The process of vinification, or wine making, begins with the growing and harvesting of grapes. The quality of the grapes is the single most important factor in determining the quality of the wine. In addition to the variety of grape chosen to harvest, the weather during the growing season and time of harvest play key roles in affecting the final wine product. For example, insufficient heat during the growing season may inhibit the production of sugar, thus inhibiting the conversion to alcohol and negatively impact the overall character of the wine. Furthermore, choosing the right time to harvest is a difficult task that will have a tremendous effect on a wine’s quality. Harvesting too soon will end up with a wine that is too thin and low in alcohol content, mainly due to the lack of time required to produce enough sugar. Harvesting too late will lead to an overproduction of sugar and a wine with lower acidity levels, which will impact the aging ability and overall flavor. Generally, wine grapes are harvested during the heart of the autumn season.
Grapes are generally crushed using a crusher/destemmer machine. Stems are usually removed prior to crushing since they contain a relatively high amount of tannin, which affect the wine’s taste and maturation process. A basic crusher will not separate the stems from the mixture of juice and crushed grapes. Therefore, stems are either manually removed beforehand or mechanically via a crusher/destemmer, especially for red wines. This machine crushes grapes and then filters out most of the stems to be disposed. Since most machines will crush the grapes and stems together, some of the harsh tannins ultimately filter through with the mixture. This juice mixture of crushed grapes, skins, pulp, stems, and seeds is referred as must.
After the crushing stage, the skins and seeds are left mixed with the juice for an extended period of time (anywhere from several hours to several weeks) in a process known as maceration. During this time, much of the wine’s color, flavor, aroma, and tannin content is defined. After maceration, pressing will occur. Generally a wine press is used which extracts the juice from the crushed grapes, leaving behind the rest of the grape. Pressure is carefully applied to the must to avoid crushing the grape seeds and releasing undesirable tannins into the wine. With red wines, grapes are pressed at the end of the maceration and fermentation allowing the broken skins to remain in contact with the juice. On the other hand, grapes are usually pressed immediately after crushing when making white wines.
Once pressing is complete, the grape juice mixture is then fermented to produce alcohol. Yeast is usually already present on the grapes while they are on the vine. While there is an inexact method of incorporating yeast into the process, usually some cultured yeast is added to the must. Carried out in stainless steel vessels (or sometimes in large oak barrels for reds), the sugar in the juice is turned into alcohol and carbon dioxide as the yeast cells feed on the sugars. Heat is also released raising the temperature of the must mixture between 65F and 85F for red wines. Fruit flavors are diminished and fermentation speeds up at higher temperatures so it is crucial to closely monitor and control the environment. White wines cool in fermentation tanks at lower temperatures between 55F and 65F. Grape skins and pulp for red wines will occasionally rise and float to the top of the fermentation tank. It is important for the winemaker to submerge the cap back into the juice (or by pumping juice from the bottom of the vat over the top of the cap). Otherwise, it could create a breeding ground for harmful bacteria and also inhibiting the juice from picking up additional color, tannin, aroma, and flavor from the cap. Sugars from ripe grapes will produce a wine with an alcohol content between 8% and 15%. If there is insufficient natural sugar produced from the grapes to generate the desired amount of alcohol, sugar can be added to the mixture. The fermentation process is said to be complete when all the natural or added yeast has been destroyed. One method of determining that the sugar has been absorbed is to float a hydrometer into the mixture. If the hydrometer sinks to the bottom, it indicates that the sugars have been converted. The first phase of fermentation takes anywhere between 5 and 10 days for red wines and 10 to 15 days for white wines.
Secondary fermentation is a much slower process that can take anywhere between 3 and 6 months. At this point, the wine is moved into an airtight container preventing any further oxygen from mixing. Some wine makers choose to incorporate malolactic fermentation into the wine making process where malic acid in the grapes is broken down into carbon dioxide and lactic acid. The lactic acid provides a softer taste, sometimes resulting in a richer or buttery flavor. This also may happen naturally during the fermentation process and is common with most red wines and some white wines.
The wine then can go through a period of time where it is aged within wood barrels where additional flavors can be absorbed from the chemicals that make up the wood. It is important that no oxygen is entered into the barrels during this aging process. The wine may be aged anywhere from several months to several years during this time. Wines then generally go through a filtering process where any residual yeast is removed to prevent re-fermentation or spoilage after the wine is bottled. Filtering also helps to stabilize a wine, removing traces of tartaric acid that can crystallize in wine. However, excessive filtering can also remove desirable particles that help shape a wine’s flavor and aroma. Thus, the wine maker must be very careful how much, if at all, filtering takes place to avoid either the spoilage by bacteria or over extracting particles resulting in a bland wine.
After filtration, the wine is ready to be bottled and often aged again. A wine must be stable prior to bottling, which means that all fermentation has stopped for good. Corking the bottle properly is crucial, since the water and alcohol can not have an opportunity to evaporate. Darker bottles can also be used to help reduce any damage that may be caused by direct light. The bottles should remain upright for a couple days and then stored on their side.
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