What is Wine?

Grape juice is fermented to create wine. Only V. vinifera, one species in the genus Vitis, is used to produce wine for human consumption (otherwise known as the European grape). Despite the name, not only wines made from the American native grape species V. labrusca are acceptable. Wine may be produced from a variety of fruit. Fruit juice is often used in the fermentation process, and wines made from peach and blackberry juice are two such examples.

what is wine

Winemaker Collecting Grapes

Enology: Scientific Winemaking

Before the nineteenth century, little was known about fermentation and what caused deterioration. The ancient Greeks stored their wine in clay amphorae, whereas the ancient Romans employed oaken cooperage to preserve their wines [1]. On the other hand, they probably consumed the majority of their wines within a year following the harvest, adding additional flavors to conceal any deterioration. Before the vast manufacture of glass bottles and the widespread usage of the cork stopper in the 17th century [2], wood barrels were often used for maturation. When it was discovered that wine preserved in bottles could be drunk at a later period without spoiling, this perception changed.

The majority of the gains of twentieth-century mechanical advancement may be traced to advancements in quality assurance. Stainless steel is a good material for storage and fermentation containers because it is sturdy, corrosion-resistant, easy to clean, and can be cooled to exact temperatures [3]. The objective of automated, hermetically sealed racks and filtration equipment is to reduce the risk of infection from airborne microbes. In the 1960s, the first grape harvesters and field crushers were introduced, accelerating the harvest and letting the grapes to move directly into the fermenting tanks[1].

The Wine Grape

Cultivation

Grapes flourish in good to warm temperatures, but may even be grown in semitropical regions. If the growing season is too short for the fruit to mature or if the low winter temperatures destroy the vine or its fruiting buds, they are not suited to the colder portions of the temperate zone. In any of these scenarios, the fruit may not reach complete maturity. V. vinifera is more frost-sensitive than V. labrusca [4]. The climate has a significant impact on the taste and perfume of fully ripe grapes. Variable levels of heat received by plants during the growing season considerably contribute to the distinctive aromas of grapes cultivated in various locales. Factors like soil temperature, sun exposure, and diurnal temperature change are vital.

what is wine

Wine Grapes Ready to be Harvested

Certain regions of France and Germany with a low heat summation may be more susceptible to the impacts of seasonal weather. This is especially true in colder environments. The fruit from these places, where the growing season is often warmer than average, is generally more mature and harmonious than fruit from colder regions. If it is too warm during the growing season, the fruit won’t be as vividly colored or acidic, and the berries won’t produce as many raisins (because they won’t lose as much water) — the warmer the environment, the sweeter the dessert wine.

Weeding and pruning are examples of agricultural practices that may impact the chemical makeup of the final product. It is uncertain how soil composition affects wine quality, which may vary greatly from area to region. Soil composition may influence grape nutrition, soil temperature, root penetration, water retention, and soil permeability.

The Wine-Making Process

Harvesting

When making wine, it is essential to select grapes that are perfectly ripe but not mushy. In colder places, like northern Europe and the east coast of the United States, when there is insufficient heat to commence ripening, it may be necessary to harvest grapes before they have achieved full maturity. To compensate for the ensuing lack of sweetness, you might add more sugar or switch to grape juice concentrate. Due to natural moisture loss during ripening on the vine or drying in the sun after harvest, grapes with these characteristics have a high sugar concentration [5].

Spain’s renowned Málaga wines are created by a procedure known as partial raisining. Utilizing the beneficial fungus Botrytis cinerea may expedite the drying process. These grapes are often used to make dessert wines. For these wines, fermentation must be stopped prior to the complete conversion of sugar to alcohol. Utilized techniques include injecting sulfur dioxide, using compact fermentation tanks, and processing at low temperatures [6].

It is essential that the grapes be picked at the optimal time, since this may have a considerable effect on their composition. In general, wines picked too early are weak and watery, while wines harvested too late may be robust but lack acidity[3]. It is conceivable that many harvesting attempts will be required.

Grape clusters are first packed in smaller containers such as buckets or cartons after their harvest before being moved to bigger containers for transit to the winery. When using a machine to harvest berries, the stems must be broken or the clusters must be shaken to release the fruit. Either the grapes may be dropped directly into the crusher at the winery, or they can be dumped into a sump and transferred to the crusher by a continuous conveyor system[4].

Crushing

A common piece of modern winemaking equipment is a crusher-stemmer, which crushes the grapes and removes the stems. It is typically shaped like a perforated cylinder with paddles that rotate between 600 and 1,200 times per minute. Grapes are crushed and dropped through the holes of the cylinder, where the majority of the stalks are expelled. Roller crushers are an additional feasible option. Crushing something with one’s feet or stomping on it with one’s shoes is an old practice that is hardly observed today[4].

what is wine

Grapes Entering a Manual Grape Crusher

In the Champagne area of France, where white juice is made from white grapes using red grapes as a base, the favored method for crushing grapes is pressing. Typically, the containers are filled with whole bunches of red grapes before being sealed. The fruit’s respiration, which consumes oxygen and emits carbon dioxide, destroys the skin cells, leaving the fruit’s outer layer completely permeable for color extraction. Additionally, malic acid respiration occurs inside the cell. This respiration process may take longer in warmer environments, resulting in wines that are lighter in color and acidity and have a unique aroma[3].

Juice Separation

Upon harvesting white grapes, the juice is typically taken from the fruit while the skins and seeds are discarded. This is done to prevent oxidation during wine fermentation. As the process is the same for both white and non-white grapes, it makes no difference which is used. Allowing the white skins to rest in the juice for 12 to 24 hours may promote the extraction of taste, but may have the reverse impact on the extraction of the color [3].

There are two primary methods for separating sediments from the juice. Crushing grapes and keeping them in a container with a plastic bottom and, in most instances, plastic sides may result in substantial juice loss. Must refer to the solid residue remaining after crushing grapes, while free-flow juice refers to the liquid that flows away without being pressed. Refers most often to unfermented grape juice, with or without skins[3].

As the creation of red wine needs simultaneous fermentation of the grape skins, seeds, and juice, continuous presses are excellent for this stage of the process. During fermentation, the grape skins become far less slippery, making it much simpler to extract the juice. Consequently, more juice may be extracted from grapes using free-flowing procedures than with unfermented musts[7]. If the particles are not very slippery, pressing may be an effective method for separating liquids and solids.

After the wine has been extracted, the pomace, or crushed grape leftovers, may be used to distill wine spirits. This trait is shared by the fermentation processes of both white and red wines. Water is often added prior to finishing the fermentation process and draining the liquid in order to reduce the alcohol concentration of the produced wine. Pomace may be further purified and crushed, or it may be rapidly distilled in specialist stills[2].

Must Treatment

Musts that are white are turbid and must be settled to eliminate suspended particles. Preventive techniques, such as infusing sulfur dioxide in advance and lowering the temperature during the settling process, may assist in preventing fermentation and guaranteeing that suspended material settles properly. In vineyards all over the globe, white must is filtered by centrifugation to remove undesirable particles.

By rotating in a circular motion, a strong pulling force is created. Musts that have acquired an unsightly brown hue are often processed to pasteurization, which eliminates the enzymes responsible for the discoloration. It is not customary to add pectin-breaking enzymes to the must prior to pressing [7]. Bentonite is a clay that may be added to musts to assist remove some nitrogen and speed up the clarification process.

In order to remove color and inactivate enzymes before to fermentation in red musts, heating has lately gained in favor. This is intended to assist pre-fermentation. This technique may aid in the production of sweet red wines if carried out quickly, at moderate temperatures, and without exposing the wine to significant oxidation[3]. Utilize red grapes afflicted with the parasitic fungus Botrytis cinerea and profit from short fermentation periods on the skins. Using this method, wine is created. There are very abundant polyphenol oxidase enzymes there, which produce browning[8].

Fermentation

Producing high-quality wines requires meticulous monitoring and control of the fermentation process. One of the conditions is the presence of adequate amounts of appropriate yeasts since they inhibit the development of undesired microorganisms. Keeping the temperature under control may avoid oxidation by ensuring the yeast has access to all the nutrients necessary for growth. Lastly, it is crucial to appropriately manage the red cap of floating skins[9].

Grapes often produce a colony of bacteria, molds, and yeasts on their surface. Consequently, this will be the result. Although Saccharomyces is the favored yeast of winemakers, wild yeasts like as Pichia, Kloeckera, and Torulopsis may overwhelm it during fermentation[6]. Despite the prevalent idea that only Saccharomyces yeasts can assure a rapid and complete alcoholic fermentation, other yeast genera may contribute considerably to the taste of the final product, especially in the early stages.

This is particularly true if the fermentation was initiated with a yeast strain than Saccharomyces. Especially if the yeast used to induce fermentation was already present in the substrate. Saccharomyces yeast is favored over other yeast species[8] because it converts sugar to alcohol more efficiently and is less susceptible to the growth-inhibiting effects of alcohol. It is thus the better yeast for fermenting any beer. Nonetheless, there have been instances in which strains of Saccharomyces cerevisiae have generated alcohol at concentrations as high as 18%, despite the normal upper limit for alcohol concentration being around 16%[6].

Clarification

The suspended material (yeast cells, skin particles, etc.) in some wines settles out rapidly, and once the sediment settles, the wine’s supernatant keeps almost all of its brightness. Due to its increased surface area-to-volume ratio than bigger containers, 50-gallon oak barrels are appropriate for this purpose[2]. The uneven inside of a wooden coffer helps suspended particles settle. This is especially true of wines produced in warmer climates or aged in huge tanks, where cloudiness may last for years.

The particles that have sunk to the bottom owing to aging are dissolved during clarification. Fining, filtration, centrifugation, chilling, ion exchange, and heating are the crucial operations performed throughout this procedure[6].

Aging and Bottling

Aging

Many wines increase in quality as they age in barrels or bottles. The wines will eventually reach their apex and then fall as they mature. As a wine matures, its acidity reduces, it becomes clearer and more stable as sediment falls to the bottom, and its many components combine to produce complex compounds that impact its flavor and aroma[6].

Oak barrels, which are wooden vessels that enable air to enter while allowing water and alcohol to evaporate, are used to mature wines for a period of time. Essences of wood have a function in giving taste. When wine is kept in situations with low humidity, its alcohol content is concentrated, but it is diluted when wine is stored in conditions with high humidity[8]. The types of compounds that evaporate are determined by the relative humidity. As the wine’s water and alcohol evaporate, headspace or ullage is produced. To compensate for the volume loss, you may transfer wine from another bottle of the same kind.

what is wine

Wine Aging in Barrels

Bottling

Before bottling, wine may need to be blended, filtered, and treated with antiseptics to prevent microbiological growth. Due to the fact that various barrels of the same wine may age differently, blending is necessary to ensure consistency in the final product. Wines that are relatively lacking in color or acidity may be enhanced by blending them with wines that are stronger in these characteristics. Blending may improve the quality of a wine by making it more complex and enjoyable to drink[3].

Conclusion

As previously stated, wine is an alcoholic beverage produced by the fermentation of grapes. Fruit wine, often known as country wine, is produced from fermented fruit juices as opposed to grapes. However, traditional wines are produced from grapes grown for this purpose. Additionally, quality grapes are required to produce a palatable wine. Despite the continuous usage of local species, vines have been exported over the globe, and new grape varieties are being produced daily to assure success in optimal growing circumstances. In addition, winemaking is a labor-intensive process that takes a long time and needs many hands, regardless of the kind of wine being produced.

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References

[1] “Wine – Flavoured Wines | Britannica,” in Encyclopædia Britannica, 2022

[2] Jancis Robinson, The Oxford Companion to Wine (Oxford: Oxford University Press, 2015).

[3] Elisa GuerraDoce, “The Origins of Inebriation: Archaeological Evidence of the Consumption of Fermented Beverages and Drugs in Prehistoric Eurasia,” Journal of Archaeological Method and Theory 22, no. 3 (2015): 751–82.

[4] Helder Fraga et al., “Integrated Analysis of Climate, Soil, Topography and Vegetative Growth in Iberian Viticultural Regions,” ed. Inés Álvarez, PLoS ONE 9, no. 9 (September 24, 2014): e108078.

[5] Jancis Robinson, The Oxford Companion to Wine (Oxford: Oxford University Press, 2015).

[6] Michael Spilling and Winnie Wong, Georgia (New York: Marshall Cavendish Benchmark, 2009).

[7] BBC News, “‘World’s Oldest Wine Found in 8,000-Year-Old Jars in Georgia,” BBC News (BBC News, November 13, 2017).

[8] “Now That’s What You Call a Real Vintage: Professor Unearths 8,000-Year-Old Wine,” The Independent, December 28, 2003.

[9] Wine Folly Research, “What Is Wine? A Beautiful Explanation | Wine Folly,” Wine Folly, 2022.

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