Wine making is a science and this specific body of knowledge is called enology. Good wine is considered a necessity of life in many parts of the world. If you enjoy this elixir, the intricate process used in producing it may interest you.
“Wine is bottled poetry” – Robert Louis Stevenson
The fruit used most in making wine is grapes. The quality of the grapes reflects in the quality of the wine. Occasionally other fruits such as plums and apricots or roots such as ginger are also used in its production. Wine can be broadly categorized as table wines, sparkling wines, and fortified wines.
The following process is usually followed, while producing most wines. However, the order of the steps may differ or there may be a few additional steps, depending on the type of wine being produced.
Harvesting of the grapes involves picking of the grapes by hand or machine. There are many factors that feature in the decision of when to pick the grapes, but they depend on the type and quality of the wine being produced. Some of the considerations are the level of sugar acid, pH level (measure of the acidity or basicity of a solution), phenological ripeness, berry flavor, and tannin development of the grapes.
While handpicking is a better method than mechanical harvesting, it is more expensive. During mechanical harvesting, several other substances from stems and leaves to birds nests get included with the grapes! Another problem it poses is that often, overripe, moldy grapes also get included with the good ones. In contrast, human harvesters can leave the raw grapes to ripen, and identify clusters that are rotting, which can then be treated. Once the grapes are picked and brought in, they are treated with free sulfur dioxide to discourage the growth of microorganisms and wild yeast species on the grapes.
The next step undertaken by many wine makers is to separate the grapes from the stems that hold them.
This process portrayed by young people stomping on grapes in a wooden tub has long been made famous in the movies. But this traditional method is seldom used anymore, as contemporary mechanical crushers are more cost-effective and efficient. The process of crushing involves putting a little pressure to cause the skin of the grapes to crack. The crushed grapes form a pulpy material called ‘must’. Destemming can also be done mechanically, though stems are often left in, as it assists the grape juice to flow away from the smashed skins.
The rich ruby color of red wines is derived from the skins of the grapes. Thus, while producing red wine, the skins are left in with the juice to soak for a few days, followed by primary fermentation. If white wine is being made from red grapes, contact between the juice and skins is minimized. Usually, the steps of destemming and crushing are skipped while making white wine. Once these grapes are picked, they are immediately processed in the wine press. Rose wine gets its pretty color from the grape skins that are left in with the juice for just the right amount of time.
The primary fermentation process is where yeast is added to the pulp. The yeast cells nourish themselves on the sugars present in the pulp and multiply, producing carbon dioxide gas and alcohol. The white powder that is found on grapes is yeast and can be used in its fermentation. But as this yeast is wild, the results are often undesirable. For good measure, cultured yeast is usually added. To facilitate the fermentation, temperatures must be maintained at about 22-25 °C for red wines, and 15-18 °C for white wines. On an average, one gram of sugar converts to about half a gram of alcohol. If the level of sugar present in the pulp is too low to produce the desired percentage of alcohol, additional sugar is added in accordance with local jurisdiction.
Carbon dioxide, a by-product of fermentation, pushes the grape skins to the top of the bin. A layer of skins, called the ‘cap’, is formed on the top. Tannins (chemicals existing in the skin and seeds) give wine its astringency, which is why the ‘cap’ needs to be mixed well with the juice daily or several times a day.
Pressing is the process when the grapes are smashed in order to extract maximum juice as well as to separate out the grape skins. In earlier times, this was done in manually operated basket presses made of wood. With red wines, the pulp is pressed after the primary fermentation period. While producing white wine, the liquid is separated from the pulp right after picking. With rose, where the skins are in contact for a short while to give color, the pulp may be pressed as well. After the ‘must’ is pressed, the juice is separated from the dead yeast and any solids that remain are transferred to a new container, where additional fermentation may take place.
Cold and Heat Stabilization
After the fermentation of the juice, it is kept at close to freezing temperatures for 1-2 weeks. This process called cold stabilization, is done for the tartrate crystals to separate from the wine and stick to the sides of the holding container. Later, when the juice is transferred, the crystals are left behind. Heat stabilization is carried out to extract unstable proteins.
Fermentation and Aging
The juice goes through a secondary fermentation process. This time it is placed into large vats, from which air is extracted to prevent oxidization and discourage the growth of bacteria. During this time, grape proteins continue to be broken down and the remaining yeast cells and other fine particles slowly settle. Some wines, such as Chardonnay are placed in oak barrels to achieve a certain flavor.
A third fermentation used in the production of several red wines is called Malolactic fermentation. Malic acid is converted into lactic acid, and results in the mellowing of the tartness in the wine. The time spent in aging the wine differs in each variety. Not all wines need to be aged, as many are ready for consumption immediately. White wines are not aged for long. Red wines may be aged from a few months to a few years, depending on the type and quality.
Blending and Bottling
Often, wines from different batches are blended together to create a certain flavor. This method can also be used to compensate for inadequacies present in a particular batch. Preservatives are also added to the wine. Lastly, the wine is filtered before it is bottled.
A popular opinion is that a good meal is not complete without a glass of wine. Not only does it enhance the flavor of the food, this antioxidant-rich drink is good for your health and great for your spirit.