The grape is the essential ingredient for wine production. The term "grape" refers to each of the fruits of the plant known as the vine. On the vine, these fruits are grouped together in different shapes and variable quantities, forming clusters.
It is very common to hear viticulturists and winemakers affirm that wine is made in the vineyard. Statements like this highlight the importance of grape quality, which, from the vineyard to the winery, plays a crucial role in producing a good wine. Nowadays, the main concern regarding grapes is their quality.
Quality is understood as the proper ripening of all grape components, as well as their perfect sanitary condition. This focus on grape quality contrasts with the previous times when achieving high production volume was the most important objective. Producing large quantities of grapes can still be a prominent goal today, especially when producing bulk or basic wines, as their lower grape quality is not a problem.
Vines belong to the vitis genus, and within this genus, we can distinguish different species. Some of them are widely used in winemaking, such as vitis vinifera, while others are much less used or not used at all. Currently, wine production is mainly carried out with hundreds of different varieties of the vitis vinifera species, such as Cabernet Sauvignon, Tempranillo, or Riesling. These varieties, used worldwide for winemaking, can only be cultivated thanks to the collaboration of other vitis genera. In the mid-19th century, a plague known as Phylloxera arrived in Europe from America,
The plants died due to the insect responsible for the infestation, and they could only be saved by using other species of vines of American origin, such as vitis rupestris, vitis riparia, or vitis berlandieri. These species were used as rootstocks planted in the ground because they are resistant to the insect, and the chosen variety of vitis vinifera was grafted onto their aerial part. Currently, almost all vineyards worldwide are planted in this way.
Grape clusters found on the vine can have different sizes and shapes, but they are always composed of two main elements: a woody part known as the stem or stalk and the actual fruits. The main function of the stem is to support and nourish the other part of the cluster, the grapes. The stem is connected to each of the grapes that make up the cluster through the peduncle or pedicel, which not only holds them but also acts as an umbilical cord between the vine and its fruit. The stem can sometimes be used during winemaking, but it is most commonly removed at the beginning through destemming. The grape, usually oval or spherical in shape, is composed of an outer skin called the "hollejo" and inside, we have the pulp and the seeds, which vary in size and quantity depending on the different varieties. From these solid parts, the winery obtains a liquid part, the must, which is essential for wine production. The must is obtained by breaking the grape skin and applying pressure to the pulp.
The grapes used in winemaking are different from those directly marketed for human consumption, known as table grapes. In general, table grapes are larger than those used for winemaking, but that is not their main difference. Table grapes usually have a thin and soft skin, a large proportion of pulp relative to the skin, which makes them more pleasant to eat, and in many cases, they don't even have seeds. On the other hand, grapes for winemaking usually have thicker and harder skins, a proportionally smaller pulp compared to the skin and seeds, a higher juice content relative to the pulp, and higher levels of sugars and acids. These grapes for winemaking are not usually sold for direct consumption, just as table grapes are not typically used for winemaking.
Different vine varieties also produce different types of grapes. The main distinction is between white and red varieties. Apart from the obvious color difference, white varieties usually have finer skins than red varieties, but there are also many shapes, sizes, and even different shades of color among them.
Each part of the grape plays a different and important role in winemaking. Beyond the nuances, we can summarize the different contributions made by each part:
The pulp and the must obtained from it are the most important part of the grape, especially in white wines, as they contain the main components that will carry through to the finished wine. The must is colorless in all grape varieties, except for a few known as tintoreras, which allows for the production of white wines from red varieties. The must is primarily composed of water, sugar, and acids, although many other elements can be found in smaller quantities. Water is the main component of the must by volume, just as it is in the final wine. The sugars in the pulp are essential for wine production because they will later be transformed into its distinguishing component, alcohol. This transformation is carried out by yeasts through a process known as alcoholic fermentation. The acids are crucial for the wine to achieve the necessary balance that allows for consumption and enjoyment. The acids present in the grape undergo modifications throughout the maturation process, but at the time of harvest, the main acids, in order of volume, are tartaric acid and malic acid, along with other acids in much smaller proportions. These acids present in the grape will be modified, reduced, increased, or even transformed into others during various winemaking processes, such as alcoholic fermentation or malolactic fermentation.
The skin, or grape skin, is important in winemaking due to what it contains on its surface and inside. The skin has an outer layer that covers it, with a waxy appearance, known as "pruina." In this layer, we can find yeasts that travel from the vineyard to the winery, and in some cases, they will be used to carry out the alcoholic fermentation of the must. The inner part of the skin contains phenolic components, which are compounds that contribute to the different organoleptic characteristics of each grape variety, such as tannins and pigments that give color to the wine. Color compounds are highly relevant in the production of red wines, where they are extracted during alcoholic fermentation in contact with the skins. This practice is generally not performed in white wines to avoid coloration. In rosé wines, the contact with the skins can be more or less prolonged, depending on the desired level of color extraction.
Finally, the stem and seeds play lesser roles in winemaking processes. During grape handling, special attention is given not to break the seeds because their content can contribute bitter characteristics to the wine. The stem, on the other hand, will only reach the winery in the case of manual harvesting, as it remains on the vine in mechanized harvesting once the grapes are separated from it. Until recent times, the stem was not commonly used in winemaking due to various reasons, as it can introduce negative characteristics to the wine. However, nowadays, an increasing number of producers use a variable proportion of stems during alcoholic fermentation.
Overall, each part of the grape contributes distinct qualities and characteristics to the winemaking process. By understanding the role of the pulp, skin, stem, and seeds, winemakers can utilize these components to produce wines with specific flavor profiles and styles.
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