The process of making red wine has not changed much in the past few thousand years. Dark grapes are harvested, crushed, fermented, stirred, and separated from the skins. The consistency and quality of today’s red wines are much better than in the past, due mostly to better equipment and storage, but the basic ingredients remain the same – grapes, yeast, and sometimes sulfur dioxide is added as a preservative.
The main difference in the production of red vs. white wine, is that red wine ferments in a vat or tank with the skins and the juice, while white wine is produced by separating the juice from the skins prior to fermentation. By leaving the skins in contact with the juice, the colors and flavors are further integrated into the juice. The yeast is the catalyst which converts sugar to alcohol.
The vineyard is a critical element in determining the end result of every wine. The grape’s life begins there, and the final product is greatly affected by the vineyard’s location, climate, terrain, soil, and roots. Length of exposure to sun and time on the vine also play critical roles in determining the development of the grape and its sugar levels.
When the green color of the grapes turns dark red or deep blue, the wine grapes are ready to harvest. This usually takes place in late summer or early fall. Grape clusters are cut from the vine by hand or machine, and collected in bins. Once at the winery, grapes are sorted out and debris or unwanted grapes are removed. The grapes are further processed by removing the whole grapes from the stems, and crushing them slightly to release some of the juices. This juice which is created prior to pressing is known as ‘free run’. Sulfur dioxide may be added at this stage in order to help preserve the wine and minimize oxidation.
The combined pulp of juice, skins, and seeds is known as ‘must’. Some winemakers choose to cool the must for a few days, which is known as cold soaking. This is done to extract additional color and flavor compounds from the skins before any alcohol is created.
At this point, yeast is added to help the fermentation process start. Some winemakers choose not to add any yeast, but allow the native yeast that clings to the grapes to start fermentation. The yeast reacts with the solution, and begins to convert the sugar into alcohol and carbon dioxide. The skins then form a cap on top of the must, which then gets blended back into the juice several times daily, during fermentation.
This process releases carbon dioxide, draws oxygen, and increases the rate of extraction from the skins. During this process, heat is released and needs to be monitored or it can reach high enough temperatures to spoil the wine.
The must is then transferred into the wine press, which separate the skins and seeds from the juice and squeezes the skins to produce ‘pressed’ wine. The winemaker decides on how hard to press the wine. Too soft, and the wine remains light in color and texture; too hard, and harsh tannins become pronounced.
Almost all red wines need to age before being bottled. The aging process is preferably done in oak barrels or vats, and can take a few months up to a few years. While the wine is maturing, a bacterial process known as malolactic fermentation takes place, which converts the wine’s crisp malic acid to softer lactic acid, which produces a softer mouthfeel.
The type of barrels that winemakers use, affects the flavors, aromas, tannins and textures of the wines. New barrels impart more intense aromas and flavors, and older or used barrels create a smoother texture to the wine. Winemakers also carefully choose the source of the barrels they use. French oak barrels, which are more expensive than American barrels, help create a more complex spicy flavor to the wine. American barrels add subtle flavors of vanilla to the wine. There are additional choices the winemaker can employ, such as using ‘toasted’ barrels which are charred by fire and add a slightly toasty flavor profile and aroma to the wine. Oak barrels protect the wine and imparts flavor, but at the same time they also allow very small amounts of oxygen to penetrate the barrel via the staves, which eases the tighter tannins in red wine and helps create greater flavor complexity.
Red wine needs to be clarified to remove sediments that accumulate at the bottom of barrels and tanks while the wine ages. The processes employed in order to clarify wine are known as racking, fining, and filtering. Racking is the process of pumping the clarified wine off of the sediment, and moving the juice to another barrel. This also aerates the wine slightly, opening up flavors and allowing further development.
The finishing process includes fining and filtration. Fining is a method that winemakers use to adjust the tannins of the wine by adding substances such as egg whites. These agents gather and bind the unwanted compounds which then fall to the bottom of the tank or barrel and are discarded.
Once a wine has reached maturity, its up to the winemaker to decide if filtration is required before bottling. The level of filtration chosen can range from one that removes only the extra sediment, to a sterile filtration which removes virtually all unwanted compounds.
If the winemaker is producing a red blend as opposed to a single varietal, he carefully chooses the various wines and calculates their percentage in the mixture, to achieve the flavor profile and attributes he is looking for.
Finally, the sulfur dioxide is adjusted just before bottling the wine. Oxygen is removed from the empty bottle, the wine is added, the bottle is topped with either nitrogen or carbon dioxide to displace any remaining oxygen, then corked and labeled.
If the winemaker has done his job right, he has transformed the sweet grape into an enjoyable red wine.