic acid equivalent in seeds to 192–375 mg/g gallic acid equivalent in skins. In addition, it is also possible to find low quantities of phenolic compounds in pulps (23.8 mg/g gallic acid equivalent) ^[25][33]. The phenolic compounds responsible for the red color of the grape berries are the anthocyanins; these phenolic compounds are glycosylated derivatives. In V. vinifera grape varieties, the 3-monoglucosides are the main anthocyanins where glucose can be acylated by acetic, p-coumaric, and caffeic acid ^[26][27][34,35]. Polymerization of flavan 3-ol units, (+)-catechin and (−)-epicatechin and their gallate esters originated oligomers and polymers named proanthocyanidins. Seeds enclosed procyanidin of (+)-catechins, (−)-epicatechin and epicatechin gallate units, while grape skin enclosed procyanidins and prodelphinidins frequently based on (−)-epicatechin and epigallocatechin units ^[28][29][36,37]. Procyanidins ranged from 1.7–4.4 g/kg of berries in skin, 1.1–6.4 g/kg in seeds, and 0.2–1 g/kg in pulp ^[30][38].

Grape flavor compounds could be divided into volatile and non-volatile compounds. Volatile flavor compounds isolated from grapes are monoterpenes in Muscat grape varieties ^[31][39] and methoxypyrazines in Cabernet Sauvignon, Sauvignon Blanc, and Semillon grape varieties ^[12][40].

Grape (Vitis vinifera L.) is one of the major crops worldwide based on cultivated hectares and economic value ^[32][50]. Grapevines comprise vegetative organs (roots, trunk, cordon, shoots, leaves, and tendrils) and reproductive organs (clusters with flowers or berry fruit). All organs are interconnected through the vascular system comprising the xylem for water and nutrient transport and the phloem to assimilate transport. The roots form the plant-soil interface, while a vine's trunk, cordons, and shoots form its stem. The shoots carry the leaves, buds, tendrils, and clusters. Leaves are arranged in spiral phyllotaxy in juvenile vines and alternate phyllotaxy in mature vines. Buds are young, compressed shoots embedded in leaf scales. Tendrils and clusters are modified shoots. After fertilization, the flower pistil develops into the berry fruit ^[33][51].

Berry size and quality depend mainly on water, sugars (glucose and fructose), organic acids (malic and tartaric acids), phenolic compounds (anthocyanins and tannins), and aroma precursors. Many advances have been made in understanding how grape berry develops and the chemical compounds necessary for winemaking ^[34][52]. Such knowledge is equally essential when it is intended to make other uses of grape berries besides manufacturing alcoholic beverages. Indeed, most fruit production is processed into wine. Still, significant portions are consumed fresh, dried into raisins, processed into nonalcoholic juice, distilled into spirits, or used directly in the kitchen ^[35][53]. The use of grape berries in cooking is currently a new reality. Thus, knowing the anatomy of the grapes from the perspective of evaluating the sensory characteristics of each one of its components is essential.

Berries represent an integrated, systematic structure of tissues consolidated almost in a spherical symmetry. These constituents are tastefully stratified in three different tissue strata: the outer exocarp (the dermal system or skin), the median mesocarp, and the inner endocarp. These strata collectively include the pericarp, whose locules reside two to four seeds, two in each locule. These three tissues' translucent and hydrated mesocarp compose the more significant portion (85–87%) of the berry’s spherical volume ^[36][6]. The chemical composition of these tissue types differs, strongly influencing final grape and grape product quality.

The exocarp or skin of the grape berry forms a heterogeneous region constituted by a cuticle, epidermis, and hypodermis ^[37][56]. According to Wilson et al. ^[38][57], grape skin ranges from 5–18% of the fruit's fresh weight. It consists of 6–8 cell layers, the outer wall of the epidermis being protected by a waxy coating called the cuticle (Figure 1). The cuticle, secreted by epidermal cells, is a continuous layer whose thickness varies depending on the variety, protecting the fruit from drying and providing a barrier to fungi and bacteria.

Contrasting other plant surfaces, grape berry skin does not contain many functional stomata. Therefore, water loss happens frequently through the waxy cuticle, a relatively slow process. One consequence of this physiology is that grape berries do not dissipate heat well via water evaporation. Another result is that grape berries cannot shed excess water quickly. Hence, they are more susceptible to splitting than other fruits [58], which is an important feature when grapes are cooked.

The outermost part, constituted of one or two layers of tangentially elongated cells whose thickness varies depending on the grape variety, is considered to be the epidermis. The four or five cell layers immediately under the epidermis are deemed to be the hypodermis. This protective layer comprises two distinguishable regions: an outer region with rectangular cells and an inner region with polygonal cells ^[37][56].

In the grape berry, the exocarp and mesocarp tissues diverge in cell expansion orientation and in the timing of this expansion ^[39][59]. Exocarp cell size in these layers is minor compared to mesocarp cells, which supports the cell size as an essential criterion for identifying a hypodermis ^[40][60]. Therefore, immediately below the hypodermis are polygonal cells with fragile, distended cell walls, considered the mesocarp.

The mesocarp grape berry cells are characteristically larger and rounder than the cells that make up the skin. These cells comprise large vacuoles, the primary sites for accumulating sugars, organic acids, aromas, flavors, ions, and water during grape berry ripening. The grape berry vacuole cells have attracted attention principally because their storage function contributes directly to fruit quality ^[34][52].

Grape berry consistency depends on skin and pulp cell wall thickness. Commonly, table grape varieties yield plump, thin-skinned grapes (the mesocarp having thick cell walls), whereas winemaking varieties have tough skins and juicy pulp (pulp with thin cell walls) ^[37][56].

As was mentioned before, grapes can be used as fresh fruit or processed into products such as jam, grape juice, jelly, molasses, wine, and raisins. Grapes are a rich source of polyphenolic compounds and antioxidants, including vitamins, flavonoids, and phenols ^[41][42][15,61].

The color of processed grape products is a factor of quality. The skin of red grapes is typically dark blue or purple. The traditional jam production process uses pectin as the gelation agent, which needs high temperatures for the gel formation. The loss of color pigments during jam processing is due to the temperature increase (over 100 °C) ^[43][62], and of course, color is an essential attribute in jams.

Pop et al. ^[44][63] aimed to evaluate the quality and the effect of jam processing of Concord black grapes without added sugar. At the end of the work, they found that the concentration of fructose, sucrose, and glucose ranged from 17–17.3 °Brix and the refractometric measurement of SDS (soluble dry substance) passed the minimum quantity of 67%, which guarantees the conservability of the product. The highest amount of polyphenols and antioxidant capacity was found in the jam compared to the initial grapes, probably due to the concentration of grape pulp during the jam production.